Synthesis And Study Of Coumarin Photo-sensitive Polymers And Branched Polymers

There are two parts in this paper, first:synthesis and properties of photo-sensitive telechelic polymer and star polymers. For the telechelic polymer:a coumarin derivative containing disulfide bond (C-S-S-C) was designed and synthesized, which can be used as chain transfer agent in the prescence of tributylphosphine (Bu3P) and water (H2O), to prepare the amphiphilic photo-sensitive telechelic polymer coumarin-poly(N-Isopropyl acrylamide) (C-PNIPAAm). And for star polymers:a three armed ATRP initiator (C-Br3) containing coumarin group was designed and synthesized, which was used to prepare amphiphilic photo-sensitive star polymers, poly(dimethylaminoethyl methacrylate) C-(PDMAEMA)3 and polystyrene-b-poly(dimethylaminoethyl methacrylate) C-(PSt-b-PDMAEMA)3. The structures of C-S-S-C, C-Br3 and polymers were characterized by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), gel permeation chromatography (GPC), liquid chromatography-mass spectrometry (LC-MS) and proton nuclear magnetic resonance spectroscopy (1H-NMR), then photo-sensitive properties, size and photo-controlled release of three polymer micelles were studied. It was found that C-PNIPAAm can form micelles in aqueous solution, and the micellar morphology in aqueous solution can be photo-switched into hollow spheres according to the photo-dimerization of coumarin end groups upon 365 nm irradiation and reform the micellar morphology after the subsequent photo-scission of dimers upon 254 nm. This instantly morphology changing phenomenon was successfully monitored by dynamic laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was shown that the small spherical shape of micelles with diameter at 30-50 nm before photo-crosslinking, the big vesicles with diameter at 200-350 nm after photo-crosslinking and the small micelles with diameter at 30-50 nm after the subsequent photo-de-crosslinking in the first irradiation cycle. And using fluorescein as a hydrophobic encapsulation, when irradiated by UV light (λ＞310 nm), the hydrophobic fluorescein was effectively released to the water. DLS showed that the average radius of the micelles increased from 56.6 nm to 101.0 nm after irradiation. In addition, it was found that the micelles prepared by two star polymers, C-(PDMAEMA)3 and C-(PSt-b-PDMAEMA)3, have good photo-sensitive property, respectively.Second:the new approach to branched polymers. A styrene monomer containing disulfide bond (St-S-S-St) was designed and synthesized, which can be used as branched monomer in the presence of Bu3P and H2O, and using St as main monomer, dioxane as solvent, AIBN as initiator, to prepare branched polystyrene (BPSt). The polymers were characterized by FT-IR,1H-NMR, GPC, and DSC analysis. It was found that the molecular weight (Mw) of BPSt increased exponentially with the increasing molar dosage of St-S-S-St, while the glass transient temperature (Tg) decreased, which meaned that the BPSt can be obtained through the copolymerization of St-S-S-St and St. In addition, branched poly(N-Isopropyl acrylamide) (BPNIPAAm) was synthesized.