CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to US Provisional Application No. 63/380,441 filed October 21, 2022, the disclosure of which is incorporated herein by reference.

FIELD

[0002] The present disclosure relates to ring-opening polymerization of cyclic esters and metal-ligand complexes having a constrained geometry for use in ring-opening polymerization of cyclic esters.

BACKGROUND

[0003] Ring-opening polymerization of cyclic esters (lactones) is one route through which aliphatic polyesters may be obtained. Depending on the lactone ring size and the presence of substitution thereon, ring-opening polymerization may take place rapidly with high conversion rates or slowly at rather limited conversion rates. For example, ring-opening polymerization of lactones containing a 5-membered ring is thermodynamically disfavored, whereas other ring sizes may undergo polymerization more effectively. Lactones containing a 7-membered ring may undergo facile ring-opening polymerization in comparison to other ring sizes. Various transition metal and lanthanide metal catalysts have been developed for promoting ring-opening polymerization.

[0004] Polycaprolactone may be produced by ring-opening polymerization of e-caprolactone (oxepan-2-one), a 7-membered ring cyclic ester. e-Caprolactone may undergo ready polymerization under a variety of conditions to produce a high-crystallinity polyester having a melting point of around 60°C and a glass transition temperature of around -60°C. A number of transition metal and lanthanide metal-ligand complexes have been used to promote catalytic ring-opening polymerization of e-caprolactone. Other 7-membered lactones may undergo polymerization much less readily. Metal-promoted ring-opening polymerization is believed to occur through a coordination-insertion mechanism involving the carbonyl group of the lactone monomer. Difficulties associated with metal-promoted ring-opening polymerization of e-caprolactone and especially other 7-membered lactones may include long reaction times, low conversion rates, and/or relatively low molar ratios of monomer to catalyst metal in order to achieve adequate conversion rates. Copolymerization of e-caprolactone with other cyclic esters, such as L-lactide, may be of interest to tailor mechanical properties of the resulting co-polyester. [0005] e-Decalactone is a substituted variant of e-caprolactone bearing an n-butyl group adjacent to the ring oxygen atom of the 7 -membered ring system. e-Decalactone may be produced biosyntheticaily through fungal oxidation of castor oil. Unlike polycaprolactone, polydecalactone is an amorphous polymer due to the presence of the n-butyl group and has differing physical properties as a result of the same. Unfortunately, e-decalactone and other 7-membered lactones bearing substitution on or within the lactone ring are considerably more difficult to polymerize in comparison to e-caprolactone, with even slower reaction rates and poorer conversion frequently occurring. Because of vastly differing reactivity values, it may be difficult to copolymerize e-decalactone with other cyclic esters, such as 6-membered cyclic esters or with E-decalactone.

SUMMARY

[0006] In various aspects, the present disclosure provides meial-ligaiid complexes that may be suitable for conducting ring-opening polymerization of cyclic esters. The metal-ligand complexes comprise a lanthanide metal atom and a ligand having a structure represented by Formula 1. wherein:

R ¹ and R ² are independently hydrogen or a C ₁ -C ₁₄ hydrocarbyl group;

R ³ and R ⁴ are independently hydrogen or a C ₁ -C ₁₄ hydrocarbyl group, or and R ⁴ are joined together to form an optionally substituted 6-membered aromatic ring;

R- is a hydrocarbyl group; are independently hydrogen or a C ₁ -C ₁₄ hydrocarbyl group; and Z is a bridging atom.

[0007] In other various aspects, the present disclosure provides methods for conducting ring- opening polymerization of cyclic esters using the metal-ligand complexes. The methods comprise: providing a feed comprising at least one cyclic ester; contacting the feed with the metal-ligand complex under polymerization reaction conditions; and forming a polyester by ring-opening polymerization of the at least one cyclic ester in a presence of the metal-ligand complex.

[0008] These and other features and attributes of the disclosed complexes, systems, and/or methods of the present disclosure and their advantageous applications and/or uses will be apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following figures are included to illustrate certain aspects of the present disclosure, and should not be viewed as exclusive embodiments. The subject mater disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to one having ordinary skill in the art and having the benefit of this disclosure.

[0010] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

[0011] FIGS. 1A and IB show alternative views of the X-ray crystal structure of the metal- ligand complex having Formula 3A-Nd.

DETAILED DESCRIPTION

[0012] The present disclosure relates to ring-opening polymerization of cyclic esters and metal-ligand complexes having a constrained geometry for use in ring-opening polymerization of cyclic esters.

[0013] The present disclosure provides metal-ligand complexes having a constrained geometry and containing a lanthanide metal atom. The metal-ligand complexes disclosed herein are capable of polymerizing cyclic ester (lactone) monomers having a range of structures under mild conditions, with high conversion rates being realized over short reaction times in many instances. Specific constrained geometry ligands disclosed herein include various bridged cyclopentadienyl-pyrrole ligands, which are described in further detail hereinafter. Advantageously, the constrained geometry ligands may complex a wide range of lanthanide metal atoms, such as neodymium or gadolinium, for example, which may be effective to promote ring-opening polymerization of various cyclic esters. Further advantageously, the metal-ligand complexes may be produced readily, either being pre-formed and isolated prior to polymerization or being generated in situ during a polymerization reaction.

Definitions

[0014] All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” with respect to the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art. Unless otherwise indicated, room temperature is about 23 °C.

[0015] As used in the present disclosure and claims, the singular forms “a,” “an,” and “the” include plural forms unless the context clearly dictates otherwise. The term “and/or” as used in a phrase such as “A and/or B” herein is intended to include “A and B,” “A or B,” “A,” and “B.” [0016] For the purposes of the present disclosure, the new numbering scheme for groups of the Periodic Table is used. In said numbering scheme, the groups (columns) are numbered sequentially from left to right from 1 through 18, excluding the f-block elements (lanthanides and actinides).

[0017] As used herein, Mn is number average molecular weight, Mw is weight average molecular weight, and Mz is z average molecular weight, wt% is weight percent, and mol% is mole percent. Molecular weight distribution (MWD), also referred to as polydispersity index (PDI), is defined to be Mw divided by Mn. Unless otherwise noted, all molecular weight units (e.g., Mw, Mn, and Mz) are in units of g/mol (g-mol ^-1 ). Procedures for analyzing polymers and determining molecular weights thereof are specified below.

[0018] For purposes of this specification and the claims appended thereto, when a polymer or copolymer is referred to as comprising a cyclic ester (lactone), the cyclic ester present in such polymer or copolymer is the polymerized form of the cyclic ester. For example, when a copolymer is said to have an "E-caprolactone" content of 35 wt% to 55 wt%, it is understood that the mer unit in the copolymer is derived from ring opening of the E-caprolactone during polymerization to provide a carboxylic acid on one end of the mer unit and a hydroxyl group at the other end of the mer unit, and the quantity of mer units derived from E-caprolactone in the copolymer is 35 wt% to 55 wt%, based upon the weight of the copolymer. A “polymer” has two or more of the same or different mer units. A “homopolymer” is a polymer having mer units that are the same. A “copolymer” is a polymer having two or more mer units that are different from each other. A “terpolymer” is a polymer having three mer units that are different from each other. Accordingly, the definition of copolymer, as used herein, includes terpolymers and the like. “Different” as used herein to refer to mer units indicates that the mer units differ from each other by at least one atom or are different isomerically. An " E-caprolactone polymer," " e-caprolactone copolymer" or “e-polycaprolactone” is a polymer or copolymer comprising at least 50 mol% E-caprolactone derived units, a " £-decalactone polymer," " E-decalactone copolymer" or “£-polydecalactone” is a polymer or copolymer comprising at least 50 mol% E-decalactone derived units, and so on.

