Linear liquid crystal polymers from phenylene-naphthalene monomers

Thermotropic main chain LC polyesters are one of the most important groups in LCPs. Many aromatic polyesters from para-substituted monomers have very high melting points, make them intractable using normal processing instruments. The most effective way to lower the melting point is introduce some structure to disturb the chain packing. New thermotropic LC polyester monomers with a core phenylene-naphthalene structure were proposed and synthesized via a Suzuki coupling reaction. This monomer structure provides a wholly aromatic backbone, maintains liquid crystalline behavior, and introduces more monomer dissymmetry and main chain dissymmetry.; Different composition copolymers were synthesized by copolymerization of TA, ABA or ANA with new phenylene-naphthalene monomers. The polymerization was carried out in bulk and at temperatures in the range of 250–330°C, and liquid crystalline polyesters with a relative high molecular weight and thermal stability were obtained. Solubility of these polymers was very poor. Only a small number of polymers could be dissolved in PFP/PFB solution. The IVs were between 1.8 and 6.7 dL/g.; The diacetoxy monomer, DAPN, was copolymerized with ABA or ANA and TA. The HBA copolymers showed much higher degrees of crystallinity and melting points, and lower solubilities than the HNA copolymers. The HNA/TA/DAPN polyesters were found to have even lower melting points than the commercial Vectra compositions. Composition of HNA/TA/DAPN=60/20/20 was synthesized in larger scale and the fiber properties were evaluated.; The A-B (CAPN) and B-A (ACPN) monomers were compolymerized with ABA or ANA. These two series of polymers showed similar properties. HBA copolyesters showed unusual high Tg transitions which was confirmed by various TMA tests. HNA copolyesters showed much lower melting points than those of HBA copolyesters. The major difference between A-B and B-A series is the orientation of the ester bonds along the polymer chain, which also affected the polymer properties. For example, HBA/ACPN polymers showed a Tg at around 210°C, while the Tg's of HBA/CAPN polymers were 160–240°C. Their melting points and degrees of crystallinity were also different. Some compositions showed degrees of crystallinity greater than 40%, which is very unusual for this kind of polyesters.