Field of the invention

The present invention relates to the field of polymerized 1 ,3- benzoxazines.

Background art

Benzoxazine is a molecule where an oxazine ring (a heterocyclic six- membered ring with oxygen and nitrogen atom) is attached to a benzene ring. A specific 1 ,3-benzoxazine has the following structure:

Benzoxazines were first synthetized in 1940s, but their potential was recognized in the late 1990s. Benzoxazines are the reaction products of amine, phenol and formaldehyde. It is known that the benzoxazine ring is stable at room temperature for a long period of time, and that it starts to homopolymerize to form oligomers or polymers at elevated temperature.

Polymerization of benzoxazines was thought to be a candidate for replacing the condensation chemistry of phenolic resins. However, it is recognized that polybenzoxazine is a class of materials that goes far beyond phenolics, epoxies and bismaleimides, because benzoxazine resins have a wide range of thermal, chemical, electrical, mechanical and physical properties, which make them suitable to various needs as disclosed in H. Ishida and T. Agag (Eds.) Handbook of Benzoxazine Resins, Elsevier, Amsterdam, 2011 , page 4.

Polybenzoxazines can be applied to areas where polyesters, vinylesters, epoxies, phenolics, bismaleimides, cyanate esters, and polyimides are used, such as composite manufacturing, powder coating or materials for the transportation industry, due to excellent processability, no volatile formation, good mechanical properties, no dark smoke, self-extinguishing, low heat release rate, and low total heat release. Polybenzoxazines may also be used in electrical insulation systems, as disclosed in International patent application WO-A-2008/037545, or in International patent application WO-A-2008/034814, wherein it is disclosed a benzoxazine polymer showing high glass transition temperature, good electrical properties, low flammability, and near-zero percent shrinkage and expansion upon demoulding, postcuring, and cooling, and that these features make them suitable to provide a coating on electronic devices.

Copolymers of benzoxazines and other monomers, such as epoxy components, are potentially useful commercially, as disclosed in, for example, European patent application EP-A-0178414. Ternary systems of benzoxazine, epoxy and phenolic resins are disclosed in Rimdusit et ai, Development of New Class of Electronic Packaging Materials Based on Ternary Systems of Benzoxazine, Epoxy, and Phenolic Resins, Polymer, 2000, 41 , 7941-49. Benzoxazines have been also combined with thermoplastic or thermosetting resin compositions, as disclosed, for example, in WO-A-02/057279 or in WO-A-042196.

The ring opening polymerization of benzoxazines is easily obtained by heating the monomer, usually at temperatures in the range between 160° C and 220° C, if no initiators and/or catalysts are added.

Depending on the conditions of the polymerization, benzoxazines lead to a polymer having phenolic- or phenoxy-type structure, wherein the latter can be transformed to the former at elevated temperature:

Phenoxy type Phenolic type

High temperatures used in the polymerization of benzoxazines result in the decomposition of the polymers, and even decomposition and/or sublimation of the monomers, which represents lower yields, or uncontrolled cross-linking, which produce increased amounts of polymers insoluble in organic solvents.

Therefore, the reduction of the polymerization temperature in benzoxazine systems has been a target in prior art to minimize the above-mentioned problems. In prior art, different approaches to manage the polymerization of benzoxazines, in particular, to reduce the temperature of polymerization, have been disclosed.

Among them, different catalysts for polymerization reactions of a benzoxazine compound have been proposed, such as, for example:

- an organic component with electron withdrawing substituents in International patent application WO-A-2008/034814;

- a pentafluoroantimonic acid in International patent application WO-A- 2011/025652;

- a specific meta-substituted aromatic compound in International patent application WO-A-2011/050834;

- a lithium organic or inorganic in European patent application EP-A-2336221 ;

- lithium iodide in Liu et ai, Benzoxazines: A Mechanistically Based Catalyst Design, Macromolecules, 2011 , 44, 4616-22;

- various catalysts (Lil, LiCICL, LiSCN, LiBr, LiOPh, LiSPh, LiCI, LiOAc, LiOTf, Nal, Zn(OTf) ₂ , FeCh, p-TsOH H ₂ 0, NH ₄ I, ZnCI ₂ , CuCI ₂ , AI(OTf) ₃ , NFUSCN, AgOTf, CoCI ₂ , NaSCN, DMAP (4-dimethylaminopyridine), EMI (2-ethyl-4- methylimidazole), 4-hydroxypyridine, 3-hydroxypyridine, and 2-hydroxypyridine) in Liu et ai, Catalyst effects on the ring-opening polymerization of 1 ,3- benzoxazine and on the polymer structure, Polymer, 2013, 54, 2873-8;

- elemental sulphur, elemental selenium, and sulphides or selenides of Group V or VI elements in International patent application WO-A-2014/052255;

- a cationic catalyst comprised of a lithium cation and an anion comprising a hexahalogenated Group 15 element in International patent application WO-A- 2016/040541 ;

- an alkylammonium salt of an acid having a pKa in acetonitrile of 9 or more in International patent application WO-A-2016/200557; and

- elemental halogen or onium polyhalide compounds in International patent application WO-A-2018/051268.

In Salabert et ai, Photochemical Polymerization of /V-Phenyl Mono-1 , 3- benzoxazines in Aqueous Media, Macromolecules, 2018, 51 , 3672-9, it is disclosed the polymerization of /V-phenyl monosubstituted mono-1 , 3-benzoxazines under appropriate UV irradiation in very diluted aqueous solutions at room temperature. Thus, in spite of multiple technical proposals available in the state of the art, there is still the need to provide further processes for polymerizing benzoxazines, with a better control on the polymerization outcome.

