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Initiation by Protonic Acids

المؤلف:  A. Ravve

المصدر:  Principles of Polymer Chemistry

الجزء والصفحة:  156

2026-01-15

446

Initiation by Protonic Acids

The ability of a proton from a protonic acid to initiate a polymerization depends upon the nucleophilicity of the conjugate base, A [10, 11]. If it is low, protonation or cationization of the olefin is a step of initiation [12]:

In protonic acids, where the complex anion assists ion generation, the acid may be considered as providing its own counterion, A . When such counterions are highly nucleophilic, then complexing agents such as metal salts, or metal oxides have to be used to immobilize the anions. Such complexing agents are in effect coinitiators. Thus, the differences in activities of protonic acids are due to the quality of the corresponding anion or to its tendency to form chemical bonds with the carbon cation. If the anion is unable to form such bonds without extensive regrouping or decomposition, the addition of the proton is followed by polymerization. Should the reactivity of the anion be suppressed by solvation, the tendency to polymerize is enhanced. Consequently, the efficiencies of protonic acids depend very much upon the polarities of the media and upon the reaction conditions [12, 13]. Also, the stronger the protonic acid the higher the reaction rate and the resultant degree of polymerization [14]. Generally, hydrogen halide acids do not initiate polymerizations of alkyl-substituted olefins. They may, however, initiate polymerizations of aryl-substituted olefins and vinyl ethers in polar solvents. The same is true of sulfuric acid [15].