CRYSTALLINE AND LIQUID-CRYSTALLINE PROPERTIES OF POLYESTERS OF PHENYL-SUBSTITUTED 4,4'-BIPHENOL .1. POLYMERS FROM TEREPHTHALIC ACID AND 2,6-NAPHTHALENEDICARBOXYLIC ACID

A group of six thermotropic aromatic polyesters was investigated using X-ray diffraction, DSC, and optical microscopy. The occurrence of nematic phases was examined, and its relationship to structural irregularities and crystallinity are discussed. The polyesters are based on 3-phenyl-4,4'-biphenol (MPBP) and 3,3'-diphenyl-4,4'-biphenol (DPBP) with terephthalic acid (TA) and/or 2,6-naphthalenedicarboxylic acid (NDA). The polymers studied form two series. In series I, MPBP was combined either with TA or with NDA to form homopolymers. In types of both polymers the randomness in the position of the substituent phenyl group depressed the melting transition and created a nematic state over a sufficiently wide temperature range to allow fibers to be drawn from the nematic melt. X-ray diffraction studies confirmed that the chain conformation is an extended ribbon with localized biaxial order. The random copolymerization of 50 mol % of each of the two acids, NDA and TA, with MPBP created an amorphous polymer as indicated by DSC and X-ray diffraction experiments. In series II, DPBP was combined either with TA or with NDA to form homopolymers. The symmetric arrangement of the two phenyl groups in the biphenol group led to fast rates of crystallization; indeed, the rates were so fast that it was not possible to draw fibers. The copolymerization (50%) of the two acids with DPBP introduced sufficient disorder to greatly depress the crystallinity and allow fibers to be drawn from the nematic fluid for examination by X-ray diffraction. In the entire group of six homopolymers and copolymers the two basic variables are the randomness of phenyl group substitution and the randomness induced by copolymerization. The results show that too much of both these elements of disorder suppressed nematic order, while too little of both increased the rate of crystallization to an extent that made the preparation of the oriented nematic state by fiber drawing technically difficult or even inaccessible.