BRANCHING EFFECTS IN PHYSICAL GELATION OF ATACTIC POLYSTYRENE

In this paper we give new results on the physical gelation of a tactic polystyrene-carbon disulfide (CS2) solutions in relation to the struc ture of the chains. We demonstrate here the starlike effect on the ons et of gelation supported by well-improved techniques such as the ball- drop method, differential scanning calorimetry, measurements of the st atic modulus, and oscillatory rheometry. The sol-gel phase diagrams sh ow that the increase of the degree of branching has a noticeable impac t on gel formation but with approximately constant melting enthalpy. T he chemical junctions between branches in the star molecules result in an increase of the gelation temperature with respect to linear chains of equal concentration and overall molecular weight and in a decrease in the gel modulus at a given concentration.