Tough conetworks composed of 4-armed star-shaped oligomers of L-lactide, D-lactide and ε-caprolactone

Enantiomeric hydroxy-terminated 4-armed star-shaped lactide oligomers (H4LLAO(15) and H4DLAO(15)) with the degree of polymerization per arm, n = 15 and a hydroxy-terminated 4-armed star-shaped epsilon-caprolactone oligomer (H4CLO(n) ) with n = 7 or 15 were crosslinked with methylenediphenyl 4,4'-diisocyanate at a weight ratio of H4LLAO(15)/H4DLAO(15) = 1/0 or 1/1 produced conetworks (MH-4LLAO(15)/4CLO (n) s or MH-4scLAO(15)/4CLO(n)s) with the weight ratios of (H4LLAO(15) + H4DLAO(15))/H4CLO(n) of 75/25, 50/50 and 25/75 in addition to the homonetworks (MH-4LLAO(15), MH-4scLAO(15) and MH-4CLO(n) ). The conetwork with a higher oligolactide (LAO) fraction and longer arm length of the oligocaprolactone segment possessed a better compatibility. Stereocomplex (sc) crystallites of the LAO segments were dominantly formed for MH-4scLAO(15) and all MH-4scLAO(15)/4CLO(n)s, which were regenerated during cooling and subsequent heating processes after melt. However, LAO homo-crystallites for MH-4LLAO(15)/4CLO(n)s were not regenerated at all. MH-4LLAO(15)/4CLO(15)s and MH-4scLAO(15)/4CLO(15)s exhibited higher tensile toughnesses than MH-4LLAO(15)/4CLO(7)s and MH-4scLAO(15)/4CLO(7)s, respectively. Especially, the tensile toughness (25.8 MJ m(-3)) of MH-4scLAO(15)/4CLO(15) 75/25 was much higher than that (14.6 MJ m(-3)) of MH-4LLAO(15)/4CLO(15) 75/25.