Synthesis of Grafted Block Copolymers Based on e-Caprolactone: Influence of Branches on Their Thermal Behavior

Abstract

Branched copolymers are a special class of polymeric materials in which are refl ected 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 fi rst 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.