[0019] The terms “group,” “radical,” and “substituent” may be used interchangeably herein. [0020] The term “hydrocarbon” refers to a class of compounds having hydrogen bound to carbon, and encompasses saturated hydrocarbon compounds, unsaturated hydrocarbon compounds, and mixtures of hydrocarbon compounds (saturated and/or unsaturated), including mixtures of hydrocarbon compounds having different numbers of carbon atoms. The term “C _n ” refers to hydrocarbon(s) or a hydrocarbyl group having n carbon atom(s) per molecule or group, wherein n is a positive integer. Such hydrocarbon compounds may be one or more of linear, branched, cyclic, acyclic, saturated, unsaturated, aliphatic, or aromatic. As used herein, a cyclic hydrocarbon may be referred to as “carbocyclic,” which includes saturated, unsaturated, and partially unsaturated carbocyclic compounds as well as aromatic carbocyclic compounds. The term “heterocyclic” refers to a carbocyclic ring containing at least one ring heteroatom. A cyclic ester is a heterocyclic ring by virtue of the ester oxygen present within the ring atoms.

[0021] The terms “hydrocarbyl radical,” “hydrocarbyl group,” or “hydrocarbyl” may be used interchangeably and are defined to mean a group consisting of hydrogen and carbon atoms only and bearing at least one unfilled valence position when removed from a parent compound. Preferred hydrocarbyls are C ₁ -C ₁₀₀ radicals that may be linear or branched. Examples of such radicals include, but are not limited to, alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl, octyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl, and/or the like. The term "hydrocarbyl group having 1 to about 100 carbon atoms" may refer to a moiety selected from a linear, cyclic, or branched C ₁ -C ₁₀₀ alkyl groups. Suitable hydrocarbyl groups may also include aryl groups in the disclosure herein, such as C ₆ -C ₁₄ aryl groups, which may contain one or more aromatic rings.

[0022] The term “optionally substituted” means that a hydrocarbon or hydrocarbyl group can be unsubstituted or substituted. For example, the term “optionally substituted hydrocarbyl” refers to replacement of at least one hydrogen atom or carbon atom in a hydrocarbyl group with a heteroatom or heteroatom functional group. Unless otherwise specified as being expressly unsubstituted, any of the hydrocarbyl groups herein may be optionally substituted. The term “substituted” means that at least one hydrogen atom in a parent hydrocarbyl group has been replaced with at least a non-hydrogen group, such as a hydrocarbyl group, a heteroatom, or a heteroatom-containing group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -AsR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR*, -SiR* ₃ , -GeR*, -GeR* ₃ , -SnR*, -SnR* ₃ , -PbR* ₃ , and the like, where each R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated, or aromatic cyclic or polycyclic ring structure, or where at least one heteroatom has been inserted in place of a carbon atom within a carbon chain or a ring structure of a parent hydrocarbyl group.

[0023] Substituted hydrocarbyl radicals are radicals in which at least one hydrogen atom of the hydrocarbyl radical has been replaced with a heteroatom, or a heteroatom-containing group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -AsR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR*, -SiR* ₃ , -GeR*, -GeR* ₃ , -SnR*, -SnR* ₃ , -PbR* ₃ , and the like, where each R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated, or aromatic cyclic or polycyclic ring structure, or where at least one heteroatom has been inserted in place of a carbon atom within a carbon chain or ring structure of a parent hydrocarbyl group.

[0024] Cyclopentadiene and fused cyclopentadienes (e.g., indene, tetrahydroindene, and fluorene) may complex a metal atom through n-bonding. Substituted cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl groups are cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl groups where at least one hydrogen atom has been replaced with at least a non- hydrogen group, such as a hydrocarbyl group, a heteroatom, or a heteroatom-containing group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -AsR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR*, -SiR* ₃ , -GeR*, -GeR* ₃ , -SnR*, -SnR* ₃ , -PbR* ₃ , and the like, where each R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated, or aromatic cyclic or polycyclic ring structure, or where at least one heteroatom has been inserted in place of a carbon atom within a carbon chain or a ring structure of a parent hydrocarbyl group.

[0025] Halocarbyl radicals (also referred to as halocarbyls, halocarbyl groups or halocarbyl substituents) are radicals in which one or more hydrocarbyl hydrogen atoms have been substituted with at least one halogen (e.g., F, Cl, Br, I) or halogen-containing group. Substituted halocarbyl radicals are radicals in which at least one halocarbyl hydrogen or halogen atom has been substituted with at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -ASR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR* ₃ , -GeR* ₃ , -SnR* ₃ , -PbR* ₃ , and the like or where at least one non-carbon atom or group has been inserted within the halocarbyl radical in place of a carbon atom, such as — O— , — S— , — Se— , — Te— , — N(R*)— , =N— , — P(R*)— , =P— , — As(R*)— , =As— , — Sb(R*)— , =Sb-, — B(R*)— , =B— , -Si(R*) ₂ -, -Ge(R*) ₂ -, -Sn(R*) ₂ -, -Pb(R*) ₂ - and the like, where R* is independently a hydrocarbyl or halocarbyl radical provided that at least one halogen atom remains on the original halocarbyl radical. Additionally, two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure.

[0026] Hydrocarbylsilyl groups, also referred to as silylcarbyl groups, are radicals in which one or more hydrocarbyl hydrogen atoms have been substituted with at least one SiR* ₃ containing group or where at least one -Si(R*) ₂ - has been inserted for a carbon atom within the hydrocarbyl radical, where R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure. Silylcarbyl radicals can be bonded via a silicon atom or a carbon atom.

[0027] Substituted silylcarbyl radicals are silylcarbyl radicals in which at least one hydrogen atom has been substituted with at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -ASR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -GeR* ₃ , -SnR* ₃ , -PbR ₃ and the like or where at least one non-hydrocarbon atom or group has been inserted within the silylcarbyl radical, such as — O— , -S-, -Se-, -Te-, — N(R*)~, =N-, -P(R*)-, =P-, -As(R*)-, =As-, -Sb(R*)-, =Sb-, — B(R*)— , =B— , — Ge(R*) ₂ — , — Sn(R*) ₂ — , — Pb(R*) ₂ — and the like, where R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure.

[0028] Germylcarbyl radicals (also referred to as germylcarbyls, germylcarbyl groups or germylcarbyl substituents) are radicals in which one or more hydrocarbyl hydrogen atoms have been substituted with at least one GeR* ₃ containing group or where at least one -Ge(R*) ₂ - has been inserted for a carbon atom within the hydrocarbyl radical where R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure. Germylcarbyl radicals can be bonded via a germanium atom or a carbon atom.

[0029] Substituted germylcarbyl radicals are germylcarbyl radicals in which at least one hydrogen atom has been substituted with at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -AsR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR* ₃ , -SnR* ₃ , -PbR ₃ and the like or where at least one non-hydrocarbon atom or group has been inserted for a carbon atom within the germylcarbyl radical, such as — O— , — S— , — Se— , — Te— , — N(R*)— , =N— , — P(R*)— , =P— , — As(R*)— , =As-, -Sb(R*)-, =Sb— , — B(R*)— , =B-, -Si(R*) ₂ -, -Sn(R*) ₂ -, -Pb(R*) ₂ - and the like, where R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure.

[0030] The terms “alkyl radical,” “alkyl group,” and “alkyl” are used interchangeably throughout this disclosure and refer to a saturated hydrocarbyl group. For purposes of this disclosure, “alkyl radicals” are defined to be C ₁ -C ₁₀₀ alkyls that may be linear, branched, or cyclic. Examples of such radicals can include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl, octyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl, and the like. Substituted alkyl radicals are radicals in which at least one hydrogen atom of the alkyl radical has been substituted with at least a non-hydrogen group, such as a hydrocarbyl group, a heteroatom, or a heteroatom-containing group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -ASR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR*, -SiR* ₃ , -GeR*, -GeR* ₃ , -SnR*, -SnR* ₃ , -PbR* ₃ , and the like, where each R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure, or where at least one heteroatom has been inserted for a carbon atom within a hydrocarbyl chain or ring.

[0031] The term “branched alkyl” means that the alkyl group contains a tertiary or quaternary carbon (a tertiary carbon is a carbon atom bound to three other carbon atoms; a quaternary carbon is a carbon atom bound to four other carbon atoms). For example, 3,5,5-trimethylhexylphenyl is an alkyl group (hexyl) having three methyl branches (hence, one tertiary and one quaternary carbon) and thus is a branched alkyl bound to a phenyl group.

