Sources of Reactivity Data

Sources of Reactivity Data Several important sources of reactivity data are described in the following paragraphs. 

Definition of a method for obtaining samples for a source of kinetic data on this reactive extmsion must take several factors into account o Extremely small initiator to polymer ratios are involved, o The rate of dispersion of the initiator and the degree of dispersion obtained is likely itiq>ortant to both the homogeneity of the product and the efficiency of the initiator. 

Existing sources of incident data are not adequate to identify the number, severity, and causes of reactive incidents or to analyze incident frequency trends. 

Sources of incident data include a variety of public-domain databases, technical literature, and news accounts (Appendix E). Sources are categorized in Appendix E as reviewed only if incident data did not meet the CSB definition of reactive chemical incident (Section 1.3). 

Although the statistics provided in Section 3.3 concerning the number and severity of reactive incidents are grave, existing sources of incident data are inadequate to identify the number, severity, frequency, and causes of reactive incidents. The following limitations affected CSB analysis of incident data ... 

Solvent Composition. The use of reactivity data obtained from systems containing non-aqueous solvents is probably the major source of uncertainty in individual rate constants, and hence in the tabulated values of log(ks/kjj2o)-... 

Two particularly significant new sources of experimental data have been developed during the past 20 years or so. Solvents of low nucleophilicity were examined, for example, TFA (14), trifluoroethanol (TFE) (15), and hexafluoroisopropyl alcohol (HFIP) (16, 17). Also, the field of gas-phase ion chemistry has expanded rapidly, and data on intrinsic gas-phase reactivity provide important supporting evidence for our interpretations of the kinetic data. 

If only the reactivity ratios and reference are given, then, either no experimental data was given or the journal was not available and the Chemical Abstracts summary was the source of the data. If a Y or N (yes or no) appears in the conversion (Conv.) column then the reactivity ratios were recalculated. If a recalculation was performed but the 95% confidence columns (95%) are still left blank, it indicates that only two feed/polymer data pairs were available. In general, if there is a citation (Y or N) in die Conv. column but no reactivity ratios are shown in the reactivity ratio columns, the copolymerization did not follow the copolymerization equation (ionic or penultimate effects were prevalent). In a few cases, the data were too scattered to allow a reactivity ratio calculation. 

In the last column of the tables presenting detailed rate data are short descriptions of the experimental method used (1) reactor type, (2) source of reactive species, and (3) method of analysis of products and/or reaction rates. Though these are necessarily very rough descriptions, they do give some feeling for the nature of the data referenced. The abbreviations used are explained in Table 1. 

Dewar and his co-workers, as mentioned above, investigated the reactivities of a number of polycyclic aromatic compounds because such compounds could provide data especially suitable for comparison with theoretical predictions ( 7.2.3). This work was extended to include some compounds related to biphenyl. The results were obtained by successively compounding pairs of results from competitive nitrations to obtain a scale of reactivities relative to that of benzene. Because the compounds studied were very reactive, the concentrations of nitric acid used were relatively small, being o-i8 mol 1 in the comparison of benzene with naphthalene, 5 x io mol 1 when naphthalene and anthanthrene were compared, and 3 x io mol 1 in the experiments with diphenylamine and carbazole. The observed partial rate factors are collected in table 5.3. Use of the competitive method in these experiments makes them of little value as sources of information about the mechanisms of the substitutions which occurred this shortcoming is important because in the experiments fuming nitric acid was used, rather than nitric acid free of nitrous acid, and with the most reactive compounds this leads to a... 

The reactivity ratios of a copolymerization system are the fundamental parameters in terms of which the system is described. Since the copolymer composition equation relates the compositions of the product and the feedstock, it is clear that values of r can be evaluated from experimental data in which the corresponding compositions are measured. We shall consider this evaluation procedure in Sec. 7.7, where it will be found that this approach is not as free of ambiguity as might be desired. For now we shall simply assume that we know the desired r values for a system in fact, extensive tabulations of such values exist. An especially convenient source of this information is the Polymer Handbook (Ref. 4). Table 7.1 lists some typical r values at 60°C. 

The tendency toward alternation is not the only pattern in terms of which copolymerization can be discussed. The activities of radicals and monomers may also be examined as a source of insight into copolymer formation. The reactivity of radical 1 copolymerizing with monomer 2 is measured by the rate constant kj2. The absolute value of this constant can be determined from copolymerization data (rj) and studies yielding absolute homopolymerization constants (ku) ... 

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