Polystyrene (PSt) radicals and poly(methyl acrylate) (PMA) radicals, derived from their monobrominated precursors prepared by atom transfer radical polymerization (ATRP), were formed in the presence of the radical trap 2‐methyl‐2‐nitrosopropane (MNP), selectively forming PSt‐PMA diblock copolymers with an alkoxyamine at the junction between the block segments. This radical trap‐assisted, atom transfer radical coupling (RTA‐ATRC) was performed in a single pot at low temperature (35 °C), while analogous traditional ATRC reactions at this temperature, which lacked the radical trap, resulted in no observed coupling and the PStBr and PMABr precursors were simply recovered. Selective formation of the diblock under RTA‐ATRC conditions is consistent with the PStBr and PMABr having substantially different KATRP values, with PSt radicals initially being formed and trapped by the MNP and the PMA radicals being trapped by the in situ‐formed nitroxide end‐capped PSt. The midchain alkoxyamine functionality was confirmed by thermolysis of the diblock copolymer, resulting in recovery of the PSt segment and degradation of the PMA block at the relatively high temperatures (125 °C) required for thermal cleavage. A PSt‐PMA diblock formed by chain extenstion ATRP using PStBr as the macroinitiator (thus lacking the alkoxyamine between the PSt‐PMA segements) was inert to thermolysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3619–3626

Chromophore end‐labeled polystyrene is synthesized using nitroxide‐mediated polymerization (NMP) by decomposing 2‐2′‐azoisobutyronitrile (AIBN) or benzoyl peroxide (BPO) in the presence of fluorene or fluorene derivatives. End‐labeling is dependent on the thermally produced radical species selectively abstracting a hydrogen atom from the 9‐position of the fluorene species prior to initiation of styrene. From gel permeation chromatography (GPC) data and UV–Vis analysis, it is found that AIBN initiation, compared to BPO, leads to a more controlled polymerization system, producing polymers with predictable molecular weights, narrower polydispersity index (PDI) values (<1.3), and higher amounts of fluorene end‐labeling. In terms of the reaction parameters, no consistent trend is observed as a function of the timing of styrene's addition or the temperature at which the hydrogen abstraction phase is performed. Analysis of the chromophore content by UV–Vis spectroscopy demonstrated that the presence of bromine atoms on the 2‐ and 7‐position of the fluorene species leads to higher percent labeling of the chromophore species, presumably due to a more facile abstraction of the hydrogen at the 9‐position.