The Synthesis And Characterization Of Topological Polymers Based On Coumarin

Topologic structures of the polymers influence remarkably their properties, precise synthesis of a special topological polymer with new functions is still challenging. Coumarins are sensitive to UV light, coumarin-based cyclic or hyperbranched polymers not only have the function of coumarin, but also are easily modified via photo chemistry of the coumarin. In this study, photoresponsive cyclic and hyperbranched polymers were obtained respectively by ATRP of styrene initiated by coumarin-modified ATRP initiators and self-condensing vinyl copolymerization (SCVCP) of coumarins-based inimer. The dissertation is briefly described as follows:1. Synthesis and characterization of cyclic-PSt with a coumarin groupAn ATRP initiator with alkynyl, bromine and coumarin moieties was synthesized at first, and then it was used in the ATRP of styrene (St) for synthesis of linear polystyrene (PSt) with controllable molecular weight and narrow distribution, followed by azidation of the terminal bromine group. The click reaction of-N3with-C=CH was carried out in highly dilute solution, and a single cyclic PSt with one coumarin group was obtained after purification. The coumarin moiety in the cyclic polymers display much stronger fluorescence in comparison with that in the linear precursors. Particularly interesting, the fluorescence resonance energy transfer (FRET) was observed when the polymer was irradiated by UV light at262nm. Due to the photodimerization of coumarin under λ>310nm irradiation, a single cyclic PS can be dimerized to form a bicyclic PSt accompanied with reduction of the UV light absorption of coumarin, and dimerization degree can be estimated by following the decrease of absorption intensities.2. Synthesis and characterization of reversible photo cross-linkable hyperbranched polymer Coumarin-containing inimer (CI) was prepared and used in the SCVP2-(2-methoxyethoxy)ethyl methacrylate(MEO2MA) to afford hyperbranched poly(MEO2MA-co-CI)(HPMC). The resultant HPMC was used as macro-ATRP initiator in the following polymerization of DMAEMA, and the multiarm hyperbranched polymers with photo-responsive properties were achieved. The star-hyperbranched copolymers can self-assembly to form micelles, and then the micelles can be cross-linked via photo dimerization of the coumarin groups. During the self-assembling and cross-linking reaction, the drug was loaded and control release of the drug was investigated. Under X<260nm irradiation, de-crosslinking reaction of the crosslinked micelles occurred, which was followed by the absorbance increase of coumarin.