Synthesis, characterization, and crystallization behaviors of poly( D -lactic acid)-based triblock copolymer

Poly(D-lactic acid) (PDLA) with different polyethylene glycol (PEG) segment synthesized PDLA-PEG-PDLA triblock copolymer through the ring-opening reaction of D-LA and PEG will be used as a toughening modifier. The microstructure, crystal structures and crystallization behaviors of this triblock copolymer were investigated by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The triblock copolymer is synthesized from the appearance of CH2 stretching vibration peak at 2910 cm−1 and C-O stretching vibration peak at 1200 cm−1 from PEG in FTIR spectra. Moreover, the chemical shift that is about 3.6 ppm in 1H NMR and 68.8ppm in 13C NMR proves this matter. The results of XRD and DSC reveal that PDLA and PEG are crystallized separately, and are not fully compatible, and microphase separation has occurred in this triblock copolymer. PEG can induce the triblock copolymer to accelerate the rate of crystallization, allowing it to crystallize more completely in the same amount of time. When the molecular weight of PEG is 6000 or the ratio of D-LA/PEG is 1/1, the crystallizability of PDLA-PEG-PDLA triblock copolymer is the best.