Macromonomeric azo initiator containing biodegradable poly(epsilon-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 degrees 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 calorimetry (DSC). DSC traces of MIM-PCL showed two different exotherms, at 98 and 127 degrees C, The first exotherm, observed at 98 degrees 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 degrees C. The average molecular weights between junction points of crosslinked homo PCL were calculated by using the Flory-Rehner equation.