The initiator-fragment incorporation radical polymerization was extended to a copolymerization system of a trivinyl monomer. The copolymerization of trimethylolpropane trimethacrylate (TMPTM) as a trivinyl monomer with alpha-methylstyrene (MSt) was examined at 70 and 80 degrees C in toluene using dimethyl 2,2 '-azobisisobutyrate (MAIB) of high concentrations as initiator. When the concentrations of TMPTM, MSt and MAIB were 0.30, 0.60 and 0.50 mol/l, the copolymerization proceeded homogeneously without gelation at 80 degrees C to yield soluble hyperbranched copolymer in a yield of 65%. The copolymer formed for 8 h consisted of 37 mol% of the TMPTM unit, 42 mol% of the MSt unit and 21 mo1% of the methoxycarbonylpropyl group as initiator-fragment, where 22% of the vinyl groups of the incorporated TMPTM units remained unreacted. The copolymer showed an upper critical solution temperature (32 degrees C on cooling) in a tetrahydrofuran(THF)-water [44: 10 (wt/wt)]. Reflecting the hyperbranched structure, the viscosity of a copolymer solution in toluene was very low. The porous film was prepared directly by casting a THF solution of the hyperbranched copolymer on a cover glass. The copolymer molecules are radially arranged on the surface layer of the spherical pores as showed by polarized optical microscope imaging. (c) 2006 Elsevier Ltd. All rights reserved.