Kinetics of the Polymerization of Styrene by Friedel–Crafts Catalysts
ALTHOUGH the mechanisms and kinetics of the free-radical catalysed polymerization of styrene have been fairly extensively investigated1,2, the polymerization employing Friedel Crafts catalysts has received much less attention. Williams3 has investigated the stannic chloride catalysed polymerization of styrene in carbon tetrachloride solution and shown that the overall rate of monomer consumption can be represented by the expression: where m is initial styrene concentration, x is styrene consumed in time t, b is initial catalyst concentration. He has also shown that induction periods are present. We are studying the aluminium chloride catalysed polymerization of styrene in carbon tetrachloride solution from a kinetic point of view, and it is proposed to summarize here the principal conclusions reached to date.
SOME ASPECTS OF THE MECHANISM OF ADDITION POLYMERIZATION
It has long been recognized and is now generally accepted that, aa a rule, the process of addition polymerization differs fundamentally from condensation polymerization. The latter involves only types of reactions with which the chemist is quite familiar, with the important characteristic feature that the monomer molecules are so constructed that the condensation process is capable of indefinite repetition to build up a polymeric. product. The reaction proceeds in a regular, stepwise manner, yielding material of steadily increasing degree of polymerization throughout the course of the reaction. This mode of formation contrasts sharply with that involved in typical addition polymerizations, which are characterized by the fact that the polymer molecules first formed are essentially the same size aa the rest. In other words, the polymer molecules do not grow gradually, but each polymer molecule grows rapidly to a certain size and is then stabilized. This behavior, coupled with the uusceptibility of these reactions to catalysis and inhibition, supports the suggestion that these reactions are chain reactions involving activation of the monomer (initiation) followed by rapid successive additions of monomer molecules to the active intermediate (propagation) until the activated polymer becomes stabilized (cessation).
THE DECOMPOSITION OF BENZOYL PEROXIDE IN BENZENE
A kinetic study has been made of the decomposition of benzoyl peroxide in benzene. Kinetic data for this study have been obtained from three separate sets of measurements. Rate measurements from evolved carbon dioxide and direct iodometric measurements of peroxide are in good agreement. Alkali-metric determinations of the product, benzoic acid, have also been made during the course of the reaction.Gravimetric determinations show that the total evolved carbon dioxide from the reaction is a function of the temperature, and indicate that the mechanism involves two parallel fast reactions, one of which evolves one mole of carbon dioxide per mole of peroxide and the other two moles of carbon dioxide per mole of peroxide. The latter reaction predominates at higher temperatures.A kinetic analysis is included and provides for a slow reaction involving the rupture of the peroxide bond, followed by free radical reactions.The secondary free radical reactions would probably form hydrogen radicals, but there is eviden...