Influence of Solvent on Radical Trap-Assisted Dimerization and Cyclization of Polystyrene Radicals

The extent of dimerization in radical trap-assisted atom transfer radical coupling (RTA-ATRC) was studied as a function of solvent composition, with accelerated rates of coupling observed in solvent mixtures consisting of THF and hydrocarbons compared to either pure solvent. Aggregation of the nitroso radical trap was speculated to be responsible for the trend in coupling rates of RTA-ATRC reactions, with less polar solvents such as hydrocarbons favoring the active, monomeric form. The mixed solvent system of THF and cyclohexane was found to be transferrable to the synthesis of macrocyclic PS by intramolecular RTA-ATRC, with 50/50 (v/v) THF:cyclohexane reaction medium giving higher yields of cyclic product compared to reactions performed in the pure solvents.