Structures in isotactic polystyrene solutions near the physical gelation threshold

Thermal, morphological, and structural investigations of isotactic polystyrene (iPS) solutions in either cis-decalin or trans-decalin near the physical gelation threshold are reported on. In iPS /cis-decalin solutions there is an intermediate state between the gel state and the crystalline state. It is shown that there exists a temperature domain, above the gelation threshold (typically 20-30 deg C), where giant spherulites can be grown that, however, possess nearly the same melting point as the gel. Despite the high macroscopic organization, X-rays and neutron diffraction experiments reveal a poor molecular order rather reminiscent of smectic arrangements. No reflection at 0.51 nm, characteristic of the 12 sub 1 helix, is seen, which leads one to dismiss the presence of this helical form both in these structures and in the gel. In addition, the large distances observed by the diffraction techniques (2.47, 1.7, and 1.1 nm) provide further support to the intercalate (or polymer-solvent) compound. In iPS/trans-decalin solutions there is no intermediate state between the gel state and the crystalline state. The difference of the isomers of decalin toward iPS gelation are emphasized. Graphs, Photomicrographs, Diffraction patterns. 19 ref.--AA