A kinetic study of the living cationic polymerization of p-methoxystyrene using 1-(4-methoxyphenyl)ethanol (1)/B(C6F5)(3) initiating system in a mixture of CH3CN with CH2Cl2 1:1 (v/v) at room temperature was carried out utilizing a wide variety of conditions. The polymerization proceeded in a living fashion even in the presence of a large amount of water ([H2O]/[B(C6F5)(3)] ratio up to 20) to afford polymers whose M. increased in direct proportion to monomer conversion with fairly narrow MWDs (M-w/M-n <= 1.3). The investigation revealed that the rate of polymerization was first-order in B(C6F5)3 concentration, while a negative order in H2O concentration close to -2 was obtained. It was also found that the rate of polymerization decreased with lowering temperature, which could be attributed to a decreased concentration in free Lewis acid, the true coinitiator of polymerization. A mechanistic scheme to explain the kinetic behavior of living p-methoxystyrene polymerization is proposed, which has been validated by PREDICI simulation on multiple-data curves obtained by H-1 NMR in situ polymerization experiment. (c) 2008 Wiley Periodicals, Inc.