Self-assembly And Application Of The Photosensitive Alternating Copolymer

Photosenstive alternating copolymer poly(styrene/(7-(4-vinylbenzyloxyl)-4-methylcoumarin)-alt-maleic anhydride) P(St/VM-alt-MAn) were synthesized through free radical copolymerization with styrene, photosensitive styrene derivative monomer VM and maleic anhydride. Photosensitve alternating copolymer P(St/VM-alt-MAn-APy) was obtained by the functional amidolysis reaction between succinic anhydride unit of P(St/VM-alt-MAn) and 2-aminopydine. These photosensitive alternating copolymers were characterized by Gel Permeation Chromatography (GPC), Fourier Infrared Spectroscopic(FTIR) and Nuclear Magnetic Resonance Spectrometer (1H-NMR).The photosensitve alternating copolymer P(St/VM-alt-MAn) could self-assemble into steady spherical micelles in the selective solvent dioxane/water (75/25, v/v) with suitable initial copolymer concentration and water content. The self-assembly process of photosensitve alternating copolymer was detected by UV spectrophotometer. The aggregates morphologies were observed by Transmission Electron Microscope (TEM),while the photo-cross-linking process of the micelles was traced by combining means of Dynamic laser light scattering (DLS) and UV spectrophotometer. With UV irradiation, the diameters of the micelles decreased firstly with the shrinkage of the whole micelles and subsequently increased due to the inter-micelles cross-linking with further irradiation. After further photo-cross-linking between the chains of the micelle, the contact angle of the micelles decreased.Analogously, as the product of amidolysis reaction between P(St/VM-alt-MAn) and 2-aminopydine, photosensitve alternating copolymer P(St/VM-alt-MAn-APy) could also self-assemble into spherical micelles in selective solvent DMF/H2O(50/50, v/v). The P(St/VM-alt-MAn-APy) chains of the self assemble micelles were photocrosslinked with UV irradiation (λ>310 nm) detected by UV spectrophotometer, while the micellar sizes (Rh = 122 nm) hardly decrease with UV irradiation (λ=365 nm). Moreover, the photocrosslinked micelles could reversible photocleavage underλ=254 nm UV irradiation. With the micellar solution pH increasing, the photo-cross-linking rate of alternating polymer chain enhanced. On the other hand, the higher salt concentration of the micellar solution, the lower rate of photo-cross-linking the micelles display.Either P(St/VM-alt-MAn) or P(St/VM-alt-MAn-APy) micelles were homogenized with equal volume toluene as oil phase, with micelles used as particle emulsifier. The stable emulsions were obtained, and the type of which was o/w. The micelles were sensitive to the solution pH, salt concentration and UV irradiation, resulting in the stimulate-responsive property of the emulsifiers. A novel method was presented to investigate the secondary self-assembly behavior of micelles in the oil/water interface in this paper, in which styrene was used as oil phase instead of toluene, meanwhile, photo-crosslinked P(St/VM-alt-MAn) micelles were used as emulsifier. Styrene in water (ie. o/w) emulsion was also obtained in this case after the homogenization. Emulsion was diluted and styrene inside of the oil droplet was polymerizated at 65°C to solidify the oil phase for SEM studies. Results indicated that the micelles were adsorbed at the surface of the solidied PS particle, suggesting that the self assemble micelles were adsorbed at the interface of the oil/water interface to prevent the coalescence of the emulsion droplets, which were consistent with previous reports about the adsorption behavior in the oil/water interface with other colloidal particles.