Investigation Of Reaction Condition Of Nitroxide Radical Coupling Reaction And The Application In The Synthesis Of Block Copolymers

Block copolymers have attracted much attention for their potential excellent properties (e.g, their self-assembling behavior in solution, the morphologies of microdomain and applications in nano-field). Therefore, the synthesis of these copolymers with well-defined structure is an important work in polymer chemistry. Nowadays, with the development of controlling/"living" polymerization and "click" chemistry, it provides the mature and reliable technical support for synthesis of these copolymers. In particular, by means of the combination of different polymerizations with the coupling techniques, it is more effective to design and synthesize these copolymers with well-defined structure.Nitroxide radical coupling reaction was investigated and developed as a potential coupling technique in this field. The "living" radicals generated by atom transfer or single electron transfer mechanisms can be trapped by nitroxide stable radical (a radical capture agent) to form a new alkoxyamine bond. In this work, we investigated the mechanism and reaction condition of nitroxide radical coupling reaction. By means of combination of this coupling technology with other polymerizations (like living anionic polymerization, atom transfer radical polymerization and ring-opening polymerization) and coupling reaction (like click chemistry), a serial of block copolymers with different structures were synthesized. The essential results obtained are showed as follows:1. The effect of temperature, catalyst system and the structure of bromine connected groups on the nitroxide radical coupling (NRC) reaction was investigated. A series of polymers with different bromine connected groups as poly(tert-butyl acrylate) (PtBA-Br), polystyrene (PS-Br) and poly(methyl methacrylate) (PMMA-Br) are prepared by ATRP first, then the bromine-containing polymers were coupled with 2,2,6,6-tetramethylpiperidinyl-l-oxy-containing poly(ε-caprolactone) (PCL-TEMPO) in different catalyst systems as CuBr/PMDETA, Cu0/PMDETA and CuBr/Cu0/PMDETA in the temperature range from 90℃to 25℃. The result shows that the catalyst system of CuBr/Cu0/PMDETA is the best one for NRC reaction, in which the NRC reaction could be conducted in high efficiency in the wide temperature range from room temperature to high temperature. The efficiency of NRC reaction between PtBA-Br and PCL-TEMPO is more than 85% in the temperature range from 25～75℃, the efficiency between PS-Br and PCL-TEMPO is more than 90% from 25～90℃, and the efficiency between PMMA-Br and PCL-TEMPO is more than 90% only at the room temperature.2. A new strategy for one-pot synthesis of ABC type triblock copolymers via a combination of "click chemistry" and atom transfer nitroxide radical coupling (ATNRC) was suggested, and poly(tert-butyl acrylate)-block-polystyrene-block-poly (ethylene oxide) (PtBA-PS-PEO) and poly(tert-butyl acrylate)-block-polystyrene-block-poly(ε-caprolactone) (PtBA-PS-PCL) were successfully prepared by this method. The precursors with predetermined number average molecular weight and low polydispersity indices, such as PS with a-alkyne and co-bromine end groups, PtBA with azide end group, PEO and PCL with a 2,2,6,6-tetramethylpiperidine-l-oxyl end group, were directly prepared by living polymerization technique using the compounds with corresponding functional groups as initiators, and no further modification of the end groups were needed except P/BA-N3. The coupling reaction between precursors was carried out in the CuBr/PMDETA system with high efficiencies. All the copolymers and precursors were characterized by1H NMR、GPC、FT-IR and DSC in detail.3. A serial of ABC triblock copolymers as polyisoprene-block-polystyrene-block-poly(ethylene oxide) (PI-PS-PEO), polyisoprene-block-poly(tert-butyl acrylate)-block-poly(ethylene oxide) (PI-PtBA-PEO) and polyisoprene-block-poly(acrylic acide)-block-poly(ethylene oxide) (PI-PAA-PEO) were obtained by combination of anionic technique, atom transfer radical polymerization (ATRP) with single electron transfer nitroxide coupling (SETNRC) reaction. Anionic polymerization of isoprene followed by end-capping with ethylene oxide yielded hydroxyl terminated PI. After esterification, PI with Br end group was used as a macroinitiator to initiate the polymerization of St and tBA by ATRP, then trapped by 2,2,6,6-tetramethylpiperidine-1-oxyl group in poly(ethylene oxide) by single electron transfer nitroxide radical coupling (SETNRC) reaction rapidly with high efficiency in THF at room temperature. The effect of reaction time and polymer chain length on SETNRC reaction was discussed in detail. In the present of Cu0/Me6TREN, SETNRC between PI-PS-Br and PEO-TEMPO was carried out with the efficiency up to 91.6% in 2 hours. With the polymer chain length increasing, the efficiency decreased fleetly.