Living cationic polymerization of vinyl ethers by electrophile/lewis acid initiating systems. XII. Phosphoric and phosphinic acids/zinc chloride initiating systems for isobutyl vinyl ether

Phosphoric and phosphinic acid derivatives (R¹R²PO₂H; R¹, R² = OPh, OPh; OnBu, OnBu; Ph, Ph; Ph, H) in conjunction with zinc chloride (ZnCl₂) led to living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene below 0°C. The number-average molecular weights (M?_n) of the polymers (M?_n > 2 × 10⁴) were directly proportional to monomer conversion and in excellent agreement with the calculated values assuming that one polymer chain forms per R¹R²PO₂H molecule. Throughout the reaction, the molecular weight distributions (MWDs) stayed narrow (M?_w/M?_n ? 1.1). A dibasic acid, PhOP (O) (OH)₂, coupled with ZnCl₂, also induced living cationic polymerization of IBVE where one molecule of the acid generated two living polymer chains. The polymerization by (PhO)₂PO₂H/ZnCl₂ and its model reactions were directly analyzed by ³¹P and ¹H-NMR spectroscopy. The analysis showed that the acid initially forms the adduct [CH₃CH(OiBu)OP(O)(OPh)₂], the phosphate linkage of which is in turn activated by ZnCl₂ so as to initiate living propagation. The finding thus indicates that (PhO)₂PO₂H indeed acts as an initiator in the living polymerization. The NMR analysis also suggested that an exchange reaction occurs between the phosphate group at the polymer terminal and the chlorine in ZnCl₂. The occurrence of living IBVE polymerization with these various R¹R²PO₂H/ZnCl₂ systems shows that phosphoric and phosphinic acids are another general class of protonic acids which are effective initiators for the living cationic polymerization assisted by Lewis acids. © 1993 John Wiley & Sons, Inc.