Structure and Mechanism of Atactic Polystyrene Physical Gel

The structure and conformation of a physical gel observed in a low temperature range of atactic polystyrene in carbon disulfide have been studied by means of small-angle neutron scattering (SANS), wide-angle neutron diffraction (WAND), and quasielastic neutron scattering (QENS). SANS reveals that a crosslink is formed between chains even in a very dilute solution and grows up to a large associating polymer, as the temperature is lowered. The chain association proceeds in two steps and is reversible. The critical exponent along the sol-gel transition line continuously changes from 3.3 to 2.0. It is explained by the co-occurrence of association and gelation on the temperatureconcentration phase diagram, suggesting that the crosslinking zone is soft. Although the global conformation of a single chain does not change upon the gelation, a conformational change occurs during the gelation. WAND reveals that the construction of (TTGG) 1-2 conformation and the subsequent formation of the crosslink between them induce the gelation. The driving force may be induced by a specific interaction between carbon disulfide and the phenyl ring in chains. QENS reveals the dynamics of the conformational ordering and of the crosslink.