PREPARATION OF ULTRAHIGH MOLECULAR-WEIGHT POLYACRYLONITRILE AND ITS TERPOLYMERS

The synthesis of high molecular weight (in excess of 10(6) million Dal tons) poly(acrylonitrile) and poly(acrylonitrile-co-methylacrylate-co- itaconic acid) is described. An inverse emulsion polymerization formul ation with AIBN as the initiator was used. However, polymer precipitat ion occurred early in the polymerization. In each case, the molecular weight distribution was surprisingly narrow ((M) over bar M(w)/(M) ove r bar M(n), similar to 1.5). Conversion vs. time plots with monomers c ontaining the inhibitor had the ''S'' shape typical of emulsion polyme rizations. The terpolymer composition and molecular weight were quite uniform throughout the polymerization. With inhibitor-free monomers, t he initial molecular weights were very high (similar to 3 X 10(6) Dalt ons), but gelation occurred at ca. 50% conversion. There was an invers e relationship between the monomer inhibitor content and the polymer m olecular weight. It is suggested that the growing polymer radicals are occluded in the precipitated polymer particles and are terminated by inhibitor diffusing into the particles, accounting for the narrow mole cular weight distribution. (C) 1995 John Wiley & Sons, Inc.