Crystallinity and crystalline confinement of the amorphous phase in polylactides

Abstract

Stereorregular polylactides such as poly (L-Iactide) (PLLA) or poly (D-lactide) result from polymerization of optically pure lactides and are semicrystalline. Optically non-active poly(D,L-lactide) (PDLLA) can be regarded as random or atactic copolymers, show a random moiety distribution, and are completely amorphous. In this work three phases, comprising mobile amorphous fraction (MAF, χMA), rigid amorphous fraction (RAF, χRA) and crystalline fraction (χc) were determined in PLLA. It will be shown that RAP fraction not only elevates Tg but also increases the dynamic fragility (m) of polylactide chains around the Tg. These results agree with reported cases in which topologycal constraints inhibit longer range dynamics and suggest a smaller length scale of cooperativity of chains in confined environments. Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.