Copolymerization of ethylene brassylate with δ-valerolactone towards isodimorphic random copolyesters with continuously tunable mechanical properties

Abstract

Ring opening copolymerization of ethylene brassylate (EB) and δ-valerolactone (δ-VL) with various feeding ratios catalyzed by triphenyl bismuth was performed to prepare poly(ethylene brassylate-co-δ-valerolactone) copolyesters. The reactivity ratios of EB and δ-VL were firstly determined to be rEB=0.64 and rVL=2.54, respectively. Then the copolymerization kinetics was traced and microstructure analysis showed that the chain structure of copolyesters were rearranged towards complete random as a consequence of transesterification reaction. The resulting random copolymers were found to cocrystallize to exhibit isodimorphism phenomenon with a pseudo-eutectic point of melting temperatures and lattice spacings at 80 mol% δ-VL units. Moreover, the variation of the lattice spacings confirmed that the comonomer units have better miscibility in the case of incorporation of shorter units into longer unit crystal than the opposite case. Finally, the continuously tunable mechanical properties of these copolyesters showed a similar pseudo-eutectic behavior at the same eutectic point of isodimorphism, which indicated that the correlation between isodimorphism and mechanical properties depending on composition is highly significant.