[0032] The term “alkenyl” means a straight-chain, branched-chain, or cyclic hydrocarbon radical having one or more carbon-carbon double bonds. These alkenyl radicals may be optionally substituted. Examples of alkenyl radicals can include ethenyl, propenyl, allyl, 1,4-butadienyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl and the like.

[0033] The term “arylalkenyl” means an aryl group where a hydrogen has been replaced with an alkenyl or substituted alkenyl group. For example, styryl indenyl is an indene substituted with an arylalkenyl group (a styrene group).

[0034] The term “alkoxy”, “alkoxy!”, or “alkoxide” mean an alkyl group bound to an oxygen atom, such as an alkyl ether or aryl ether group/radical and can include those where the alkyl group is a Ci to Cio hydrocarbyl, for example. The alkyl group may be straight chain, branched, or cyclic. The alkyl group may be saturated or unsaturated. Examples of suitable alkoxy groups and radicals can include methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy, tert-butoxy, and the like.

[0035] The term “aryloxy” or “aryloxide” means an aryl group bound to an oxygen atom, such as an aryl ether group/radical wherein the term aryl is as defined herein. Examples of suitable aryloxy radicals can include phenoxyl and the like.

[0036] The term “aryl” or “aryl group” means a carbon-containing aromatic ring such as phenyl or fused phenyl. Likewise, heteroaryl means an aryl group where a ring carbon atom (or two or three ring carbon atoms) has been replaced with a heteroatom, such as N, O, or S. As used herein, the term “aromatic” also refers to pseudoaromatic heterocycles which are heterocyclic substituents that have similar properties and structures (nearly planar) to aromatic heterocyclic ligands, but are not by definition aromatic.

[0037] Heterocyclic means a cyclic group where a ring carbon atom (or two or three ring carbon atoms) has been replaced with a heteroatom, such as N, O, or S. A heterocyclic ring is a ring having a heteroatom in the ring structure as opposed to a heteroatom-substituted ring where a hydrogen on a ring atom is replaced with a heteroatom or heteroatom functional group. For example, tetrahydrofuran is a heterocyclic ring, and 4-N,N-dimethylaminophenyl is a heteroatom-substituted ring.

[0038] Substituted heterocyclic means a heterocyclic group where at least one hydrogen atom of the heterocyclic radical has been substituted with at least a non-hydrogen group, such as a hydrocarbyl group, a heteroatom, or a heteroatom-containing group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -ASR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR*, -SiR* ₃ , -GeR*, -GeR* ₃ , -SnR*, -SnR* ₃ , -PbR* ₃ , and the like, where each R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure.

[0039] A substituted aryl is an aryl group where at least one hydrogen atom of the aryl radical has been substituted with at least a non-hydrogen group, such as a hydrocarbyl group, a heteroatom, or a heteroatom-containing group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR* ₂ , -OR*, -SeR*, -TeR*, -PR* ₂ , -AsR* ₂ , -SbR* ₂ , -SR*, -BR* ₂ , -SiR*, -SiR* ₃ , -GeR*, -GeR* ₃ , -SnR*, -SnR* ₃ , -PbR* ₃ , and the like, where each R* is independently a hydrocarbyl or halocarbyl radical, or two or more R* may join together to form a substituted or unsubstituted saturated, partially unsaturated or aromatic cyclic or polycyclic ring structure, or where at least one heteroatom has been inserted within a hydrocarbyl ring. For example, 3,5-dimethylphenyl is a substituted aryl group. [0040] The term “substituted phenyl, ” or “substituted phenyl group” means a phenyl group having one or more hydrogen atoms replaced by a hydrocarbyl, substituted hydrocarbyl, heteroatom or heteroatom-coataining group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as - - % and the like, where each R* is independently a hydrocarbyl, halogen, or halocarbyl radical , .Preferably the “substituted phenyl” group is represented by the formula: where each of is independently selected from hydrogen hydrocarbyl or substituted hydrocarbyl, a heteroatom, such as halogen, or a heteroatom- containing group (provided that at least one of is not H), or two or more of are joined together to form a cyclic or polycyclic ring structure, or a combination thereof. Fused bicyclic and polycyclic aromatic rings are included within the definition of substituted phenyl groups. [0041] The term “substituted naphthyl,” means a naphthyl group having I or more hydrogen atoms replaced by a hydrocarbyl, substituted hydrocarbyl, heteroatom or heteroatom-containing group.

[0042] A “fluorophenyl or “fluorophenyl group” is a phenyl group substituted with one, two, three, four or five fluorine atoms. [0043] The term “substituted fluorenyl” means a fluorenyl group having 1 or more hydrogen atoms replaced by a hydrocarbyl, substituted hydrocarbyl, heteroatom or heteroatom -containing group.

[0044] T he term “arylalkyl” means an aryl group where a hydrogen atom has been replaced with an alkyl or substituted alkyl group. For example, 3,5’-di-teri-butylphenyl indenyl is an indene substituted with an arylalkyl group. When an arylalkyl group is a substituent on another group, it is bound to that group via the aryl .

[0045] The term “alkyl ary I” means an alkyl group where a hydrogen atom has been replaced with an aryl or substituted aryl group. For example, phenethyl indenyl is an indene substituted with an ethyl group bound to a phenyl group. When an alkylaryl group is a substituent on another group, it is bound to that group via the alkyl.

[0046] Reference to an alkyl, alkenyl, alkoxide, or aryl group without specifying a particular isomer (e.g., butyl) expressly discloses all isomers (e.g., n-butyl, iso-butyl, sec-butyl, and tert- butyl), unless otherwise indicated.

[0047] The term “ring atom” means an atom that is part of a cyclic ring structure. Accordingly, a benzyl group has 6 ring atoms and tetrahydrofuran has 5 ring atoms.

[0048] As used herein, and unless otherwise specified, the term “C _n ” means hydrocarbon(s) or hydrocarbyl groups having n carbon atom(s) per molecule, wherein n is a positive integer.

[0049] “Complex” or “metal-ligand complex” as used herein, refers to a metal compound bonded to one or more organic or inorganic substituents that donate a pair of electrons to a metal atom.

[0050] An “anionic ligand” is a negatively charged ligand which donates one or more pairs of electrons to a metal atom, such as a transition metal atom or a lanthanide metal atom. A “neutral donor ligand” is a neutrally charged ligand which donates one or more pairs of electrons to a metal atom, such as a transition metal atom or a lanthanide metal atom.

[0051] The term “metallocene” describes an organometallic compound with at least one cyclopentadienyl moiety or substituted cyclopentadienyl moiety (such as substituted or unsubstituted cyclopentadienyl (Cp) and/or indenyl (Ind)) and more frequently two (or three) cyclopentadienyl moieties or substituted cyclopentadienyl moieties (such as substituted or unsubstituted Cp and/or Ind).

[0052] The following abbreviations may be used herein: Me is methyl, Et is ethyl, Pr is propyl, cPR is cyclopropyl, nPr is n-propyl, iPr is isopropyl, Bu is butyl, nBu is normal butyl, iBu is isobutyl, sBu is sec-butyl, tBu is tert-butyl, Oct is octyl, Ph is phenyl, dme is 1 ,2-dimethoxyethane, p-tBu is para-tertiary butyl, TMS is trimethylsilyl, p-Me is para-methyl, Bz and Bn are benzyl (i.e. THF (also referred to as thf) is tetrahydrofuran, RT is room temperature (and is 23°C unless otherwise indicated), tol is toluene, EtOAc is ethyl acetate, Cbz is Carbazole, and Cy is cyclohexyl.

[0053] “Catalyst productivity” is a measure of the mass of polymer produced using a known quantity of polymerization catalyst. Typically, “catalyst productivity” is expressed in units of (g of polymer)/(g of catalyst) or (g of polymer)/(mmols of catalyst) or the like. If units are not specified then the “catalyst productivity” is in units of (g of polymer)/(grams of catalyst). For calculating catalyst productivity only the weight of the metal component of the catalyst is used. "Catalyst activity" is a measure of the mass of polymer produced using a known quantity of polymerization catalyst per unit time for batch and semi-batch polymerizations. For calculating catalyst productivity only the weight of the metal component of the catalyst is used. Typically, “catalyst activity" is expressed in units of (g of of catalyst )/hour or (kg of polymer)/(mmol of catalyst)/hour or the like. If units are not specified then the “catalyst activity” is in units of (g of polymer)/(mmol of catalyst)/hour,

[0054] ’’Conversion" is the percentage of a monomer that is converted to polymer product in a polymerization, and is reported as % and is calculated based on the polymer yield, the polymer composition, and the amount of monomer fed into the reactor.

