Radical Addition-Coupling Reaction And Its Application In Svnthesis Of Polvmers With Different Structure

Radical addition reaction, such as radical addition polymerization, was widely used in polymer synthesis. Although radical-radical coupling reaction is a kind of rapid reaction with high efficiency, it is scarcely used in organic and polymer synthesis. The reason is that radicals can still undergo disproportionation and transfer reactions besides coupling reaction, which leads to the termination of coupling reactions. We reported a consecutive radical addition-coupling (RAC) reaction to double bonds compounds for preparation of polymers with different structure.The carbon-centered radical generated from a,ω-dibromo dibasic ester promoted by Cu(O)/ligand can be efficiently captured by C-nitroso compound, which results in nitroxide radical. The in-situ formed nitroxide radical immediately undergoes cross-coupling reaction with carbon-centered radical. The alternating copolymers with high molecular weight and unimodal molecular weight distribution can be synthesized by consecutive RAC. This polymerization method was named radical addition-coupling polymerization (RACP). The RACP of dimethyl2,13-dibromotetradecanedioate and2-methyl-2-nitrosopropane was monitored with gel permeation chromatograph (GPC) at various polymerization times. The evolution of molecular weight distribution clearly demonstrated that the polymerization follows the step-growth mechanism. The feed ratio, side-reactions, reaction temperature and monomer concentration, as well as monomer types, affect the results of RACP.The monomer can be well designed, and the polymerization is tolerated to various functional groups. A variety of symmetrical and asymmetrical a,ω-dibromo compounds containing ester, amide, ether or ethylene function groups were subjected to RACP, in order to prepare periodic copolymers possessing [AAB],[ABAC], and [ABCDCBAD] repeating structure. Since alkoxyamine groups are present along the backbone of the RACP product, it can be themodegraded to the precursor. The intermediate polymer prepared by RACP can also be applied as macroinitiator for atom transfer radical polymerization (ATRP) to synthesize triblock copolymer.Monobromo polystyrene was reacted with2-methyl-2-nitrosopropane by RAC reaction to produce the symmetrical polymer with doubled molecular weight (MW) and similar polydispersity index (PDI), which demonstrated that the coupling efficiency is close to100%.The reaction of a,ω-dibromo polymer with a stoichiometric amount of nitroso compounds paved the way to the synthesis of multisegmented polymers. Up to37poly(tery-butyl acrylate)(PtBA) segments constitutes the final product of the reaction of a,ω-dibromo PtBA with2-methyl-2-nitrosopropane, which is the highest block number for a multisegmented polymer prepared by radical coupling. A multiblock copolymer (PtBA-b-PS)m was successfully prepared when the same strategy was applied to a,ω-dibromo poly(tert-butyl acrylate)-b-polystyrene-b-poly(tert-butyl acrylate)(Br-PtBA-b-PS-b-PtBA-Br) precursors.Ethyl2-bromopropionate and (1-bromododecyl)benzene were reacted with1,1-diphenylethylene by radical addition cross-coupling (RACC) reaction. The bromined chain ends of well-defined polystyrene prepared using ATRP were successfully transformed into various functional end groups by RACC. Two different monobromo polymers (P1-Br and P2-Br) were reacted with Cu(0)/ligand in the presence of ethyl dithiobenzoate or1,1-diphenylethylene (X) and the block copolymer (P1-X-P2) can be obtained with high efficiency (up to95%), which cannot be prepared by normal atom transfer radical coupling (ATRC) of mixture of P1-Br and P2-Br.