Kinetics of methacrylic acid polymerization in aqueous solution

Abstract

The kinetics and reaction mechanism of the catalytic polymerization of methacrylic acid were investigated in aqueous solution. At pH 3-5-3-6, the overall reaction was found to be of first order with respect t o the monomer and t o vary as the square root of the catalyst concentration. From the decrease in reaction velocity with increasing pH (up t o pH 6, a t which the reaction velocity is practically zero), i t was concluded, that, t o a first approximation, only the non-ionized monomer takes part in the reaction. The true velocity constant K O for undissociated monomer was found to be (1-84 j, 0.08) x I O -~ sec.-1 a t 75" C and for a catalyst concentration of 0.98 g./Ioo ml. The weight average degree of polymerization was determined a t different pH values. The overall activation energy was measured in the temperature range 55-75' C and found t o be 10.8 & 0.3 kcal./mole. Chloride ions exert a strong inhibitory effect on the polymerization a t pH values below 2-5. This effect is not shown by sulphate and nitrate ions. A mechanism for the reaction in agreement with the experimental data obtained has been suggested. * Part of a thesis submitted by G. Blauer t o the Senate of the Hebrew University, Jerusalem, in partial fulfilment of the requirements for the degree of Doctor of Philosophy.

Solvent Influence on Propagation Kinetics in Radical Polymerizations Studied by Pulsed Laser Initiated Polymerizations

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Free-Radical-Induced Chain Breakage and Depolymerization of Poly(methacrylic acid): Equilibrium Polymerization in Aqueous Solution at Room Temperature

“…Here an electrostatic potential barrier must be overcome, when a monomeric methacrylate anion approaches a terminal radical of a strongly charged poly-(methacrylic acid) chain. Low rate constants of propagation, as well as relatively high (as compared with acrylic acid) equilibrium monomer concentration allow us to explain the failure of the first attempts [112] to polymerize methacrylic acid in alkaline aqueous solution. Polymerization under these conditions is in fact possible, but its overall rate is lower by more than an order of magnitude than in acidic media, in which all species are protonated.…”