Controlled Preparation And Photoresponsive Property Of Azobenzene-Hydrophilic Polymer Conjugate Materials

In this article, hydrophilic polymers such as polyethylene glycol(PEG), soluble starch(Starch) and polyvinyl alcohol(PVA) was used as raw materials to prepare unsaturated polyethylene glycol-cased macromonomer(PEGM), unsaturated starch-based macromonomer(SM) and unsaturated polyvinyl alcohol-based macromonomer(PVAM), via the esterification of PEG, Starch or PVA with maleic anhydride. Then three kinds of azobenzene-hydrophilic polymer conjugate materials are formed by thiol-ene click reaction through three macromonomers and azobenzene-containing intermediate respectively. The structure and properties of various conjugates were studied. The results were summarized as following:1. Diazo coupling reaction between aniline and phenol was carried out to prepare 4-hydroxyazobenzene(p-HAB) intermediate. Then acylation reaction between p-HAB and acryloyl chloride was carried out to prepare a monomer containing mesogenic unit, 4-acryloyoxyazobenzene(AHAB). The structures and photoresponsive test of p-HAB and AHAB were analyzed by Fourier transform infrared spectrometer(FTIR), thermogravimetric analysis(TGA) and ultraviolet visible spectrophotometer(UV). Then the main-chain azo liquid crystal polymer azobenzene-hydrophilic polymer conjugate materials are formed by thiol-ene click reaction through PEGM and AHAB. The structures and photosensitive test of conjugate materials were analyzed by FTIR, TGA, and UV. The results show that the expected structure of azobenzene-polyethylene glycol conjugates is obtained. The product has good water solubility. By changing the time of the radiation of the ultraviolet lamp, it can be seen that the absorption intensity of the product at 365 nm changes obviously. The longer the time, the lower the degree of absorption. The product shows obvious photoresponsive property. By changing the molecular weight of PEG, the photosensitivity of azobenzene-polyethylene glycol conjugates is changed accordingly. The results showed that the higher molecular weight, the better photosensitivity it exhibits.2. The said-chain azo liquid crystal polymer azobenzene-hydrophilic polymer conjugate materials are formed by thiol-ene click reaction through SM and AHAB. The structures and photosensitive test of conjugate materials were analyzed by FTIR, TGA, and UV. The results show that the expected structure of azobenzene-starch conjugates is formed. By changing the time of the radiation of the ultraviolet lamp, it can be seen that the absorption intensity of the product at 365 nm change obviously. The longer the time, the lower the degree of absorption it is. In other words, the product has obvious photoresponsive property.3. A series of polyvinyl acetate(PVAc) of different molecular weight were prepared by reversible addition-fragmentation chain transfer(RAFT) polymerization. Then PVAc is transformed into PVA of controlled chain length through alcoholysis. PVAM of different molecular weight were obtained through the esterification of PVA with maleic anhydride. Conjugates of PVA and AHAB were prepared through the way mentioned above. The structures and photosensitive test of conjugate materials were analyzed by FTIR, TGA, UV and polarizing microscope(POM). The results show that the azobenzene-polyvinyl alcohol conjugates are obtained as expected. By changing the time of the radiation of the ultraviolet lamp, it can be seen that the absorption intensity of the product at 365 nm changes obviously. The longer the time, the lower the degree of absorption. Evidently, the product has obvious photoresponsive property..By varying the molecular weight of PVA, the photosensitivity of azobenzene-polyvinyl alcohol conjugates is changed too. The results showed that the conjugate of lower molecular weight shows better photosensitivity.In short, the esterification reaction, Diazo coupling reaction, RAFT polymerization, and thiol-Click reaction were applied to synthesize intermediates which were subsequently utilized to form various azobenzene-hydrophilic polymer conjugates materials.