Initiator-Fragment Incorporation Radical Polymerization of Divinyl Adipate with Dimethyl 2,2‘-Azobis(isobutyrate): Kinetics and Formation of Soluble Hyperbranched Polymer

Abstract

The polymerization of divinyl adipate (DVA) as an effective cross-linker with dimethyl 2,2‘-azobis(iosbutyrate) (MAIB) was performed at 70 and 80 °C in benzene. When the MAIB concentrations as high as 0.05−0.50 mol/L were used, the polymerization of DVA (0.30 mol/L) proceeded homogeneously at 80 °C without any gelation to give soluble polymers in the yields of 45−87%. Kinetic investigation on the homogeneous polymerization at 70 °C gave the following rate equation: Rp = k[MAIB]0.3[DVA]1.7 (Rp = initial polymerization rate), indicating a significant contribution of the primary radical termination. The overall activation energy of the polymerization was estimated to be 26.8 kcal/mol. The polymer formed in the polymerization of DVA (0.30 mol/L) with MAIB (0.50 mol/L) at 80 °C for 4 h was composed of the DVA units without (48 mol %) and with (8 mol %) double bond and the methoxycarbonylpropyl group (44 mol %) from MAIB. The large fraction of the incorporated initiator-fragment implies that an initiator-fragment incorporation polymerization proceeded to give hyperbranched polymer in the present polymerization. The results of the multiangle laser light scattering and viscometric measurements and also transmission electron microscopic observation indicate that the polymer was of compact hyperbranched structure. The polymer showed an upper critical solution temperature (36 °C on cooling) in an acetone−water [7:40 (v/v)] mixture and also exhibited the encapsulation and transport properties for Rhodamine 6G as a dye probe.