Atom transfer radical bulk copolymerization of MA and MMA was performed in the presence of CuCl/PMDETA as catalyst system and trichloromethyl‐terminated poly(vinyl acetate) macroinitiator at 80°C. The overall monomer conversion was followed gravimetrically and chemical composition of the copolymer was determined by 1H‐NMR spectrometry. The results have been used to calculate monomer reactivity ratios by linear and nonlinear methods. Reactivity ratios calculated were in the range of 0.3766–0.4988 and 1.8832–2.0963 for MA and MMA, respectively. These values were in good agreement with the values reported for a similar system in the free radical copolymerization. It was observed that the copolymerization system tends to produce a random copolymer with longer sequences of MMA than MA in the initial stage of polymerization before any significant decrease of the concentration of MMA in the monomer mixture. Copolymer microstructures in this study indicated that radical stabilization capability of MMA compared to MA is higher. The accuracy of the reactivity ratios were confirmed by 95% joint confidence limits. It was found that considering the effect of conversion in these methods makes the calculation result more accurate. The theoretical composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion are also reported.
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