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

초록

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(ε-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<inf>n</inf>) of 77,000 and the weight fraction of PCL block (W<inf>PCL</inf>) of 0.32 showed microphase-separated structures at molten state up to 220°C, as determined from rheological measurement. But, the PLLA-b-PCL(L) with M<inf>n</inf> = 19,000 and W<inf>PCL</inf> = 0.374 became homogeneous at temperatures higher than 175°C. From the crystallization behavior at 110 and 140°C, 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. © 2001 Published by Elsevier Science Ltd.

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