Living cationic polymerization of isobutyl vinyl ether by the diphenyl phosphate/zinc iodide initiating system

Summary

The first example of the living cationic polymerization of isobutyl vinyl ether via the phosphate counteranion has been achieved in toluene below 0°C with a new initiating system that consists of diphenyl phosphate and zinc iodide, (C₆H₅0)₂P(0)0H/ZnI₂. The number-average molecular weight of the polymers increased in direct proportion to monomer conversion, and was in excellent agreement with the calculated value assuming that one polymer chain forms per unit diphenyl phosphate. On addition of a fresh feed of monomer at the end of the polymerization, the added feed was smoothly polymerized at nearly the same rate as in the first stage, and the polymer molecular weight further increased in direct proportion to monomer conversion. Throughout the reaction, the molecular weight distribution of the polymers stayed very narrow (¯M/¯M_n ≤ 1.1). At room temperature (+25 °C), however, the molecular weight distribution of the polymers slightly broadened (¯M_w/¯M_n ∼ 1.2) at high conversions where the polymer molecular weight became smaller than the calculated value. Evidently, the (C₆H₅0)₂-P(0)0H/ZnI₂ system indeed generates a propagating species of a long life-time at room temperature, but the perfectly living polymerization by this system operates below 0°C.