PURPOSE: To obtain the title composition which is meltable, having adequate processability and good compatibility with other polymers, by the reaction on heating in the presence of an organic peroxide between a butyl rubber and a vinyl acetate copolymer both of which have specific properties.

CONSTITUTION: The objective composition can be obtained by incorporating a polymer mixture consisting of (1) a butyl rubber composed of a relatively low molecular weight (pref. ≤500,000) isobutylene and a small amount of a copolymer of a diene compound and (2) a vinyl acetate copolymer having comparatively low molecular weight (gref. with a melt index ≥50) with 0.1W0.5wt%, based on the polymer mixture, of an organic peroxide (e.g., t-butyl perbenzoate) followed by carrying out a radical reaction at 150W200°C for ≤30min to effect partial curing.

USE: Hot-melt adhesives and sealants with incorporating a brittleness modifier for thermoplastic polymer at low temperatures and with blending a stickiness-imparting resin.