Ligands and Metal-Ligand Complexes

[0055] Metal-ligand complexes of the present disclosure may comprise a lanthanide metal atom and a ligand having a structure represented by Formula 1 below.

In Formula L are independently hydrogen or a optionally substituted hydrocarbyl, halocarbyl, silylcarbyl, aminocarbyl, gennylcarbyl, oxyhydrocafbyl, halide, or siloxyl group, more preferably independently hydrogen or a optionally substituted hydrocarbyl group, or still more preferably independently hydrogen or a hydrocarbyl group; are independently hydrogen or a optionally substituted hydrocarbyl, halocarbyl, silylcarbyl, aminocarbyl, gennylcarbyl, oxyhydrocarbyl, halide, or siloxyl group, more preferably independently hydrogen or a optionally substituted hydrocarbyl group, or still more preferably independently hydrogen or a hydrocarbyl group, or ’ and R ⁴ are joined together to form an optionally substituted 6-membered aromatic ring; R ⁵ is an optionally substituted hydrocarbyl group, more preferably a hydrocarbyl group; are independently hydrogen or a optionally substituted hydrocarbyl, halocarbyl, siiylcarbyl, aminocarbyl, germylcarbyl, oxyhydrocarbyl, halide, or siloxyl group, more preferably independently hydrogen or a optionally substituted hydrocarbyl group, or still more preferably independently hydrogen or a hydrocarbyl group, or still more preferably hydrogen; and Z is a bridging atom, preferably a carbon atom. The ligand having a structure represented by Formula 1 may be bonded in at least a bidentate fashion to a metal atom, preferably a lanthanide metal atom, in the metal- ligand complexes disclosed herein. Alternative metal-ligand complexes that may also be used in the embodiments disclosed herein may substitute a transition metal atom for the lanthanide metal atom. Metal- ligand complexes containing transition metal atom may also be suitable for conducting ring- opening polymerization of cyclic esters in some instances.

[0057] In some embodiments, the metal-ligand complex may have a structure represented by Formula 1 A below.

In Formula 1A, M is the lanthanide metal atom; sol is a solvent coordinated to M, preferably a solvent containing a heteroatom coordinated to M; n is 0 or 1 , preferably n is 1; and X is independently a leaving group, or two Xs are joined and bound to M to form a metallocycle ring, a chelating ligand, a diene ligand, or an alkylidene. The other variables are defined as further specified herein,

[0058] A solvent molecule may or may not be coordinated to the lanthanide metal atom in Formula 1 A. That is, variable n may be 0 or 1. When n is 1 , a solvent, such as tetrahydrofuran, may be coordinated to M, The term “solvent,” as used herein, refers to organic compounds containing a heteroatom that may serve as a Lewis base when coordinating a lanthanide metal atom. Suitable solvents may be liquids at room temperature, but alternately may be solids. In addition to tetrahydrofuran (THF), other suitable solvents that may coordinate to the lanthanide metal atom include, for example, diethyl ether, thiophene, furan, or the like. Moreover, the term “solvent” is also inclusive of other organic Lewis base compounds that may coordinate to the lanthanide metal atom, even organic Lewis base compounds that are not traditionally thought of as solvents. Suitable organic Lewis base compounds that may alternately be coordinated to the lanthanide metal atom include, for example, phosphines, phosphine oxides, aliphatic amines, aromatic amines (e.g, pyridine or functionalized pyridines), or the like.

[0059] In Formula 1 A, X is independently a leaving group, where each X group can be same or different. Examples of suitable leaving groups X include, but are not limited to, a hydrocarbyl group (e.g., an alkyl group or an aryl group), a hydride, an amide, an alkoxide, a sulfide, a phosphide, a halide, an amine, a phosphine, an ether, or any combination thereof. Leaving groups X may be in a deprotonated or protonated (neutral) form. Preferably, one or more of the leaving groups X is a halide, an aryl group, a C ₁ to C ₂₀ alkyl group, an amide, or a combination thereof. More preferably, one or more of the X groups is an amide (e.g., dimethylamido, diethylamido, or dimethylsilylamido). Preferably, both X groups may be dimethylsilylamido. In the context of a leaving group, the term “amide” refers to an amine compound that has been deprotonated to leave a negative charge on nitrogen. Thus, dimethylamine may be deprotonated to form a dimethylamido ligand and bis(dimethylsilyl)amine may be deprotonated to form a bis(dimethylsilyl)amido ligand.

[0060] The lanthanide metal atom may be any one or a combination of lanthanide metals. A combination of lanthanide metals may be present when multiple metal-ligand complexes are combined together. Suitable lanthanide metals that may be present in the metal-ligand complexes include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. In more preferred examples, the lanthanide metal atom may be neodymium (Nd) or gadolinium (Gd).

[0061] In Formulas 1 and 1A, Z is a bridging group. Examples of suitable bridging groups where R' is hydrogen or a C ₁ -C ₂₀ hydrocarbyl, substituted hydrocarbyl, halocarbyl, substituted halocarbyl, silylcarbyl or germylcarbyl substituent. Optionally, two or more adjacent R' can be joined to form a substituted or unsubstituted, saturated, partially unsaturated or aromatic, cyclic or polycyclic substituent. More preferable examples of suitable bridging groups Z have one atom bridging between the pyrrole ring and the cyclopentadiene ring in Formulas 1 and 1 A. Particularly suitable examples of bridging groups Z include, R' ₂ Si (more preferably, R' is methyl) and CR'2 (more preferably, R' is H). That is, in a particular example, Z may be CH2.

[0062] In Formulas 1 and 1 A, R ¹ and R ² and/or R ⁶ and R ⁷ may be independently hydrogen or a C ₁ -C ₄₀ optionally substituted hydrocarbyl, halocarbyl, silylcarbyl, aminocarbyl, germylcarbyl, oxyhydrocarbyl, halide, or siloxyl group. Preferably, R ¹ and R ² and/or R ⁶ and R ⁷ are independently hydrogen or a C ₁ -C ₄₀ optionally substituted hydrocarbyl. More preferably, R ¹ and R ² and/or R ⁶ and R ⁷ are independently hydrogen or a C ₁ -C ₁₄ optionally substituted hydrocarbyl. Still more preferably, R ¹ and R ² and/or R ⁶ and R ⁷ are independently hydrogen, C ₁ -C ₁₀ alkyl, or C ₆ -C ₁₀ aryl. Example R ¹ and/or R ² and/or R ⁶ and R ⁷ groups may include, but are not limited to hydrogen, optionally substituted C ₁ -C ₁₀ alkyl groups (e.g., methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group), and optionally substituted phenyl. In a particular example, R ⁶ and R ⁷ may both be hydrogen and/or R ¹ and R ² may both be hydrogen.

[0063] In Formulas 1 and 1A, R ³ and R ⁴ may be independently hydrogen or a C ₁ -C ₄₀ optionally substituted hydrocarbyl, halocarbyl, silylcarbyl, aminocarbyl, germylcarbyl, oxyhydrocarbyl, halide, or siloxyl group. Preferably, R ³ and R ⁴ are independently hydrogen or a C ₁ -C ₄₀ optionally substituted hydrocarbyl. More preferably, R ³ and R ⁴ are independently hydrogen or a C ₁ -C ₁₄ optionally substituted hydrocarbyl. Optionally, R ³ and R ⁴ may be joined together to form an optionally substituted carbocyclic or heterocyclic ring. For instance, R ³ and R ⁴ may be joined to form an optionally substituted cycloaliphatic, aromatic or heteroaromatic ring. In one example, R ³ and R ⁴ may be joined to form an optionally substituted 6-membered aromatic ring. Further, R ³ and R ⁴ may be joined to form a fused 6-membered aromatic ring that bears one or more additional fused rings. Example R ³ and/or R ⁴ groups may include, but are not limited to, hydrogen, optionally substituted C ₁ -C ₁₀ alkyl groups (e.g., methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group), and optionally substituted phenyl. [0064] In Formulas 1 and 1A, is hydrogen or a ydrocarbyl group. Preferably, is a hydrocarbyl group, more preferably a . In more specific examples, may be methyl or t-butyl. In another embodiment, may be a aryl group or a aryl group. [0065] The ligand having a structure represented by Formula 1. may be alternately represented by Formula 2 below.

