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

• Published in: Macromolecular chemistry and physics Vol. 216; no. 24; pp. 2331 - 2343
• Main Authors: Ninago, Mario D., De Freitas, Augusto G. O., Hanazumi, Vivina, Muraro, Paulo I. R., Schmidt, Vanessa, Giacomelli, Cristiano, Ciolino, Andrés E., Villar, Marcelo A.
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.12.2015
• Subjects: Addition polymerization; Block copolymers; Branched; branched copolymers; Copolymers; Crystallization; Density; Grafting; poly(2-hydroxyethylmethacrylate) (PHEMA); poly(ε-caprolactone) (PCL); Polymerization; RAFT and ROP polymerization; thermal behavior
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.201500248

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. Comb‐like block copolymers based on ε‐caprolactone with different branching density are prepared using ring opening polymerization and radical addition fragmentation transfer polymerization methods. Poly(hydroxyethyl methacrylate‐graft‐poly(ε‐caprolactone)‐block‐poly(ε‐caprolactone) and P(HEMA‐co‐HEMA‐g‐PCL)‐b‐PCL modify the crystallization behavior with respect to linear PCL homopolymer. The branching density decreases up to 20 °C the melting temperature values.