Preparation And Characterization Of Liquid Crystal Crosslinker

Today, material science is advancing toward multifunctional and oriented structures. One example of such super molecular systems is liquid crystalline elastomers(LCEs), which combine the properties of liquid crystalline with spontaneous reversible shape change(The samples contract spontaneously along the director n when heating or illuminated by UV, and elongate to the original length spontaneously when cooling or illuminated by other UV.) and rubber elasticity(There is no needs or little needs strength when deformed.) and electric or optic with stress or strain etc. So, LCEs has considerable interest in its potential applications and theoretical research. The result showed that LCEs had the characteristics of ability to undergo a polydomain to monodomain transition and only about 20% stress-induced macroscopic orientation can lead to the formation of monodomain liquid crystal elastomers. And the monodomain liquid crystal elastomers with nematic texture had the most remarkable property of large extent of shape change, which can be used as reversible shape memory material. We pay attention to the property of two way shape memory and do some preliminary works for preparing single liquid crystal elastomers with nematic texture. The main objective of this dissertation is expressed as follows:(1) Different types of liquid crystal crosslinkers were synthesized and the phase transition temperature and texture were analysed;(2) The technical route of LCEs' preparation was investigated in order to control the crosslink density;The factors which influence LCEs' properties were researched in order to realize the control of crosslink density and monodomain for polysiloxane LCEs' preparation.In this dissertation, four kinds of crosslinker monomers were synthesized, 4,4'-bis(10-undecenoyl acid)diphenyl ester, 4,4'-bis(10-undecenamide)diphenyl, PP'-bis(10-undecenamide)-diphenyl-methane and 4,4'-bis(10-undecenoyl ester)benzoic acid ester, which include two mesogenic nematic monomers 4,4'-bis(10-undecenoylacid) diphenyl ester and 4,4'-bis(10-undecenoyl ester) benzoic acid ester. Each factor which was involved in the polysiloxane elastomers' preparation and influenced the crosslink density was investigated. Four elastomers were prepared by BPO initiated, in which two kinds of mesogenic crosslingker monomers were grafted to the main chain of polysiloxane. Moreover, the mesogenic crosslingker monomers and technical line are novel.The structures and properties of the obtained crosslinker monomers were investigated by IR spectroscopy, differential scanning calorimetry(DSC), polarizing optical microscopy(POM) measurements. The elastomers were tested on the mechanism equipment of the properties of dynamics and gel contents and then find out the most feasible method for its preparation. The addition of liquid crystal crosslinker monomers was also discussed. The results were expressed in detail as follows:(1) Monomer 4,4'-bis(10-undecenoyl acid)diphenyl ester and monomer 4,4'-bis(10-undecenoyl ester)benzoic acid ester are both thermotropic enantiotropic reversible liquid crystalline crosslinker with nematic texture. 4,4'-bis(10-undecenoyl acid)diphenyl ester exhibits schlieren texture during the heating process and shows mesophase at 78.62°C and disappears at 108.38°C 4,4'-bis(10-undecenoyl ester) benzoic acid ester exhibits threaded texture during the heating process and shows mesophase at 22.13°C and disappears at 93.84°C. 4,4'-bis(10-undecenamide)diphenyl and PP'- bis(10-undecenamide)-diphenyl-methane both show one heat absorption peak during heating process, are neither thermotropic liquid crystalline crosslinker.(2) Mould patterned method was feasible for preparing the elastomers.(3) In the crosslink experiments of polysiloxane monomer, the addition of BPO, the reaction temperature and reaction time had effects on the gel contents, but when BPO was over 0.25%, reaction temperature was higher than 100°C and reaction time exceeded 5min, polysiloxane can crosslink very well, which the gel contents were higher than 90%, and the influences were not obvious.(4) In the system of polysiloxane elastomers grafted with liquid crystalline croslinker, the addition of BPO, the reaction temperature and reaction time had largeeffects on the gel contents, and when the crosslink experiments were done under the condition of the BPO addition was 0.5%, the reaction temperature was 120°C and the reaction time was 30min, the elastomers can crosslink appropriately. Compared with the single polysiloxane elastomes, the elastomers grafted with liquid crystalline crosslinker had low gel contents, large shear elongation ratios (the larger addition of crosslinker, the lower gel contents, the larger shear elongation ratios). The results showed that when the addition of crosslinker was 10%, the elongation at break of the samples was more 200 times than the samples of pure polysiloxane.(5) Only when the addition of the croslinker was higher than 10%, the polysiloxa -ne elastomers had property of liquid crystalline and exhibited mesophase. And when the liquid crystalline croslinker was grafted into the elastomers, the phase transition of whole elastomers would slip to the lower temperature region. The elastomers with 4,4'-bis(10-undecenoyl acid)diphenyl ester, its melting temperature dropped to 68.96°C from 78.62°C, and its clearing temperature dropped to 103.12 °C from 108.38°C.(6) When the LCEs were heated again, the gel contents would changed, which is favorable for the orientation and crosslink of the elastomers.