Formula 2 wherein Cp represents an optionally substituted cyclopentadienyl portion of the ligand, Pyr represents an optionally substituted pyrrolidinyl portion of the ligand, and Z is defined as above.

Optionally substituted cyclopentadienyl portions include, but are not limited to, fused cyclopentadienyl rings, such as indenyl rings. The optionally substituted cyclopentadienyl portion of the optionally substituted pyrrolidinyl portion of the ligand may be substituted with one or more substituents specified in more detail above. [0066] Specific examples of structures that may be present in the cyclopentadienyl (Cp) portion of Formula 2 include, but are not limited to, those having structures represented by the following formulas (the wavy line indicates bonding to Z):

[0067] Specific examples of structures that may be present in the pyrrol idinyl (Pyr) portion of Formula 2 include, but are not limited to, those having structures represented by the following formulas (the wavy lines indicate bonding to Z or to a metal-ligand bond from the pyrrol idinyl nitrogen atom):

[0068] Specific examples of ligands defined by Formula 2 may include, but are not limited to, those defined by Formulas 3-7 below,

[0069] In more specific examples, the present disclosure provides metal-ligand complexes having structures represented by Formulas 3A through 7 A below, wherein M represents the lanthanide metal in Formula I A being complexed by the ligand, specifically the ligands represented by Formulas 3-7:

Formula 7 A

In any of the foregoing specific examples, M may be Nd and n may be 1. For purposes of discussion below, such metal-ligand complexes may be referred to as Formula 3A-Nd, Formula 4A-Nd, Formula 5A-Nd, Formula 6A-'Nd, and Formula 7A-Nd. In another example, M may be Gd. It is again to be appreciated that other solvents or organic Lewis base compounds may replace THF in alternative metal-ligand complexes.

[0070] Scheme 1 below shows an example scalable synthetic route for ligands having 2-aryl substituted pyrroles, which may be accessed via commercially available N-Boc-2-pyrrole boronic acid (BOC = 2-t-butoxycarbonyl). In Scheme 1 , reaction step (i) is a cross-coupling reaction, where “Ar” is an aryl group and “X” is a leaving group (eg., a halide). For example, the reaction step (i) can be a Suzuki-Miyaura crossing coupling reaction using palladium or nickel catalysts. Reaction step (ii) is an ester deprotection reaction to form the 2-aryl substituted pyrrole. Reaction step (iii) is formyiation reaction, where the 2-aryl substituted pyrrole is functionalized with a formyl group at the 5 -position. In reaction step (i v), the 2-aryl substituted pyrrole is functionalized with an indeny 1 group to form the bridged structure of the ligand.

Reaction step (v) is a reduction of the alkylidene group to form a bridge. Finally, reaction step (vi) forms the metal-ligand complex from the ligand and a suitable metal atom precursor. As shown in Scheme 1 , the metal compound can comprise a lanthanide metal atom M and one or more amido leaving groups

Scheme 2 illustrates an example scalable synthetic route for ligands having 2-aIkyl substituted pyrroles. In reaction step (i), pyrrole can be functionalized with a precursor to a formyl group and subsequently alkylated with an alkyl group in step (ii). In reaction step (iii), the 2-alkyl substituted pyrrole is functionalized with an indeny 1 group to form the bridged structure of the ligand. Reaction step (i v) is a reduction of the alkylidene group to form a bridge. Reaction step (y) forms the metal-ligand complex from the ligand and a suitable metal atom precursor. As shown in Scheme 2, the metal compound can comprise a lanthanide metal atom M and one or more amido leaving groups X (e.g., f ) [0072] Polymerization processes of the present disclosure may comprise providing a feed comprising at least one cyclic ester, contacting the feed with a metal-ligand complex of the present disclosure under polymerization reaction conditions, and forming a polyester by ring- opening polymerization of the at least one cyclic ester in the presence of the metal-ligand complex. Without being bound by any theory or mechanism, the lanthanide metal of the metal- ligand complex may coordinate a carbonyl group within the at least one cyclic ester, thereby promoting ring-opening and subsequent chain growth during the polymerization reaction. Advantageously, the polymerization reaction conditions may tolerate a wide range of reaction temperatures and not require inert atmosphere conditions to maintain catalytic activity of the metal-ligand complex. Preferably, the reaction temperature may be maintained at a temperature at or above which the reaction proceeds at a suitable rate but significant reversal of the polymerization reaction does not occur to reform cyclic ester monomer. That is, if the polymerization reaction temperature is too high, at least partial depolymerization may occur to result in incomplete conversion of monomer. The temperature at which depolymerization begins to occur for a given cyclic ester may vary based on the structure thereof. As a further advantage, the metal-ligand complexes disclosed herein may be effective to promote ring-opening polymerization of one or more cyclic esters in accordance with the foregoing without an activator or co-catalyst being present. As discussed further below, at least one chain-transfer agent may be present in some cases.

[0073] One metal-ligand complex may be utilized to promote polymerization in accordance with the foregoing, or two or more different metal-ligand complexes may be used. For purposes of this disclosure, one metal-ligand complex is considered different from another if the two complexes differ by at least one atom in the structure of the ligand, contain a different transition metal, or have a different coordinated solvent (or no coordinated solvent at all). For example, two different metal-ligand complexes maybe used to promote copolymerization of two or more cyclic esters, where polymerization of at least one of the cyclic esters is not effectively promoted by one of the metal-ligand complexes. When two metal-ligand complexes (A and B) are used to promote polymerization, the molar ratio of (A) metal-ligand complex to (B) metal-ligand complex may fall within the range of (A:B) 1 :1000 to 1000:1, alternately 1 :100 to 500:1, alternately 1 : 10 to 200 : 1 , alternately 1 : 1 to 100 : 1 , and alternately 1 : 1 to 75 : 1 , and alternately 5 : 1 to 50:1. The particular ratio chosen may depend upon the cyclic ester monomer(s) undergoing polymerization and/or the metal-ligand complexes chosen for promoting polymerization of the same. [0074] To conduct a polymerization reaction, the metal-ligand complex may be pre-formed and isolated prior to conducting the polymerization reaction or be formed in situ during the polymerization reaction. Surprisingly, depending on whether the metal-ligand complex is pre- formed or formed in situ may impact the molecular weight and polydispersity of the polyester resulting from ring-opening polymerization. Specifically, a pre-formed metal-ligand complex may afford a higher molecular weight polyester having a lower polydispersity compared to reaction conditions in which the metal-ligand complex is formed in situ during the polymerization reaction. When pre-formed, the metal-ligand complex may be mixed in a suitable solvent and heated to a suitable polymerization temperature, and the feed comprising at least one cyclic ester may be combined therewith. When the metal-ligand complex is formed in situ, a suitable lanthanide metal precursor and the ligand may be mixed together in a suitable solvent and heated for a sufficient period of time to form the metal-ligand complex. After the metal ligand complex has sufficiently formed, the feed comprising at least one cyclic ester may be combined therewith. Whether pre-formed or formed in situ, the metal-ligand complex may be added to the at least one cyclic ester, or the at least one cyclic ester may be added to the rnetal- ligand complex. The temperature used to form the metal-ligand complex in situ may be higher, lower, or the same as that used to promote the polymerization reaction, as discussed subsequently.

[0075] In non-limiting examples, the polymerization reaction conditions may include a temperature ranging from about 25°C to about 150°C, or about 40°C to about 100°C, or about 50°C to about 80°C, or about 60°C to about 110°C. Again, it is to be understood that the temperature for promoting the polymerization reaction may be chosen to afford a sufficiently rapid reaction rate while disfavoring the reverse reaction to reform cyclic ester monomer. That is, the polymerization reaction may be conducted within a temperature window under which ring-opening polymerization may occur for a specified monomer but without a significant amount of depolymerization occurring. Otherwise, incomplete monomer conversion may occur. Contact times between the metal-ligand complex and the at least one cyclic ester during a polymerization reaction may range from about 1 minute to about 8 hours, or about 5 minutes to about 5 hours, or about 15 minutes to about 4 hours, or about 20 minutes to about 2 hours, or about 30 minutes to about 1 hour.

