High-pressure free-radical copolymerization of ethene-methacrylic acid andof ethene-acrylic acid, 1 (Meth)acrylic acid reactivity ratios

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 conten ts of the copolymerizing mixtures, below 0.5 mol-%, the resulting copolymer is not soluble in the reaction mixture at contents of acid units well abov e 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 copolym er compositions to the differential copolymerization equation is not applic able. 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 fr om relative amounts of (M)AA-centered triad sequences that are available fr om quantitative C-13 NMR spectroscopy of the copolymer. Because of assignme nt problems for the E-(M)AA copolymers, the C-13 NMR studies have been carr ied out on product samples after complete methyl-esterification to yield E- methyl(meth)acrylate copolymeric material. The resulting r(MAA) data are sl ightly above the r(AA) values. The numbers, e.g., for 240 degrees C and 200 0 bar, are: r(MAA) = 11 +/- 3 and r(AA) = 8 +/- 2. The r(MAA) and r(AA) val ues are compared with (meth)acrylate reactivity ratio data of several ethen e-(meth)acrylate high-pressure copolymerizations.