Crystallization and morphology of a polymer blend based on linear PPDO and branched poly(p-dioxanone)–poly(lactic acid) block copolymer with immiscible blocks

Abstract

The crystallization behaviour and morphology of a polymer blend based on branched poly(p-dioxanone)–poly(lactic acid) block copolymer (PLA-b-LCB-PPDO) and linear PPDO with immiscible PPDO and PLA blocks has been investigated. Although the PPDO and PLA blocks are immiscible with each other, an interesting interpenetrating spherulite morphology, which always occurs in miscible blends, was observed. Since the chemical bonding and branching molecular structure of the copolymer may resulted in a relatively small phase separation, the crystals of PPDO can nucleate and grew confined inside the matrix of pre-crystallized PLA spherulites. The morphologies of both PLA and PPDO crystals were significantly affected by the crystallization condition and process. Both the growth rate and nucleation rate of PPDO segments were enhanced rather than depressed under the confinement crystallization imposed by pre-crystallized PLA when relatively small amounts of PLA were added. The nucleation density of PPDO increased obviously with a small change in the self-nucleation temperature of PLA suggesting that the pre-crystallized PLA may serve as a heterogeneous nucleation agent for the crystallization of PPDO segments.