PLLA Mesophase and Its Phase Transition Behavior in the PLLA−PEG−PLLA Copolymer As Revealed by Infrared Spectroscopy

• Published in: Macromolecules 2010-05, Vol.43 (9), p.4240-4246
• Main Authors: Zhang, Jianming, Duan, Yongxin, Domb, Abraham J, Ozaki, Yukihiro
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma100301h

A detailed analysis of the IR spectrum of melt-quenched PLLA−PEG−PLLA sample and its change with temperature is presented. It was found that, in the initial state of the melt-quenched PLLA−PEG−PLLA sample, the PLLA constituent does not exist as a normal amorphous or crystalline phase but as a kind of mesophase, which is confirmed by the WAXD data. The IR data suggest that both chain conformation and chain packing are disordered to some extent in such a mesophase. Therefore, this mesophase is less thermally stable than the ordered α phase and even the disordered α phase (α′) of PLLA. In the heating process, the mesophase of PLLA in the PLLA−PEG−PLLA copolymer starts the partial melt first upon heating in a stepwise way, and subsequently it is reorganized directly into the stable α phase but not through the α′ phase of PLLA. These phase transition behaviors are examined and discussed at the molecular functional group level.