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Slow initiation relative to propagation has previously prevented photodimers of 9‐bromoanthracene or 9‐chloroanthracene, formed by [4 + 4] photocyclization reactions of the analogous 9‐haloanthracene, from being viable initiators in atom transfer radical polymerization (ATRP) reactions. The resulting polymers were found to possess high polydispersity index (PDI) values, much higher than expected number average molecular weight (Mn) values, with the reaction displaying a nonlinear relationship between monomer conversion and Mn. We report here the use of silane radical atom abstraction (SRAA) to create initiating bridgehead radicals in the presence of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) to mediate the polymerization. When using SRAA coupled with nitroxide mediated polymerization, a dramatic decrease in PDI values was observed compared with analogous ATRP reactions, with Mn values much closer to those anticipated based on monomer‐to‐initiator ratios. Analysis using UV‐Vis spectroscopy indicated only partial anthracene labeling (∼ 25%) on the polymers, consistent with thermolysis of the anthracene photodimer coupled with competition between initiation from the bridgehead photodimer radical and silane‐based radical. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6016–6022, 2008

No abstract

Slow initiation from the bridgehead radical in atom transfer radical polymerization (ATRP) reactions initiated by 9‐bromoanthracene photodimers leads to polymers' products possessing high PDI values and higher than expected $\overline M _{\rm n}$ values. We report here the effects of changing the ligand from N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) to the highly active tris[2‐(dimethylamino)ethyl]amine (Me6TREN) or tris[(2‐pyridyl)methyl]amine (TPMA) in an attempt to push the initial equilibrium further toward the initiating bridgehead radical. Overall, the ligand choice was found to add negligible control to the ATRP of styrene with any increase in the rate of initiation offset by an increase in the rate of propagation, leading to anthracene‐labeled polystyrene with similar PDI (≈1.6) and $\overline M _{\rm n}$ values regardless of the ligand choice.

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