[0076] The polymerization reaction may be conducted in a solvent, such as a non-polar hydrocarbon solvent. Suitable non-polar hydrocarbon solvents include alkanes, such as isopentane, hexane, n-heptane, octane, nonane, or decane, and cycloalkanes, such as cyclopentane or cyclohexane. Aromatic hydrocarbons, such as benzene, toluene, and ethylbenzene, may also be employed.

[0077] The polyesters produced by ring-opening polymerization according to the disclosure herein may be homopolymers, copolymers, or any combination thereof. When the polyesters produced by ring-opening polymerization are copolymers, the cyclic ester monomers used to produce the polyester may include two or more cyclic esters of the same ring size or of different ring sizes. Suitable cyclic esters for undergoing ring-opening polymerization according to the disclosure herein may include 4-membered cyclic esters, 5-membered cyclic esters, 6-membered cyclic esters, 7-membered cyclic esters, or any combination thereof. Cyclic esters containing a 7-membered ring may be preferred (e.g., due to their lower propensity to undergo depolymerization in the presence of the metal-ligand complexes) and comprise at least a portion of the feed subjected to the polymerization reaction conditions. Suitable cyclic esters containing a 7-membered ring may include e-caprolactone or any alkylated variant thereof, e-decalactone or any alkylated variant thereof, the like, or any combination thereof. Other suitable cyclic esters containing a 7-membered ring may include (-)-menthide, dihydrocarvide, and carvomenthide, all of which are biologically derived. Any of the foregoing biologically derived 7-membered cyclic esters may be homopolymerized, copolymerized with each other in any combination, and/or copolymerized in combination with E-caprolactone and/or £-decalactone. In some embodiments, a cyclic ester containing a 6-membered ring, such as L-lactide, may be copolymerized with a cyclic ester containing a 7-membered ring, such as E-caprolactone or any alkylated variant thereof, £-decalactone or any alkylated variant thereof, or any combination thereof. Other suitable cyclic esters containing a 6-membered ring that may be copolymerized with a cyclic ester containing a 7-membered ring may include, for example, p-dioxanone (l,4-dioxan-2-one) or any alkylated isomer thereof, m-dioxanone (l,3-dioxan-2-one) or any alkylated isomer thereof, γ-valerolacone or any alkylated isomer thereof, L-lactide, or any combination thereof. In some embodiments, a 4-membered cyclic ester, such as β-butyrolactone, may be homopolymerized or co-polymerized with a 7-membered cyclic ester, such as ε-caprolactone or E-decalactone.

[0078] The metal-ligand complexes may be present at a molar ratio of monomer:catalyst metal sufficient to promote polymerization. In non-limit examples, the molar ratio may range from about 1 :1 to about 10000:1, or about 50:1 to about 7500:1, or about 100:1 to about 5000:1, or about 500:1 to about 4000:1, or about 750:1 to about 3000:1, or about 800:1 to about 2500:1, or about 1000:1 to about 2000:1. [0079] In any embodiment, the metal-ligand complexes disclosed herein may be disposed on a solid support. The solid support may allow the ring-opening polymerization reaction to be conducted under heterogeneous conditions. In more specific embodiments, the solid support may comprise silica. Other suitable solid supports may include, but are not limited to, alumina, magnesium chloride, talc, inorganic oxides, or chlorides including one or more metals from Groups 2, 3, 4, 5, 13, or 14 of the Periodic Table, and polymers such as polystyrene, or functionalized and/or crosslinked polymers. Other inorganic oxides that may suitably function as solid supports include, for example, titania, zirconia, boron oxide, zinc oxide, magnesia, or any combination thereof. Combinations of inorganic oxides may be suitably used as solid supports as well. Illustrative combinations of suitable inorganic oxides include, but are not limited to, silica-alumina, silica-titania, silica-zirconia, silica-boron oxide, and the like.

[0080] In any embodiment, solid supports suitable for use in the disclosure herein can have a surface area ranging from about 10 to about 700 m ² /g, a pore volume in the range of about 0.1 to about 4.0 cc/g and average particle size in the range of about 5 to about 500 pm. More preferably, the surface area of the support material is in the range of about 50 to about 500 m ² /g, a pore volume of about 0.5 to about 3.5 cc/g, and average particle size of about 10 to about 200 pm. Most preferably, the surface area of the support material is in the range is from about 100 to about 400 m ² /g, apore volume is from about 0.8 to about 3.0 cc/g, and an average particle size is from about 5 to about 100 pm. The average pore size of the support material may range from about 10 to about 1000 A, preferably 50 to about 500 A, and most preferably 75 to about 350 A. In some embodiments, the support material may be a high surface area, amorphous silica (surface area=300 m ² /gm; pore volume of 1.65 cm ³ /gm). Preferred silicas are marketed under the tradenames of DAVISON™ 952 or DAVISON™ 955 by the Davison Chemical Division of W.R. Grace and Company. In other embodiments DAVISON™ 948 is used.

[0081] Polymerization processes of the present disclosure may be carried out in any manner known in the art. Any suspension, homogeneous, bulk, solution, slurry, or gas-phase polymerization process known in the art may be used. Such processes can be run in a batch, semi-batch, or continuous mode. The term "continuous" means a system that operates without interruption or cessation. For example, a continuous process to produce a polymer would be one where the reactants are continually introduced into one or more reactors and the polymer product is continually withdrawn. Homogeneous polymerization processes and slurry processes can be utilized in this manner, for example. A homogeneous polymerization process, including a solution polymerization process, is defined to be a process where at least 90 wt% of the product is soluble in the reaction media. A bulk homogeneous process may be particularly preferred. A bulk process is defined to be a process where monomer concentration in all feeds to the reactor is 70 vol% or more. Alternately, no solvent or diluent is present or added in the reaction medium. Further alternately, the polymerization process may be a slurry process. As used herein the term “slurry polymerization process” means a polymerization process where a supported catalyst is employed and monomers are polymerized on the supported catalyst particles. At least 95 wt% of polymer products derived from the supported catalyst may be in granular form as solid particles (not dissolved in the diluent). A heterogeneous process, including a slurry polymerization process, is defined to be a process where the catalyst is not soluble in the reaction medium.

[0082] Chain-transfer agents (CTAs) may be utilized in any of the polymerization processes disclosed herein. Chain-transfer agents may allow the polymerization reaction to produce additional polymer chains other than those originating from the cyclic ester and/or to control the molecular weight of the resulting polymer. Suitable chain-transfer agents may include water, alcohols (including diols and higher polyols), carboxylic acids (including dicarboxylic acids and higher polycarboxylic acids), or compounds containing amines, carboxylates, or thiol groups. More specific examples of suitable chain-transfer agents include water, ethanol, methanol, 1,4-benzenedimethanol, 1,2-trans-dihydroxycyclohexane, and terephthalic acid. Bifunctional chain-transfer agents (such as polyols) can be used in conjunction with the polymerization reactions disclosed herein to produce telechelic polymers having functional groups at both chain ends. Other suitable chain-transfer agents may include an oligomer or a polymer featuring one or more alcohol or carboxylic acid end groups. Telechelic polyol oligomers may be utilized as a chain transfer agent to produce telechelic polymers having a higher molecular weight. Suitable telechelic polyol oligomers may have alcohol groups at both ends of the oligomer chain, optionally in combination with further alcohol side chain groups.

[0083] In the polymerization reactions disclosed herein, the chain-transfer agent may be added separately to the polymerization reaction, or the chain-transfer agent may be released internally from the metal-ligand complex, preferably the leaving group X bound to the lanthanide metal. For example, bis(dimethylsilyhnine) released from the metal-ligand complex during polymerization may promote chain transfer in some cases. Internal release of the leaving group X during ring-opening polymerization may be facilitated in some case by forming the metal- ligand complex in situ during polymerization.

