M. Buback, L. Wittkowski, St.A. Lehmann und F.-O. Mähling
High Pressure free-radical Copolymerization of Ethene-Methacrylic Acid and of Ethene-acrylic Acid - I. (Meth)acrylic Acid Reactivity Ratios
Macromol. Chem. Phys. 200, 1935-1941 (1999)

Free-radical copolymerizations of ethene (E)-methacrylic acid (MAA) and of E-acrylic acid (AA) have been carried out in a continuously operated device at 2000 bar and at temperatures between 240 and 280 degrees C. Even at low degrees of overall monomer conversion, below 1%, and at small (M)AA contents of the copolymerizing mixtures, below 0.5 mol-%, the resulting copolymer is not soluble in the reaction mixture at contents of acid units well above 6 mol-%. At such low (M)AA contents, the classical procedure of deriving both reactivity ratios, r(E) and r((M)AA), from fitting monomer and copolymer compositions to the differential copolymerization equation is not applicable. r(E) may be estimated by this procedure, but the composition range is too small to derive r((M)AA) Data for r((M)AA) may, however, be deduced from relative amounts of (M)AA-centered triad sequences that are available from quantitative C-13 NMR spectroscopy of the copolymer. Because of assignment problems for the E-(M)AA copolymers, the C-13 NMR studies have been carried out on product samples after complete methyl-esterification to yield E-methyl(meth)acrylate copolymeric material. The resulting r(MAA) data are slightly above the r(AA) values. The numbers, e.g., for 240 degrees C and 2000 bar, are: r(MAA) = 11 +/- 3 and r(AA) = 8 +/- 2. The r(MAA) and r(AA) values are compared with (meth)acrylate reactivity ratio data of several ethene-(meth)acrylate high-pressure copolymerizations.