Synthesis of Star-Comb Double Crystalline Diblock Copolymer of Poly(ε-caprolactone)-block-poly(l-lactide): Effect of Chain Topology on Crystallization Behavior

Abstract

A series of highly branched star‐comb poly(ε‐caprolactone)‐block‐poly(l‐lactide) (scPCL‐b‐PLLA) are successfully achieved using star‐shaped hydroxylated polybutadiene as the macroinitiator by a simple “grafting from” strategy. The ration of each segment can be controlled by the feed ratio of comonomers. These star‐comb double crystalline copolymers are well‐defined and expected to illustrate the influences of the polymer chain topology by comparing with their counterparts in linear‐shaped, star‐shaped, and linear‐comb shape. The crystallization behaviors of PCL‐b‐PLLA copolymers with different architectures are investigated systematically by means of wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscopy analysis. It is shown that the comb branched architectures promote the crystallization behavior of each constituent significantly. Both crystallinity and melting temperature greatly raise from linear to comb‐shaped copolymers. Compared to linear‐comb topology, the star‐comb shape presents some steric hindrance of the graft points, which decrease the crystallinity of scPCL‐b‐PLLA. Effects of copolymer composition and chain topology on the crystallization are studied and discussed.

Toughening modification of PLLA with PCL in the presence of PCL‐b‐PLLA diblock copolymers as compatibilizer

“…Furthermore, the presence of copolymers could provide another route to enhance the toughness and compatibility of immiscibility blend systems, whose chemical nature was identical to the main components of blends . Thus, the different molecular structures of PCL‐co‐PLLA copolymer were extensively synthesized and widely acted as compatibilizer in reducing interfacial tension and improving interfacial adhesion of PCL and PLLA blends …”

“…31 Thus, the different molecular structures of PCL-co-PLLA copolymer were extensively synthesized and widely acted as compatibilizer in reducing interfacial tension and improving interfacial adhesion of PCL and PLLA blends. [32][33][34][35][36][37][38] Zhang et al 32 added a random copolymer P (LLA-ran-CL) into PLLA/PCL blend, and found the size of the dispersed PCL domains decreased from 5 to <1 um, the tensile results showed an improvement in the elongation at break and the ductility of the blends. Rizzuto et al 33 melt mixed P (LLA-ran-CL) with PLLA/PCL blends.…”

Recent progress in block copolymer crystallization

“…Here, blocks are tethered/constrained in ways different than the single tether; however, the crystallization behavior is related. Recent work has been focused on the morphologies of highly branched copolymers, such as graft copolymers, brush copolymers, and hyperbranched copolymers . For this review, we have focused only on highly branched BCP architectures (molecular schematics in Figure ) where polymer chains are involved in the crystallization process.…”

“…Double crystalline graft copolymers with comb‐like structures were evaluated with different compositions and architectures. PCL‐ b ‐PLLA chains were grafted onto PB backbones by Leng et al . Here, T c PCL < T c PLLA is an additional factor in the development of polymer crystals.…”

“…Hyperbranched block copolymers have attracted some attention in recent years as well. The examples provided here have a star comb‐like BCP graft architecture or a linear Block A chain with dendritic Block B ends similar to an ABA triblock . Leng et.…”