Statistical models in the study of stereospecific polymerization

Abstract Triad tacticity data obtained by NMR analysis have previously been interpreted in terms of two basic statistical models in order to elucidate the stereospecific polymerization mechanism. In this paper the characteristics of these two basic models for stereospecific polymerization, the enantiomorphic‐sites (EMS) model, and the polymer‐end control (PEC) model, are examined and compared. The tacticity values accessible to the two‐parameter EMS model, which includes the influence of the chain end unit, are shown to be highly restricted. Only about 20% of the isotacticity versus syndiotacticity plot is accessible to this model. To this extent the consistency of a set of triad tacticity data with the model can be tested. No such tacticity limits are exhibited by the two‐parameter PEC model, which includes the influence of the penultimate unit. Any set of tacticity values which can be interpreted in terms of the two‐parameter EMS model can also be interpreted in terms of the two‐parameter PEC model.