Subject-matter of the invention

The subject-matter of the present invention is a process for polymerizing benzoxazines.

Another aspect of the invention relates to the polymerized benzoxazine obtainable according to that process.

Another aspect of the invention relates to the use of that polymerized benzoxazine.

Figures

Figures 1a and 1 b shows typical ¹ H NMR spectra in deuterated DMSO of cured mixtures of benzoxazine compound of formula (VII) under different conditions. In Figure 1a it is shown the spectrum of the product resulting from an incomplete conversion, and Figure 1 b shows full conversion. As exposed below, Figure 1a may be used in the calculation of conversion, and in Figure 1 b in the calculation of the ratio of phenolic to phenoxy polymers after the polymerization.

Figure 2 shows a list of compounds.

Detailed description of the invention

The object of the present invention is a process for polymerizing 1 ,3- benzoxazines by photoinduction, which comprises:

a) dissolving a 1 ,3-benzoxazine compound according to general formula (I)

wherein at least one of R, Ri, R2, R3 and R4 is an organic group, which contains an aryl group,

and a catalyst in a suitable solvent, and b) irradiating the mixture of step a) with light at a wavelength selected from 450 nm to 700 nm.

The inventors of the present invention have developed a process for polymerizing 1 ,3-benzoxazines by photoinduction, which surprisingly takes place irradiating the components at room temperature and without using UV radiation. The irradiation at a specific wavelength generates a heating in the component, arriving at temperatures clearly lower than those used in thermal polymerization processes disclosed in prior art. The process is suitable to provide full conversion, i.e. quantitative yield, because decomposition and/or sublimation are not observed. Additionally, polymer obtained according to the process of the invention is soluble in organic solvents, because uncontrolled crosslinking is prevented or, at least reduced, due to working at lower temperatures. Polymerized 1 ,3-benzoxazines obtained with that process show mainly a phenoxide structure, which can be converted into a phenolic structure simply by heating, as exposed above.

The process, based on irradiation at specific wavelength, allows selective polymerization, yielding polymers showing different Tg values from polymers obtained by thermal polymerization without catalyst.

It is also surprising that the phenolic type polymers obtained according to the process of the invention show better solubility organic solvents than the phenolic type polymers obtained directly by thermal polymerization at 200° C.

Throughout the present description and in the claims, the expressions in singular preceded by the articles“a” or“the” are understood to also include, in a broad manner, the reference to the plural, unless the context clearly indicates the contrary.

In the context of the present invention, it is understood that the term “approximately” referred to a determined value indicates that a certain variation for said value is accepted, generally of +/- 5 %.

The numerical ranges disclosed herein are meant to include any number falling within the ranges and also the lower and upper limits.

The description herein of any aspect or aspect of the invention using terms such as "comprising", "having," "including," or "containing" with reference to an element or elements is intended to provide support for a similar aspect or aspect of the invention that "consists of", "consists essentially of", or "substantially comprises" that particular element or elements, unless otherwise stated or clearly contradicted by context. Benzoxazine compound

In the context of the invention, terms 1 ,3-benzoxazine and benzoxazine are used indistinctly.

In the process of the invention it is used a 1 ,3-benzoxazine compound according to general formula

wherein at least one of R, Ri , R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group.

In a preferred embodiment, the benzoxazine is compound of formula (I), wherein

R is H, alkyl, aryl, heteroaryl, aralkyl, or a residue of formula (II):

wherein

Y is -(CH ₂ ) _n -, wherein n is 2 - 12, p-phenylene, o-phenylene, 4,4’-biphenyl, p-phenylene-CH ₂ -p-phenylene or -p-phenylene-CMe ₂ -p-phenylene; and

R”i , R ^M ₂ , R’ ₃ and R’ ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR” ₅ , C0 ₂ R” ₆ , NR” ₇ R” ₈ , CN, N0 ₂ ; or any of R”i and R” ₂ or R” ₂ and R’ ₃ or R’ ₃ and R’ ₄ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N; preferably R”i , R’ ₂ , R’ ₃ and R” ₄ are H; R” ₅ and R” ₆ are, independently of each other, alkyl or aryl; preferably R'V and R” ₆ are Me or Et;

R’V and R”s are, independently of each other, H, alkyl, aryl or aralkyl; preferably R’V is H and R”s is Ph, o R’V and R”s are Ph; preferably R is methyl, ethyl, propyl, or phenyl, more preferably methyl or phenyl, and more preferably phenyl;

R is preferably methyl, ethyl, propyl, or phenyl, more preferably methyl or phenyl, and more preferably phenyl;

Ri , R ₂ , R ₃ and R ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR5, CO2R6, NR7R8, CN, NO2, or Ri and R2 or R2 and R3 or R3 and R4 form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N; preferably Ri is H or Me, and more preferably Ri is H; yet more preferably Ri , R ₂ and R ₄ are H, and R ₃ is Me, CN, OMe, CC> ₂ Et, NO ₂ , or NPh ₂ ; or Ri and R ₂ are H and R ₃ and R ₄ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or Ri and R ₄ are H and R ₂ and R ₃ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or R ₃ and R ₄ are H and Ri and R ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3;

R ₅ and Re are, independently of each other, alkyl or aryl; preferably R ₅ and Rs are Me or Et; and

