Cationic polymerisation rate constants

Thus, in Table 7.2 the polymerisation rate constants of PO and EO in anionic and in cationic catalysis are compared. 

Plesch, P. H. The Propagation Rate-Constants in Cationic Polymerisations. Vol. 8, pp. 137-154. Porod, G. Anwendung und Ergebnisse der Rontgenkleinwinkelstreuung in festen Hochpolymeren. Vol. 2, pp. 363-400. 

Plesch, P. H. The Propagation Rate-Constants in Cationic Polymerisations. Vol. 8, pp. 137-154. 

P. H. Plesch, The Propagation Rate-Constants of the Cationic Polymerisation of Alkenes, Progress in Reaction Kinetics, 1993, 18, 1. 

P. H. Plesch, The Propagation Rate-Constants of the Cationic Polymerisation of some Alkenes in Nitrobenzene - Part IV. Not the real kp, (Developments in the Theory of Cationic Polymerisation, Part XII), European Polym. J., 1993, 29, 121. 

In the context of cationic polymerisations it is convenient to take stability and reactivity not to be antonyms. We will take stability as a measure of the survival capacity of an ion in a particular environment, which could be measured by its half-life its antonyms are instability and lability. The reactivity, which can be measured by a rate-constant, has the antonym inertness-, both nouns can be qualified by the adjectives high or low . Within the present framework we are interested in the stability and the reactivity of organic cations from several points of view ... 

About Propagating Species and Propagation Rate-Constants in Cationic Polymerisations... 

For a physical chemist a reaction is not completely defined until its rate-constant has been measured, preferably over a range of temperatures and in a variety of solvents. Despite enormous efforts towards this goal, it has been achieved for only very few cationoid polymerisations, and with respect to the cationic systems the quest could not be considered ended until the discrepancy between the best values of kp and the rate-constants k2 for the attack of small cations on alkenes under non-polymerising conditions had been resolved. This was done in the last of this author s papers included here [154]. 

Once again, in this paper, the electrochemical aspects of the ions and their equilibria are prominent. The Fuoss-Kraus equation is applied to the pairing of the carbenium ions with the anions. It is shown that since an increase in the solvent polarity reduces the propagation rate-constant, the increase in rate in changing from a less polar to a more polar solvent must be due to the increase in polarity augmenting the ratio of the concentrations of unpaired to paired cations, (here called Up and in later papers yip) on the assumption that as in anionic polymerisations, the unpaired ions propagate faster than the paired ions. 

In the mid-1960s the first measurements of propagation rate-constants for unsaturated monomers became available, from polymerisations initiated by y-radiation [5]. The circumstances of these experiments were such that it was immediately clear that these very high rate constants (106 to 108 1 mol"1 s 1) were those of unpaired cations, kp. All these reactions were carried out with bulk monomer, i.e., the polymerisations occurred in a medium of very low polarity (e c. 2 for hydrocarbons and 5 to 6 for alkylvinylethers). Unfortunately, the y-radiation method is not applicable to polymerisations in solution, especially in polar (usually alkyl halide) solvents. The methods which have been used to... 

Propagation Rate-Constants in the Cationic Polymerisation of Alkenes (1984)... 

No doubt some will say What - again , since I first reviewed this subject of propagation rate-constants in cationic polymerisations in 1971 [1] and discussed it briefly in 1973 [2]. Of the other reviews which have dealt with this subject thereafter, that by D. J. Dunn... 

Since all three types of rate-constants are essentially affected by the same factors - although in a different way - it may be useful as a background to the following discussion to specify briefly the principal variables which are now known to affect the phenomenology of any cationic polymerisation these include the following ... 

Several workers have attempted to use the common ion technique to depress [Pn+] and thus to achieve a monoeidic Pn+A system, as was done so successfully for anionic systems. However, because generally the solvents used for cationic polymerisations are much more polar, the KD of the chain-carriers and of the common-ion salts are considerably greater than in the anionic systems. Therefore the electro-chemical situation is likely to be complicated by triple ion formation and the effects of ionic strength on the KD and on the rate-constants, so that any results obtained by extrapolations to infinite ionic strength need to be scrutinised most carefully. 

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