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Intramolecular chain transfer topolymer and subsequent propagationof tertiary radicals cause extensive branching in radical polymerizationof acrylic monomers. Studies in the literature have shown that undercontrolled radical polymerization conditions the extent of branchingis significantly reduced. There are two competing theories to explainthis effect. In one, the cause of reduced branching is attributedto a reduction in the number of backbiting events, and in the otherthat has been specifically applied to atom-transfer radical polymerization(ATRP), the cause is due to trapping of the tertiary radical by afast deactivation step. In this article we show that trapping of thetertiary radical is not the cause for the reduction in branching fraction.This is shown by the absence of the corresponding patched midchainbromide structure as revealed by quantitative 13C NMR andby the ability to chain extend from a poly(butyl acrylate-co-butyl 2-bromoacrylate) copolymer by ATRP. These resultsare complemented by quantum mechanical computations. [ABSTRACT FROM AUTHOR]