Naturally renewable butyrolactone-based vinylidene monomers, α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-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 R 3 Si + 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 R 3 Si + catalyst) and activator (thus the resulting counteranion) structures have revealed that the Me 2 C═C(OMe)OSi i Bu 3 /Ph 3 CB(C 6 F 5 ) 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 × 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. Atactic homopolymers, PMBL and PMMBL, produced herein exhibit high glass transition temperatures ( T g ’s) of 194 and 225 °C, respectively, representing T g enhancements of ∼90 °C (for PMBL) and ∼120 °C (for PMMBL) over the T g of the typical atactic PMMA. The critical MW of PMMBL has been estimated to be ∼47 kg/mol.
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Miyake et al. (2010) studied this question.