Optical anisotropy and flexibility of poly(meta-phenyleneoxadiazole) in sulfuric acid

For a series of poly[2,5-(1,3-phenylene)-1,3,4-oxadiazole] samples with mol ecular masses in the range 1.9 x 10(3) to 97 x 10(3), the flow birefringenc e (the Maxwell effect) and orientation of macromolecules in sulfuric acid s olutions were studied. The results are compared with the properties of poly [2,5-(1,4-phenylene)-1.3,4-oxadiazole]. It was shown that the reduced biref ringence [n]/[eta] grows with an increase in molecular mass, as predicted b y the theory of the kinetically rigid wormlike chains, and, for the first p olymer, this value is 1.8 times lower than that for the second one. The opt ical anisotropy of the chain length unit of poly[2,5-(1,3-phenylene)-1 3,4- oxadiazole] was found to be beta = 11 x 10(-17) cm(2). The polydispersity o f the samples was estimated from the molecular mass dependence of the chara cteristic orientation [chi/g], and the results are compared with the data o f hydrodynamic measurements. The hindrance of the intramolecular rotational mobility in the chains of meta- and para-phenylene isomers of the polymers is discussed.