R ₇ and Rs are, independently of each other, H, alkyl, aryl or aralkyl; preferably R ₇ is H and Rs is aryl, more preferably Ph, or R ₇ and Rs are aryl, more preferably Ph; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III): wherein

X is -0-, -CH2-, -CMe2-, p-phenylene, o-phenylene, -ChV-p-phenylene-ChV-, -CMe2-p-phenylene-CMe2-; preferably -CH2-, -CMe2-, -ChV-p-phenylene-ChV- or - CMe2-p-phenylene-CMe2-;

R’ is H, alkyl, aryl, heteroaryl, or aralkyl; preferably methyl, ethyl, propyl, or phenyl, more preferably methyl or phenyl, and more preferably phenyl;

R’i , R’ ₂ , and R’ ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR’5, CC>2R’6, NRVR’e, CN, NO2; or R’I and R’2 form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N; preferably R’I is H or Me, and more preferably R’I is H; yet more preferably R’I , R’ ₂ and R’ ₄ are H, or R’I and R’ ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, and R’ ₄ is H;

R’ ₅ and R’ ₆ are, independently of each other, alkyl or aryl; preferably R’ ₅ and R’ ₆ are Me or Et;

RV and R’s are, independently of each other, H, alkyl, aryl or aralkyl; preferably RV is H and R’s is Ph, or RV and R’s are Ph; more preferably R’ is methyl or phenyl, R’I , RV and RV are H, and X is -CMe ₂ -; wherein in compound of formula (I) at least one of R, Ri , R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group, preferably a Ph group. In the present description, "alkyl" includes straight-chained, branched, and cyclic alkyl groups and includes both unsubstituted and substituted alkyl groups. Unless otherwise indicated, the alkyl groups typically contain from 1 to 20 carbon atoms. Examples of "alkyl" as used herein include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n- pentyl, isobutyl, f-butyl, isopropyl, n-octyl, n-heptyl, ethyl hexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and the like. Unless otherwise noted, alkyl groups may be mono- or polyvalent.

In the present description, "aryl" is an aromatic group containing 6-18 ring atoms, which may be substituted, and can contain fused rings, which may be saturated, unsaturated, or aromatic. Examples of an aryl group include phenyl, naphthyl, biphenyl, phenanthryl, and anthracyl. As used herein “heteroaryl” is aryl containing 1-3 heteroatoms such as nitrogen, oxygen, or sulfur and can contain fused rings. Some examples of heteroaryl are pyridyl, furanyl, pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl, indolyl, benzofuranyl, and benzothiazolyl. Unless otherwise noted, aryl and heteroaryl groups may be mono- or polyvalent.

In the present description,“aralkyl” is an alkyl group, usually containing from 1 to 20 carbon atoms, wherein at least one hydrogen atom is replaced by an aryl group, defined as above. Examples of an aralkyl group are benzyl, phenylethyl, and phenylpropyl.

In a preferred embodiment the benzoxazine is compound of formula (I), wherein

R is H, alkyl, aryl, heteroaryl, aralkyl, or a residue of formula (II):

wherein

Y is -(CH2) _n -, wherein n is 2 - 12, p-phenylene, o-phenylene, 4,4’-biphenyl, p-phenylene-CH2-p-phenylene or -p-phenylene-CMe2-p-phenylene; and R”i , R” ₂ , R” ₃ and R’ ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR” ₅ , C0 ₂ R” ₆ , NR” ₇ R” ₈ , CN, N0 ₂ ; or any of R”i and R” ₂ or R” ₂ and R’ ₃ or R’ ₃ and R’ ₄ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N;

R’ ₅ and R” ₆ are, independently of each other, alkyl or aryl;

R” ₇ and R”s are, independently of each other, H, alkyl, aryl or aralkyl;

Ri , R ₂ , R ₃ and R ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR ₅ , C0 ₂ R ₆ , NR ₇ Rs, CN, N0 ₂ , or Ri and R ₂ or R ₂ and R ₃ or R ₃ and R ₄ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N;

R ₅ and Re are, independently of each other, alkyl or aryl; and R ₇ and Rs are, independently of each other, H, alkyl, aryl or aralkyl; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III):

wherein

X is -0-, -CH ₂ -, -CMe ₂ -, p-phenylene, o-phenylene, -CH ₂ -p-phenylene-CH ₂ -, -CMe ₂ -p-phenylene-CMe ₂ -; -CH ₂ -, -CMe ₂ -, -CH ₂ -p-phenylene-CH ₂ - or -CMe ₂ -p- phenylene-CMe ₂ -; R’ is H, alkyl, aryl, heteroaryl, or aralkyl;

R’i , R’ ₂ , and R’ ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR’ ₅ , CC> ₂ R’ ₆ , NRVR’e, CN, NO ₂ ; or R’I and R’ ₂ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N;

R’ ₅ and R’e are, independently of each other, alkyl or aryl;

RV and R’s are, independently of each other, H, alkyl, aryl or aralkyl; wherein in compound of formula (I) at least one of R, Ri , R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group, preferably a Ph group.

