Crystallization and Alkaline Degradation Behaviors of Poly(<span style="font-variant: small-caps">l</span>-Lactide)/4-Armed Poly(ε-Caprolactone)-Block-Poly(<span style="font-variant: small-caps">d</span>-Lactide) Blends with Different Poly(<span style="font-variant: small-caps">d</span>-Lactide) Block Lengths

• Main Authors: Suyang Dai, Min Wang, Zhuoxin Zhuang, Zhenbo Ning
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Polymers
• Subjects: stereocomplex; crystallization; degradation; block length
• Online Access: https://www.mdpi.com/2073-4360/12/10/2195

Four-armed poly(ε-caprolactone)-<i>block</i>-poly(<span style="font-variant: small-caps;">d</span>-lactide) (4-C-D) copolymers with different poly(<span style="font-variant: small-caps;">d</span>-lactide) (PDLA) block lengths (<i>M_n,PDLA</i>s) were synthesized by sequential ring-opening polymerization (ROP). The formation of stereocomplex (SC) crystallites in the 80/20 poly(<span style="font-variant: small-caps;">l</span>-lactide) (PLLA)/4-C-D blends were investigated with the change of <i>M_n,PDLA</i> from 0.5 to 1.5 kg/mol. It was found that the crystallization and alkaline degradation of the blends were profoundly affected by the formed SC crystallites. The PLLA/4-C-D0.5 blend had the lowest crystallization rate of the three blends, and it was difficult to see spherulites in this blend by polarized optical microscopy (POM) observation after isothermal crystallization at 140 °C for 4 h. Meanwhile, when <i>M_n,PDLA</i> was 1 kg/mol or 1.5 kg/mol, SC crystallites could be formed in the PLLA/4-C-D blend and acted as nucleators for the crystallization of PLLA homo-crystals. However, the overall crystallization rates of the two blends were still lower than that of the neat PLLA. In the PLLA/4-C-D1.5 blend, the Raman results showed that small isolated SC spherulites were trapped inside the big PLLA homo-spherulites during isothermal crystallization. The degradation rate of the PLLA/4-C-D blend decreased when <i>M_n,PDLA</i> increased from 0.5 to 1.5 kg/mol, and the degradation morphologies had a close relationship with the crystallization state of the blends. This work revealed the gradual formation of SC crystallites with the increase in <i>M_n,PDLA</i> in the PLLA/4-C-D blends and its significant effect on the crystallization and degradation behaviors of the blend films.