CONSECUTIVE 2-STATE STATISTICAL POLYMERIZATION MODELS

In polymerizations of vinyl monomers and olefins it may happen that the propagating polymer species can exist in two states, e.g., as a result of solvent interaction (in ionic polymerization) or multiple catalytic sites (in Ziegler-Natta polymerization). If the switching between the states occurs during propagation, the resulting polymer would be a block copolymer, each block obeying a different propagation statistics. The polymer microstructure would follow a two-state model, an example being the Coleman-Fox statistics. In this work, a different approach is taken to treat this general problem of consecutive two-state models. Included in the treatment (for tacticity) are the two-state Bernoullian/Bernoullian, Bernoullian/enantiomorphic, and enantiomorphic/enantiomorphic models. The theoretical expressions corresponding to NMR tetrad and pentad tacticity analysis are derived. These expressions are then combined with a computerized analytical approach to facilitate their application. Illustrative examples are shown of the use of this methodology to treat tacticity tetrads of poly(methyl methacrylate) and tacticity pentads of polypropylene. The same methodology can be readily used for copolymer sequence analysis.