Li, L. Crystal structure and morphology of poly(L-lactide-b-D-lactide)diblock copolymers

Li, L., Zhong, Z., Jeu, W. de, Dijkstra, P.J. and Feijen, J

Macromolecules 37, 8641-8646

Abstract
The isothermal crystallization behavior of low-molecular-weight (DP 50) poly(l-lactide-b-d-lactide) diblock copolymers is reported, as studied by small- and wide-angle X-ray scattering. The symmetric diblock copolymer crystallizes in the stereocomplex form for the whole range of crystallization temperatures, while the one with a block ratio of 80/20 grows into homocrystallites. For an intermediate block ratio (66/33), the stereocomplex form is obtained at high crystallization temperatures while a coexistence region with homocrystal phase exists at low temperatures. In addition to the transition enthalpy, size effects and kinetic routes play a role in the competition between the stereocomplex and the homocrystalline forms. The lamellar spacing (long period and crystal thickness) shows a different temperature dependence for the three diblock copolymers, which is discussed in relation to the specific morphology and molecular constitution.