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

摘要

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 280deg 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 ~(13)C NMR spectroscopy of the copolymer. Because of assignment problems for the E-(M)AA copolymers, the ~(13)C 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 240deg 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.