Biosynthesis and characterization of liquid-crystalline polyesters.

摘要

Functional polymers are considered to be potential candidate materials for future electronic, electro-optical and photonic devices. One of the promising concepts involves the covalent coupling of the purposefully tailored mesogen units to a polymeric backbone. This can not only enhance stability and processability of materials, but also in many cases lead to a liquid-crystalline phase and other ordered phases. Liquid-crystalline (LC) materials are characterized by long-range orientation order but a lack of positional order in at least one dimension. Compared to amorphous polymers, liquid-crystalline polymers, which possess an inherently highly ordered state of the LC phase, have shown large birefringence values, which is useful for optical storage media with a higher recording efficiency and lower recording power.; The focus of this dissertation is the design and synthesis of liquid-crystalline polyesters using chemo-enzymatic route. Three kinds of LC polyesters, side-chain LC polyesters, main-chain LC polyesters and chiral main-chain LC polyesters were synthesized. Side-chain liquid-crystalline polyesters were synthesized using two steps methods. First, the aliphatic polyesters were polymerized in bulk state using lipase as catalyst. Second, the azobenzene- and biphenyl-containing mesogen units were grafted onto the synthesized aliphatic polyesters using potassium carbonate as catalyst. The degree of substitution (DS) of the LC polyesters was determined by 1H-NMR and UV-Vis method. The grafting reaction was a mono-substituted reaction confirmed from 13 C-NMR spectra. The liquid-crystalline properties were measured by DSC and polarized optical microscope (POM).; Main-chain liquid-crystalline polyesters were synthesized by lipase-catalyzed reactions of azobene- or biphenyl-containing diester monomers with different diol monomers. High boiling point solvents, such as tetraethylene glycol dimethyl ether or phenyl ether, were used in the polymerization because of the high melting point of mesogen monomers. The monomers and polymers were characterized using NMR and FT-IR. DSC and POM were used to monitor the liquid properties of the synthesized polyesters.; Isoregic (head to tail) chiral main-chain liquid-crystalline polyesters were synthesized using AB-type chiral azobenzene-containing monomers. NMR and FT-IR were used to characterize the structure of the monomers and polymers. Circular dichroism (CD) measurements were used to monitor the chirality of the synthesized monomer and polymers. CD experiments proved that the chiral center was successfully connected onto the polymer. DSC and POM were used to monitor the liquid-crystalline transition temperature and texture of the LC polyesters.