RELATION BETWEEN PHYSICAL GELATION AND TACTICITY IN POLYSTYRENE

In order to throw some light on the physical gelation of polystyrene in solution, we have prepared samples of differing tacticities by means of epimerization of an isotactic sample. After careful characterization by 1H nuclear magnetic resonance, light scattering, viscometry and gel permeation chromatography, the gelation propensity has been studied by differential scanning calorimetry and the ball-drop method in carbon disulphide (CS2) and in diethyl malonate. For a fraction of isotactic triads higher than 58%, gelation characteristics remain those of isotactic polystyrene. Between 58 and 35%, no gelation occurs whatsoever. Below 30%, the gelation characteristics of atactic polystyrene are retrieved only in CS2. The main conclusion is that the gelation phenomenon in atactic polystyrene in CS2 is due to the syndiotactic sequences.