Synthesis And Properties Of New Chiral Liquid Crystalline Monomers And Cholesteric Elastomers

As a new functional polymer material, cholesteric liquid crystalline elastomers (LCEs) combine unique optical properties of cholesteric LC with good mechanical property, thermal and chemical stabilities of polymer networks, which have been an important research project in the field of LCPs. In this dissertation, the new chiral liquid crystalline (LC) monomers and cholesteric LCEs were mainly studied. Therefore, study on cholesteric LCEs is not only affluent in the content of LCPs, but also provides theoretical basis and necessary experimental data and technology to explore their applications in the fields of piezoelectric materials, ferroelectric materials, and microelectronic materials etc.Seven chiral LC monomers (M1-M7) containing cholesteryl groups, a chiral LC monomer (M8) containing menthyl group, a non-mesogenic crosslinking agent (Ni) and a nematic crosslinking agent (N2) were synthesized. They include 4-(10-undecylen-1-yloxy)phenyl-4'-cholesteryloxycarboxylvalerate (M1),4-(10-undecylen-l-yloxy)biphenyl-4'-cholesteryloxycarboxylvalerate (M2),4-(10-undecylen-l-yloxybenzoyloxy)phenyl-4'-cholesteryloxycarboxylvalerate (M3), 4-(10-undecylen-1-yloxy)phenyl-4'-cholesteryloxycarboxylvalerylbenzoate (M4), 4-(10-undecylen-1-yloxybenzoyloxy)biphenyl-4'-cholesteryloxycarboxylvalerate (M5), 4-(10-undecylen-1-yloxy)biphenyl-4'-cholesteryloxycarboxylvalerylbenzoate (M6), 4-(10-undecylen-1-yloxybenzoyloxy)phenyl-4'-cholesteryloxycarboxylvaleryl benzoate (M7),4-(10-undecylen-1-yloxy-benzoyloxy)biphenyl-4'-menthyloxyacetate (M8), phenyl 4,4'-bis(10-undecylenate) (N1), and phenyl 4,4'-bis(10-undecylen-1-yloxy benzoate) (N2). The homopolymers (P1-P8), LCEs P1 series (P1-3-P1-35), P2 series (P2-3-P2-35) and P8 series (P8-5-P8-25) were obtained by graft polymerization of M1-M8, M1 and N2, M2 and N1, M8 and N2, and PMHS, respectively. All the obtained chiral monomers and polymers or elastomers are novel. The chemical structures of the obtained monomers and polymers were characterized by FT-IR or 'H-NMR spectroscopy. The mesomorphic properties and phase behavior were investigated polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetric analyses (TGA). The effect of structure and copolymerization composition on the phase transition temperatures, phase types and textures is discussed.The rotation direction of M1-M7 are all negative, as well as menthol. The configuration of the introduced menthyl group in the chiral compounds must be retained. Moreover, the absolute specific optical rotation value decreased with increasing the rigidity of mesogenic core. M1-M8 all showed the oily streak texture and focal conic texture of cholesteric phase, in addition, M2 and M7 also revealed cholesteric finger print texture, M3, M5 and M6 also displayed cholesteric spiral texture, M8 also showed the fan-shaped texture of chiral smectic C phase (Sc*). Moreover, the selective reflection of light shifted to the short wavelength region (blue shift) with increasing temperature. N1 showed no texture. N2 exhibited enantiotropic nematic threaded texture and monotropic smectic fan-shaped texture. All obtained homopolymers and elastomers revealed Grandjean textures.Except for N1, other monomers showed a melting transition and LC to isotropic phase transition, moreover, M5 and M6 also revealed a glass transition, M8 also showed a Sc* phase transition, and N2 revealed a smectic A phase transition on cooling. The clearing temperatures (Ti) increased with increasing the rigidity of mesogenic groups. The homopolymers and elastomers showed a glass transition and LC to isotropic phase transition, and good thermal stability.With increasing the concent of crosslinking agent, Tg and Ti of elastomers P1 series all increased; Tg of P2 series and P8 series first decreased and then increased, and Ti of P2 series decreased; but Ti of P8 series first increased and then decreased.