Line‐intersection method for determining the configurational parameters of cross propagation in copolymerization

Abstract

AbstractFor the evaluation of the configurational parameters in cross propagation, Σs and Σp for binary vinyl type copolymers whose monomer units both contain an asymmetric carbon atom in the chain, a method is proposed which relies on intersecting straight lines in a Σs versus Σp diagram. We define Σs = σAB + σAB and Σp = σAB·σBA, σ being the probability of forming an isotactic enchainment between the monomer units when B adds to a chain ending in A, or A adds to a chain ending in B, respectively. For these definitions it is assumed that σAB and σBA are not necessarily equal in their numerical values. The method described is applicable to triad probabilities obtained both from copolymers and such homopolymers which have been prepared from copolymers under retention of configuration by a polymer analogous reaction. In this work, triad data have been evaluated which were obtained by NMR from methyl methacrylate‐methacrylic acid copolymers, wherein the methyl methacrylate units were pentadeuterated on the αCH3 and βCH2 groups, as well as from methyl methacrylate homopolymers, the latter being prepared from undeuterated methyl methacrylate‐methacrylic acid copolymers by esterification. The approximate values Σs = 0.38, Σp = 0.02 were obtained for the deuterated copolymers, while Σs = 0.392 ± 0.003 and Σp = 0.037 ± 0.003 were found for the undeuterated homopolymers.