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

Free-radical copolymerizations of ethylene (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 degrees C. The (M)AA c ontent of the polymer, F-(M)AA, that may be reached by polymerization in ho mogeneous phase, e.g., at 260 degrees C, is below 10 mol-% and the associat ed (M)AA content of the monomer mixture is below 1 mol-%. Under such condit ions, the ethene and the comonomer reactivity ratios, r(E) and r((M)AA), re spectively, 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), h owever, being available from a preceding C-13 NMR study(1)), r(E) may be ca lculated from each pair of experimental F-(M)AA and f((M)AA) values. F-(M)A A values are determined by means of elemental analysis of carbon and oxygen with consistency checks of copolymer composition brine performed via FT-IR spectroscopy on polymeric films. f((M)AA) is deduced from the measured mon omer feed fluxes and from the amount and composition of the copolymer produ ced within given intervals of stationary polymerization. The r(E) data for the E/MAA and E/AA systems are presented and discussed. At identical polyme rization pressure and temperature, the measured r(E) values of both systems agree within about +/-10%. The r(E) values, in addition, are very close to the ethene reactivity ratios that were recently measured for several E/(me th)acrylate copolymerizations. Arguments for this family-type behavior of r (E) are discussed.