LEWIS-ACID COORDINATION-COMPLEXES OF POLYMERS .3. POLY(BENZOBISIMIDAZOBENZOPHENANTHROLINE) LADDER AND SEMILADDER POLYMERS

The structures, solution properties and solid state properties of comp lexes of poly(benzobisimidazobenzo-phenanthroline) ladder (BBL) and it s semiladder analogue (BBB) with the Lewis acid aluminium(III) chlorid e (AlCl) and gallium(III) chloride (GaCl3) are reported. At a 4:1 mole ratio of Lewis acid to polymer (BBB or BBL) repeat unit, electron don or-acceptor complexes of Lewis acid-base type, which are highly solubl e in organic solvents, are formed. A detailed spectroscopic investigat ion shows that complexation of both polymers involves coordination of the Lewis acids to the electron-rich carbonyl oxygens and the imine ni trogens in the polymer backbones. The complexes of BBL exhibit the cha racteristic rigid-rod behaviour of the pristine ladder polymer. BBL co mplexes have rigid, rod-like chain conformations in dilute solution as evidenced by their solvent independent intrinsic viscosities. The com plexes form liquid crystalline solutions above 8 wt% BBL in AlCl3/nitr omethane and above 9-9.5 wt% in GaCl3/nitromethane. The solid complexe s of BBL have slightly smaller optical absorption edges than BBL and s imilar to 50% larger absorption coefficients at lambda(max). D.s.c. re vealed a glass transition (T-g) of the 4:1 GaCl3:BBL complex at 15 deg rees C. Dynamic mechanical experiments indicated the T-g, measured at the loss tangent peak, was in the range 29-37 degrees C depending on f requency, with an activation energy of 448 kJ mol(-1). The complexes o f BBB by contrast exhibit flexible-coil behaviour due to the polymer t opology. In solution, BBB complexes have intrinsic viscosities which d epend on the solvent and Lewis acid used, due to differing degrees of coil expansion in different solvent media. Coil expansion in solution leads to improved conjugation of BBB complexes as evidenced by compari son of the electronic absorption spectra with those of BBL. BBB comple xes, like the pure polymer, are apparently not liquid crystalline at h igh concentrations in solution. The solid 4:1 GaCl3:BBB complex has a T-g at 30 degrees C, and a dynamic mechanical analysis T-g in the rang e 12-24 degrees C. The T-g activation energy, at 293 kJ mol(-1), is lo wer than that of the BBL/GaCl3 complex. The overall results of the pre sent studies provide a basis for understanding the structure and prope rties of these polymers in terms of intermolecular interactions and al so have implications for the processing of the polymers for diverse ap plications.