Study On Grafting Polymer With ARGET ATRP Modification And Application Of Vesicular Mesoporous Silica

In this paper, vesiclular mesoporous silica was synthesised using a hydrothermal method and then functionalized with (3-aminopropyl)triethoxysilane(APTES) by post-synthesis-grafting method, and then the product was modified with 2-bromoisobutyryl bromide(BiB) and the sample was designated as Br-modified vesiclular mesoporous silica. We designed and synthesized pH-sensitive poly 2-(diethylamino)ethyl methacrylate polymer brushes on the surface of the Br-modified vesiclular mesoporous silica via activator regenerated by electron transfer atom transfer radical polymerization(ARGET ATRP). Finally, the composite materials were employed for the controlled release of drug. The main contents were as follows:(1) Vesiclular mesoporous silica with well-defined multilamellar structure have been prepared at mild conditions, through a dual-templating way by using didodecyldimethylammonium bromide and cetyltrimethylammonium bromide as structure directing agent and tetraethylorthosilicate as silica source. The hydrothermally synthesised vesiclular mesoporous silica has diameters of 50-100nm, shell thicknesses of 2-5 nm and interlamellar voids of 2-3nm.(2) The vesiclular mesoporous silica was modified with APTES and BiB in turn. Thermogravimetric analysis and fourier transform-infrared spectroscopy (FT-IR) show that there is physically absorbed water in the surface of vesiclular mesoporous silica, and indicationg there is larger percentage of weight loss after the modified vesiclular mesoporous silica successful resulted from the organic composition of modifying agent. As shown in FT-IR, there are new peaks of modifying agent(1380,1280 cm-1). These tesults show that the vesiclular mesoporous silica was modified successfully.(3) pH-sensitive poly 2-(diethylamino)ethyl methacrylate-vesiclular silica was synthesized by applying ARGET ATRP. In this experiment, FeCl3/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N-dimethylformamide as the solvent, Br-modified vesiclular mesoporous silica as a macroinitiator. Adjusting the amount of the monomer, the obtained products were named as SM1, SM2, and SM3, respectively. The obtained materials were characterized by HRTEM, FESEM, FT-IR. The results indicated that the polymer was successfully grafted on the surfaces of vesiclular mesoporous silica. The HRTEM show that with the increase of the monomer amount, the outermost shell thicknesses of SM1, SM2 and SM3 do not change and the interlamellar voids become small because of excess monomer polymerisation in the inner layers.(4) The vesiclular mesoporous silica and composite material were employed for the controlled release of captopril. The captopril loading contents of vesiclular mesoporous silica and SM3 are approximately 26.0 and 43.0%, respectively. The entrapment efficiencies of vesiclular mesoporous silica and SM3 are estimated to be 30.0 and 50.0 %, respectively. After modification with poly 2-(diethylamino)ethyl methacrylate, the loading content obviously increases. The in-vitro drug release behaviour of vesiclular mesoporous silica and SM3 was studied in phosphate buffer saline with different pHs (4.0,6.0 and 7.4). The captopril released from vesiclular mesoporous silica is 20.0% at pH 4.0,14.0% at pH 6.0 and 12.8% at pH 7.4. These data show that the release amount is small and that the difference in release amount between different pHs is not significant. The cumulative amount of drug release could reach up to 70.0% at pH 4.0, which is significantly higher than that at pH 6.0 (38.0%) and 7.4 (31.5%). The aforementioned results show that the amount of captopril released depends on the solutions’pH.The method can be extended to prepare other composite materials and expanding its application scope.