Analysis of the linear methods for determining copolymerization reactivity ratios. IV. A comprehensive and critical reexamination of carbocationic copolymerization data

Abstract

Increased insight into the mechanism of carbocationic copolymerization has been achieved by classifying and reviewing in detail 334 monomer pairs in terms of the extended Kelen‐Tüdös method. The reactivity ratios (r values) of essentially all published olefin–olefin, olefin–vinyl ether, vinyl ether‐vinyl ether, and some miscellaneous systems have been reexamined and classified. Of the systems reviewed, only 121 (36.2%) contained sufficiently detailed information for comprehensive reevaluation and classification. Of these, only 49 (14.7%) were found to contain sufficiently accurate and reliable data to satisfy acceptance in class I, i.e., systems which are adequately described by the conventional copolymer composition equation, while 40 (12%) were accepted only in class I(!), i.e., systems for which the available data are somewhat less reliable than for class I and some caution is in order when employing r values for quantitative purposes. Six (1.8%) monomer pairs were judged to belong to class II, i.e., systems for which the approximations implicit in the conventional copolymer composition equation do not hold and published r values are probably erroneous and misleading. Finally, 26 (7.8%) monomer pairs were placed in class III, i.e., systems that exhibit unacceptable data scatter in the η versus ξ plot and published r values are meaningless. In some instances, even the existence of true copolymers is questioned.