Synthesis And Characterization Of Liquid Crystalline Poly(p-phenylene Ethynylene)s With Laterally Attached Dipolar Unit

Four kinds of the Poly(p-phenylene ethynylene)s containing laterally attached dipolar unit were synthesized, in order to restrain the formation of aggregates of the Poly(p-phenylene ethynylene), improve the solubility and optical performance, and prepare the ideal high-performance active of linearly polarized light-emitting materials.Firstly, with 1,4-diethynylbenzene and 1,4-dibromo-2-(bromomethyl)benzene derivatives as monomers, the polymers were synthesized by Sonogashira coupling reaction using Pd(PPh3)4 as catalyst in anhydrous DMF. The structures and properties of monomers were identified by using elementary analysis, IR and NMR.The polymers are yellow powder solid and soluble in common organic solvents such as Chloroform and THF at room temperature.The effects of the different length of end alkoxy group and difference of dipolar units on polymer structure of the main chain regularity, liquid crystal and the optical propertie were investigated by NMR, DSC, Polarizing microscope with heat stage, UV-vis spectra and photoluminescence excitation and emission spectra. It is found that the length of the alkoxy group can dramatically improve the polymer structure of the main chain regularity, lower the melting point and clearing point of the polymers and raise the fluorescence quantum efficiency of solution. But the full width at half-maximum (fwhm) of spin-coating film and annealed film of the polymers in fluorescence spectrum become larger. Besides, different dipole moments of the dipole units only influence the stereoregularity in a small degree, while increase the dipole moments will increase the melting point and clearing point. In addition, introducting of the dipolar unit can effectively prevent aggregation between the poly (p-phenylene ethynylene)s chains, inhibit the formation of aggregates. In the case of small dipole moment, the blue-emission material of which the chroma is very close to the standard 475nm of blue color is obtained. Increasing the dipole moment of dipolar units will decrease the band gap of the polymers and make further red-shift to get green light emitting material. Finally, by virtue of spontaneous orientation of liquid crystalline side chains under external force, the orientation ability of the polymers have studied through the commercialized PA orientation board. It is found that increasing the dipole moment of the polymers has a little effect on the orientation ability of the polymers in the polyamide orientation board. However, the full width at half-maximum (fwhm) of the polymers in polarized fluorescence spectrum become narrower. The length of the alkoxy in the end does affect the orientation ability in some degree, as the longer the length of the alkoxy is, the easier the polymer will orient.