Direct copolycondensation of ϵ-caprolactone with δ-valerolactone in the absence of catalysts

Abstract

Waxy and pasty copolymers of ϵ-caprolactone (CL) and δ-valerolactone (VL) with relatively low molecular weights were synthesized by direct copolycondensation without catalysts in the presence of water at 200° under nitrogen. This reaction proceeds by direct condensation between two linear monomers, i.e. linear 6-hydroxycaproic acid and linear 5-hydroxyvaleric acid produced by hydrolysis of the cyclic CL and VL, respectively. It was found by 1H-NMR that the molar ratio in the copolymer is markedly different from that in the initial monomer mixture; the CL contents in the copolymers are ca 92, 78, 71, 53 and 19 mol% for initial CL contents in the feed of 85, 70, 50, 30 and 15 mol%, respectively. The crystallinities of the copolymers were determined by differential scanning calorimetry and X-ray diffraction. Each homopolymer had relatively high melting point but it showed a marked decrease by copolycondensation, reaching a minimum for equimolar composition of copoly(CL/VL). This effect is closely related to the distortion of crystal structure because of a rapid decrease in block lengths of ϵ-oxycaproyl and δ-oxyvaleryl units in the copolymer, the so-called sequence effects.