Design, Synthesis, And Phase Reentrant Behavior Of Mesogen-jacketed Liquid Crystalline Polymers

This dissertation is focused on the investigation of the phase behavior and phasestructures of mesogen-jacketed liquid crystalline polymers (MJLCPs) with thedifferent chemical structures in order to study the structure–phase reentrantrelationship in liquid crystalline polymers. Meantime, phase reentrant behavior ofMJLCPs can be tailored through copolymerization and blends. Through the studying,we can obtain knowledge about the phase reentrant behavior and can get theinformation of the structure variation of MJLCPs and pocking mode molecular chain.The main topics of this paper are as follows:(1) Four series of polymers, poly{2,5-bis[(4-alkoxyphenyl)oxycarbonyl]styrenes}(P-OCm, m=1,2,4,6,8,10,12,14,16and18), poly{2,5-bis[(4-alkoxy carbonylphenyl)oxycarbonyl]styrenes}(P-OOCm, m=1,2,3,4,6,8,10,12,14,16and18),poly{2,5-bis [(4-Y-alkoxy carbonylphenyl)oxycarbonyl]-styrenes}(P-OOYm, m=1,2and3) and poly{2,5-bis [(4-alkoxybiphenyl)oxycarbonyl]-styrenes}(P-Cm, m=8,10,12,14and18) were designed and successfully synthesized via free radicalpolymerization. The phase structures and transitions of the polymers wereinvestigated by the combination of techniques including differential scanningcalorimetry, wide-angle X-ray diffraction, polarized optical microscopy, andrheological measurement. The experimental results revealed that the phase reentrantbehavior of MJLCPs was strongly depended on the length of rigid core and tail. ForP-OCm, when m was1and2, the polymers showed only a stable liquid crystallinephase above Tg. Second, with the increasing length of alkoxy tails, the P-OCm (m=4,6,8) presented a re-entrant isotropic phase above Tg and a liquid crystalline phase athigher temperature. They are considered to be the first kind of MJLCPs with are-entrant phase.Third, the P-OCm (m=10,12,14,16,18) exhibited an unusualre-entrant isotropic phase which was separating smectic A (SA) phase (in lowtemperature) and columnar phases (in high temperature). They are considered to bethe second kind of MJLCPs with a re-entrant phase. For P-OOCm, the most ofpolymers hard formed the columnar phases in high temperature. For P-OOYm, allpolymers formed a re-entrant isotropic phase above Tg. For P-Cm, the polymersdeveloped into a well-defined SAphase, which indicated that the lateral substitution oflong rigid mesogens strongly reduced the ability of forming columnar polymers. (2) A series of comb-like polymers, poly{2,5-bis[(4-octadecyloxyphenyl)oxycarbonyl]-styrenes}(P-OC18s) with different molecular weights (Mn) and lowmolecular weight distributions have been successfully synthesized via atom transferradical polymerization. One hand, phase behaviors of the alkyl tails were stronglyinfluenced by the mesogens of polymers, leading to the poor packing of the alkyl tailsand the low melting. The other hand, the liquid crystalline (LC) phase structures ofpolymers were found to be strongly Mndependent. The samples with Mn≤4.6×104formed a SAphase in low temperature and an isotropic phase in high temperature. Thesamples with Mn≥5.2×104displayed a re-entrant isotropic phase which was separatingthe SAphase and columnar nematic phase. Meantime, the experiment results showedthat Tg and the transition temperature from SAphase to isotropic phase both slightlyincreased with the increase of the Mns, however, the transition temperature fromisotropic phase to columnar phase sharply decreased with the molecular weightsimproved.(3) Based on2,5-bis[(4-alkoxyphenyl)oxycarbonyl]styrenes (M-OCm, m is thenumber of the carbons of alkyl tails,, m=1,4and18), three series of binarycopolymers with high Mn,{poly(M-OC1-co-M-OC4), poly(M-OC1-co-M-OC18)and poly(M-OC4-co-M-OC18)} have been prepared via free radical polymerization.The results showed that LC phase structures of copolymers, containing SAphase,re-entrant isotropic phase, columnar phase and isotropic phase, were stronglydepended on the composition and the alkyl length due to the competing among thesteric effect, the microphase separation and the driving force of the entropy. Whenone of them occupied a dominant position, the LC phase structure can be presentedfor the copolymers. Otherwise, the LC phase structure is lost despite the pair ofcorresponding homopolymers forming mesogenic structure.(4) A series of binary copolymers, poly{2,5-bis[(4-octadecyloxyphenyl)oxycarbonyl]-styrene-co-2,5-bis[(4-octadecyloxybiphenyl)oxycarbonyl]-styrene}{poly(M-OC18-co-M-C18)}, were synthesized via free radical polymerization. Theexperimental results revealed that Tg of the copolymers and the phase transitiontemperature from SAphase to isotropic phase both increased with the molar fractionof2,5-bis[(4-octadecyloxybiphenyl)oxycarbonyl]-styrene (M-C18) in feed. Inaddition, when the feed was below0.3, a column nematic phase was formed in hightemperature.(5) The octadecanol solution of P-OC18s with different the mass concentration of P-OC18s were prepared by solution method. The experiment results showed thatwhen the mass concentration of octadecanol was below5%, the SA—re-entrantisotropic phase—columnar phase transition takes place upon increasing thetemperature in the octadecanol solution of P-OC18s. Secondly, when the massconcentration of octadecanol was between5%and30%, a re-entrant isotropic phaseand columnar phase (at high temperature) were presented. Moreover, with theincrease of octadecanol, one hand, the transition temperature from isotropic phase tocolumnar phase decreased to119from240oC. On the other hand, the diameter ofcolumnar phase increased. Thirdly, when the mass concentration of octadecanol wasabove30%, the isotropic phase was only formed.