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Ungar,**+ J. L. Feijoo, and A. Keller H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 lTL, U.K. R. Yourd and V. Percec Department zyxwvuts of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106-2699 Received July zyxwvutsrq 24, 1989; Revised Manuscript Received November 30, 1989 ABSTRACT: In order to investigate the limits of macromolecular chain flexibility tolerated by the nem- atic state, a new group of polyethers has recently been synthesized, where not only the spacer but also the mesogen provide a degree of flexibility. This is achieved by introducing a rotationally mobile ethylene group linking the two phenyl rings in the l-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane (MBPE). These *mesopens”are separated by flexible -O(CHz),,O- spacers, where n is either a single value (homopoly- mers) or has two different values (copolymers). Results of X-ray diffraction studies of MBPE polymers using the simultaneous X-ray diffraction and DSC technique (XDDSC) conclusively prove the existence of the nematic phase in most homopolymers and all copolymers. Depending on the polymer, the phase is either mono- or enantiotropic. While in a few cases the phase is thermodynamically stable, in most cases it is metastable. The weak first-order transition below the I-N transition temperature appears not to be the nematic-smectic transition as previously suspected, and its nature is still being investigated. Current X-ray evidence shows further that the molecular packing density in the nematic phase is considerably higher for polymers with even spacers than it is in polymers with odd spacers. Introduction bv introducing a rotationally mobile ethylene group link- - - ing the two ghenyl rings in the 1-(4-hjdroxyphenyl)-2- (2-methyl-4-hydroxypheny1)ethane (MBPE). Both homo- and copolymers were prepared, the latter containing spac- ers of tWol-3 or three4 different lengths in a random sequence, The beneficial effect of liquid crystallinity in the pro- cessing of polymers with superior mechanical properties is now well established. However, in order to facilitate processing of main-chain nematogenic polymers, the intro- duction of flexible spacers into the chain has been exper- imented with extensively. In order to investigate &ill further the limits of flexibility tolerated by the nematic state, a new group of polyethers has recently been synthesized,1-4 where not only the spacer but also the mesogen provide a degree of flexibility. This is achieved t Present address: School of Materials, University of Sheffield, Original studies by DSC and optical microscopy sug- gested that the polymers exhibit liquid-crystal phases, presumed nematic and possibly also smectic. Presently we show results of X-ray diffraction studies of MBPE polymers using the simultaneous X-ray diffraction and DSC technique (XDDSC).5 The results conclusively prove the existence of the nematic Phase in most homopoly- mers and all copolymers. Depending on the polymer, the Northumberland Road, Sheffield SI0 2TZ, U.K. 0024-9297/90/2223-3411$02.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB 0 1990 American Chemical Society