Molecular Deformation Studies Of Crosslinked Polystyrene Networks.

Abstract

The molecular deformation of multilinked polystyrene networks in the swollen and stretched states was investigated by small angle neutron scattering. The degree of polymerization of the protonated and deuterated polystyrene used in constructing the network was closely matched. Chemical methods are more efficient in random crosslinking of polystyrene than (gamma)-ray irradiation. The relative crosslinking rate of protonated and deuterated polystyrene with crosslinking agent was determined by FTIR. A small isotope effect was observed with the deuterated species being more reactive. In the swelling experiments, the high-concentration technique was used to extract the single-chain form factor S(,s)(q) so that the radius of gyration can be calculated. The experiments were performed over a wide range of concentration. The SANS results show that molecular deformation in swollen polystyrene networks is close to that predicted by the fixed junction model. The measurements of the screening length as a function of concentration were also made in the range c = 0.12-0.24. Within experimental limits, the data were fitted to a power law and the screening length was found to be concentration-dependent with (xi) = 10.57c('-0.72). For polystyrene networks swollen in cyclohexane, no molecular deformation maximum was observed in the temperature range 20-60(DEGREES)C. SANS measurements of stretched polystyrene networks were employed for the determination of the projections of the radius of gyration in the parallel and perpendicular directions. Two methods were used to analyze the data. The results show that molecular deformation parallel to the stretching direction is in between the prediction of the fixed junction and the phantom network model, while in the perpendicular direction molecular deformation is approximated by the fixed junction model. In summary, molecular deformation in the networks can not be simply characterized by a single model in both swelling and stretching experiments. A more penetrating analysis is needed to provide a satisfactory explanation for the rubber elasticity of polymer networks.