Permeability and time‐lag measurements for H2 and CO in poly(vinyl chloride) (PVC) plasticized with tricresyl phosphate show that the apparent diffusion coefficients at first decrease as the plas‐ticizer concentration is increased. The diffusion coefficients then increase as the additive concentration is raised above 15 wt %. These changes in the apparent diffusion coefficients can be related to the behavior of a variety of mechanical properties and are attributed to antiplasticization and plasticization effects of low and high concentrations of tricresyl phosphate, respectively. The antiplasticization‐plasticization effects reflect altered molecular motions of the polymer. Carbon‐13 NMR rotating‐frame relaxation rate measurements show directly that the cooperative main‐chain molecular motions of PVC are reduced when the additive acts as an antiplasticizer and are increased when the polymer is plasticized. Both the apparent diffusion coefficient and the rotating‐frame relaxation rate have a similar dependence on additive concentration. An application of the molecular theory of diffusion of Pace and Datyner accounts qualitatively for the way in which additives alter the average chain interaction energy, cooperative polymer main‐chain motions, and the diffusion coefficients of gaseous penetrants.
The gas-polymer-matrix model for sorption and transport of gases in polymers is consistent with the physical evidence that; 1) there is only one population of sorbed gas molecules in polymers at any pressure, 2) the physical properties of poly mers are perturbed by the presence of sorbed gas, and 3) the perturbation of the polymer matrix arises from gas-polymer interactions. Rather than treating the gas and polymer separately, as in previous theories, the present model treats sorp tion and transport as occurring through a gas -polymer matrix whose properties change with compo sition.Simple expressions for sorption, diffu sion, permeation and time lag are developed and used to analyze carbon dioxide sorption and trans port in polycarbonate.Nonlinear, pressure-dependent sorption and transport of gases and vapors in glassy polymers have been observed fre quently. The effect of pressure on the observable variables, solubility coefficient, permeability coefficient and diffusion timelag, is well documented (1, 2). Previous attempts to explain the pressure-dependent sorption and transport properties in glassy polymers can be classified as "concentration-dependent" and "dual-mode" models.While the former deal mainly with vapor-polymer systems (_1) the latter are unique for gas-glassy polymer systems (2).The concentration-dependent models attribute the observed pressure dependence of the solubility and diffusion coefficients to the fact that the presence of sorbed gas in a polymer affects the structural and dynamic properties of the polymer, thus affecting the sorption and transport characteristics of the system (3). On the other hand, in the dual-mode model, the pressure-dependent sorption and transport properties arise from a
SynopsisThe investigation of the thermal degradation of the char-forming phenol-formaldehyde resins is conducted to provide information for the systematic design of high temperature flame-resistant phenolics. Three different processes of curing are used (1) Formaldehyde or s-trioxane is reacted with m-substituted phenol-formaldehyde oligomers under acidic conditions to give the methylene bridged-novolac resins. (2) Phenol and rn-substituted phenols are reacted with CH20 under basic conditions and then heated to give the methylene bridged resol resins. (3) p-Terephthaloyl chloride and m-and p-substituted novolac oligomers are reacted to give cured resins with ester linkages. The evaluation of the effect of various substituents indicates that the oxygen index (01) increases from about 33 for unsubstituted phenolics to about 75 for meta-halogen substituted phenolics. The evaluation of the effect of various crosslinking agents shows that the 01 for CHzO-cured phenolics is 75 as compared to 50 for the trioxane cured phenolics and to 40 for the terephthaloyl chloride cured phenolics. A set of phenolic copolymers with different weight percentage content of halogen substituted phenols are synthesized as novolacs and resols. The results surprisingly indicate no increase of 01 for the cured novolac copolymers, whereas the increase is observed for the cured resol copolymers. The activation energy for the thermooxidative degradation of the cured novolacs is about 12-15 kJ/mol lower as compared to tpt of the cured resols.
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