Temperature-dependent crystal structure and structural evolution of poly(glycolide-co-lactide) induced by comonomeric defect inclusion/exclusion

Abstract

Comonomeric defects can lead the semicrystalline polymers to form unique crystal structures; this offers potential way to tailor the microstructure and macroscopic property of polymers. However, the role of comonomeric defects in the crystal structure and structural evolution of copolymer is not well understood. Herein, we synthesized the poly (glycolide-co-lactide) (PGLA) copolymers with minor L-lactide (LA) units and investigated their crystallization kinetics, crystal structure, and thermally-induced structural evolution. Crystallization of PGLA is strongly influenced by copolymer composition and crystallization temperature (Tc). Crystallization rate of PGLA reduces with increasing the LA content and the PGLA cannot crystallize at high LA content (≥40%). LA units can be included in crystal lattice as defects during the crystallization of PGLA, which is kinetically-controlled and results in the enlargement of crystal unit cell. Inclusion of LA units in crystal lattice is favored at low Tc but unfavored at high Tc, causing the contraction of crystal unit cell with increasing Tc. The defect-rich crystals of PGLA formed at low Tc are metastable and transform into thermodynamically stable crystals upon heating and annealing. This study shed light on the role of comonomeric defects in the crystal structure and structural evolution of random copolymers.