STRUCTURE AND GAS-PERMEABILITY OF SILYLATED POLYPHENYLENE OXIDE

Silylated derivatives of poly(2,6-dimethyl-1,4-phenylene oxide) (silyl-PPO) were prepared by metalation of PPO with n-butyllithium in tetrahydrofuran followed by treatment with (CH3)3SiCl. Derivatives with ring-to-methyl substitution ratios ranging from 1.7 to 3.3 and an overall content of (CH3)3Si groups up to 88% molar were obtained. In silyl-PPO, free volume and gas permeability were found to increase as a function of degree of silylation, the rate of increase showing a breakpoint at ca. 30% silylation. Increases in permeability are related to increases in diffusivity, the solubility of the penetrants remaining substantially the same as in unmodified PPO. The results are tentatively interpreted in terms of a different size of gaps, dynamically formed during the diffusion process, when considering the tight macromolecular packing of unmodified PPO (prevailing at low silylation) with respect to the more loose packing of silylated moieties (prevailing at high silylation), a transition value being found at 30% silylation.