In a more preferred embodiment, the benzoxazine is compound of formula (I), wherein

R is methyl, ethyl, propyl, or phenyl, or a residue of formula (II):

wherein

Y is -(CH ₂ ) _n -, wherein n is 2 - 12, p-phenylene, o-phenylene, 4,4’-biphenyl, p-phenylene-CH ₂ -p-phenylene or -p-phenylene-CMe ₂ -p-phenylene; and

R”i , R” ₂ , R” ₃ and R” ₄ are H;

Ri , R ₂ , R ₃ and R ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR ₅ , CO ₂ R ₆ , NR ₇ R ₈ , CN, NO ₂ ; or Ri and R ₂ are H and R ₃ and R ₄ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or Ri and R ₄ are H and R ₂ and R ₃ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or R ₃ and R ₄ are H and Ri and R ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3;

R ₅ and Re are, independently of each other, Me or Et; and

R ₇ is H and Rs is aryl, or R ₇ and Rs are aryl; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III):

wherein

X is -CH2-, -CMe2-, -CH2-p-phenylene-CH2- or -CMe2-p-phenylene-CMe2-;

R’ is methyl, ethyl, propyl, or phenyl;

R’ ₁ , R’ ₂ , and R’ ₄ are H; wherein in compound of formula (I) at least one of R, Ri , R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group.

In a more preferred embodiment, the benzoxazine is compound of formula (I), wherein

R is phenyl;

Ri , R ₂ and R ₄ are H, and R ₃ is Me, CN, OMe, CC> ₂ Et, NO ₂ , or NPh ₂ ; or Ri and R ₂ are H and R ₃ and R ₄ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or Ri and R ₄ are H and R ₂ and R ₃ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or R ₃ and R ₄ are H and Ri and R ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3;

R ₅ and Re are, independently of each other, Me or Et; and

R ₇ is H and Rs is Ph, or R ₇ and Rs are Ph; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III):

wherein

X is -CH2-, -CMe2-, -CH2-p-phenylene-CH2- or -CMe2-p-phenylene-CMe2-;

R’ is phenyl;

R’ ₁ , R’ ₂ and R’ ₄ are H, or R’ ₁ and R’ ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, and R’ ₄ is H;

R’ ₅ and R’e are, independently of each other, Me or Et;

RV is H and R’s is Ph, or RV and R’s are Ph.

In another preferred embodiment, the benzoxazine is compound of formula (I), wherein

R is phenyl; Ri , R ₂ and R ₄ are H, and R ₃ is Me, CN, OMe, CC> ₂ Et, NO ₂ , or NPh ₂ ; or Ri and R ₂ are H and R ₃ and R ₄ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3;

R ₅ and Re are, independently of each other, Me or Et; and

R ₇ is H and Rs is Ph, or R ₇ and Rs are Ph; or

R ₃ in compound of formula (I) is a residue of formula (III):

wherein

X is -CH2-, -CMe2-, -CH2-p-phenylene-CH2- or -CMe2-p-phenylene-CMe2-;

R’ is phenyl;

R’ ₁ , R’ ₂ and R’ ₄ are H;

R’ ₅ and R’e are, independently of each other, Me or Et;

RV is H and R’s is Ph, or RV and R’s are Ph.

Preferred benzoxazines are compounds of formula (IV) to (XXI):

(XVIII) More preferred benzoxazine compounds are compounds of formula (IV) to (XVI).

Benzoxazine compounds are presently available commercially from several sources, including Huntsman Advanced Materials; Georgia-Pacific Resins, Inc.; and Shikoku Chemicals Corporation, Chiba, Japan, the last of which offers among others Bisphenol A-aniline, Bisphenol F-aniline benzoxazine resins.

Benzoxazine compounds can also be prepared according processes disclosed in the art, such as, for example, Holly et ai, Condensation Products of Aldehydes and Ketones with o-Aminobenzyl Alcohol and o-Hydroxybenzylamine, J. Am. Chem. Soc., 1944, 66, 1875 - 1879; Andreu et ai, Studies on the thermal polymerization of substituted benzoxazine monomers: Electronic effects, J. Polym. Sci. Part A Polym. Chem., 2008, 46, 6091 - 101 ; Allen et ai, Effect of phenol substitution on the network structure and properties of linear aliphatic diamine-based benzoxazines, Polymer, 2009, 50, 613-26; Saiev et ai, Modeling the formation and thermomechanical properties of polybenzoxazine thermosets, Polym. Chem., 2017, 8, 5988-99; Yildirim et ai, Sustainable synthetic approaches using [Ci ₆ lm][Oxa] as a flexible organocatalyst and DFT studies toward 3,4-dihydropyrimidinones and benzoxazines, Monatsh. Chem., 2017, 148, 1085-94; and JP-A-2011231196.

Catalyst

In the process of the invention, catalyst is preferably selected from Li I, Zn(OTf)2, FeC and LiCICL, and more preferably selected from Lil and Zn(OTf)2. In a preferred embodiment the catalyst is Lil; in another preferred embodiment, the catalyst is Zn(OTf)2, wherein OTf represents the triflate group (i.e. trifluoromethanesulfonate, CF3SO3 )· When Zn(OTf)2 is used as catalyst, shorter reaction times are observed.

The molar ratio of the catalyst over the benzoxaxine compound is comprised from 1 % to 20%, preferably from 3% to 17%, more preferably from 5% to 15%, and yet more preferably from 10% to 15%.

Solvent

In the process of the invention, the benzoxazine compound and the catalyst are dissolved in a suitable solvent, which is preferably selected from acetone, THF, acetonitrile and ethanol, more preferably is acetone.

In a preferred embodiment, the solvent is not substantially dry, that is, usually a solvent that contains an amount of water from 0.001% to 10% by weight of water, preferably from 0.002% to 5% by weight. Usually it is used a ratio of solvent to the catalyst from 10:1 to 60:1 , preferably from 20:1 to 50:1 , and more preferably from 25:1 to 45:1 , in a volume/weight ratio, wherein the volume is expressed in mL and the weight in g.

