STRUCTURE AND GAS-PERMEABILITY OF ALKYNYLATED POLY(PHENYLENE OXIDE)

Selective introduction of bulky aryl substituents on poly(2,6-dimethyl -1,4-phenylene oxide) (PPO) leads to a 10-fold increase in PPO gas per meability. Aryl substitutions are obtained by reacting aryl-brominated PPO with an alkyne R-C=CH, using a Pd catalyst, where R is either Me( 3)Si or Me(3)C. The gas permeability increase is a consequence of the packing density decrease and is quantitatively related to the composit ion of the derivatives, ranging from 15 to 85% repeat unit substitutio n. The Me(3)Si-C=C substituent is slightly more effective in increasin g the permeability than the Me(3)C-C=C substituent; Me(3)C-C=C-substit uted PPO raises the glass-transition temperature (T-g) towards higher temperatures while Si-containing groups leave T-g unchanged. Starting from this finding, a comparison has been made among the effects of sev eral permeability-increasing functional groups on the PPO structure: P PO gas permeability can be enhanced by increases in both the intrasegm ental stiffness and intersegmental distance. Depending on which of the se is prevailing, the T-g of the product will accordingly increase or decrease.