Semipermeable membranes for fluid separations are well known in the art. These membranes typically are either dense or asymmetric membranes that include a dense separating layer.
The semipermable membranes of the prior art may be polymers of aromatic imides, aromatic esters, and aromatic amides. Membranes of the prior art such as polyester membranes can be derived from bisphenol A and mixtures of iso- and tere-phthaloyl chlorides. Aromatic polyesters prepared from iso/tere-phthalic acids or their halogen derivatives, with substituted biphenols also are known. These polymers, however, are subject to specific structural requirements.
The polyester membrane compositions of the prior art, although useful as gas separating membranes, not only suffer from the disadvantages of having to satisfy specific structural constraints, but also are difficult to fabricate into configurations such as hollow fiber membranes since these compositions tend to be soluble in relatively few solvents. Moreover, the membranes of the prior art tend to have relatively low flux.
A need therefore exists for fluid separation membranes that avoid the fabrication and solubility problems of the prior art but also provide improved gas separation properties.