Source of light

In the process of the invention, it is used a source of light having a wavelength selected from 450 nm to 700 nm, preferably from 475 nm to 600 nm, preferably from 490 nm to 550 nm, more preferably from 500 nm to 540 nm, yet more preferably from 525 to 535 nm, and yet more preferably 532 nm The power of the source of light is comprised from 0.7 W to 1.2 W, preferably from 0.8 W to 0.9 W, and more preferably 0.9 W.

The source of light is preferably a pulsed laser, which refers to any laser not classified as continuous wave, so that the optical power appears in pulses of some duration at some repetition rate. Pulsed lasers are commercially available, for example, from companies such as Quantel, Spectra-Physics, Melles-Griot, or Coherent.

In a preferred embodiment, the source of light is a pulsed laser emitting at 532 nm and with a power comprised from 0.8 W to of 0.9 W, more preferably 0.9 W.

Polymerization process

The polymerization process of 1 ,3-benzoxazines by photoinduction, according to the invention comprises the following steps:

a) dissolving a 1 ,3-benzoxazine compound according to general formula (I)

wherein at least one of R, Ri, R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group,

and a catalyst in a suitable solvent, and

b) irradiating the mixture of step a) with light at a wavelength selected from 450 nm to 700 nm.

In a preferred embodiment, after step a) the solvent is removed, and the irradiation is performed in bulk, that is, the reaction mixture is substantially free of solvent and the polymerization takes place in bulk. Substantially free of solvent means in the context of the invention that the content of solvent in the mixture of benzoxazine and catalyst is not more than 10%, preferably not more than 5%, and yet more preferably not more than 1 % by weight over the weight of the mixture of benzoxazine and catalyst.

In the process of the invention the mixture comprising the benzoxazine compound and the catalyst is irradiated at room temperature using light of a specific wavelength, which generates a heating in the mixture.

Irradiation of the mixture at a wavelength selected from 450 nm to 700 nm, preferably from 475 nm to 600 nm, preferably from 490 nm to 550 nm, more preferably from 500 nm to 540 nm, yet more preferably from 525 to 535 nm, and yet more preferably 532 nm, produces a heating, which is enough to polymerize the benzoxazine compound. This is surprising result because benzoxazines absorb in the UV, as disclosed in Salabert op. cit.

Usually, the conversion of the benzoxazine compound into a polymer is substantially quantitative.

Reaction times are dependent on the catalyst used in the polymerization, being comprised from 5 min to 1 h. Usually, reaction is completed after 1 h of irradiation when using Lil as catalyst, and after 10 min when using Zn(OTf)2.

The calculation of conversion of benzoxazine compound may be carried out, for example, using the signals recorded in ¹ H-NMR spectra.

In Figure 1 are shown ¹ H NMR spectra of benzoxazine compound of formula (VI) polymerized under different conditions. Spectrum shown in Figure 1a) refers to an incomplete conversion, and spectrum shown in Figure 1b) refers to total conversion of the benzoxazine into a polymer.

The calculation of conversion is based on the signals around 5.4 and 4.6 ppm in spectrum a), which are due to the CH2 units of oxazine ring of benzoxazine (VI), and on the signals at 6.0 - 3.5 ppm, which are attributed to all the CH2 units of polymer and starting benzoxazine. If x represents the signal integration intensity of the CH2 unit of benzoxazine (VI) and y represents the signal integration intensity of all the CH2 units of polymer and starting benzoxazine, the conversion of compound (VI) is calculated according to the following equation: [(y - 2x)/y] x 100%.

The calculation of the ratio of phenolic to phenoxy CH2 units is based on the signal at 4.7 - 4.0 ppm, which is ascribed to phenoxy CH2 units, and on the signal at 4.0 - 3.5 ppm, which is attributed to phenolic CH2 units. If m and n represent the signal integration intensity of phenolic and phenoxy CH2 units respectively, the ratio of phenolic to phenoxy CH2 units is m/n.

The process of the invention may include further components to prepare copolymerized hybrid systems, such as epoxy, as disclosed in, for example, Kimura et al., J. Appl. , Polym. Sci., 1999, 74, 2266-73; isocyanate prepolymers, as disclosed, for example, in Kirschbaum et al., Macromolecules, 2015, 48(12), 3811-6, polysiloxanes, as disclosed, for example, in Ardhyananta et al., Polymer, 2008, 49, 4585-4591 ; polyimides, as disclosed, for example, in Takeichi et al., Polymer, 2005, 46, 4909-16; and phenolic resins, as disclosed, for example, in Rimdusit et al., Rheologica Acta, 2002, 41 , 1-9. In an embodiment of the invention, further components are included in step a) of the process, which are selected from the group comprising epoxy, isocyanate prepolymer, polysiloxane, polyimide, and phenolic resin.

Polymerized benzoxazine

The polymerized benzoxazine obtainable according to the process on the invention is another aspect of the invention.

The product resulting from the process of the invention shows different features from those obtained by thermal polymerization, even in the presence of catalysts. Main differences are: soluble in organic solvents, such as, for example, acetone, THF, chloroform, dichloromethane, acetonitrile, ethyl acetate, ether, Tg, ratio phenolic:phenoxy, as shown in the Examples.

Use

Another aspect of the invention relates to the use of the polymerized benzoxazine of the invention in composite materials, lithography, 3D-printing, adhesives, sealants and coatings.

