Structural ordering on physical gelation of syndiotactic polystyrene dispersed in chloroform studied by time-resolved measurements of small angle neutron scattering (SANS) and infrared spectroscopy

Physical gelation of syndiotactic polystyrene (SPS) dispersed in chloroform was found to proceed very slowly in the time scale of 10 h or longer. Time evolution of gel-network structure on the gelation process was investigated by time-resolved measurements of SANS and FTIR spectroscopy for various combinations of such factors as the molecular weight of SPS (M w ), the polymer concentration (C), and temperature, on which the kinetic behavior of the gelation depends remarkably. For every case, the total SANS intensity Q, as a measure of the degree of gelation, increased with time in parallel to the TTGG-type conformational ordering of the SPS molecules dispersed in the gel measured by time-resolved FT-IR. At an early stage of gelation, the SANS functions were reproduced well by the equation presented by Dozier et al. for semidilute solutions of star polymers and then converted to the form characteristic of continuous fractal objects as the gelation proceeded. The parameters describing gel-network structure, such as the radius of gyration of stars R g , the correlation length ξ, and the mass-fractal dimension D' inside the star were evaluated as a function of gelation time through a nonlinear least squares fitting. ξ' and D' were found to exhibit a divergence-like abrupt change at a particular gelation time. At the same time the Q and the conformational order started to increase, indicating that the sol-gel transformation occurred at this point. The sol-gel transformation was found to be delayed with lowering M w or C or with raising temperature. The time dependencies of the SANS functions after the transformation regime was analyzed by the theoretical equation derived by Freltoft et al. for continuous fractal objects.