The polymer product spectra of poly(butyl acrylate), polyBA, samples obtained by full conversion bulk polymerization in the temperature range of 60−140 °C in presence of the chain transfer agent (CTA) octylthiol is analyzed via electrospray ionization−mass spectrometry (ESI−MS) and quantitative 13C NMR. The combination of both these analytical techniques allows for very detailed information on the reaction products associated with the formation of midchain radicals to be obtained. At 60 °C, highly uniform polyBA is generated that consists of the structure alkyl−S−(BA)n−H. With increasing temperature, several other peaks emerge that can be assigned to either conventional termination product or to the three different β-scission products of the so-called midchain radicals that are known to be formed in acrylate polymerization via transfer to polymer reactions. Because of the formation of β-scission products that were formed by scission to either side of the radical functionality, intermolecular transfer to p...