Tracer diffusion of four arm polystyrene star molecules into linear and star polymer matrices from nuclear reaction analysis

Abstract

A series of linear and four arm star polystyrene polymers have been synthesised by anionic polymerisation and using deuterated star polymers the tracer diffusion coefficients for diffusion of star polymers into linear and star polymer hydrogenous matrices have been determined using nuclear reaction analysis. For diffusion into linear polystyrene, constraint release effects are evident for linear polymer molecular weights up to circa 250 000 g mol⁻¹, the scaling relation between the tracer diffusion coefficient, D*, and the matrix degree of polymerisation below this molecular weight is D* = 6.82 × 10⁻¹¹N^−1.4_matrix, the exponent being smaller than observed previously. This weakened dependence is attributed to the non-equivalence of constraints along a star arm and the contribution of the arm molecular weight to the overall dependence of constraint release leading to a weaker dependence of D* on matrix molecular weight. Tracer diffusion coefficients for the diffusion of star polymers into star polymer matrices were compared with theoretical predictions by combining expressions for the self-diffusion coefficient with a proposed relation that incorporates both self-diffusion and constraint release in star polymers. Although the data available is somewhat limited at present, the predictions of a dilated tube theory, i.e. dynamic dilution, describe the observed dependence of D* on the star arm degree of polymerisation more faithfully than in the absence of tube dilation.