Synthesis and thermal characterization of macromonomeric azo initiator containing poly(?-caprolactone): Styrene and methyl methacrylate copolymerization

Macromonomeric azo initiator containing biodegradable poly(?-caprolactone, (PCL) was synthesized by the condensation reaction of PCL with 4,4'-azobis(4-cyanopentanoyl chloride) and methacryloyl chloride. This macromonomeric azo initiator (MIM-PCL) was further used in the polymerization of styrene (St) or methylmethacrylate (MMA) via a radical initiated process at 60°C in bulk in order to obtain polystyrene (PS) -b -PCL or poly (methyl methacrylate ) (PMMA)-b-PCL crosslinked block copolymers. Thermal decomposition kinetics of MIM-PCL and its copolymers were studied by using thermogravimetric analysis and differential scanning calorime-try (DSC). DSC traces of MIM-PCL showed two different exotherms, at 98 and 127°C. The first exotherm, observed at 98°C, was due to the polymerization of the terminal methacrylic groups; the other was due to the exothermic decomposition of azo groups of MIM-PCL. PCL-b-PS and PCL-b-PMMA crosslinked block copolymers showed single glass transition temperatures due to the compatibility of the crosslinked block segments. The polymer-solvent interaction parameter of PCL in chloroform was determined by vapor pressure osmometry to be 0.1 for the PCL-chloroform system at 30°C. The average molecular weights between junction points of crosslinked homo PCL were calculated by using the Flory-Rehner equation. ©1998 John Wiley & Sons, Inc.