High-pressure free-radical copolymerization of ethene and butyl methacrylate

The free-radical copolymerization of ethene (E) and butyl methacrylate (BMA ) is studied between 160 and 250 degrees C at 2000 bar. The reactions which were induced thermally are carried out in a continuously operated device a t total monomer conversions mostly below 1%. Monomer feed concentrations ar e obtained from measured mass fluxes. Copolymer composition is determined v ia elemental analysis. Reactivity ratio data, r(E) and r(BMA), are derived from non-linear least squares fitting of the monomer mixture and copolymer compositions. r(E) and r(BMA), e.g. at 190 degrees C and 2000 bar, are foun d to be 0,044 +/- 0,003 and 10,9 +/- 1.1. respectively. Simulation studies suggest that depropagation of BMA units has no major influence on the copol ymerization kinetics at the reaction conditions of the present study. The r (BMA) data are clearly different from r(A), the acrylate reactivity ratio f or E-methyl acrylate, E-butyl acrylate and E-2-ethylhexyl acrylate copolyme rizations. By adopting the simplifying terminal model, from reactivity rati os and from extrapolated home-propagation rate coefficients, cross-propagat ion rate coefficients are derived. The activation energy of such coefficien ts primarily reflects the type of monomer molecule whereas the free-radical chain-end influences the pre-exponential factor. A few experiments were ca rried out to estimate the pressure dependence of r(E). It turns out that th e arithmetic mean of home-propagation activation volumes provides a reasona ble estimate of the pressure dependence of cross-propagation. The available data for r(E) and r(BMA) allow to model monomer concentration vs. polymer composition behavior of free-radical E-BMA copolymerization at technically relevant temperatures and pressures.