Radiation-induced postcopolymerization of isoprene with sulfur dioxide

Mechanism of the postradiation copolymerization of isoprene with sulfur dioxide was studied by thorough calorimetric analysis of the phase state and the copolymerization dynamics in the entire range of monomer concentrations. Cooling of the liquid mixture of monomers to 77 K leads to the formation of a glassy solution. On heating the system after radiolysis at 77 K, the heat evolution due to copolymerization is observed upon passage of the temperature interval corresponding to softening of the glass. The reaction rate rapidly reaches a maximum in the region of existence of supercooled liquids, and then slows down at 105-115 K because of the crystallization process leading to a sharp decrease in the molecular mobility. A maximum polymer yield was observed for an SO2 content of similar to 60 mol % in the initial mixture. Excess isoprene and SO2 can attach to the propagating polymer chain in the entire range of relative monomer concentrations. The process dynamics and the product composition are determined by the involved phase state of the system and by the parallel process of mutual phase transformations.