Copolymerization Kinetic Constants and Their Prediction from Dyad/Triad Distributions

When any degree of inhomogeneity exists in a copolymer—regardless of source-distributions of dyads and triads will deviate from values calculated under the assumption of homogeneity. For copolymer systems described by the Wall equation (r1r2 = 1), the triads (111) and (222) will always be higher than predicted; (112 and (121) will be less than predicted at m1 <0.33; greater when m1 >0.33. The triads (221) and (212) will be less when m1 <0.67, greater at m1 <0.67. When nonhomogeneity is taken into account, and the probability equations adjusted accordingly, monomer distributions can be predicted accurately from simple Markovian statistics. Further, in the presence of inhomogeneity, pseudore-activity ratio products calculated from dyads will always be fallaciously high. Published data for olefin copolymerizations using heterogeneous Ziegler-Natta catalysts confirm that these systems follow the Wall equation but are nonhomogeneous.