LIVING CARBOCATIONIC COPOLYMERIZATIONS .2. REACTIVITY RATIOS AND MICROSTRUCTURE OF ISOBUTYLENE/P-METHYLSTYRENE COPOLYMERS

A novel method was developed for the quantitative description of copolymerization behavior, specifically for the derivation of reactivity ratios and micro- and macro-compositions of monomer pairs with significantly different reactivities. The novelty of the method lies in the manner of generating instantaneous feed and copolymer composition data from experimentally readily obtainable cumulative copolymer compositions, although the latter drifts with progressing copolymerization. It is demonstrated that such copolymer systems can be described by two reactivity ratios, albeit the values are valid only over the narrow feed composition range within which they were determined, The great advantage of this method is that whereas the differential copolymer composition equation is strictly valid only at 0% conversion, the method produces corresponding instantaneous feed and copolymer compositions at any conversion, Assumptions or approximations are unnecessary to calculate reactivity ratios, Subsequently the procedure was applied to obtain reliable monomer reactivity ratios of isobutylene (IB)-p-mehtylstyrene (pMeSt) copolymers, r(IB) and r(pMest), prepared by living carbocationic copolymerizations with [IB]/[pMeSt] feeds compositions of 90:10 and 97:3 mol/mol, i,e., with feed compositions of industrial importance, According to our procedure, r(IB) = 0.74 +/- 0.11 and r(pMeSt) = 7.99 +/- 3.34, These reactivity ratios were then used to calculate overall IB-pMeSt copolymer compositions over the entire comonomer conversion range and to compare calculated with experimental compositions. The good quantitative agreement between calculated and experimental compositions indicates that the description of both macro- and micro-compositions of IB-pMeSt copolymers obtained in the 90:10 and to 97:3 mol/mol feed composition range is satisfactory.