Effect of pressure on free‐radical copolymerization kinetics. I. A concept of additivity of partial molar volumes of activation

Abstract

SynopsisA short review of the effect of pressure on copolymerization kinetics shows the necessity of simple models for a better understanding of activation volumes. Therefore, a simple concept, possibly generally valid for free-radical polymerization, is proposed, based on the assumption that molar volumes of activation can be expressed as an addition of a characteristic radical and a monomer contribution, regardless of the combination involved. The scheme may facilitate the visualization of the transition state and contribute to the understanding of reaction mechanisms of radical polymerizations. Ethylene-vinyl acetate copolymerization at 62OC with tert -butyl alcohol as solvent agrees with the proposed scheme, appearing from the pressure independence of the product of reactivity ratios at the different levels (35,600, and 1200 kg/cm2). Implicitly it can be shown that an ethylene monomer contributes about 2 cm3/mole more to the activation volumes of the propagation reactions than does the vinyl acetate monomer, whereas for the radicals the difference of the respective contributions to the activation volumes is opposite in sign.

High-Pressure Kinetics of Oxidative Copolymerization of Styrene with -Methylstyrene

“…Although the rate of propagation increases considerably with pressure, r is less sensitive to pressure, since $\Delta V_{{\rm AOA}}^\# $ − $\Delta V_{{\rm AOS}}^\# $ (= 191 cm 3 /mol) is smaller than either $\Delta V_{{\rm AOA}}^\# $ or $\Delta V_{{\rm AOS}}^\# $ . Normally, the values24 of ($\Delta V_{{\rm AOA}}^\# $ − $\Delta V_{{\rm AOS}}^\# $ ) for vinyl copolymerization range from −1 to −5 cm 3 /mol. This rather high value of ($\Delta V_{{\rm AOA}}^\# $ − $\Delta V_{{\rm AOS}}^\# $ ) could be attributed to (i) the pressurizing fluid oxygen, which itself is a reactant in the copolymerization reaction, and (ii) the occurrence of side reactions chiefly, thermal degradation, chain‐transfer and chain unzipping reactions that the propagating macro‐radical undergoes during the process of copolymerization.…”

FTIR Study Measuring the Monomer Reactivity Ratios for Ethylene−Vinyl Acetate Polymerization in Supercritical CO2

“…As well, both r ethylene and r VAc were found to be weakly dependent on temperature from 60 to 135 °C by theoretical calculations. 10 For the effect of pressure, Van der Meer et al 32 found that the dependence was insignificant at 62 °C for the polymerization of ethylene and VAc under pressures between 3.4 and 58.8 MPa using tert-butyl alcohol as solvent. However, Erusalimskii et al 33 found that the reactivity ratios of ethylene and VAc both increased significantly at 60 °C when the pressure was increased from 10 to 120 MPa using ethylene as the monomer/solvent.…”

Kinetics of a pressure-induced polymerization reaction of cyanogen

“…of activation for cycloadditions are -10 cm3/mol. 18,19 Another interesting observation can be made by extrapolating these data to lower pressures and temperatures. Figure 8 is a plot ^of the measured fractional conversion to paracyanogen after 50 ^h at several pressures and temperatures.…”