Absolute electron spray ionization mass spectrometry (ESI-MS) data are reported, for the first time, over the complete chain length range for the synthesis of well-defined macromonomers (MMs) obtained via activation of bromine-capped poly(n-butyl acrylate) (0.1 mass %; solvent: anisole; 140 °C) with CuBr2/Me6TREN (Me6TREN: tris(2-(dimethylamino)ethyl)amine) and tin ethylhexanoate. These data are generated based on bivariate kinetic Monte Carlo simulations, tracking the chain lengths and the positions of radicals/characteristic groups along the chains (>100 reactions, 12 radical/dormant species types, and 7 characteristic end/mid-groups). Based on qualitative tuning to experimental data, migration is found to be 50 times slower than backbiting but 15 times faster than βC-scission, making it a dominant reaction. Benefiting from the absence of monomer, the chain transfer to polymer rate coefficient is assessed as 6 × 102 L mol-1 s-1 (140 °C). Model analysis shows that consecutive backbiting/migration/βC-scission leads to a favoring of MMs with even chain lengths and a hydrogen chain end over MMs with the nonreactive chain end originating from the initial dormant polymer. The obtained insights contribute to a better fundamental understanding of hydrogen abstractions in acrylate radical polymerization and open the path for a more detailed polymer product characterization in general.