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Composition, Morphology and Properties of Poly(lactic acid) and Poly(butylene succinate) Copolymer System via Coupling Reaction

The poly(lactic acid) (PLA) and poly(butylene succinate) (PBS) copolymer systems with different reactive time were synthesized for the first time via the homo-/cross-coupling reaction of PLA and PBS. Nuclear magnetic resonance spectroscopy (1H-NMR) results showed that the homo-coupling of PLA occurred much earlier than the cross-coupling of PLA with PBS. Also, the compositions of PLA and PBS copolymer systems contained homo-coupled PLA (h-PLA) but not homo-coupled PBS, cross-coupled PLA-b-PBS copolymer (mainly PLA terminated with hydroxyl group and PBS terminated with carboxyl group, up to 24 h), PLA and PBS. There was little difference of the molecular weight between all the PLA and PBS copolymer systems and PLA/PBS blends demonstrated by size exclusion chromatography (SEC) results, which indicated that the morphologies of the samples might have greater effect on the final properties than the molecular weight. Scanning electron microscope (SEM) results showed that the morphologies of PLA and PBS copolymer systems changed with reactive time. The compatibility of PLA and PBS phases was improved obviously via the homo-/cross-coupling reaction of PLA and PBS comparing with PLA/PBS blends without reaction. Notably, the elongation at break of the sample with 4 h reactive time could be improved over three times higher than that of PLA/PBS blends. Extensional rheological results showed that the system with the best elongation at break also had the highest extensional viscosity among all the PLA and PBS copolymer systems. Differential scanning calorimetry (DSC) results indicated the crystallization behaviors of PLA and PBS were not affected by the homo-/cross-coupling reaction.