Synthesis, characterization, thermal, and photophysical properties of carbon-carbon chain polymers with pendant terphenyl side-chains
Light emitting diode devices fabricated from conjugated polymeric materials have received considerable attention over the past five years because of the possible application of these devices in flat panel displays and polymeric lasers. However, several obstacles, including solubility, processability and color tunability, must be overcome in order to achieve the anticipated utilization. Several polymers with conjugated side-chains have been prepared. Suspending the conjugated moiety from the flexible carbon-carbon backbone addresses the problems associated with conjugated main chain polymers. The flexibility of the carbon-carbon backbone should impart enhanced solubility as compared to main chain conjugated polymers. Lower melting transitions are observed for the polymers prepared in this study as compared to conjugated main chain polymers. This could lead to improved processing capabilities. By changing the identity of the conjugated side-chain moiety, color tunability can be easily achieved. Because of the stacking expected in the side-chain, enhanced charge transport is anticipated. Poly(styrene-g-biphenyl) was prepared by the coupling of biphenylmagnesium bromide to brominated polystyrene. The polymer is soluble in common organic solvents and displays blue photoluminescence. The quantum yield of fluorescence of the polymer in solution as compared to terphenyl was 0.51. Poly(vinyl p-terphenyl) was prepared by the free radical polymerization of the corresponding monomer. Despite the relatively low molecular weight of the polymer, thin films could be cast from solution. The polymer displays blue photoluminescence in the solid state and solution. The quantum yield of fluorescence of the polymer in solution as compared to terphenyl was 0.48. A series of liquid crystalline methylmethacrylate based polymers and copolymers with 8, 10, and 11 spacers were prepared. The intermediate compounds, polymers, and 1:1 mole % copolymers display smectic mesophases. The polymers and 1:1 mole % copolymers display limited solubility; however they exhibit blue photoluminescence in the solid state. The quantum yields of fluorescence of the copolymers in solution as compared to terphenyl ranged from 0.39-0.88.