Radical Trap-Assisted Atom Transfer Radical Coupling of Diblock Copolymers as a Method of Forming Triblock Copolymers

The formation of ABA‐type triblock copolymers is studied as a function of chain end structure of the second block (benzylic alkyl bromides compared to α‐bromo esters) and the inclusion of the radical trap 2‐methyl‐2‐nitrosopropane (MNP) in the coupling reaction. In the case of coupling poly(methyl methacrylate)‐block‐polystyrene (PMMA‐b‐PSBr), both traditional atom transfer radical coupling (ATRC) reactions and analogous radical trap‐assisted ATRC (RTA‐ATRC) reactions lead to ABA‐type triblock copolymers. Contrastively, coupling of polystyrene‐block‐poly(methyl acrylate) precursors is unsuccessful in ATRC reactions lacking the nitroso radical trap, yet forming high amounts of triblock in analogous RTA‐ATRC reactions, consistent with lower KATRP values of the chain end α‐bromo ester. Synthesis of the triblocks is also attempted using coupling reactions of dibrominated PS and monobrominated poly(methyl acrylate), relying on selective coupling to be successful. In the presence of the radical trap MNP, substantial coupling is observed with gel permeation chromatography data indicating the formation of the triblock. Traditional ATRC reactions performed in an analogous manner do not produce the triblock to an appreciable extent, with lowered extents of coupling overall. A combination of consecutive atom transfer radical polymerization reactions followed by atom transfer radical coupling (ATRC)‐type reactions is used to synthesize ABA triblock copolymers. The inclusion of a radical trap in the ATRC reaction phase allows for the deployment of brominated chain ends not compatible with traditional ATRC reactions, such as poly(acrylates).