A SMALL-ANGLE NEUTRON-SCATTERING INVESTIGATION OF THE CONFIGURATION OF POLY(P-PHENYLENE) PRECURSORS IN SOLUTION

Small-angle neutron scattering (SANS) has been used to investigate the configuration of partially aromatized precursor polymers of poly(p-phenylene) in N-methylpyrrolidinone solution. The range of aromatization covered was 0-80%, and a number of precursor polymer molecular weights were used. Although the aromatization process is accompanied by degradation and aggregation, it has been possible to interpret the SANS data using scattering laws for stiff chains. From this analysis,persistence lengths and shift factors have been obtained for aromatizations up to 40%; persistance lengths range from 22 to 32 Angstrom and shift factors from an average of 40 to 20 Angstrom(-1). Above this degree of aromatization there is a distinct change in the SANS profile. When these data are plotted in Kratky format, a distinct maximum was observed. For aromatizations greater than 40%, the configuration in solution has been interpreted as the formation of starlike aggregates where insoluble polyphenylene cores are maintained in solution by solvated unaromatized portions of the aggregate which form the arms of the star. As aromatization increased from 50% to similar to 80%, the radius of gyration of three different molecular weight fractions varied little but the number of arms increased. The suitability of the polydisperse star model for the highest percentage aromatization is questionable, and possible alternatives are discussed. The complications of degradation and increase in polydispersity prevent the use of more complex models. Aromatization does not lead to any significant increase in rodlike configuration of the molecules. The dominant effect is aggregation to form clusters that have starlike characteristics.