ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Equations are derived for the time dependence of the extent of functional group reaction, pA, for catalyzed and uncatalyzed, irreversible, stoichiometric polycondensations of the AB and AA/BB type following pseudo-second-order and third-order chemical kinetics, resp., based on amount-of-substance concentrations. The resulting functions 1/(1 - pA) - f(t) for pseudo-second-order polycondensations and 1/(1 - pA)2 - f(t) for third-order polycondensations are predicted to be non-linear for low extents of reaction and practically linear for higher ones which agree with previous, hitherto unexplained experimental observations. The slope of the linear part does not give the true rate constant, contrary to traditional assumptions. The extent of non-linearity at small conversions and the deviation of the apparent rate constant from the true one depends on the initial amount of A groups, the molar mass of the leaving molecules, and the initial mass of the reaction mixture, if the molar concentrations are based on masses (“molalities”). The density of the leaving molecules enters, in addition, if the molar concentrations are volume related (“molarities”). The equations predict, for a given system, that the range of the non-linear region increases with decreasing rate constants, i.e., with decreasing temperature, in accordance with experimental observations.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1985.021860416
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