SIZE-EXCLUSION CHROMATOGRAPHIC INVESTIGATION OF THE CONVERSION OF A PRECURSOR POLYMER TO POLY(P-PHENYLENE)

A substituted poly(cyclohexadiene) precursor polymer has been pyrolysed (aromatized) in N-methylpyrrolidinone solution to poly(p-phenylene). For aromatizations up to 40% the polymer remains in solution, but size exclusion chromatography shows that the initially narrow molecular weight distribution fractions become bimodal with a high molecular weight peak appearing even at low percentage aromatizations. At the same time, the main component of the polymer rapidly decreases in molecular weight. Size exclusion chromatography using detection specific for phenylene residues indicates that their concentration is the same across the whole distribution. These results were confirmed by fractionating a partially aromatized polymer. The data indicate that aromatization occurs both randomly and in sequences and is accompanied by scission. Molecules with long sequences of phenylene groups aggregate, forming the high molecular weight fraction observed by size exclusion chromatography. The low molecular weight fraction has the same degree of aromatization but the phenylene units are randomly distributed and do not aggregate intermolecularly.