Diffusion of polymer molecules into polymer networks: Effect of stresses and contraints

Fine threads of cis‐1, 4‐polyisoprene, diameter ca. 50 μm, were prepared by drawing from solution and drying. They were crosslinked by reaction with H2S and SO2 and then swollen with linear cis‐polyisoprene liquids of varied molecular weight Ms, from 1,000 to 24,000 g/mol. Diffusion coefficients were determined from the initial rate of uptake, for both unrestrained and stretched threads. They were found to be in good agreement for stretches of up to about 300%. On the other hand, the equilibrium uptake increased markedly (> 100%) over this range of strain, similar to the increase in swelling observed with low‐molecular‐weight liquids. Values of diffusion coefficient were also obtained from the rate of deswelling upon release of swollen threads from tension, and from the rate of uptake of polymer liquids by a thin coating of crosslinked polymer, bonded onto glass fibers. Satisfactory agreement was obtained in all cases. A number of simple experiments thus give similar values for the diffusion coefficient of polymer liquids in lightly crosslinked polymer networks, in the range 10−13−10−16 m2/s, depending upon the molecular weight Ms of the polymer liquid approximately weight as M−2s. The amount of liquid absorbed was strongly dependent on its molecular weight, Ms, the degree of crosslinking of the host material, and applied stresses or constraints.