CHAIN DIFFUSION IN ION CROSS-LINKED POLYSTYRENE GEL

Concentration profiles and diffusion coefficients of deuterated polystyrene chains (27 000-104 000 amu) diffusing into hydrogenated polystyrene (h-PS) matrices (90 000 and 590 000 amu) were measured by forward recoil of 2.0 MeV He ions. This experimental procedure allows us to detect the diffusion coefficient in the range 3 X 10(-15)-3 X 10(-13) cm2/s. The irradiation of the h-PS layer with ion beam changes the interdiffusion properties. The diffusion coefficient, measured in h-PS irradiated with 300 keV H+ in the 5 X 10(11)-2 X 10(14) ions/cm2 fluence range, does not change at low fluence, instead it is reduced for a threshold fluence whose value depends on the matrix molecular weight. High fluence irradiation of h-PS decreases the polymer solubility because crosslinks between the original chains, produced by ion irradiation, yield a three-dimensional network (gel). By combining diffusion and solubility measurements, for both molecular weights, we observed that the diffusion process is slowed down when, in the irradiated h-PS is produced a gel fraction of 0.8, which corresponds to a polymer structure containing an average of 1.0 crosslink per chain. This result does not depend on the marker molecular weight.