[0084] Processing of the resulting polyesters can take place following the polymerization reaction. Suitable processing operations may include, but are not limited to, blending or co- extrusion with any other polymer. Non-limiting examples of other polymers include, but are not limited to: linear low-density polyethylenes, elastomers, plastomers, high-pressure low-density polyethylene, high-density polyethylenes, polypropylenes, and/or the like. Preferably, a polymer blended with the polyesters produced according to the disclosure herein is at least partially miscible with the polyesters. The polyesters formed according to the present disclosure can also be blended with additives to form compositions that may then be used in articles of manufacture. Suitable additives may include, but are not limited to, antioxidants, nucleating agents, acid scavengers, plasticizers, stabilizers, anticorrosion agents, blowing agents, ultraviolet light absorbers, quenchers, antistatic agents, slip agents, phosphites, phenolics, pigments, dyes, fillers, curing agents, the like, and any combination thereof.

[0085] Polyesters produced according to the present disclosure may have a weight average molecular weight (Mw), determined as specified below, of about 500 to about 1,000, or about 1,000 to about 5,000, or about 5,000 to about 10,000, or about 10,000 g/mol to about 500,000 g/mol, or about 15,000 g/mol to about 350,000 g/mol, or about 20,000 g/mol to about 300,000 g/mol, or about 15,000 g/mol to about 50,000 g/mol, or about 50,000 g/mol to about 500,000 g/mol, or about 100,000 g/mol to about 400,000 g/mol. In some or other embodiments, polyesters produced according to the present disclosure may have a number average molecular weight (Mn), determined as specified below, of about 1,000 to about 5,000, or about 5,000 to about 10,000, or about 10,000 g/mol to about 300,000 g/mol, or about 15,000 g/mol to about 250,000 g/mol, or about 20,000 g/mol to about 200,000 g/mol, or about 10,000 g/mol to about 50,000 g/mol, or about 10,000 g/mol to about 25,000 g/mol, or about 100,000 g/mol to about 250,000 g/mol.

[0086] Based on the Mw and Mn values, polyesters produced according to the present disclosure may have a polydispersity (Mw/Mn) of about 1 to about 4, or 1.2 to about 4, or about 1.2 to about 2.5, or about 1.2 to about 2, or about 2 to about 2.5.

[0087] Polymer molecular weights in the disclosure herein are determined by size-exclusion chromatography (SEC). SEC data was collected using a Tosoh BioScience HLC-8320 GPC equipped with an internal differential refractive index (dRI) detector, an internal UV absorbance detector UV-8320 (254 nm absorbance detector), a Wyatt Technology miniDawn TREOS light scattering detector with three angles (45°, 90°, and 135°), and a Wyat Technology ViscoStar-II viscometer detector. Online determination of dn/ dc assumes 100% mass elution under the peak of interest. The mobile phase was THF with a 1 mL/miin flow rate, with the GPC pump oven and column oven temperatures set at 40°C. Wyat Technology’s Astra 6.1.7.17 Gel Permeation Chromatography Software was used for data analysis. [0088] Differential Scanning Calorimetry measurements were performed on a TA-QI 00 instrument to determine the melting point of the polymers. Samples were pre- annealed at 220°C for 15 minutes and then allowed to cool to room temperature overnight, The samples were then heated to 220°C al a rate of 100°C/minute and then cooled at a rate of 50°C/minute. Melting points [Tm (°C)] were collected during the heating period,

[0089] T he present disclosure further relates to the following non-limiting clauses:

[0090] Clause 1 , A metal-ligand complex comprising a lanthanide metal atom and a ligand having a structure represented by Formula 1 wherein: are independently hydrogen or a hydrocarbyl group; are independently hydrogen or a hydrocarbyl group, or are joined together to form an optionally substituted aromatic ring; hydrocarbyl group; are independently hydrogen or a 4 hydrocarbyl group; and

Z is a bridging atom.

[0091] Clause 2 , The metal-l igand complex of clause 1 , wherein the metal-ligand complex has a structure represented by Formula 1 A

wherein:

M is the lanthanide metal atom; sol is a solvent coordinated to M; n is 0 or 1 ; and

X is independently a leaving group, or two Xs are joined and bound to M to form a metallocycle ring, a chelating ligand, a diene ligand, or an alkylidene,

[0092] The metal-ligand complex of clause 2, wherein M is neodymium or gadolinium.

[0093] The metal-ligand complex of clause 2 or clause 3, wherein each X is bis(dimnethylsilylamido).

[0094] Clause 5. The metal-ligand complex of any one of clauses 2-4, wherein sol is tetrahydrofaran.

[0095] Clause 6. The metal-ligand complex of any one of clauses 2-5, wherein n is 1.

[0096] Clause 7 The metal-ligand complex of any one of clauses 1 -6, wherein Z is

[0097] Clause 8. The metal -ligand complex of any one of clauses 1 -7, wherein and are independently hydrogen alkyl, or aryl.

[0098] Clause 9. The metal-ligand complex of any one of clauses 1 -8, wherein are both hydrogen.

[0099] Clause 10. The metal-ligand complex of any one of clauses 1-9, wherein are both hydrogen. Clause 1 1 . The metal-ligand complex of any one of clauses 1-10, wherein and R ⁴ are each optionally substituted phenyl, or and R* are joined to form an optionally substituted 6-membered aromatic ring.

[0101] Clause 12. The metal-ligand complex of any one of clauses 1 -10, wherein R ³ and R ⁴ are joined together to form an optionally substituted 6-membered aromatic ring.

[0102] Clause 13. The metal-ligand complex of any one of clauses 1 -12, wherein is

[0103] Clause 14. The metal-ligand complex of any one of clauses 1 -13, wherein is methyl or t-butyl. [0104] Clause 15. The metal-ligand complex of any one of clauses 1 -14, wherein the ligand has a structure represented by one or more of Formulas 3-7

[0105] Clause 16. The metal-ligand complex of any one of clauses 1 - 15, wherein the metal - ligand complex has a structure represented by one or more of Formulas 3 A-7A

[0106] C lause 17. The metal-ligand complex of clause 16, wherein M is Nd and n is 1.

[0107] C lause 18. A method comprising: providing a feed comprising at least one cyclic ester; contacting the feed with the metal -ligand complex of clause 1 under polymerization reaction conditions; and forming a polyester by ring-opening polymerization of the at least one cyclic ester in a presence of the metal-ligand complex.

[0108] Clause 19. The method of clause 18, wherein the metal- ligand complex has a structure represented by Formula I A wherein:

M is the lanthanide metal atom; sol is a solvent coordinated to M; n is 0 or 1; and

X is independently a leaving group, or two Xs are joined and bound to M to form a metallocycle ring, a chelating ligand, a diene ligand, or an alkylidene.

[0109] Clause 20. The method of clause 19, wherein M is neodymium or gadolinium.

[0110] Clause 21. The method of clause 19 or clause 20, wherein each X is bis(dimethylsilylamido) . Clause 22. The method of any one of clauses 19-21, wherein sol is tetrahydrofuran.

[0112] Clause 23. The method of any one of clauses 19-22, wherein n is 1.

[0113] Clause 24. The method of any one of clauses 18-23, wherein Z is CH ₂ .

[0114] Clause 25. The method of any one of clauses 18-24, wherein R ¹ , R ² , R ⁶ , and R ⁷ are independently hydrogen, C ₁ -C ₁₀ alkyl, or aryl.

[0115] Clause 26. The method of any one of clauses 18-25, wherein R ¹ and R ² are both hydrogen.

[0116] Clause 27. The method of any one of clauses 18-26, wherein R ⁶ and R ⁷ are both hydrogen.

[0117] Clause 28. The method of any one of clauses 18-27, wherein R ³ and R ⁴ are each optionally substituted phenyl, or R ³ and R ⁴ are joined to form an optionally substituted 6-membered aromatic ring.

[0118] Clause 29. The method of any one of clauses 18-27, wherein R ³ and R ⁴ are joined together to form an optionally substituted 6-membered aromatic ring.

[0119] Clause 30. The method of any one of clauses 18-29, wherein R ⁵ is C ₁ -C ₁₀ alkyl or

[0120] Clause 31. The method of any one of clauses 18-30, wherein R ⁵ is methyl or t-butyl.

