Lars Wittkowski

Acid-Induced Decomposition of Di-tert-butyl Peroxide in n-Heptane Solution up to High Temperatures and Pressures

The decomposition of di-feri-butyl peroxide (DTBP) in «-heptane with varying amounts of pivalic acid (PA) being added was studied via online FT-IR spectroscopy at elevated temperatures, 180 to 200°C, and pressures up to 2000 bar. A pronounced acid-induced DTBP decomposition is found without any PA consumption. Decomposition rates are adequately described by first-order kinetics. The pressure and the temperature dependence of acid-induced decomposition are investigated. The data suggest that the rate enhancement is due to the formation of a DTBP-PA complex. The acid-induced DTBP decomposition yields the same products as does the non-induced process (without acid being present). It thus appears justified to use the rate data observed for the model system DTBP-PA-n-heptane for the simulation of initiation rates in technical polymerizations where DTBP acts as the initiator and where acid is present, e.g. as a monomeric species.

High‐pressure free‐radical copolymerization of ethene with methacrylic acid and ethene with acrylic acid, 2. Ethene reactivity ratios

Full Paper: Free-radical copolymerizations of ethene (E) with methacrylic acid (MAA) and of E with acrylic acid (AA) were carried out in a continuously operated tank reactor at 2000 bar and temperatures up to 280°C. The (M)AA content of the polymer, F (M)AA , that may be reached by polymerization in homogeneous phase, e.g., at 260°C, is below 10 mol-% and the associated (M)AA content of the monomer mixture is below 1 mol-%. Under such conditions, the ethene and the comonomer reactivity ratios, r E and r (M)AA , respectively, can not be simultaneously derived by fitting the measured F (M)AA and f (M)AA data according to the classical procedure. With r (M)AA , however, being available from a proceding 13 C NMR study 1) , r E may be calculated from each pair of experimental F (M)AA and f (M)AA values. F (M)AA values are determined by means of elemental analysis of carbon and oxygen with consistency checks of copolymer composition being performed via FT-IR spectroscopy on polymeric films. f (M)AA is deduced from the measured monomer feed fluxes and from the amount and composition of the copolymer produced within given intervals of stationary polymerization. The r E data for the E/MAA and E/AA systems are presented and discussed. At identical polymerization pressure and temperature, the measured r E values, in addition, are very close to the ethene reactivity ratios that were recently measured for several E/(meth)acrylate copolymerizations. Arguments for this family-type behavior of r E are discussed.