STRUCTURE OF PHYSICAL GELS FORMED IN SYNDIOTACTIC POLYSTYRENE SOLVENT SYSTEMS STUDIED BY SMALL-ANGLE NEUTRON-SCATTERING

The molecular aggregation state in physical gels of syndiotactic polystyrene (SPS) dispersed in various organic solvents was investigated by means of small-angle neutron scattering (SANS). The SANS intensity profiles measured for the momentum transfer q range of 0.02-2.0 nm-1 were reproduced well by the equation derived by Freltoft, Kjems, and Sinha for describing SANS profiles of fractal objects. The relevant structural parameters such as the correlation length (the upper cutoff length) xi, the lower cutoff length r0, the mass fractal dimension D(m), and the surface fractal dimension D(s) were obtained from the least-squares fittings to the data. The SANS profiles measured at 25-degrees-C, and the structural parameters derived from them, varied depending on the solvent in which SPS molecules were dispersed. In particular, the profile of SPS/chloroform gel differed remarkably from those of SPS/o-dichlorobenzene and SPS/carbon tetrachloride gels. The obtained structural parameters suggested that, in SPS/chloroform gel, the coagulates of polymer segments were less-developed, forming loosely packed clusters compared with the latter two cases. The result was consistent with the fact revealed by infrared spectroscopy that the orderliness of the TTGG skeletal conformation of polymer molecules in SPS/chloroform gels at room temperature is far less than that in SPS/o-dichlorobenzene and SPS/CCl4 gels. The SANS profiles were analyzed also by other commonly used methods such as the Guinier plot, the Kratky plot, and the Zimm plot, and their usefulness was considered.