[0121] Clause 32. The metal-ligand complex of any one of clauses 18-31, wherein the ligand has a structure represented by one or more of Formulas 3-7

[0122] Clause 33. The method of any one of clauses 18-32, wherein the metal -ligand complex lias a structure represented by one or more of Formulas 3A-7A

[0123] Clause 34. The method of clause 33, wherein M is Nd and n is 1 . Clause 35. The method of any one of clauses 18-34, wherein the at least one cyclic ester comprises a lactone having a 7-membered ring.

[0125] Clause 36. The method of any one of clauses 18-34, wherein the at least one cyclic ester comprises or in combination with at least one lactone having a 7-membered ring. [0126] Clause 37. The method of any one of clauses 18-36, wherein the at least one cyclic ester comprises e-caproiactone, E-decalactoiie, or any combination thereof.

|0127[ Clause 38. The method of any one of clauses 18-37, wherein the feed is contacted with the metal-ligand complex in the presence of added chain-transfer agent.

|0128[ Clause 39. The method of any one of clauses 18-38, wherein the polymerization reaction conditions comprise heating the at least one cyclic ester at a temperature of up to about 100°C.

[0129] To facilitate a better understanding of the disclosure herein, the following examples of various representative embodiments are given. In no way should the following examples be read to limi t, or to define, the scope of the present disclosure.

Examples

[0130] Representative syntheses for ligands and metal -ligand complexes follow. The metal-ligand complexes may be pre-synthesized and isolated prior to polymerization or formed in situ during polymerization. Conditions for conducting ring-opening polymerization reactions using the metal-ligand complexes are described in further detail below.

Synthesis of Ligands

1 H-cyclopenta[l]phenanthrene (2.535 g) and were dissolved in 1% KOH-ethanol (60 mL) and the mixture was heated to reflux for two days. The color of the reaction deepened and ranged from orange to red. The solvent was reduced and then the reaction mixture was cooled io room temperature. The mixture was taken up into dichloromethane and washed with water and brine. The organics were collected, dried with MgSCu, and filtered. The solvent was removed and the resulting residue was carried to the next step without further purification. The compound was dissolved in 25 mL of tetrahydrofuran and cooled to was added as a powder, and the reaction was left to stir overnight. Further, the reaction was cooled to and quenched with ice water. The mixture was extracted with diethyl ether (3 x 50 ml), and the combined organics were washed with water and brine, dried over and filtered. TLC in 10% EtOAc/Hex was taken of the solution and showed good separation with some immobile material. After column chromatography (5-20% EtAcO/Hex), 2. 15 g (37%) of the title compound ligand was collected.

To a cold 5 niL methanol solution of 5-methyl-l H-pyrrole-2-carbaldehyde (535 mg) and 4,5, 6,7- tetramethyl-1Hindene (426 mg), pyrrolidine (281 mg) and acetic acid (599 mg) were added. The solution was warmed to room temperature and stirred for 2.5 hours, during which time the reaction mixture slo wly turned orange. The solution was cooled on ice and acetic acid was added at 0°C, followed by 10 mL of cold dichloromethane and 1 ml. waler. The resulting solids were stirred for 15 minutes at room temperature. The organics were separated by dichloromethane extraction, and the dicloromethane extracts were stirred over and filtered through Celite. The solvent was removed, and the remaining solids were stirred and washed with minimum hexane and diethyl ether to isolate a fulvene intermediate as a red powder which was used without further purification.

[0133] The fulvene intermediate was dissolved in 25 ml of tetrahydrofuran and cooled to -20°C. was added as a powder io the reaction mixture, which was then stirred overnight. The reaction mixture was then cooled to 0°C and quenched with ice water. The mixture was extracted with diethyl ether (3 x 50 m'L). The combined organics were washed with water and brine, dried ove , and filtered. After solvent removal under vacuum, the title compound (267 mg) was obtained as an orange solid.

The title compound (267 mg) was obtained in a similar manner to that described for Formula 4 in Example 2, except 2.3-dipheny1cyc1openta-l ,3-d.iene was substituted for 4,5,6,7-tetramethyl-

The title compound ( 594 mg) was obtained in a similar manner to that described for Formula 4 in Example 2, except was substituted for 4,5,6,7 indene.

The title compound (593 mg) was obtained in a similar manner to that described tor Formula 4 in Example 2, except was substituted for

4,5,6,7-tetramethyl- 1 H -inde ne. [0137] Example 6: Synthesis of Neodymium Complex of Formula 3 Ligand (Formula

3A-\d).

The ligand of Example 1 (Formula 3) and were combined in 4 mF toluene and stirred at 60°C for 16 hours. The solvent was removed, and the solids were extracted into 4 ml., filtered through Celile, and dried to give 40 mg orange powder in 40% yield. The structure was confirmed by X-ray crystallography. FIGS . 1 A and 1 B show alternative views of the X-ray crystal structure of the metal-ligand complex having Formula 3A-Nd, Polymerization Examples

[0138] Ring-opening polymerization reactions of E-caprolactone or £~decalactone were carried out using a lanthanide metal-ligand complex that was either generated in situ or previously synthesized and isolated. The conditions for each type of polymerization reaction are specified below. Further details regarding the polymerization reactions and characterization of the polymers obtained (herefrom are specified in Tables 1 A and 1 B below.

[0139] Pre-formed metal-ligand complexes: Polymerization reactions using pre-formed metal -ligand complexes Formula 3 A -Nd) were conducted by adding a 1 g toluene solution of the isolated metal-ligand complex to neat lactone (818 mg) at 70°C. The solution instantly gelled and was kept, at 70°C for an additional 2 hours. The gel was then cooled to room temperature and agitated with excess methanol. After agitation, the methanol, residual solvent, and soluble byproducts were removed by decantation. The isolated polymer was dried in a vacuum oven and then characterized. [0140] metal-ligand complexes. A 1 g toluene solution of was added to the ligand in a 1 : 1 molar ratio and the resulting solution was maintained at 70°C for 1 or 2 hours. The neat lactone was then added to the stirring reaction mixture, and the solution gelled within one minute. The gel was then cooled to room temperature and agitated with excess methanol. After agitation, the methanol, residual solvent, and soluble byproducts were removed by decantation. The isolated polymer was dried in a vacuum oven and then characterized.

[0141] Reverse addition of the in metal-ligand complexes was also performed by forming the toluene solution as above, adding the toluene solution to the neat lactone, and maintaining the reaction mixture at 70°C for 1-2 hours. Progress of the reaction was monitored by 'H NMR.

[0142] Polymer characterizations were conducted in accordance with the procedures set forth above.

[0143] As shown in Table 1A below, the metal-ligand complexes were effective for polymerizing both e-caprolactone and e-decalactone, either when pre-formed or generated in situ. [0144] As shown in Table IB below, the metal-ligand complexes were effective for polymerizing e-caprolactone and e-decalactone, both when pre-formed or generated in situ. The molecular weight values in Table IB are corrected values.

Surprisingly, the pre-formed metal-ligand complex (Entry 1) generated e-polycaprolactone with a much higher molecular weight and a lower polydispersity index (Mw/Mn) than when the same metal-ligand complex was generated in situ (Entry 2). A possible explanation for the vastly different molecular weight is a greater tendency for the metal precursor to release bis(dimethylsilyl)amine as a chain transfer agent when forming the complexes in situ, thereby lowering the polymer molecular weight. Otherwise, the polymerizations conducted upon each lactone exhibited similar molecular weights and polydispersity indices for the various metal- ligand complexes tested.

[0145] The in situ formed metal-ligand complexes were also effective to polymerize e-decalactone (Entries 3 and 8). The lower conversion in Entry 8 may result from the higher monomer: catalyst metal ratio used in this instance or the differing order of addition of the lactone to the catalyst solution. In either case, omitting the ligand when polymerizing e-decalactone (Entry 9) afforded a much lower percent conversion to polymer product.

[0146] All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.

[0147] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0148] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.

[0149] One or more illustrative embodiments are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for one of ordinary skill in the art and having benefit of this disclosure.

[0150] Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one having ordinary skill in the art and having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein.