Analysis of a styrene–divinylester copolymerization: reaction heats, double bond conversions and average sequence lengths

Abstract

A simple model, based on the free radical copolymerization theory of Mayo and Lewis, is developed to predict reaction heats, calorimetric and molar conversions and average sequence lengths, during the crosslinking reaction between a monounsaturated monomer (M1) and a multiunsaturated comonomer (M2). The M2-double bonds are assumed to react independently with equal initial reactivities. The input variables of the model are the initial reactivity ratios (r10, r20) and their variation with the global molar conversion, the initial composition of the reactive mixture (f10) and the molar heat of formation of the different bonds formed during the copolymerization (ΔH11, ΔH22, ΔH12). The application of this model allows to calculate the overall molar and calorimetric double bond conversions (Pm and Pc), the heat developed during the reaction (ΔHT), the conversions corresponding to each type of unsaturations (Pc1, Pc2, Pm1, Pm2), and the average sequence lengths of the reacted bonds (〈N11〉 and 〈N22〉). Published data of experimental comonomers conversions in the system styrene–divinylester (S–DVER) were satisfactorily reproduced by including a functionality of both reactivity ratios with the overall conversion. Finally, it was shown that the assumption implicitly made in most published kinetic studies from the differential scanning calorimetric (DSC) data, that Pc and Pm are equivalent, is not general and this feature must be investigated in order to perform correct kinetic calculations.