LIVING CATIONIC POLYMERIZATION OF P-METHYLSTYRENE BY HYDROGEN IODIDE ZINC HALIDE INITIATING SYSTEMS

Living cationic polymerization of p‐methylstyrene has been investigated with use of hydrogen iodide/zinc halide initiating systems (HI/ZnX2; X = Cl, I) in toluene and methylene chloride solvents. The best results were obtained with HI/ZnCl2 below 0°C where the zinc salt was employed in excess over hydrogen iodide (HI/ZnCl2 = 1/5 molar ratio). Under these conditions, the number‐average molecular weights \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\overline {M_n } } \right)$\end{document} of the produced polymers increased proportionally to monomer conversion, further increased upon addition of fresh feeds of p‐methylstyrene into completely polymerized reaction mixtures, and were in good agreement with the calculated values assuming that one living polymer chain forms per molecule of hydrogen iodide; the molecular weight distributions (MWDs) of the polymers were fairly narrow \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{{\overline {M_w } } \mathord{\left/ {\vphantom {{\overline {M_w } } {\overline {M_n } }}} \right. \kern-\nulldelimiterspace} {\overline {M_n } }} = 1.1 - 1.3} \right) $\end{document} throughout these processes. In contrast, when equimolar mixtures of hydrogen iodide and zinc chloride or iodide were employed, the polymerizations were rather slow even in methylene chloride at +25°C, and the product polymers exhibited bimodal MWDs, the lower‐molecular weight fraction of which was mediated by long‐lived growing species. Addition of tetra‐n‐butylammonium iodide as a common ion salt (nBu4NI/HI = 1/200 molar ratio) led to unimodal MWDs consisting of the long‐lived lower polymer fraction alone. Copyright © 1990 John Wiley & Sons, Inc.