Synthesis Of Novel Photoresponsive Azobenzene-Containing Functional Polymer Materials And Study On Their Properties

The molecular imprinting technique is a new and facile method to synthesize artificial receptors, developed with a combination of polymer chemistry, analytical chemistry, biochemistry and many other related subjects. The resulting molecularly imprinted polymers have a high affinity and specificity towards the template molecules, and are characterized by their easy preparation, good thermal and chemical stability, which makes them highly promising in many potential applications (such as chromatographic stationary phase, solid phase extraction, immunoassays, enzyme mimics, drug delivery and biomimetic sensors).Recent years have witnessed considerable interest in the development of liquid crystalline elastomers due to their combined properties of the anisotropy of the liquid crystals, rubbery elasticity of the polymer network, as well as the excellent mechanical properties, thermal properties and chemical stability. The monodomain liquid crystalline elastomers can deform upon the external stimuli (such as heat, electricity, magnetism and light) through the mesogenic alignment change, and therefore making them promising candidates for the application of artificial mustles and actuators.In this dissertation, a variety of photoresponsive azobenzene monomers were synthesized and introduced to molecularly imprinted polymers or liquid crystalline elastomers, respectively, in order to prepare a series of novel photoresponsive azobenzene-containing functional polymer materials. The unique reversible photoisomerization and photoinduced reorientation ability of the azobenzene group provides many unprecedented properties to these materials, which helps to solve some critical problems existed in the research field of either molecularly imprinted polymers or liquid crystalline elastomers for their real applications. The content of this paper mainly includes:1. An acetonitrile-soluble photoresponsive azobenzene functional monomer (i.e.,4-((4-methacryloyloxy)-phenylazo)pyridine, MAzoPy) was designed and synthesized for the first successful preparation of molecularly imprinted polymer microspheres with photoresponsive template binding properties via precipitation polymerization. Their morphologies, diameters and structures were characterized by scanning electron microscopy (SEM), Fourier transfrom infrared spectroscopy (FT-IR) and elemental analysis. Systematic binding property tests confirmed that the obtained MIP microspheres had rather fast rebinding kinetics, appreciable affinity and selectivity towards the template molecule2,4-dichlorophenoxyacetic acid (2,4-D). More importantly, this molecular recognition ability was found to be photoresponsive, indicated by the repeatable photo-controllable release and uptake of2,4-D under certain conditions.2. Atom transfer radical polymerization (ATRP) and precipitation polymerization were combined to prepare "living" molecularly imprinted polymer microspheres with surface-immobilized alkyl halide groups, using MAzoPy and2,4-D as the functional monomer and template molecule, respectively. Thermorespnsive poly(N-isopropylacrylamide)(PNIPAAm) hydrophilic polymer brushes were then introduced onto the surface of the microspheres via surface-initiated ATRP. The successful grafting of PNIPAAm brushes and the improvement of the hydrophilicity for the surface of the microspheres was confirmed by FT-IR, static contact angle and water dispersion stability studies. Systematic binding property tests revealed that the obtained molecularly imprinted polymer microspheres maintaned excellent affinity and selectivity towards the template molecule2,4-D in pure water. Furthermore, this molecular recognition ability was found to be both photo-and thermoresponsive.3. A series of acrylate type azobenzene monomers bearing an easily crosslinkable mesogen were designed and synthesized for the preparation of side-chain azobenzene homopolymers and random copolymers with a low glass transition temperature via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Their structures, thermal stability and phase transition behaviors were studied by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). Post-crosslinked liquid crystalline elastomer fibers were fabricated by using the simple melt spinning method firstly and the subsequent post-crosslinking reaction, which proved to have a high order of mesogen along the fiber axis and exhibit excellent reversible photoinduced bending and unbending behaviors under ultraviolet (UV) or visible light irradiation. Through this strategy, a precise control for the uniform orientation of the fibers is realized by separating the spinning alignment and crosslinking fixation processes.4. A series of acrylate type azobenzene monomers bearing an amino end-group (in its trifluoroacetate salt form) were designed and synthesized for the preparation of main-chain azobenzene polymers with a low glass transition temperature via Michael addition polymerization. Their structures, thermal stability and phase transition behaviors were studied by NMR, GPC, TGA, DSC, POM and small angle X-ray scattering (SAXS). The presence of secondary amino groups in the backbones of these main-chain azobenzene polymers not only made them highly reactive precursors for post-modification or post-crosslinking, but also led to the formation of hydrogen-bonding interactions among their polymer chains. Supramolecular hydrogen-bonding crosslinked liquid crystalline elastomer fibers were directly fabricated by using the simple melt spinning method, which proved to have a high order of mesogen along the fiber axis and exhibit excellent reversible photoinduced bending and unbending behaviors under UV or visible light irradiation. This facile strategy does not need any chemical crosslinking, which is quite necessary for the reconstruction and recycle of the used fibers.