| Abstract: | The presence of small amounts of CO2 in poly(vinyl chloride) (PVC) results in increased main-chain molecular motions of the polymer as measured by the carbon rotating-frame relaxation rate. This effect increases with increasing gas concentration. Since molecular motions of the polymer and the diffusion coefficient of the gas are related, the latter must be concentration dependent. Main-chain motions of PVC also increase upon exposure to CO2 followed by degassing. This result is interpreted in terms of the effect of the penetrant gas on the interchain packing in amorphous PVC. These results cannot be reconciled with the dual-sorption-mobility model, which claims that gas molecules preferentially occupy preexisting sorption sites in a conditioned polymer with no perturbation of the polymer matrix. |
