Termination Kinetics of Methyl Acrylate and Dodecyl Acrylate Free-Radical Homopolymerizations up to High Pressure

Abstract

The single pulse (SP) – pulsed laser polymerization (PLP) technique has been applied to measure kt /kp, the ratio of termination to propagation rate coefficients, for free-radical bulk homopolymerizations of methyl acrylate (MA) and dodecyl acrylate (DA) between 10 and 50°C at pressures from 10 to 2 500 bar. kt /kp is obtained from experimental monomer concentration vs. time traces that are determined via time-resolved (μs) near infrared monitoring of monomer conversion induced by single excimer laser pulses of about 20 ns width. With kp being known from PLP–SEC experiments, chain-length averaged kt is immediately obtained from kt /kp. For MA, kt remains constant up to about 15% monomer conversion and clearly decreases upon further polymerization. For DA at pressures of 100 bar and above, a plateau value of constant kt is observed up to about 60% monomer conversion whereas at lower pressure, e. g. at 10 bar, kt slightly increases in the very initial conversion region, but also exhibits a plateau kt value at moderate and high conversions. The occurrence of such plateau kt values and their pressure and temperature dependence are consistent with the view that plateau regions of kt are best understood in terms of diffusion control via segmental mobility.