Synthesis of Grafted Block Copolymers Based on ε‐Caprolactone: Influence of Branches on Their Thermal Behavior

Abstract

Branched copolymers are a special class of polymeric materials in which are reflected the combined effects of polymer segments and architectural constraints of the branched architecture. This study employed two methodologies to obtain copolymers with different branching density. In the first case, poly(hydroxyethyl methacrylate‐graft‐poly(ε‐caprolactone)‐block‐poly(ε‐caprolactone), P(HEMA‐g‐PCL)‐b‐PCL, copolymers were synthesized by a “grafting through” method in a three‐step reaction pathway involving ring opening polymerization (ROP) and radical addition fragmentation transfer (RAFT) polymerization. In the second case, a combination of simultaneous “grafting through” and “grafting from” methods in a one‐pot RAFT and ROP reaction afforded P(HEMA‐co‐HEMA‐g‐PCL)‐b‐PCL comb‐like copolymers with comparatively less dense branching. Samples with molar masses between 5500 and 46 000 g mol−1 and polydispersity indexes (Mw/Mn) lower than 1.3 were successfully obtained through both approaches. According to thermal analyses, the presence of branches reduces PCL melting temperature by as much as 20 °C, without affecting thermal stability. This fact was particularly evident for the most densely branched copolymers with higher molar masses. Nonisothermal crystallization process was successfully described using Ozawa's method, which showed a clear dependence of crystallization rate and cooling on grafting density.

Thermal Characterization of “Comb‐Like” Block Copolymers Based on PCL Obtained by Combining ROP and RAFT Polymerizations

“…In this sense, compared to previous work reported by Choi and Kwak, this last fact represents a great advantage: it provides less synthetic reactions and chemical workup. In addition, the degree of polymerization and the degree of branching in the resulting copolymers were confirmed by 1 H‐NMR analysis …”

“…Besides, an increase in the signals at 1,447 cm −1 and 740 cm −1 could be associated to the vibration of CH 2  bonds in methacrylic polymers . In addition, absorption bands corresponding to the >CO group in PHEMA and PCL segment (observed at 1,728, 1,240 and 1,174 cm −1 ), and the absorption band assigned to the >CS bond in the CTA end group (at 1,066 cm −1 ) are also distinguishable …”

“…Scheme shows the polymerization pathways employed in this work. Block copolymers COP1 and COP2 (Scheme , route 1) were obtained by RAFT polymerization employing the grafting through methodology, the CTA–PCL and a methacryloyl‐terminated PCL macromonomer (mPCL) . Regarding to this methodology, mPCL, CTA–PCL, VAZO catalyst 88 and toluene as reaction solvent were introduced into a Schlenk reactor.…”

Effects of Branches on the Isothermal Crystallization of Copolymers Based on Poly(ϵ‐caprolactone)

“…The reaction was left to proceed during 24 h and the final product was precipitated in cold methanol and dried in vacuum until constant weight . Copolymers were named from lower to higher molar masses as HEMACL1, HEMACL2, and HEMACL3 (Table ).…”

“…2‐hydroxyethylmethacrylate (HEMA) can be copolymerized with others biocompatible monomers (such as ϵ‐caprolactone, ϵ‐CL) by employing conventional free‐radicals polymerization. As example, PCL chains grafted onto PHEMA backbone were obtained by combining ROP with reversible addition fragmentation chain transfer (RAFT) polymerization, which is a controlled radical polymerization that allows tuning molecular weight and polydispersity indexes of complex macromolecular architectures like stars, blocks, or grafted copolymers . This combination of polymerization techniques allows the synthesis of complex macromolecular architectures with thermal, mechanic, or physicochemical particularities.…”