Preparation Of Carbosiloxane Dendrimers Via Orthogonal Thiol-Ene Click Strategy

This thesis mainly covers the design and syntheses of novel bifunctional silanes, and the design and syntheses of novel carbosiloxane dendrimers via combination of thiol-ene click chemistries through orthogonal click strategy. The novel bifunctional silanes are all synthesized by hydrolysis reactions among commercial silanes. Starting from commercial available silane coupling agents, the pure products are obtained through one-step reactions after simple purification procedures such as extraction or column chromatography. The carbosiloxane dendrimers are constructed by the combination of thiol-Michael addition reaction and radical-mediated thiol-ene addition reaction. By iterative click thiol-ene reactions, the dendrimers are step-growth rapidly with excellent yields.We tried several strategies to introduce click chemistry functional groups into structures of silanes. After the advent of the concept of "click chemistry", there are lots of reports on this type of high efficiency reactions. Benefit from its instinct nature of high reaction rate, quantitative conversion, and simple purification steps, click chemistry is extensively employed in many fields. So it is worthwhile to synthesize silanes containing two different kinds of clickable functional groups. We synthesize three types of bifunctional silanes. The first product contains thiol and azide groups, the thiol functional groups play major role in thiol-ene chemistry, and azide functional groups are main reagent for the well-known CuAAC reaction. The second bifunctional silane contains conjugated carbon-carbon double bonds and non-conjugated carbon-carbon double bonds. Carbon-carbon double bonds are important functional groups in click chemistry, and different kinds of carbon-carbon double bonds have different reactivity in different click reactions. We made a little alternation in the structure of the second product to get the third silane, introducing a methyl hindrance into the structure, which changes its reactivity in many click reactions, such as aza-Michael addition reaction. All the integrity of products are verified by FTIR and 1H NMR.Starting from the aforementioned bifunctional silanes, we design the synthesis routes of carbosiloxane dendrimers. A combination of thiol-Michael addition reaction and free-radical mediated thiol-ene reaction is employed as a facile and efficient approach of carbosiloxane dendrimer synthesis. For the first time, carbosiloxane dendrimers is constructed rapidly by an orthogonal click strategy without protection or deprotection procedures. The chemoselectivity of these two thiol-ene click reactions lead to a design of a new monomer containing both electron-deficient carbon-carbon double bond and unconjugated carbon-carbon double bond. Condensation reactions among silicon compounds provide an easy way to obtain the monomer with two kinds of carbon-carbon double bonds, and siloxane bonds were formed as the linker between them. Starting from a bifunctional thiol core, the dendrimers is constructed by iterative thiol-ene click reactions under different but both mild reaction conditions. Simple purification steps required, the fifth dendrimer with 54 peripheral functional groups is obtained with an excellent overall yield in a single day.