Naturally renewable butyrolactone-based vinylidene monomers, alpha-methylene-gamma-butyrolactone (MBL) and gamma-methyl-alpha-methylene-gamma-butyrolactone (MMBL), have been successfully polymerized in a rapid and living fashion, using ambiphilic silicon propagating species consisting of both the nucleophilic silyl ketene acetal (SKA) initiating moiety and the electrophilic silylium catalyst. Uniquely, the R3Si+ catalyst is derived directly from the SKA initiator upon in situ oxidative activation with a catalytic amount of the trityl borate activator. Investigations into effects of SKA (thus the resulting R3Si+ catalyst) and activator (thus the resulting counteranion) structures have revealed that the Me2C=C(OMe)(OSiBu3)-Bu-i/Ph3CB(C6F5)(4) combination is the most active and controlled system for (M)MBL polymerizations. Thus. under ambient conditions and with a low catalyst loading (0.05 mol % relative to monomer), this polymerization system rapidly (within 10 min) and completely converts MMBL to PMMBL with controlled low to high (M-n = 5.43 x 10(5) kg/mol) MW's and narrow MW distributions (1.01-1.06). Well-defined block copolymers of MBL and MMBL with MMA as well as block and statistical copolymers of MBL with MMBL have also been readily synthesized. A tactic homopolymers. PMBL and PMMBL, produced herein exhibit high glass transition temperatures (T-g's) of 194 and 225 degrees C, respectively, representing T, enhancements of similar to 90 degrees C (for PMBL) and similar to 120 degrees C (for PMMBL) over the T-g of the typical emetic PMMA. The critical MW of PMMBL has been estimated to be similar to 47 kg/mol.