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-ph enylene) in N-methylpyrrolidinone solution. The range of aromatization covered was 0-80%, and a number of precursor polymer molecular weight s were used. Although the aromatization process is accompanied by degr adation and aggregation, it has been possible to interpret the SANS da ta using scattering laws for stiff chains. From this analysis,persiste nce lengths and shift factors have been obtained for aromatizations up to 40%; persistance lengths range from 22 to 32 Angstrom and shift fa ctors from an average of 40 to 20 Angstrom(-1). Above this degree of a romatization there is a distinct change in the SANS profile. When thes e 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 insolu ble polyphenylene cores are maintained in solution by solvated unaroma tized portions of the aggregate which form the arms of the star. As ar omatization increased from 50% to similar to 80%, the radius of gyrati on of three different molecular weight fractions varied little but the number of arms increased. The suitability of the polydisperse star mo del for the highest percentage aromatization is questionable, and poss ible alternatives are discussed. The complications of degradation and increase in polydispersity prevent the use of more complex models. Aro matization does not lead to any significant increase in rodlike config uration of the molecules. The dominant effect is aggregation to form c lusters that have starlike characteristics.