Synthesis Of Carbazolyl-containing Monomers And Their Photoinitiated Living Cationic Copolymerization

In recent years, photopolymerization has been attracting much interest for it’s aneconomic and environmental friendly process. In contrast to thermally basedpolymerizations, photopolymerization can be performed at room temperature or evenlower which prevents side reactions such as chain transfer. In general photoinitiated radicalpolymerization, molecular oxygen always inhibit the polymerization. Due to the problemof volume shrinkage in radical polymerization, it is expected that photoinitiated cationicpolymerization will be a better choice in various applications. Photoinitiated cationicpolymerizations are generally accomplished with the aid of onium salts. The generalmechanism of photoinitiated cationic polymerization relies on the decomposition ofphotoinitiator and the generation of initiating species.In addition, living cationic polymerization is an elegant way to synthesizewell-defined polymers with narrow molecular weight distribution and end functionalgroups. However, photoinitiated living cationic polymerization is still a challenge. Itshould be noted that in most photoinitiated living cationic polymerizations, thephotochemical step is involved in the very first step, the propagation step is generally athermal reaction.In this system, we firstly synthesized several vinyl ethers with carbazolyl groups.2-(9-carbazolyl) ethyl vinyl ether (CEVE),3-Iodo-9-[2-(vinyloxy)ethyl]carbazole (IVEC),3-[dibenz(b,f)azepinyl]-9-[2-(vinyloxy)ethyl]carbazole (DBVEC),3-[10,11-dihydrodibenz(b,f)azepinyl]-9-[2-(vinyloxy)ethyl]carbazole (DHBVEC) weresynthesized successfully. Subsequently, photoinitiated living cationic copolymerization ofCEVE and IBVE was carried out using diphenyliodonium chloride (DPICl) as the initiator,2,2-dimethoxy-2-phenylacetophenone (DMPA) as the photo sensitizer, zinc bromide(ZnBr2) as the catalyst in dichloromethane. The polymerization was allowed to carry out invarious temperatures such as5oC,-5oC,-15oC. Polymer with relatively narrow moleculeweight distribution was obtained in-15oC (Mn,GPC=52000g/mol, Mw/Mn=1.27). Some other conventional characterization methods such as1H NMR, DSC and fluorescencespectra were used to confirm the successful synthesis the copolymers. The results indicatethat well-defined copolymers can be obtained, in addition, the copolymer has good thermalstability and has a Tgbelow-10oC. It was also found that the copolymer showfluorescence properties both in solution and thin film.