Preparation And Characterization Of Thermo/Photo Sensitive Liquid Crystal Elastomers By EB Irradiation

Irradiation technology has developed rapidly in the recent years as a high efficient, energy-saving, pollution-free and easy to control clean chemical process, and become an important means of production of some hig-quality products (such as flame-retardant wire and cable, battery separators, heat-shrinkable tube, etc.). For irradiation polymerization doesn’t need to add any initiator and no limitation for the temperature and phase of monomers, some difficult reactions for conventional methods can be achieved by electron beam irradiation. Thermo-sensitive or photo-sensitive liquid crystal elastomers could be obtained by polymerizing side-on side-chain nematic liquid crystal monomer under the tropism condition. These liquid crystal elastomers are of many bio-functions, could be used in artificial muscles, biosensors, etc. The general conventional polymerization methods are difficult to achieve the uniform between reaction condition and tropism condition, which restricts the basic properties of this kind of liquid crystal elastomers and their further research. By collaborating with the Curie Laboratory, France, electron beam irradiation polymerization was used for preparation of thermo-sensitive or photo-sensitive liquid crystal elastomers for the first time, the relevant conditions of the process were studied, the main work is as following:A setup with temperature-controllable, fast speed for heating and cooling, perfect performance on temperature controlling and an additional magnetic field for the reaction of irradiation polymerization was designed, according to the tropism conditions of side-on side-chain nematic liquid crystal monomers. The results of the experiments with this setup show that it is easy to control and adjust temperature, it is easy for the tropism and it is easy to operate the process. Based on the irradiation from electron accelerator, the polymerization reaction of liquid crystal monomers was carried on at the tropism temperature and under the magnetic field. The reaction is very fast and the resulting liquid crystal elastomers have good therm-/photo-sensitivity and recurrence.Electron beam irradiation polymerization was carried separately on two kinds of thermo-sensitive nematic side-on side-chain liquid crystal monomers (A444 and MA444) based on the 4-butoxy-2’-(4-methacryloyloxybutoxoacryl)-4’-(4-butoxy benzoyloxy) phenylbenzoate and two kinds of photo-sensitive nematic side-on side-chain liquid crystal monomers (Aazo444 and MAazo444) based on the 4-butoxy-2’-(4-methacryloyloxybutoxy)-4’-(4-butoxy benzoyloxy) azobenzene. The effects of the ratio between liquid crystal monomer and cross-linker, delivery dose, the temperature during the irradiation polymerization reaction, the condition of tropism, the additional magnetic field and the rate of increasing/decreasing temperature on the irradiation polymerization reaction and the deformation performance of thermo-variable/photo-variable of liquid crystal elastomers were studied.The phase transition point and the absorption/releasing heat behavior of liquid crystal monomers and their elastomers under various formulations and conditions were studied by differential scanning calorimetry (DSC) method; the softening temperature of the film of LCEs, the clearing point of the liquid crystal state, the phase transition temperature and the morphological characteristics such as the texture and the tropism defects at different temperature were investigated, using polaring optical microscopy (POM); the stability of azobenzene in photo-sensitive liquid crystal monomers under the delivery dose was detected by using nuclear magnetic resonance (NMR) apparatus.