In the preparation of composite materials, the polymerized benzoxazine can include toughening agents, plasticizers, extenders, microspheres, fillers and reinforcing agents, for example coal tar, bitumen, textile fibres, glass fibres, asbestos fibres, boron fibres, carbon fibres, mineral silicates, mica, powdered quartz, hydrated aluminium oxide, bentonite, kaolin, silica, aerogel, and also pigments and dyes, such as carbon black, oxide colours and titanium dioxide, fire-retarding agents, thixotropic agents, flow control agents, such as silicones, waxes and stearates, which can, in part, also be used as mould release agents, adhesion promoters, and antioxidants.

Composite materials may be used in diverse application such as, for example, aerospace (primary and secondary structures as well as interior panels, bulkheads, galleys, lavatories and tray tables), transportation (automotive under-the- hood components as well as frames, body panels and structural reinforcements for trucks, buses, light rail cars and trains), oil/gas (composite pipes, risers, down-hole plugs and high-pressure vessels), and electronic (prepregs, halogen-free laminates for printed circuit boards).

The use of the polymerized benzoxazine may be in the form of an adhesive, sealant or coating, in which case one or more of an adhesion promoter, a flame retardant, a filler (such as, for example, the above-mentioned inorganic fillers), a thermoplastic additive, a reactive or non-reactive diluent, and a thixotropic agent may be included.

The polymerized benzoxazine may be used in combination with other polymers such as epoxy, as disclosed, for example, in Jubsilp et ai, Bioresour. Technol., 2008, 99(18), 8880-6; polyurethane, as disclosed, for example, in Takeichi et ai, J. Polym. Sci. Polym. Chem., 2000, 38, 4165-76; isocyanate-terminated polyurethane prepolymers, as disclosed, for example, in Kirschbaum op. c/T; poly(£- caprolactone), as disclosed in, for example, Ishida et ai., Polymer, 2001 , 42, 6971-9; liquid rubber, as disclosed in, for example, Jang et ai, J. Appl. Polym. Sci., 1998, 67, 1- 10; polydimethylsiloxane, as disclosed, for example, in Ardhyananta op. cit.

In an embodiment of the invention, the polymerized benzoxazine is used in combination with a polymer selected from the group comprising epoxy, polyurethane, isocyanate-terminated polyurethane prepolymers, poly(£-caprolactone), liquid rubber, and polydimethylsiloxane.

The invention comprises the following embodiments:

1.- A process for polymerizing 1 ,3-benzoxazines by photoinduction, characterized in that it comprises:

a) dissolving a 1 ,3-benzoxazine compound according to general formula (I)

wherein at least one of R, Ri, R2, R3 and R4 is an organic group, which contains an aryl group,

and a catalyst in a suitable solvent, and

b) irradiating the mixture of step a) with light at a wavelength selected from 450 nm to 700 nm.

2 - The process according to embodiment 1 , characterized in that the catalyst is selected from Lil, Zn(OTf)2, FeC and LiCICU. e process according to embodiment 1 or 2, characterized in that the benzoxazine pound of formula (I), wherein

R is H, alkyl, aryl, heteroaryl, aralkyl, or a residue of formula (II):

wherein

Y is -(CH2) _n -, wherein n is 2 - 12, p-phenylene, o-phenylene, 4,4’-biphenyl, p-phenylene-CH2-p-phenylene or -p-phenylene-CMe2-p-phenylene; and

R”i, R ^M ₂ , R” ₃ and R” ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR” ₅ , C0 ₂ R” ₆ , NR” ₇ R” ₈ , CN, N0 ₂ ; or any of R”i and R” ₂ or R” ₂ and R” ₃ or R’ ₃ and R’ ₄ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N;

R’ ₅ and R” ₆ are, independently of each other, alkyl or aryl;

R” ₇ and R”s are, independently of each other, H, alkyl, aryl or aralkyl;

Ri, R ₂ , R ₃ and R ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR ₅ , CO ₂ R ₆ , NR ₇ R ₈ , CN, NO ₂ , or Ri and R ₂ or R ₂ and R ₃ or R ₃ and R ₄ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N;

R ₅ and R ₈ are, independently of each other, alkyl or aryl; and R ₇ and Rs are, independently of each other, H, alkyl, aryl or aralkyl; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III):

wherein

X is -0-, -CH2-, -CMe2-, p-phenylene, o-phenylene, -Chh-p-phenylene-Chh-, -CMe2-p-phenylene-CMe2-; -CH2-, -CMe2-, -CH2-p-phenylene-CH2- or -CMe2-p- phenylene-CMe2-;

R’ is H, alkyl, aryl, heteroaryl, or aralkyl;

R’ ₁ , R’ ₂ , and R’ ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR’ ₅ , CC> ₂ R’ ₆ , NRVR’e, CN, NO ₂ ; or R’ ₁ and R’ ₂ form a 5- or a 6-ring of carbon atoms, containing at least one heteroatom selected from O and N;

R’ ₅ and R’e are, independently of each other, alkyl or aryl;

RV and R’s are, independently of each other, H, alkyl, aryl or aralkyl; wherein in compound of formula (I) at least one of R, Ri , R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group, preferably a Ph group.

