Calorimetric investigation of polymerization reactions. II. Copolymerization of diethyl fumarate with styrene

The bulk copolymerization of diethyl fumarate with styrene initiated by benzoyl peroxide or azobisisobutyronitrile was investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of copolymerization decreased almost linearly with the increase in diethyl fumarate content in the copolymer. The heat of homopolymerization for diethyl fumarate was equal to 15.5 ± 0.3 kcal/mole. Monomer reactivity ratios at 100°C were also determined. The rate of copolymerization was followed over the whole range of conversion. A gel effect was noticed in copolymerizations at lower but not at higher temperatures. The initial rate of copolymerization exhibited a maximum at an intermediate monomer feed composition, differing from the previously reported tendency. The difference was found to be due to the method used for determining the rate of copolymerization, and the superiority of the DSC method was proved. The mechanism of the radical‐radical termination process was discussed. From the viewpoint of chemically controlled termination, the cross‐termination factor ϕ was estimated to be 2.0, which is reasonable considering the steric hindrance; assumption of the predominance of a diffusion‐controlled termination reaction was also consistent with the results.