Synthesis and Characterization of Segmented Copolymers of a Methylated Polyamide and a Thermotropic Liquid Crystalline P
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SYNTHESIS AND CHARACTERIZATION OF SEGMENTED COPOLYMERS OF A METHYLATED POLYAMIDE AND A THERMOTROPIC LIQUID CRYSTALLINE POLYESTER Gregory T. Pawlikowski, R. A. Weiss and S. J. Huang Box U-136, Institute of Materials Science, University of Connecticut, Storrs, CT 06269 ABSTRACT A block copolymer consisting of liquid crystalline polyester segments and methylated polyamide segments has been synthesized. Solution polycondensation of acid chloride end-capped poly(terephthaloyl phenylhydroquinone) (LCP portion) with an amine terminated poly(N,N'dimethylethylene sebacamide) was utilized to prepare the block copolymer. Characterization by differential scanning calorimetry, infrared spectroscopy, thermogravimetric analysis, optical microscopy and elemental analysis has been performed to verify the existence of the block copolymer that may have potential as a molecular composite material or self-reinforcing thermoplastic. INTRODUCTION Much of the high strength/high modulus composites currently available stem from the use of macrophase reinforced materials such as fiber reinforced composites and self reinforced thermoplastics where the reinforcement fiber phase is on the order of microns in diameter. Although these composite systems have attained widespread use as high strength materials, their strengths have been limited due to fiber imperfections, the tendency of the fibers to fibrillate and poor interfacial adhesion between the fiber reinforcement and matrix phase.1 It is believed that reinforcement on a much finer scale (10 - 30 nm or less) would result in more efficient reinforcement and create stronger materials. 2 These types of materials have been termed molecular composites. Molecular composites have been found to possess very high strength and stiffness. Hwang and coworkers 3 prepared molecular composites by solution blending poly(p-phenylenebenzobisthiazole) (PPBT) and poly(2,5(6')-benzimidazole) (ABPBI) (30/70). Spun fibers of this blend were found to have a Young's modulus of 117.0 GPa and a tensile strength of 1270 MPa. Molecular composites also require much less reinforcement loading for equivalent strength. Takayanagi 2 used solution blending techniques to prepare molecular composites of poly(p-phenyleneterephthalamide) (PPTA) with nylon 6 and nylon 66. He reported that this material, which contained only a few percent rigid-rod molecules, displayed the same mechanical properties as fiber reinforced plastics which employ 40 percent fiber reinforcement. The majority of work on molecular composites is being done on solution blended systems. While these systems have been successful in achieving high strength molecular composites, the technique has limited processing potential and requires large amounts of harsh solvents. It would be more desirable to have a truly melt processible molecular composite capable of 'in situ' fiber formation of the reinforcement phase during processing. One possible route for obtaining such a material may be through the use of block copolymers of the reinforcing rigid-rod phase with the
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