Effect of naphthalene ring content on gas permeation properties of polyarylates

The effect of increasing naphthalene content in bisphenol-A: iso/terephthalic acids based copolymers on gas permeability has been examined. The naphthalene moiety has been introduced either in the diol (2,7-naphthalenediol, ND) or diacid (2,6-naphthalenedicarboxylic acid, NDA) form to obtain two series of amorphous naphthalene containing copolyesters. Increasing the naphthalene content causes a linear increase in the glass transition temperature as expected. As opposed to this, the increase in the packing density is not monotonic. A local minimum in the packing density is seen in both NDA and ND copolymer series at 40% naphthalene incorporation. These nonlinear trends in the packing density are attributed to the random distribution of monomers in the chain. The gas permeability and selectivity of the copolymers correlate well with the trend in the packing density. The nonlinear dependence of packing density parameters and permeation characteristics on copolymer composition is particularly marked in the case of the ND copolymer series. The ND containing polyarylates have better retention of He/N-2 selectivity with increasing temperatures than their NDA counterparts.