The gelation mechanism of solutions of isotactic polystyrene in cis-decalin

The gelation of isotactic polystyrene in cis-decalin was investigated with calorimetric, infrared and rheological measurements. At temperatures above 30°C a crystalline structure similar to the one obtained by crystallization from the melt is formed. Below 30°C thermoreversible gels are formed with a molecular conformation different from that in the melt crystallized samples. They can be formed during a cooling process below 19°C and can increase their helix content and modulus on isothermal annealing. Gels formed in this temperature domain exhibit a two-stage melting as observed by calorimetry, infrared spectroscopy and rheology. At higher temperature gels can only be formed after isothermal annealing. These gels melt in one single step. A mechanism is proposed for the gelation in both temperature domains. At low temperature, bundle-like entities composed of long helices are formed giving rise to the high melting structure. In a second step, additional helix formation increases the modulus and induces the low melting structure. In the high temperature domain, only the low melting structure is formed. This model is in agreement with morphological data reported in the literature.