Esterification of ethylene-vinyl alcohol copolymers in homogeneous phase using N,N′-dimethylpropyleneurea as solvent

Ethylene-vinyl alcohol copolymers (EVAL) were esterified with 3,5-dinitrobenzoyl chloride using the cycled urea N,N′-dimethylpropyleneurea (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone) (DMPU) as the solvent. Ethylene-vinyl alcohol-vinyl-3,5-dinitrobenzoate terpolymers (EVALVDNB) and ethylene-vinyl-3,5-dinitrobenzoate copolymers (EVDNB) were obtained. Both EVAL copolymers (6-73 mol% VAL) and esterified polymers, EVDNB, and EVALVDNB dissolve in DMPU. The substitution may become total under the experimental conditions. The degree of transformation was determined by 1H NMR. EVDNB copolymers were characterised by IR spectroscopy and 1H and 13C NMR. Thermal properties were studied by DSC. The glass transition temperature of the EVDNB copolymers having a low VDNB content (up to 14 mol%) is roughly constant, whereas above 50 mol% increases. Melting temperature decreases as the VDNB content is increased, owing to the fact that the VDNB groups are excluded from the polyethylene crystal lattice.