Synthesis And Liquid Crystalline Properties Of Carbonate Monomers And Polymers Containing Diosgenyl Groups

Recently, the functional polycarbonate materials have increased considerable attention because of their broad applications in biological system, such as disease diagnosis, treatment and living tissue enhancement, repair and replace. As known, some basic life materials, such as DNA and phospholipids, belong to biological liquid crystalline (LC) compounds. It is no doubt that LC state exists in living cells widely. As an important biological molecule, diosgenin and its derivatives are extensively used to prepare steroidal molecule drugs, and to study their multiple biological activities. However, to the best of our knowledge, no study has been reported on the design and synthesis of functional aliphatic LC polycarbonates containing diosgenyl group. To enhance the biocompatibility of polycarbonates and develop new biological LC polymer materials, herein, a novel class of functional LC carbonate monomers based on diosgenin and amphiphilic block-graft copolymers were for the first time designed and synthesized.In the second chapter, four new diosgenyl derivatives bearing primary hydroxyl groups were synthesized and named as 2-diosgenoxyethanol (C1),4-diosgenoxybutane-1-ol (C2), 6-diosgenoxyhexane-1-ol (C3) and 8-diosgenoxyoctane-1-ol (C4) Then four new LC cyclic carbonate monomers containing diosgenyl group were synthesized by reacting C1～C4 with carbonate 5-methyl-5-carboxyl-1,3-dioxan-2-one (MCC), respectively. The monomers were named as 2-diosgenoxyethyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (M1),4-diosgenoxy-butyl 5-methyl-2-oxo-1,3- dioxane-5-carboxylate (M2),6-diosgenoxyhexyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (M3) and 8-diosgenoxyoctyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (M4) Their molecular structures were characterized by FT-IR,1H-NMR and 13C-NMR. Polarimeter was used to measure their specific optical rotations. Thermal properties and optical textures were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM). X-ray diffraction (XRD) was used to investigate their LC structure.Polarimeter analysis showed that C1～C4 and M1～M4 were all levorotatory. With an increase of methylene in molecular structures, the specific optical rotation values of all compounds reduce gradually. POM results showed that the compounds C1～C4 exhibited fan-shaped textures of a smectic A (SmA) phase, and M1～M4 exhibited focal conic textures of the choleteric phase during heating and cooling process. In addition, with increasing the methylene flexible chain in molecular structure, the melting temperature (Tm) and isotropic temperature (Ti) of C1～C4 decreased, and the mesophase temperature ranges broadened because the corresponding Tm decreased more than T1. For LC monomers, the glass transition temperature (Tg) of M1～M4 and Ti of M1～M3 also decreased gradually, while the Ti of M4 increased slightly, and the mesophase temperature range broadend. Moreover, the LC phase structure of C1～C4 and M1～M4 were further confirmed by XRD. For C1～C4, a sharp reflection associated with the smectic layers at small angle region, and a broad peak associated with the lateral packing at wide angle were observed, showing that C1～C4 belonged to a SmA phase As an example, a sharp peak at 20=4.4° and a broad peak at 20=15.7° were observed for C3, and the d-spacing of the first-order reflections was 20.1 A. For M1 and M3, only a broad peaks was observed at 20=15.0°～16.0°, showing that they belonged to cholesteric phase.In the third chapter, amphiphilic block copolymer mPEG43-b-PBC11 was synthesized by ring-opening polymerization of benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (MBC) with poly (ethylene glycol) monomethyl ether (mPEG) as an initiator and Sn(Oct)2 as catalyst. The protective benzyl groups in mPEG43-b-PBC11 chains was removed by Pd/C hydrogenation to get mPEG43-b-PCC11 with carboxyl groups. Then, a new amphiphilic block-graft LC copymer mPEG43-b-P(MCC-g-C3)11 was obtained by the reaction of diosgenyl derivative C3 and mPEG43-b-PCC11. The sturcture and molecular weight of the amphiphilic block copolymers were characterized by FT-IR and 1H-NMR. POM showed that mPEG43-b-P(MCC-g-C3)11 exhibited broken-fan like textures during heating and cooling process.