Synthesis And Properties Of Polysiloxane Materials Containing Imidazole

Polysiloxane has a Si-O-Si main structure combined with organic groups, resulting in physical rigidity, negligible swelling in both aqueous and organic solutions, excellent heat and weather resistance, oxidative stability and chemical inertness. Functional groups can be introduced into polysiloxane by the hydrolysis and condensation of appropriate silanes, which is a way to prepare functional polysiloxane material. The imidazole ring is an important chemical component in nature that plays various critical roles. For example, it has been shown that histidine is one of the primary metal binding sites in proteins and imidazole groups are responsible for metal complexation. Imidazole was kept as a member playing catalytic role in the active center of natural enzyme. Imidazole and derivatives thereof are used as ligands in polymeric matrixes for separating metal ions and catalytic sites. In this study, the imidazole used as metal-chelating ligand and catalytic sites was combined with polysiloxane matrix by a long chain. We conducted detailed investigation on the properties of this novel polysiloxane materials bearing imidazole.Firstly, we synthetized silane monomer, by carrying out a reaction between (3-isocyanatopropyl)triethoxysilane and N-(3-aminopropyl)imidazole. Sol-gel method was used to prepare polysiloxane materials containing imidazole (ImSR). The surface properties, thermal stability, complexation and adsorption properties with respect to Cu2+ions were studied. ImSR is a hydrophilic material with a water contact angle of56°on a flat surface. It possesses good thermal stability and exhibits rapid weight loss above230℃. ImSR was evaluated as a promising adsorbing material for Cu2+ions. It exhibited a high affinity for Cu2+ions, with a maximum adsorption ability of69.5mg/g. Langmuir, Freundlich and Dubinin-Radushkevich isotherm models were used to analyze the experimental data. The results showed that the ImSR absorbent exhibited chemisorption and monolayer distribution on homogenous active sites. The equilibrium adsorption capacity remained relatively constant after5use cycles. ImSR show adsorption capacity for Cu2+, Ni2+, Zn2+, Cd2+, revealing that ImSR is a promising adsorbing material.Then, we prepared molecularly imprinted polysiloxane materials containing imidazole (mip-ImSR) based on the molecular imprinting technique. The p-nitrophenyl acetate (NPA) was chosen as the substrate to evaluate the catalytic activity of the mip-ImSR. Based on the theory of transition state stabilization that preferred binding of the transition state lowers the activation energy of the reation, the transition state analoge for the hydrolysis of p-nitrophenyl acetate, was used as template molecule. ImTES and methyl triethoxysilane (MTES) was functional monomer and crosslinking monomer, respectively. The hydrolysis rate was16fold in the presence of mip-ImSR, compared with the rate of self-hydrolysis of NPA. The reaction catalyzed by mip-ImSR accorded with Michaelis-Menten kinetics. However, the mip-ImSR show comparable catalytic activity with the nonimprinted polysiloxane materials containing imidazole (nip-ImSR), demonstrating that the performance of imprinting process is poor. Km and kcat was calculated as1.66mmol/L and1.35min-1, respectively.