Thermal Degradation of Polymethyl Methacrylates


(3) J.H. Baxendale, S. Bywater and M. G. Evans, Trane. Faraday. Soe., 42, 675 (1946). (4) J. . Baxendale, S. Bywater and M. G. Evans, J. Polymer Sci.,...
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Dee., 1953

THERMAL DEGRADATION OF POLYMETHYL METHACRYLATES

879

The present study shows clearly the experimental difficulties in obtaining true values of formation constants of metal complexes even in apparently simple systems. The interference of the MeY-Me and similar ion pairs is to be expected in all cases where polyvalent cations and (or) anions are presOur values 1.78 2.2 300 340 140 1.1 ent in a complex equilibrium. Although the inSohwaraenbach values’ 1.2 1.5 80 170 110 2.1 fluence of those ion pairs on the complex equilibria necessary, by similar extrapolation. The possible may be quite large, it has been, up to now, considerror of those “thermodynamic” constants is, of ered only in a few cases (see ref. 21). Still greater course, greater than the error of the “concentra- may be the interference of the “neutral” electrotion” constants given in Table I1 and valid at lytes as potassium chloride and nitrate and espe0.10 m total nitrate concentration only. This is cially of complexing admixtures as acetates, phosetc., commonly used as buffer solutions. essentially due to the nature of the approximations phates, Only few formation constants of weak ion pairs are introduced in eq. 13. However, even for systems known exactly. Their numerical application to exshowing a great variation of Kel with total nitrate perimental data obtained at high ionic strengths concentration (systems involving lead) the values (0.1 up to l), cambe, with our present knowledge of given in Table I11 should be correct within *25%. For comparison Table I11 gives also equilibrium thermodynamics of concentrated solutions, only constants as calculated from the concentration very approximate. Measurements a t low ionic formation constants of the individual complexes strengths ( p