Thermal properties and solid-state structure of copolyesters based on smectic poly(diethylene glycol 4,4'-bibenzoate) (PDEGBB) and non-liquid crystalline poly(diethylene glycol isophthalate) (PDEGI) were characterized previously. The present study examined the oxygen transport properties and free volume characteristics of quenched films with 10-50 mol % isophthalate. Isophthalate was not accommodated in the smectic lattice; as a result, copolymerization effectively disrupted the LC character. The estimated smectic volume fraction of PDEGBB was 0.84. Copolymerization with 10 and 20 mol % isophthalate decreased the smectic fraction to 0. 59 and 0. 16, respectively. The copolymer with 30 mol % isophthalate did not exhibit any LC character. Decreasing density and increasing free volume hole size accompanied the loss of LC features. Oxygen permeability also increased due to increases in both solubility and diffusivity. Oxygen solubility of LC glasses conformed to a two-phase model consisting of a less permeable smectic lattice phase and permeable interlamellar and interdomain amorphous phase. The calculated solubility of the smectic lattice was about 1/3 that of the amorphous phase. A simple model for sorption and diffusion, which considered free volume holes arranged on a cubic lattice, was successfully tested against experimental measurements. Taking hole size from PALS and lattice spacing from the activation energy for diffusion, the model gave good correlations with oxygen solubility, fractional free volume (FFV), and specific volume.