Liquid-Crystalline Polymers Downloaded from pubs.acs.org by UNIV OF TEXAS AT EL PASO on 11/02/18. For personal use only.
Chapter 9 Structures and Thermal Properties of Liquid-Crystalline Poly(ester-co-carbonate) M. Kawabe, I. Yamaoka, and M. Kimura Research and Development Laboratories—1, Nippon Steel Corporation, 1618 Ida, Nakahara-ku, Kawasaki 211, Japan The thermotropic liquid crystalline copoly(estercarbonates) (PECs) were synthesized from p-hydroxybenzoic acid (HBA), 4,4'-dihydroxybiphenyl (DHBP), and diphenylcarbonate (DPC). Threaded textures, a characteristic of nematic phase, were observed over the investigated composition range. The liquid crystalline transition temperatures (LCTT) of PECs were found significantly low, compared with those of copolyesters based on biphenylene terephthalate and HBA. Density measurement revealed that the structural orders in injection-molded specimens were well developed. The degrees of preferred orientation were increased and thefibrousstructures were significantly developed by heat treatment. These results suggested development in lateral order and overall perfection of the structure that occurred upon annealing. Thermotropic liquid crystalline polymers have recently been a topic of scientific investigation (1-3). Because of their thermotropic liquid crystalline character from rigid structural moieties incorporated in the polymer backbone, these polymers possess outstanding melt processability and excellent mechanical properties. Jackson and Kuhfuss reported a thermotropic polymers system comprised of poly(ethylene terephthalate) modified with HBA £4}. They demonstrated not only the thermotropic liquid crystalline behavior but also the excellent melt processability of these materials to yield specimens with high modulus values. However these copolymers had very low use temperatures as reflected by low heat deflection temperatures. Economy and co-workers reported the copolyesters based on biphenylene terephthalate and HBA (5-6). These polymers exhibited excellent mechanical properties up to 250-300 C, but these copolyesters had poor processability because of their high LCTTs. The purpose of this research is to synthesize a series of thermotropic liquid crystalline PECs consisting of HBA, DHBP, and carbonyl units with good melt processability and high heat deflection temperatures. The carbonate linkage is expected to reduce LCTT without reduction of the chain rigidity and heat resistance. The thermal properties and solid state structures of PECs are elucidated. The effects of heat treatment on the thermal properties and the structures are also discussed.
