Abstract
Effect of Poly(l‐lactide)/Poly(d‐lactide) (PLLA/PDLA) block length ratio on the crystallization behavior of star‐shaped poly(propylene oxide) block poly(d‐lactide) block poly (l‐lactide) (PPO–PDLA–PLLA) stereoblock copolymers with molecular weights (Mn) ranging from 6.2 × 104 to 1.4 × 105 g mol−1 was investigated. Crystallization behaviors were studied utilizing differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Only stereocomplex crystallites formed in isothermal crystallization at 140 to 156°C for all samples. On one hand, the overall crystallization rate decreased as PLLA/PDLA block length ratio increased. As PLLA/PDLA block length ratio increased from 7:7 to 28:7, the value of half time of crystallization (t1/2) delayed form 2.85 to 5.31 min at 140°C. On the other hand, according to the Lauritzen–Hoffman theory, the fold‐surface energy (σe) was calculated. σe decreased from 77.7 to 73.3 erg/cm2 with an increase in PLLA/PDLA block length ratio. Correspondingly increase in nucleation density was observed by the polarized optical microscope. Results indicated that the PLLA/PDLA block length ratio had a significant impact on the crystallization behavior of PPO–PDLA–PLLA copolymers. POLYM. ENG. SCI., 55:2534–2541, 2015. © 2015 Society of Plastics Engineers
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