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.
Lewis acid controlled regioselectivity in styrene hydrocyanation.
According to present knowledge, the Ni-catalyzed hydrocyanation of styrene leads predominantly to the branched product 2-phenylpropionitrile (98 %). We observed a dramatic inversion of the regioselectivity upon addition of a Lewis acid. Up to 83 % of the linear product 3-phenylpropionitrile was obtained by applying phosphite ligands in the presence of AlCl(3). The mechanism of the Ni-catalyzed reaction and the influence of additional Lewis acids have been investigated by means of deuterium labeling experiments, NMR studies, and DFT calculations. Furthermore, the behavior of different Lewis acids, such as CuCN, could be rationalized and predicted by DFT calculations.
The mechanism of polymerization reactions. I. The polymerization of styrene and methyl methacrylate
In the polymerization of styrene, methyl methacrylate, the acrylates including acrylic acid, vinyl acetate, methylvinyl-ketone, vinyl halides, indene and coumarone, the monovinyl compound of the formula CH2 : CH. R is capable of growing into long saturated molecules through the reaction of the olefinic link: n CH2 : CH R → (—CH2. CH— Ṙ ) n . The type of polymerization which is manifested by all these compounds is of a very simple character because only one reactant is involved and one, moreover, whose functionality is limited to two. This means that only straight chains can be produced, and with the simple monovinyl compounds no cross-linking is possible.