Applications Of Single Electron Transfer And Nitroxide Radical Coupling Techniques In Polymer Synthesis

Synthesis of polymers with specific topologies is a hot spot in macromolecular synthesis chemistry all the time, for these novel molecular structures would arouse new discoveries in the fields of physical and chemical property, phase separation behavior, assembly, etc. Conventional synthetic tools could not suffice the gradually heavy demand from new polymer synthesis, which therefore raised new requests for polymerization and coupling techniques. Single electron transfer living radical polymerization (SET-LRP) is a hot controlled/"living" radical polymerization and has been rapidly developed for its ultra-fastness, ambient condition, monomer diversity and well controlling on super high molecular weight. For coupling strategies, beside the famous "click" chemistry, high efficient nitroxide radical coupling (NRC) reaction based on stable nitroxides capturing living radicals attracts a lot of attention, since the reactive groups are selective, effective and could be easily stored. This work is the very application based on these 2 strategies. The results obtained are showed as follows:1. Synthesize telechelic a,ω-alkyne PMMA(Alkyne-PMMA-Alkyne) via single electron transfer radical coupling reaction (SETRC). Firstly, we designed initiator propargyl 2-bomoisobutyrate (PgBiB) containing target functional alkyne groups, initiated ATRP reaction of methyl methacrylate from it and obtained a-alkyne-ω-Br PMMA(alkyne-PMMA-Br). Then, under the condition with Cu(0)/PMDETA as catalyst, THF as solvent and room temperature, alkyne-PMMA-Br produced PMMA chain radicals by the SET mechanism, and then the radicals underwent radical couplings, forming the carbon-carbon bond connected product a-alkyne-ω-alkyne PMMA(alkyne-PMMA-alkyne). Obtained coupling efficiency was all high (>90%) when changing molecular weight of the precursors. At the same time, we investigated the dependence of efficiency on time and found that coupling efficiency increased with time extending and got to more than 90% after 24 h. Measurements of 1H NMR, SEC, FT-IR were used to characterize intermediate product and final product in detail.2. Synthesize amphiphilic H-shaped A3BA3 copolymer [poly(ethylene oxide)]3-polystyrene-[poly(ethylene oxide)]3 (PEO3-PS-PEO3) via 2-methyl-2-nitrosopropane (MNP) induced single electron transfer nitroxide radical coupling reaction (SETNRC).3-arm PEO (PEO3-OH) having a hydroxyl group at the connecting center was transformed intro the macroinitiator (PEO3-Br) by bromination of the hydroxyl with 2-bromoisobutyryl bromide. Coupling precursor PEO3-PS-Br was then obtained by initiating ATRP polymerization of styrene on PEO3-Br. In the system with Cu(I)Br/Me6TREN as catalyst and DMSO as solvent, the bromide at PS chain end was sequentially transformed into carbon-centered radical and then nitroxide radical by reaction with MNP, and simultaneously, macronitroxide capturing macroradical produced the H-shaped PEO3-PS-PEO3 copolymer by SETNRC in one-pot. Comparing results at 10,60,360 min, we found that coupling efficiency increased with time extending and 360 min having the same efficiency as 60 min meant the reaction was quickly finished in only 1 hour. Measurements of 1H NMR, SEC, FT-IR were used to characterize intermediate product and final product in detail.