Moderately Concentrated Solutions of Polystyrene. 6. Gel Formation in Carbon Disulfide

Abstract

Gel formation of moderately concentrated solutions of anionically polymerized polystyrene in carbon disulfide is studied to conclude that association of the two sulfur atoms on CS 2 with phenyl rings on different polystyrene chains results in a few cross-link loci per polymer chain, creating an elastomeric gel. The equilibrium compliance J e of a gel sample is evaluated from creep and recoverable strain measurements, and a light scattering method to analyze constrained oscillations in the gel is used to determine the storage modulus G'(ω) and the dynamic viscosity η'(ω) for ω small enough that G'(ω) G e = 1/J e . The sharp increase of the relative viscosity as T is reduced to within a few degrees of T gel is modeled by the viscosity for a branched chain, with the number of cross-links per primary chain approaching unity as T goes to T gel . The carbon disulfide/polystyrene interaction is supported by light scattering measurements on dilute solutions of polystyrene in a toluene-CS 2 mixed solvent, which show preferential solvation of polystyrene by CS 2 and the observation that the temperature T gel required to form a gel with moderately concentrated solutions of polystyrene in a toluene-CS 2 mixed solvent is essentially independent of the toluene concentration. Further, the temperature dependence of the NMR spin-lattice relaxation time of the 13 C nucleus of CS 2 in solutions with polystyrene is about the same as that observed for J e . It is noted that for high molecular weight polymer, T gel scales with the condition for effective chain overlap, expressed by c[η] o α c , 3 with α c the expansion factor at concentration c, and [η] o the intrinsic viscosity under Flory Θ conditions.