Synthesis and crystallization behavior of poly(L-lactide)-block-poly(ε-caprolactone) copolymer

We investigate, via wide and small angle X-ray scattering methods (WAXS and SAXS), differential scanning calorimetry (DSC), and optical microscopy (OM), the crystallization behavior of poly(L-lactide)-block-poly(epsilon -caprolactone) copolymer (PLLA-b-PCL) which is classified as a semicrystalline-semicrystalline block copolymer. The synthesis of PLLA-b-PCL was done by using a macroinitiator of hydroxy-terminated PCL (PCL-OH) with various molecular weights and followed by ring opening polymerization of L-lactide. The PLLA-b-PCL(H) with the number-average molecular weight (M-n) of 77,000 and the weight fraction of PCL block (w(PCL)) of 0.32 showed microphase separated structures at molten state up to 220 degreesC, as determined from theological measurement. But, the PLLA-b-PCL(L) with M-n = 19,000 and W-PCL = 0.374 became homogeneous at temperatures higher than 175 degreesC. From the crystallization behavior at 110 and 140 degreesC, we conclude that the chain folding of the crystalline PLLA block in PLLA-b-PCL(H) was quite different from that in PLLA-b-PCL(L). This result suggests that the chain segregation between the blocks at molten state affected significantly the chain folding of a semicrystalline block during the crystallization. (C) 2001 Published by Elsevier Science Ltd.