Semi-interpenetrating polymer networks composed of poly(L-lactide) and diisocyanate-bridged 4-arm star-shaped ε-caprolactone oligomers

Semi-interpenetrating polymer networks (semi-IPNs) were prepared by reactions of methylenediphenyl 4,4'-diisocyanate (MDI) and hydroxy-terminated 4-arm star-shaped epsilon-caprolactone oligomers (H4CLO(n)'s) with the degrees of polymerization per one arm, n = 3, 5 and 10 in the presence of poly(L-lactide) (PLA). Morphologies, thermal and mechanical properties of the MDI-bridged H4CLO(n) (MH4CLO(n))/PLA semi-IPNs were evaluated by comparing with those of poly(epsilon-caprolactone) (PCL)/PLA blends. Two tan delta peaks related to MH4CLO(n) and PLA were observed in a dynamic mechanical curve of the semi-IPN. Although all the semi-IPNs and blends had micro-phase separated morphologies, the phase-separated droplets of MH4CLO(5)/PLA 50/50 were much finer than those of PCL/PLA 50/50. Differential scanning calorimetry (DSC) analyses revealed that MH4CLO(3) and MH4CLO(5) are substantially amorphous, while MH4CLO(10) is semi-crystalline, and that cold crystallization of the PLA component of MH4CLO(n)/PLA is more strongly disturbed for the semi-IPN with a smaller n value and more MH4CLO(n), content. Tensile modulus, toughness and elongation at break of MH4CLO(5)/PLA 50/50 semi-IPN were much higher than those of PCL/PLA 50/50 blend. (C) 2014 Elsevier Ltd. All rights reserved.