Efficient metal‐free coupling of polystyrene chains using silane radical atom abstraction

Chain extension and block copolymer synthesis using silane radical atom abstraction coupled with nitroxide mediated polymerization

“…This appears to be inconsistent with our previously reported results that show near-quantitative activation and coupling of PStBr chains at this temperature (Scheme 1) [15]. In order to probe this discrepancy, reactions were performed in the presence of all reactants except PStBr, to observe if the t-butoxy radicals or tris(trimethylsilyl)silane radicals were alone capable of initiating PSt chains.…”

“…Previous research in our group has shown that SRAA is capable of near-quantitative activation of PStBr chains, as verified by a doubling of M n values and similarly low PDI values after a radicaleradical coupling reaction had occurred (Scheme 1) [15]. In this study, PStBr was activated by SRAA in the presence of a second monomer and TEMPO at temperatures suitable for SRAA but not NMP, after which the reaction temperature was elevated to allow NMP to occur.…”

“…The title compound was synthesized using procedures adapted from literature [21], and its synthesis was previously reported by our group [15]. Briefly, t-butyl bromide (4.0 mL, 35 mmol) and ether (4.0 mL) were added to a clean, dry flask and stirred at room temperature.…”

“…In the initial reactions, styrene (St) was used as the second monomer, and the components (PStBr, St, TEMPO, tBHN, and TTMSS) were added together in a 5 mL hexanes/benzene (3:2 v/v) solution and allowed to react initially at 80 C, before being placed in a separate oil bath held at 130 C. We [15] and others [14] have previously had success using this mixed solvent system in reactions between silane radicals and halogens. A typical GPC trace of polymer formed by the SRAA/NMP combination and the corresponding PStBr precursor is shown in Fig.…”

“…Our group has recently reported silane radical atom abstraction (SRAA) as a means to activate brominated polystyrene (PStBr), forming polymer radicals that undergo radicaleradical coupling reactions to give polystyrene (PSt) of controllable molecular weight values and low polydispersity indices (PDIs) (Scheme 1) [15]. Activation by silane radicals, in contrast to activation by atom transfer to a metaleligand catalyst, does not require the addition of metals to the reaction mixture.…”