Synthesis And Properties Of Mesogen Jacketed Polyascetylenes Containing Terphenyl Mesognes As Pendants

Introducted mesogenic moieties into the polymer, liquid crystalline conjugated polymers (LCCP) are combined with liquid crystallinity and luminescence. For the spontaneous orientation of mesogenic under external force field, we can increase the conjugation in the main chain and obtain new type of functional materials with excellent properties. In Mesogen Jacketed Liquid Crystalline Conjugated Polymers (MJLCCPs), the mesogenic units are laterally attached to the polymer backbone and form a liquid crystalline "shell" or "jacket" around the backbone. So it can protect the main-chain from the perturbations by heat and attacks by the degradative species. The terphenyl is not only a chromophore but also a mesogenic core. If combining electronically active polyacetylenes and optically active terphenyl at the molecular level, the chromophoric and spontaneous orientation property of the terphenyl mesogens might likely lead to materials with outstanding properties, such as mesomorphism, thermal properties, photoluminescence.A series of jacketed liquid crystalline mesogen polyacetylene containing terphenyl pendent group have been designed and synthesized. The effects of the structural variation on their properties and the spontaneous orientation of the mesogens enhances the properties of the polymers, especially their thermal properties, photoluminescence and mesomorphism, were studied. The effects of different substituents and spacers on the photoluminescence and mesomorphism of liquid crystal polymer were studied. The mechanism of energy transfer in the process of photoluminescence and the influence of the linking way of mesogens with the backbones and the "jacket effects" on the properties are also illustrated.First of all, we have synthesized three kinds of acetylenes containing terphenyl pendants with different substituents, namely,5-{[2,5-Bis(4'-hexyloxyphenyl) carbonyl]oxy}-1-pentyne (HATP(OC6)2); 5-{[2,5-Bis(4'-hexyloxyphenyl)carbonyl] oxy}-1-phenyl-l-pentyne (PATP(OC6)2) and 6-{[2,5-Bis(4'-hexyloxyphenyl) carbonyl]oxy}-2-hexyne (MATP(OC6)2). The monomers HATP(OC6)2 and PATP(OC6)2 were polymerized with WCl6/PhSn4 catalyst successfully, but the polymerization of MATP(OC6)2 was failure. The polymers are stable (Td≥340℃) and soluble in common solvents. The monomers and polymers show enantiotropic SmA phases in the heating and cooling processes, and the lateral side chains of the mesogenic units are perpendicular to the main chain. The "jacket effect" of chromophoric terphenyl core "shell" around the main chain also contributes to polymers with high photoluminescence, and the pendant-to-backbone energy transfer path is involved in the luminescence process of this polymers. In comparison with monosubstituted polyacetylene PHATP(OC6)2, the disubstituted polyacetylene PPATP(OC6)2 shows better photoluminescence in both THF solution and film, and exhibited about 40 nm red-shifted than PHATP(OC6)2, indicating that the "jacket effect" of terphenyl mesogens forces poly(1-phenyl-1-alkyne) backbone to extend in a more planar conformation with a better conjugation.For investigating the effects of structural variations on the thermal, mesomorphic and luminescent properties, A group of novel mesogen jacketed mesomorphic polyacetylene containing terphenyl pendent group with varying spacer lengths (-{HC=C-[(CH2)mOOC-terpheyl-(OC6H13)2]}n-, where m= 5, PHA5TP(OC6)2; m= 9, PHA9TP(OC6)2) are synthesized. The results show that the terphenyl mesogens endow the monomers and their polymers with good liquid crystalline, and the monomers exhibit enantiotropic smectic C phases, while the polymers possess enantiotropic smectic A phases in the heating and cooling processes. The "jacket effect" from terphenyl mesogenic pendants at the waist position linked to the main chain contributes to the two polymers with high thermal decomposition temperature and excellent photoluminescence, which can lose almost no weight when they were heated above 370℃and emit strong blue light at 410nm when they were excited by the photons of 325nm wavelength. In comparison with PHA5TP(OC6)2, the polymer with longer flexible spacer, this is, PHA9TP(OC6)2, have better liquid crystalline, stronger UV light absorption and higher photoluminescence.