CONFORMATIONAL ORDER IN CRYSTALLINE STATES AND GELS OF ISOTACTIC, SYNDIOTACTIC AND ATACTIC POLYSTYRENES STUDIED BY VIBRATIONAL SPECTROSCOPY

Stable conformations and their sequential order of isotatic (IPS), syndiotactic (SPS) and atactic polystyrenes (APS) in various aggregation states have been investigated by infrared (IR) spectroscopy, C-13 NMR and X-ray diffraction. It has been demonstrated that the partially ordered skeletal conformation existing in IPS/CS2 gels is of a (3/1) helix (TG) type having the pendant phenyl groups oriented in a disordered fashion, rather than the near-TT [(12/1) helix] form proposed previously for IPS/decalin gels. The process of conformational change during gelation of IPS/CS2 and APS/CS2 systems has been followed by IR spectroscopy, and it has been concluded that the construction of regular sequences of a particular conformation promotes the gelation of both crystallizable and non-crystalizable polystyrenes. As-cast film specimens prepared from a chloroform solution are found to be a crystalline polymer-solvent complex (the gamma phase) having a TTGG conformation. On heating, the gamma phase transforms to a beta phase at about 120-degrees-C, accompanied by removal of the solvent, while the TTGG conformation is retained. On further heating, the beta phase transforms to an alpha-1 or alpha-2 phase at about 200-degrees-C accompanied by a change in conformation from TTGG to TT. The process of conformational change (in both type and sequence) during these phase transformations has been clarified by IR spectroscopy.