4 The process according to embodiment 3, characterized in that the benzoxazine is compound of formula (I), wherein

R is methyl, ethyl, propyl, or phenyl, or a residue of formula (II): wherein

Y is -(CH ₂ ) _n -, wherein n is 2 - 12, p-phenylene, o-phenylene, 4,4’-biphenyl, p-phenylene-CH ₂ -p-phenylene or -p-phenylene-CMe ₂ -p-phenylene; and

R”i , R” ₂ , R” ₃ and R” ₄ are H;

Ri , R ₂ , R ₃ and R ₄ are, independently of each other, H, halogen, alkyl, aryl, aralkyl, OR ₅ , CO ₂ R ₆ , NR ₇ R ₈ , CN, NO ₂ ; or Ri and R ₂ are H and R ₃ and R ₄ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or Ri and R ₄ are H and R ₂ and R ₃ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or R ₃ and R ₄ are H and Ri and R ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3;

R ₅ and Re are, independently of each other, Me or Et; and

R ₇ is H and R ₃ is aryl, or R ₇ and R ₃ are aryl; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III): wherein

X is -CH2-, -CMe2-, -CH2-p-phenylene-CH2- or -CMe2-p-phenylene-CMe2-;

R’ is methyl, ethyl, propyl, or phenyl;

R’ ₁ , R’ ₂ , and R’ ₄ are H; wherein in compound of formula (I) at least one of R, Ri , R ₂ , R ₃ and R ₄ is an organic group, which contains an aryl group.

5.- The process according to embodiment 4, characterized in that the benzoxazine is compound of formula (I), wherein

R is phenyl;

Ri , R ₂ and R ₄ are H, and R ₃ is Me, CN, OMe, CC> ₂ Et, NO ₂ , or NPh ₂ ; or Ri and R ₂ are H and R ₃ and R ₄ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or Ri and R ₄ are H and R ₂ and R ₃ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, or R ₃ and R ₄ are H and Ri and R ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3;

R ₅ and Re are, independently of each other, Me or Et; and

R ₇ is H and Rs is Ph, or R ₇ and Rs are Ph; or one of Ri , R ₂ , R ₃ or R ₄ in compound of formula (I) is a residue of formula (III):

wherein

X is -CH2-, -CMe2-, -CH2-p-phenylene-CH2- or -CMe2-p-phenylene-CMe2-;

R’ is phenyl;

R’ ₁ , R’ ₂ and R’ ₄ are H, or R’ ₁ and R’ ₂ form a saturated 6-ring of carbon atoms containing and O in position 1 , and N-Ph in position 3, and R’ ₄ is H;

R’ ₅ and R’e are, independently of each other, Me or Et;

RV is H and R’s is Ph, or RV and R’s are Ph.

6.- The process according to embodiment 1 , characterized in that the benzoxazine is selected from the group consisting of compound of formula (IV) to (XXI).

7.- The process according to embodiment 6, characterized in that the benzoxazine is selected from the group consisting of compounds of formula (IV) to (XVI).

8.- The process according to any of embodiments 1 to 7, characterized in that the catalyst is selected from Lil and Zn(OTf) ₂ .

9.- The process according to embodiment 8, characterized in that the catalyst is Lil. 10.- The process according to embodiment 8, characterized in that the catalyst is Zn(OTf) ₂ .

11.- The process according to any of embodiments 1 to 10, characterized in that the molar ratio of the catalyst over the benzoxaxine compound is comprised from 1 % to 20%.

12.- The process according to any of embodiments 1 to 11 , characterized in that the solvent is selected from acetone, THF, acetonitrile and ethanol.

13.- The process according to embodiment 12, characterized in that the solvent is acetone.

14.- The process according to any of embodiments 1 to 13, characterized in that the solvent is not substantially dry.

15.- The process according to any of embodiments 1 to 14, characterized in that the source of light has a wavelength selected from 475 nm to 600 nm.

16.- The process according to embodiment 15, characterized in that the source of light has a wavelength selected from 490 nm to 550 nm.

17.- The process according to embodiment 16, characterized in that the source of light has a wavelength selected from 500 nm to 540 nm.

18.- The process according to embodiment 17, characterized in that the source of light has a wavelength selected from 525 to 535 nm.

19.- The process according to any of embodiments 1 to 18, characterized in that the power of the source of light is comprised from 0.7 W to 1.2 W.

20.- The process according to embodiment 19, characterized in that the power of the source of light is comprised from 0.8 W to 0.9 W. 21.- The process according to any of embodiments 1 to 20, characterized in that the source of light is a pulsed laser.

22.- The process according to any of embodiments 1 to 21 , characterized in that the source of light is a pulsed laser emitting at 532 nm and with a power comprised from 0.8 W to of 0.9 W.

23.- The process according to any of embodiments 1 to 22, characterized in that after step a) the solvent is removed, and the irradiation is performed in bulk.

24.- The process according to any of embodiments 1 to 23, characterized in that further components are included in step a) of the process, which are selected from the group comprising epoxy, isocyanate prepolymer, polysiloxane, polyimide, and phenolic resin.

25.- A polymerized benzoxazine obtainable according to the process of any of embodiments 1 to 24.

26.- Use of the polymerized benzoxazine of embodiment 25 in composite materials, lithography, 3D-printing, adhesives, sealants and coatings.

27.- The use according to embodiment 26, characterized in that the polymerized benzoxazine is used in combination with a polymer selected from the group comprising epoxy, polyurethane, isocyanate-terminated polyurethane prepolymers, poly(£- caprolactone), liquid rubber, and polydimethylsiloxane.

Examples

Example 1 : Polymerization of benzoxazine of formula (VI) with Lil

The aim of this example was to illustrate the general process for polymerizing liquid benzoxazines with Lil as catalyst.

