Premium
Effect of poly( l ‐lactide)/poly( d ‐lactide) block length ratio on crystallization behavior of star‐shaped asymmetric poly( l ( d )‐lactide) stereoblock copolymers
Author(s) -
Li Wei,
Ma Yan,
Fan Zhongyong
Publication year - 2015
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.24144
Subject(s) - crystallization , lactide , materials science , nucleation , copolymer , crystallite , differential scanning calorimetry , polymer chemistry , optical microscope , morphology (biology) , chemical engineering , scanning electron microscope , composite material , polymer , chemistry , organic chemistry , thermodynamics , physics , genetics , biology , engineering , metallurgy
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 ( M n ) ranging from 6.2 × 10 4 to 1.4 × 10 5 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 ( t 1/2 ) 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 ( σ e ) was calculated. σ e decreased from 77.7 to 73.3 erg/cm 2 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