Study On The Preparation And Electro-Optical Properties Of Liquid Crystal Polyurethane With Aromatic Azo Group

Liquid crystal polyurethane with aromatic azo group, new kind of functional materials, have special performances, such as the liquid crystal polyurethane and aromatic azo polymer double excellent features. Therefore, they had been became more and more important in the development of the new materials research. This thesis was mainly to design and synthesis a new azo-benzene and bis-azo liquid crystal unit with-NH2and-OH as end group, on the basis, a new series of aromatic azo liquid crystal polyurethane (LCPU) were designed and synthesized. Thermal stability and photochromic properties of Liquid crystal polyurethane which combined with aromatic azo group at different ways were researched.First,12kinds of azobenzene compound (LCs) were successfully synthesized with aniline, p-nitro aniline, p-phenylenediamine and benzidine as diazotization components, respectively with aniline, N, N-dimethyl aniline and salicylic acid by coupling reaction. The structures of LCs were characterized by FTIR; TGA indicated that the thermal stability of LCs was good; UV showed a good response of the LCs in the range of230-600nm for UV light; Compared with single azo compound, bis-azo compound had a wide range of absorption and the maximum absorption wavelength have been redshift to visible light area; LCs had a good photochromic proerties for monochromatic excitation of365nm light, the trans-cis isomerization reaction was confirmed as typical of the first order reaction; The shortest of photochromic response time tR was23.90s; In conclusion, LCs was suitable for photochromic materials.Secondly, a series of azo liquid crystalline polyurethane films(LCPU) were synthesized by end capping reaction of azo benzene liquid crystalline units(terminal groups contain-NH2, LC1and LC4) and polyurethane prepolymers which were prepared by different ratio polyethylene glycol (PEG400) and4,4-diphenylmethane diisocyanate (MDI). The structures of LCPU were characterized by FTIR; TGA indicated that LCPU film’s the maximum decomposition temperature was above245℃, showed that it had good thermal stability; LCPU were indicated thermotropic nematic liquid crystalline polyurethane by POM and XRD; UV showed a good response of the LCPU in the range of350～390nm for UV light, the trans-cis isomerization reaction was confirmed as typical of the first order reaction in the LCPU, The shortest of photochromic response time tR was23.30s, LCPU was very suitable for photochromic materials; When n(NCO):n(OH) was4;3, the comprehensive performance of LCPU film was best, because LCPU film exhibited a relatively modest value of static contact angle, the water resistance and hardness properties.Thirdly, a series of main chain type bis-azo LC polyurethane (MLCPU) were synthesized with different ratio bis-azo liquid crystal (LC7, LC9, LC10and LC12) instead of PEG400, reacting with toluene diisocyanate (TDI) and MDI again. The structures of MLCPU were characterized by FTIR; TGA showed that MLCPU’s the weightlessness temperature higher than220℃; UV showed a good response in the range of350-450nm for UV light; Compared with LCs, the maximum absorption wavelength of the MLCPU had different degree of blueshift, the degree of blueshift increased trend along with the increasing of azo group content; MLCPU had a good photochromic proerties for monochromatic excitation of365nm light; UV proved that the main chain of the LCPU which the LCs was reaction to influenced the cis-trans isomerization reaction rate, extinction coefficient decreased obviously, but the trans-cis isomerization reaction was confirmed as typical of the first order reaction in the MLCPU; The shortest of photochromic response time tR was59.63s; To sum up, the photochromic response time of MLCPU was longer, it was not appropriate for photochromic materials.Final, polyurethane acrylate (PUA) by end capping reaction of hydroxyl ethyl acrylate (HEA) with polyurethane prepolymer which were prepared by different ratio PEG400and MDI. Polymer dispersed liquid crystal films (PDLC) were prepared with the PUA as matrix, LCs as the liquid crystal molecules, HEA as the active diluents, benzophenone (BP) as initiator. The best ratio:the quality of PUA and HEA ratio was1:3, BP quality score was3%, the gap of the liquid crystal box was20μm. If a kind of LC was selected for the liquid crystal molecules, So the mass fraction of LC2, LC5and LCg was32%,28%and32%respectively; If the mixed LCs were used for the liquid crystal molecules, So the total LCs quality score was33%, LC2, LC5and LCg accounted for a third.