Role of the branched PEG-b-PLLA chain in morphological structures and thermodynamics for PEG-b-PLLA-g-glucose copolymers with different architectures

Abstract

The branched poly(ethylene glycol)-poly(lactic acid)-glucose (PEG-b-PLLA-g-glucose) copolymers were synthesized by using CDI as the bonding agent. There is a significant inhibition between PEG segments and PLLA segments in PEG-b-PLLA-g-glucose copolymers. When the weight fraction of PLLA is low, the PEG segment as the diluting agent increases the flexibility and chain diffusion ability of PEG-b-PLLA-g-glucose copolymers, and also improves the formation of the α-form for the extensive melting process of the PLLA matrix. The initial decomposition temperature (T_5%) of PEG-b-PLLA-g-glucose copolymers was significantly reduced, due to the enhanced transesterification of the PLLA segment at both ends under the low melting PEG to promote the thermal degradation of copolymers. When the PLLA content reaches a certain level, due to the PEG segment as a plasticizer to enhance the interaction between PLLA chains, T_5% is slightly improved during the heating process. With an increase of the branched PEG-b-PLLA grafted segments, the morphological structure and surface morphology of PEG-b-PLLA-g-glucose copolymers changed from the spherical micelles and irregular surfaces to tightly fused circular lamellas and corrugated dense surfaces, respectively. This work provides a potential theoretical basis for broadening PLLA application by the crystallization behaviors and morphologies of the branched PEG-b-PLLA copolymers with various architectures and different compositions.