Abstract Mechanistic understanding of polymerization kinetics at elevated pressure requires quantitative, time‐resolved access to reaction dynamics. Herein, we developed an integrated framework coupling in situ high‐pressure ATR‐IR spectroscopy with a kinetic model based on the method of moments. Using ethylene/maleic anhydride (E (1)/MAH (2)) copolymerization as a benchmark, this platform enabled real‐time quantification of monomer consumption and in situ determination of copolymer composition, directly confirming strict alternating incorporation. The kinetic model showed excellent agreement with experiments, with deviations below 10%. Analysis revealed the cross‐propagation of MAH to ethylene‐terminated radicals ( k 12 ≈ 5.62 × 10 3 L mol −1 s −1 ) is over an order of magnitude faster than the reciprocal step ( k 21 ≈ 3.92 × 10 2 L mol −1 s −1 ), identifying the latter as rate‐determining. Extrapolation of the model guided the precise synthesis of a high‐molecular‐weight copolymer ( M w = 107 kDa). This work establishes a generalizable in situ platform for elucidating kinetics in complex polymerization systems at elevated pressure.
Yu et al. (Wed,) studied this question.