α-Substituent Effect on o-Vinylbenzaldehyde Cyclopolymerization

Abstract

The cationic cyclopolymerization of o-vinylbenzaldehydes initiated by boron trifluoride is described. Unlike the incomplete conversion of o-vinylbenzaldehyde (1) at 0 °C, α-methyl-substituted monomers (2) and (3) undergo cyclopolymerizations with complete conversions at -78 °C. On the other hand, α-phenyl-substituted monomer (4) generated indenyl alcohol (7) when subjected to cationic polymerization conditions. The proposed mechanism for o-(α-methyl)vinylbenzaldehyde polymerization explains the importance of reaction temperature for polymer formation. Resulting amorphous poly(o-(α-methyl)vinylbenzaldehyde (10) exhibited good thermal stability (T_onset = 340 °C) with a T_g of 153 °C. Polymer (10) is a brittle and glassy plastic with a storage modulus (E') of 3 × 10⁸ Pa and elongation at break of ∼3%.