A Universal Photochemical Strategy To Introduce Monolayer Of Specific Functional Groups Onto The Surface Of Polymeric Substrates

The outmost surface of most commercial polymers is mainly consisted with inert C-H bonds which result low surface energy and inertness in chemical reactivity. Thus the surface modification of polymer materials is necessary for many applications, such as biomaterials, microelectronics and constructing a monolayer. At present, photo-grafting polymerization is one of the widely used technologies in polymer surface modification. But there is no existing technology to introduce a desired functional group onto the polymer surface. So it is rationale to develop a universal, clean, effective and cheap method to functionalize polymer surface.In this dissertation, a novel method based on photoreduction of acetone to abstract hydrogen from the C-H bonds of polymer surface to generate carbon-centered chain free radicals and bring functional groups to the polymer surface by scavenging the chain free radicals has been developed. Three kind of chemicals, succinic acid acyl peroxides, BPO and phenol derivatives, which can be used to functionalize the polymer surface have been systematically investigated.1. A method of introducing mono-layer carboxylic groups onto polymer surfaces by ultraviolet irradiation assisted process was developed. Under UV irradiation, excited acetone substracted the hydrogen from the C-H bonds to form chain free radicals, then these radicals coupled with the carboxylic group free radicals from the succinic acid acyl peroxides precursor to form a momnolayer of carboxylic functionality onto the surface of the substrates. Contract angle (CA), UV-vis spectra(UV), X-ray Photoelectron Spectroscopy(XPS), fluorescent microscope and titration demonstrated that carboxyl groups were successfully introduced onto the surfaces. The factors affect the reaction were investigated in details. The optimal process parameters are intensity of UV light at 8500μW/cm2 with 1% BOS in the mixture of AC/H2O=3/7.2. Under UV irradiation, BPO was used to bring benzene groups onto the surface of the polymer substrates. By sulfonation reaction, the sulfonic acid group was introduced to the substrates. Contract angle (CA), UV spectra(UV), X-ray Photoelectron Spectroscopy (XPS), fluorescent microscope and titration demonstrated that benzene and sulfonic acid groups were successfully introduced onto the surfaces. The optimal process parameters for photoreaction are as follows:injecting 18μl of 15% BPO solution in the mixture of ether and AC in the middle of two 4.5x4.5cm2 films, irradiated at 9500μW/cm2 for 18min. For sulfonic eaction, the optimal process parameters are reacted with 60%(wt%) sulfuric acid for 2h at 40℃.3. We further proposed a universal strategy to incorporate a broad range of functional groups onto the surface of organic polymeric substrates. Specifically, a phenol with para-substituent was used as reactant. Under UV irradiation, the triplet state of excited AC would either abstract surface-H to generate the carbon-centered surface radical or abstract H of phenol OH to produce the oxygen-centered phenoxy radicals (XRPhO·). The XRPhO·could predominately couple with the surface radicals to form stable surface C-OPhRX bond and thus resulted to bring desired group X to polymer surface with a R spacer. Contract angle (CA), Ultraviolet spectra (UV), X-ray Photoelectron Spectroscopy (XPS), fluorescent microscope, titration and dye experiences were taken to demonstrate that different groups, including sulfonic acid group (SO3H), amino groups (NH2), thiol (SH), amino acid and azobenzene, were successfully introduced onto the surfaces. With a photomask, the desired functional groups can be precisely implanted onto the substrates.