Calculation of relative reactivity ratios from composition–conversion data through use of a computer

The classical methods of determining relative reactivities of monomers to free‐radical polymerization, namely polymerization to low conversion of several initial monomer compositions, purification of the polymers formed, compositional analysis, and fitting of the data to the differential form of the copolymer equation by any of several techniques, suffer from several problems. In particular, the various methods of treating the data assume no change in monomer composition at low conversion. This is a reasonable approximation when the reactivities are similar, but when they are grossly different (e.g., r1/r2 > 100), even 2 to 3% conversion can cause highly significant shifts in the monomer composition, particularly for those points where the more reactive monomer is present in relatively small amounts. Illustrations of the potential magnitude of these errors are provided. A computer program has been written that utilizes one of the integrated forms of the copolymer equation and thereby includes the conversion corrections in the treatment of the data. This procedure should yield more precise r1 and r2 values than the classical techniques, with less direct computational effort on the part of the investigator.