| http://www.w3.org/ns/prov#value | - Examples of such polymers, which are described in the literature, include those consisting essentially of repeating units having the following formula: ##STR1## wherein X is NH, N??, O or S, where ?? is phenyl, and wherein Ar is ##STR2## In the foregoing formulas, n is an integer equal to the number of recurring units and has a value such that the polyners have an intrinsic viscosity of as least 5
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