Consideration of Macromonomer Reactions in n-Butyl Acrylate Free Radical Polymerization

n‐Butyl acrylate (BA) starved‐feed solution semibatch experiments with varying final polymer content and monomer feed times were carried out at 138 °C. A full mechanistic model of the system implemented in Predici includes intermolecular chain transfer to polymer and macromonomer propagation as well as backbiting, chain scission, and midchain radical propagation and termination. The importance of macromonomer propagation under these conditions of industrial interest is illustrated by experiment and simulation, with the macromonomer reaction responsible for the significant increase in polymer weight‐average molecular weight ($\overline M _{\rm w}$) with time. Rate coefficients for macromonomer propagation (kmac) and β‐scission (kβ) of kmac/kp = 0.55 and kβ = 12 s−1 (with kp the rate coefficient for BA chain‐end propagation) provide a good representation of experimental $\overline M _{\rm w}$ and macromonomer end group data at 138 °C. The importance of butyl acrylate macromonomer propagation under conditions of industrial interest is illustrated by experiment and simulation, with the macromonomer reaction responsible for the significant increase in polymer weight‐average molecular weight with time. The reactivity of terminally unsaturated chains needs to be considered whenever their production rate (via β‐scission) is significant.