Abstract
The gas transport characteristics of main chain liquid crystalline polymers have been examined in order to understand the nature of the mesophase and what opportunities these materials offer for useful membranes or barriers. Is the liquid crystalline state more like a liquid (or amorphous glass) or a crystal? Experimental investigations of commercial aromatic polyamide and polyester liquid crystalline materials are reviewed. All of these materials prove to be exceptional barriers to permeation. For the polyesters, this is largely due to an extraordinarily low gas solubility. Analyses in terms of two phase and free volume models suggest that most of the transport may be occurring in a small volume fraction of a less dense boundary phase. The polyamides do not show the unusually low solubility; thus, a different physical model must be imagined for these materials.