Investigation On The Phase Structure And Thermo-responsive Behavior Of "Mesogen-Jacketed Liquid Crystal Polymers" With Skin-core Structure

Combined the semi-rigid chain of mesogen-jacketed liquid crystalline polymers (MJLCPs) with the property of thermoresponsive groups, a series of thermoresponsive MJLCPs with skin-core structure were designed and successfully synthesized. In order to explore the formation mechanism of liquid crystal phase and the thermoresponsive mechanism of MJLCPs, the effect of the number and length of oligo(ethylene oxide) chain on the phase structures and solution properties of MJLCPs were investigated. The influence of the lithium complex on the phase structure of MJLCPs was studied, as well as the shielding effect on thermoresponsive properties of the copolymers was researched. The specific conclusions are as follows:1. A series of mesogen-jacketed liquid crystalline mononmers with different number and length of oligo(ethylene oxide) chain were successfully synthesized, namely2,5-bis[(4-methoxyoligo(oxyethylene) benzyl)oxycarbonyl]styrene (mono-mEOBCS),2,5-bis[(3,5-di(methoxyoligo (oxyethylene))benzyl)oxycarbonyl] styrene (di-wEOBCS), and2,5-bis[(3,4,5-tri(methoxyoligo(oxyethylene))benzyl) oxycarbonyl] styrene (tri-mEOBCS), and "m" was the number of repeat unit (w=l,2,3). The chemical structures of the monomers were confirmed by!H NMR,13C NMR and Mass Spectrometry. The phase structures and transition behaviors were studied by DSC and POM. The results showed that monomers (mono-3EOBCS, di-wEOBCS(箩=2,3) and tri-/wEOBCS(m=2,3)) were liquid, mono-lEOBCS and di-lEOBCS were crystal molecules, mono-2EOBCS was amorphous solid, and tri-lEOBCS was liquid crystal molecules, indcating that the phase structures of monomers was influenced by the number and length of oligo(ethylene oxide) chain. The solution propties of monomers were investigated with turbidity measurements using UV-vis spectroscopy. The results showed that the monomers (di-3EOBCS, tri-2EOBCS and tri-3EOBCS) were thermoresponsive molecules, while the other six monomers were insoluble in water, suggesting that with the increase of the number of hydrophilic group, the monomers presented the thermoresponsive behavior.2. A series of polymers had been prepared via free radical polymerization, namely poly{2,5-bis[(4-methoxyoligo(oxyethylene)benzyl)oxycarbonyl]styrene}(P-mono-tmEOBCS, m=\,2,3), poly{2,5-bis[(3,5-di(methoxyoligo(oxyethylene)) benzyl)oxycarbonyl]styrene}(P-di-wEOBCS, m=\,2,3), and poly{2,5-bis[(3,4,5-tri (methoxyoligo(oxyethylene))benzyl)oxycarbonyl]styrene}(P-tri-/wEOBCS, m=\,2,3). The characterization of the polymers was performed with’H NMR, GPC, DSC, TGA, ID WAXD and2D WAXD. The results showed that P-mono-mEOBCS{m=\,2,3) couldn’t form LC phase due to the poor’"jacketing effect" when the number of oligo(ethylene oxide) chain was single; When the number of oligo(ethylene oxide) chain changed to2or3, the "jacketing effect" increased, leading to that P-di-mEOBCS and P-tri-wEOBCS (w=l,2,3) exhibted the stable hexagonal columnar phase (Oh). However, P-di-3EOBCS showed the columnar nematic phase, indicating the "jacketing effect" decreased when the length of oligo(ethylene oxide) chain increased.3. The thermoresponsive behavior of the P-mono-wEOBCS, P-di-wEOBCS and P-tri-wEOBCS (w=l,2,3) were studied by variable temperature UV-vis spectroscopy. The experiment results showed that P-mono-wEOBCS (m=l,2,3) were insoluble. While P-di-mEOBCS and P-tri-wEOBCS (except P-di-lEOBCS) showed a low critical solution temperature (LCST) own to the increase of number hydrophilic group and shielding effect and the LCST of polymers increased from22癈to60癈.4. The influence of lithium salt on the phase structures and behaviors of the MJLCPs with the oligo(ethylene oxide) chain as peripheral chain was studied. The experimental results showed that, with the increase of lithium salt concentration, one hand, the glass transition temperature of polymers with lithium salt increased significantly. On the other hand, the phase structure of polymers changed from the Oh phase to isotropic phase, suggesting that the order structure of polymers decrease. Meantime, with the increase of the number of length of the oligo(ethylene oxide) chain, the lithium salt concentration decreased when the polymers losed the order structure, such as the lithium salt content reduced from0.2to0.1for P-di-/;?EOBCS, from0.3to0.15for P-tri-/wEOBCS.5. Two series of binary copolymers poly{2,5-bis [(3,4,5-tri(4-methoxy)benzyl) oxycarbonyl] styrene}-co-poly{2,5-bis[(3,4,5-tri(methoxytri(oxyethylene))benzyl) oxycarbonyl]styrene}(P-tri-MBCS-co-P-tri-3EOBCS) and poly{2,5-bis [(3,4,5-tri(4-decyoxy)benzyl) oxycarbonyl] styrene}-co-poly{2,5-bis[(3,4,5-tri (methoxytri(oxyethylene))benzyl)oxycarbonyl] styrene}(P-tri-DBCS-co-P-tri-3EOBCS) were synthesized successfully via free radical polymerization. The results showed that, one hand, when the molar fraction of2,5-bis [(3,4,5-tri(4-methoxy)benzyl) oxycarbonyl] styrene (tri-MBCS) in feed (x) was below30%, the copolymers could form the LC phase. When x was above30%, the copolymers couldn’t show the LC phase. On the other hand, the changes of the LCSTs for the copolymers presented a multistep change with the increases of the content for hydrophobic monomer tri-MBCS. When x<20%, the LCST of P-tri-MBCS-co-P-tri-3EOBCS kept at58癈due to the strong shielding effect of the long hydrophilic chain. When20%<x<50%, the LCST decreaed own to the weak shielding effect. When x<50%, the copolymers were insoluble because the hydrophobic group was completely dominant. For the copolymers P-tri-DBCS-co-P-tri-3EOBCS with stronger hydrophobicity, the LCST of copolymers kept at58癈as the molar fraction of2,5-bis [(3,4,5-tri(4-decyoxy)benzyl) oxycarbonyl] styrene (tri-DBCS) in feed was below7%, but the copolymers were insoluble as the molar fraction of tri-DBCS in feed was above9%.