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.
Olefin Polymerizations and Copolymerizations with Aluminum Alkyl-Cocatalyst Systems. IV. The Polymerization of Styrene
Abstract The mechanism of cationic styrene polymerization with the AlEt2Cl/RCl (R = alkyl or aryl) catalyst-cocatalyst system has been investigated. Polymerization initiation, i.e., cocatalyst efficiency, is apparently determined by the relative stability and/or concentration of the initiating carbonium ions provided by the cocatalyst RCl. Whereas n-butyl, isopropyl, and sec-butyl chlorides exhibit low cocatalyst efficiencies because of low ion concentrations, triphenyl methyl chloride is a poor cocatalyst because the stability of the derivative triphenyl methyl ion is much higher than that of the propagating styryl ion. Alkyl halides that give ions of intermediate stability are efficient cocatalysts. Isobutyl chloride and benzyl chloride seem to be exceptions and the reasons for this are discussed. A general simple scheme of the polymerization mechanism is proposed.
RECENT RESULTS ON THE KINETICS AND ELEMENTARY STEPS OF POLYREACTIONS
If one wants to follow quantitatively the course of a polymerization or polycondensation reaction, one has first of all to carry out certain measurements. Usually the following quantities are recorded : The total amount of monomer which has been converted into polymer (dimer and higher) as a function of time, nature of catalyst and solvent, monomer concentration and temperature. This corresponds to the weight of polymer (of all degrees of polymerization) formed at any infitant. Particularly important is the initial rate with which the polymer is produced (the monomer disappears) , because, in t,he early stsages of the reaction, the conditions are usually not yet too complicated and can, with some success, be expressed by appropriate rate equations. There are many experimental methods available to determine the rate of polymer formation in each individual case,” 2 , but it would lead us too far afield to enumerate them in this article. The number or weight average degree of polymerization of the polymer produced as a function of time and of the other experimental parameters mentioned above, such as amount and nature of solvent, concentration and character of catalyst or inhibitor, temperature, etc. It is well known that a reliable determination of these quantities at present still meets with considerable uncertainties and difFicu1tie^,^-^ but it seems that osmotic pressure memurements in very dilute solution provide a comparatively safe way to secure the number average for the degree of polymerization, if the membrane is such that it does not let too much of the lower molecular weight