Synthesis, homopolymerization, and block copolymerization ofN-ethyl-2-ethynyl-pyridinium trifluoromethanesulfonate with styrene and butadiene

Abstract

A novel acetylenic monomer 2-N-ethyl pyridinium trifluoromethane sulfonate (2EPyEtTf) was synthesized and polymerized. Diblock copolymers of 2EPyEtTf with styrene and with butadiene were prepared. Initiation of the polymerization by living anionic polystyryl - -Li + and polybutadienyl - -Li + (Scheme 1) resulted in polystyrene-block-poly(N-ethyl-2-ethynylpyridinium trifluoromethanesulfonate) (PS 57 PA 8 ), and polybutadiene-block-poly(N-ethyl-2-ethynylpyridinium trifluoromethanesulfonate)(PB 30 PA 8 ). These amphiphilic block molecules contain rigid, conjugated, and strongly hydrophilic polyacetylene chain fragments attached to hydrophobic polystyrene or flexible polybutadiene chain fragments. The structure of these copolymers was studied by FTIR, UV-visible, and NMR spectroscopy. GPC and viscometry were also used to obtain information on the molecular mass and the molecular mass distribution. Thermal behavior was investigated by means of TGA and DSC. Both block copolymers were shown to form stable monolayers at the air-water interface. The positively charged rigid polyacetylene portion of the copolymer is believed to be partially submerged, while the more flexible hydrophobic chains are forced out of the water. Multilayers of PB 30 PA 8 deposited using the Langmuir-Blodgett technique were found to be less uniform than in the case of the previously reported polystyrene-block-poly(2E-PyMeTf)(PS 12 PA 4 ) copolymer (Balogh et al., Macromolecules, 29, 1996). Polycation-polyanion self-assembly deposition was also investigated, using polystyrenesulfonate (PSS) as polyanion. While PS 57 PA 8 /ASS layer-by-layer deposition was not uniform, it was found that PB 30 PA 8 /ASS gave homogenous and stable films on hydrophilic glass substrates.