Dimerization of Poly(methyl methacrylate) Chains Using Radical Trap-Assisted Atom Transfer Radical Coupling

End-brominated poly(methyl methacrylate) (PMMABr) was prepared by atom transfer radical polymerization (ATRP) and employed in a series of atom transfer radical coupling (ATRC) and radical trap-assisted ATRC (RTA-ATRG) reactions. When coupling reactions were performed in the absence of a nitroso radical trap-traditional ATRC condition-very little coupling of the PMMA chains was observed, consistent with disproportionation as the major termination pathway for two PMMA chain-end radicals in our reactions. When 2-methyl-2-nitrosopropane (MNP) was used as the radical trap, coupling of the PMMA chains in this attempted RTA-ATRC reaction was again unsuccessful, owing to capping of the PMMA chains with a bulky nitroxide and preventing further coupling. Analogous reactions performed using nitrosobenzene (NBz) as the radical trap showed significant dimerization, as observed by gel permeation chromatography (GPC) by a shift in the apparent molecular weight compared to the PMMABr precursors. The extent of coupling was found to depend on the concentrion of NBz compared to the PMMABr chain ends, as well as the temperature and time of the coupling reaction. To a lesser extent, the concentrations of copper(I) bromide (CuBr), nitrogen ligand (N,N,N\u27,N\u27,N -pentamethyldiethylenetriamine = PMDETA), and elemental copper (Cu) were also found to play a role in the success of the RTA-ATRC reaction. The highest levels of dimerization were observed when the coupling reaction was carried out at 80 degrees C for 0.5h, with ratio of 1:4:2.5:8:1 equiv of NBz: CuBr:Cu:PMDETA:PMMABr

Straightforward Preparation of Telechelic H-bonding Polymers From Difunctional Trithiocarbonates and Supramolecular Block Copolymers Thereof

International audienceWe report an original strategy toward the straightforward preparation of precisely defined telechelic H-bonding polymers and the generation of supramolecular block copolymers thereof. Making use of an alpha,omega-functionalized symmetrical trithiocarbonate bearing thymine groups at both chain ends, a series of heterocomplementary H-bonding polymers were effortlessly generated by RAFT polymerization in a one step process. The resulting telechelic macromolecules selectively interacted with heterocomplementary alpha-DAP-functionalized chains to afford supramolecular block copolymers in solution and in bulk. These self-assemblies were evidenced by (1)H NMR and rheological measurements. As a consequence of these associations, whereas non functional homopolymer blends tended to microphase separate as observed by AFM analysis, H-bonding homopolymer blends exhibited homogeneous microstructures in accord with the formation of supramolecular block copolymers promoting the stabilization of the interface between the polymers