Design And Synthesis Of Coumarin Photo-sensitive Block Polymers

There are two parts in this paper, the first part: synthesis and properties of new photo-sensitive soluble coumarin derivative. The water soluble coumarin derivative 7-hydroxy-4-methyl-8-(4'-methylpiperazin-1'-yl) methylcoumarin (HMPC) was synthesized via the Mannich reaction between 7-hydroxy-4-methylcoumarin and N-methylpiperazine which possessed the electrondonating piperazine group with pH responsivity. Since the piperazine group is a pH-sensitive electron donor, which would form HMPC interesting photo-physical and chemical properties in different pH solution.We made an investigation on the characteristic UV absorption and photo-dimerization Behavior of the coumarin derivative. It was shown that the characteristic UV absorption and also the photo-dimerization of HMPC which was on irradiated by UV light(λ>310 nm) could be effectively changed in pH solution. And the photo-dimerization experiments showed that in the neutral solution the dimerization reaction rate was most rapid, followed by that in the alkaline solution and it was the slowest in the acidic solution under the same concentration.Second: synthesis and properties of the photo-sensitive star polymer C-(PDMAEMA)3 and amphiphilic photo-sensitive star block copolymer C-(PDMAEMA-b-PSt)3. A three armed ATRP initiator (C-Br3) containing photo-sensitive coumarin group was designed and synthesized in the multi-step, which was used to prepare amphiphilic photo-sensitive star polymer C-(PDMAEMA)3 by ATRP with 2-(dimethylamino)ethyl methacrylate (DMAEMA) as hydrophilic monomer, CuBr/ PMDETA as the catalytic system. And amphiphilic photo-sensitive star block polymer C-(PDMAEMA-b-PSt)3 was synthesized with 2-(dimethylamino)ethyl methacrylate (DMAEMA) as hydrophilic monomer and styrene (St) as hydrophobic monomer as the same condition. The structures of C-(PDMAEMA)3 and C-(PDMAEMA-b-PSt)3 were confirmed by FT-IR, GPC and 1H-NMR. It was found that the star polymer C-(PDMAEMA)3 could form polymer micelles in aqueous solution. And the coumarin center group of the star polymer can be reversibly photo-dimerized upon 365 nm and 254 nm irradiation. However, the hydrodynamic size analysis determined by Malvern Zetasizer Nano-ZS showed that the polymer micelles were in gaussian distribution (87.7±27.8 nm) before photo-crosslinking, and changed slightly upon 365 nm and 254 nm irradiations. The reason for this slight size changes maybe that there were very minor changes in the polymeric amphiphilic structure before and after photo-reactions. Then photo-sensitive properties of the micelles of copolymer C-(PDMAEMA-b-PSt)3 under diferent pH condtion was study. It was found that the polymer micelles with favourable photo-sensitive properties would change in deferent pH condtion and largen as adding Natronlauge, meanwhile the photo-dimerization degree of C-(PDMAEMA-b-PSt)3 raised.