The Sol-gel Method Photoresponsive Molecularly Imprinted Polymer And Its Application Research

Molecularly imprinted polymers (MIP) are a new type of three-dimensional, highly cross-linked smart materials, which have been demonstrated to be a useful technique for the preparation of molecular recognition materials. The imprint is like a lock that is only compatible with the correct key, similar to biological systems, such as antibodies and antigens, enzymes and substrates, and hormones and receptors. A crosslink polymerization is performed to fix the desired complex. After the template molecules are removed, binding cavities that recognize the applicable template are left to rebind selected molecules. Generally, a functional monomer has an appreciative group to match the active site of the template molecule, which makes the complex stable and improve the selectivity of the MIPs.In this study, a novel photoresponsive functional monomer, bearing a siloxane polymerisable group and azobenzene moieties was synthesized, and then a photoresponsive molecularly imprinted sol-gel polymers are successfully fabricated from the synthesized functional monomer, using 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxy acetic acid (MCPA) as a molecular template. The photoisomerization properties of the functional monomer are retained after incorporation into the rigid 3D crosslinked polymer matrix. The template is then removed from the resulting polymer to generate pores, which are complementary to the template in shape, size and functionality.The main component of the experimental study as follows:1. Frist, a novel photoresponsive functional monomer, containing molecule template 2,4-D and MCPA was synthesized using organic synthesis. This new type of azobenzene functional monomer covalently bound at one end to the template molecule and the other end with 3-Iodopropyltrimethoxysilane; then the functional monomer we prepared was characterized by infrared spectroscopy.2. In this study, a route to two types of photoresponsive molecularly imprinted sol-gel materials was presented, which have a photoswitchable and selective affinity with molecule template accordingly. The photoresponsive molecularly imprinted polymers were structured from different functional monomers (azobenzene functional monomer including 2,4-D, or MCPA) and crosslinker (tetraethoxysilane) using molecular imprinting technique by a sol-gel route.3. Two kinds of molecularly imprinted materials we prepared were characterized by IR; scanning electron microscopy (SEM) was characterized for research of the surface morphology and structure of polymer materials prepared; spectral analysis was made to the materials, the results confirm that after photoresponsive azobenzene functional monomer grafted to the organic-inorganic hybrid materials, the photoisomerization properties were maintained, and the molecularly imprinted polymers we prepared possess good response to external stimulation.4. Application and performance were explored on 2,4-D imprinted polymer materials prepared. Binding experiments showed that the imprinted polymer materials have a good binding capacity with the template 2,4-D, indicating that imprinting cavities and the active binding site in the cavities lead the MIP to the specific recognition of template molecules. Investigation of photoregulated release and uptake shows that the near-quantitative uptake of the template molecule after isomerization of the azobenzene chromophores in the MIP receptor sites over three irradiation cycles demonstrated that the binding sites exhibited good reversibility, without loss of specificity. The relationship between the concentration of the 2,4-D and the trans-to-cis photoisomerization rate constant was investigated, the standard curve was made, and the curve was feasible theoretically analyzed.5. Computational simulation theoretically confirms that the design of the molecularly imprinted polymer (MIP) was feasible. Application and performance were explored on MCPA molecularly imprinted polymer materials prepared, such as adsorption binding capacity, ability of specific molecular recognition, and investigation of photoregulated release and uptake of target analyte. In addition, the relation between the concentration of the MCPA and the trans-to-cis photoisomerization rate constant was investigated, and we have successfully shown that the concentration of the MCPA can be quantitatively determined through the trans-to-cis photoisomerization rate of the azobenzene chromophore. The standard curve was made, opening up new applications in chemical sensing and environmental analysis about molecularly imprinted polymer.