0.5 mL (2.96 mmol) of benzoxazine of formula (VI) and 59.4 mg (0.44 mmol, 15 % molar) of Lil were mixed in 2.4 mL of acetone (0.04 mL acetone/mg catalyst, ratio volume:weight 40:1). Then, the mixture was concentrated under vacuum and an orange/red oil was obtained.

The product was placed in a glass vial under magnetic stirring and irradiated by a pulsed laser (Nd:YAG, l = 532 nm, P = 0.9 W) during 50 min. Initial temperature was room temperature, but during irradiation the temperature of the mixture increased up to about 100° C.

Finally, a dark red solid was obtained. ¹ H-NMR confirmed that full conversion was achieved.

Example 2: Polymerization of benzoxazine of formula (VII) with Lil

The aim of this example was to illustrate the general process for polymerizing solid benzoxazines with Lil as catalyst.

0.1 g (0.44 mmol) of benzoxazine of formula (VII) and 8.9 mg (0.07 mmol, 15 % molar) of Lil were mixed in 0.4 mL of acetone (0.04 mL acetone/mg catalyst, ratio volume:weight 40:1).

Then, the mixture was concentrated under vacuum and a yellow solid was obtained.

The product was placed in a glass cuvette (5 x 0.8 x 0.4 cm ³ ) and irradiated by a pulsed laser (Nd:YAG, l = 532 nm, P = 0.9 W) during 50 min. Initial temperature was room temperature, but during irradiation the temperature of the mixture increased up to about 100° C.

Finally, a dark red solid was obtained. ¹ H-NMR confirmed that full conversion was achieved.

Example 3: Polymerization of benzoxazine of formula (VI) with Zn(OTf)2

The aim of this example was to illustrate the general process for polymerizing liquid benzoxazines with Zn(OTf)2 as catalyst.

0.5 mL (2.96 mmol) of benzoxazine of formula (VI) and 159.9 mg (0.44 mmol, 15 % molar) of Zn(OTf)2 were mixed in 4 mL of hot acetone (0.03 mL hot acetone/mg catalyst, ratio volume:weight 30:1).

Then, the mixture was concentrated under vacuum and a dark brown oil was obtained.

The product was placed in a glass vial under magnetic stirring and irradiated by a pulsed laser (Nd:YAG, l = 532 nm, P = 0.9 W) during 6 min. Initial temperature was room temperature, but during irradiation the temperature of the mixture increased up to about 100° C.

Finally, a black solid was obtained. ¹ H-NMR confirmed that full conversion was achieved.

Example 4: Polymerization of benzoxazine of formula (VII) with Zn(OTf)2

The aim of this example was to illustrate the general process for polymerizing solid benzoxazines with Zn(OTf)2 as catalyst.

0.1 g (0.44 mmol) of benzoxazine of formula (VII) and 24.2 mg (0.07 mmol, 15 % molar) of Zn(OTf)2 were mixed in 0.6 ml_ of hot acetone (0.03 ml_ hot acetone/mg catalyst, ratio volume:weight 30:1).

Then, the mixture was concentrated under vacuum and a yellow solid was obtained.

The product was placed in a glass cuvette (5 x 0.8 x 0.4 cm ³ ) and irradiated by a pulsed laser (Nd:YAG, l = 532 nm, P = 0.9 W) during 6 min. Initial temperature was room temperature, but during irradiation the temperature of the mixture increased up to about 100° C. It was observed that after 3 min of irradiation, the polymerization was nearly finished.

Finally, a dark red solid was obtained. ¹ H-NMR confirmed that full conversion was achieved.

Examples 5 - 24: Polymerization of benzoxazines of formulas (IV) - (XIII)

The following Table I illustrates the results obtained in the process of the invention for different benzoxazines, catalysts, and reaction conditions:

TABLE I

a: It was observed that after 3 min of irradiation, the polymerization was nearly finished.

It can be observed that high conversion rates are obtained with the process of the invention starting from different benzoxazine compounds, using different catalysts and different reaction conditions.

Comparative examples 1 - 4: Thermal polymerization of benzoxazines

Benzoxazine compounds of formula (III) - (VI) were polymerized by heating at 200° C for 2 h, without any solvent. The ratio phenoxide:phenolic was determined as above-exposed for the soluble part of the polymers. In particular, thermal polymerized benzoxazines (III) and (VI) were insoluble in organic solvents, such as DMSO.

Example 25: Ratio phenoxide:phenolic polymer in polymerized benzoxazines

The following Table II shows the percentages of both polymer types obtained by polymerizing benzoxazine compounds of formula (IV) - (VII) according to the process of the invention, and for polymers obtained according to Comparative examples 1 - 4, as well as Tg for the obtained polymers:

TABLE II

Tg was determined by DSC (Differential Scanning Calorimetry) using TA Instrument Q20 using Tzero™, wherein pans and lids calibrated with indium (T _m = 429.75 K, and DH = 3267 KJ/mol). The phenolic:phenoxide ratio was determined by ¹ H- NMR as exposed above.

It can be seen that the ratio phenoxide: phenolic of the polymers prepared according to the process of the invention is substantially different from the ratio of the polymers prepared by thermal polymerization. Additionally, the latter polymers are less soluble in organic solvents due to higher reaction temperatures, which facilitates crosslinking, thus reducing the solubility of the polymers. Tg measurements show that polymers obtained by irradiation are different from polymers obtained by thermal polymerization starting from the same benzoxazine compound.