Ethylene, propylene, and styrene oxides have been polymerized by a range of metal halide catalysts, high molecular weight products being obtained from the two firstnamed. The limited quantitative evidence presented is consistent with the view that these polymerizations proceed by a coordinate propagation mechanism. The effective catalyst for this stage is essentially a metal alkoxide, formed in an initial cationic polymerization in which a small number of monomer units are attached to the metal atom. The propylene oxide polymers generally contain a fraction of crystalline material, but the proportion of this can be reduced practically to zero (with FeCl3 catalysis) by careful exclusion of water.
The existence of S-H * --S hydrogen bonds has been confirmed by infrared spectroscopy of phosphinodithioic acids. A comparison with thiocarboxylic acids suggests that the highly polar P S bonds and S-H bonds are responsible for the high degree of association. THERE is little evidence for the existence of S-H * S hydrogen bonds, although the corresponding s-H * * * 0 and S-H -* -N bonds are fairly common.l Recently, however, Menefee, Alford, and Scott in a study of the infrared spectra of two phosphorodithioic acids, (MeO),PS*SH and (EtO),PS*SH, interpreted the shift in the vSH frequency on passing from the pure liquid to dilute solution in carbon tetrachloride as being due to the Bellamy, " Infra-red Spectra of Complex Molecules," Methuen, London, 1954, p. 289.
The polymerization of propylene oxide at 80°C. catalyzed by aluminium trimethyl has been studied kinetically, using a dilatometric method combined with a high‐vacuum technique to exclude adventitious water and oxygen. Both in bulk and in methylene chloride solution, the reaction is not stereospecific in the absence of oxygen or moisture. When catalytic quantities of water are present, approximately 5% of the product is crystallizable. The reaction shows first‐order dependence on monomer concentration and a complex variation with water and catalyst concentrations, the critical factor being their molar ratio. In bulk, the reaction goes to completion smoothyl, giving maximum molecular weights of approximately 300,000 for the crystalline polymer and 20,000 for the amorphous product. In solution, the reaction involves two distinct stages: in the first, a rapid reaction up to a conversion determined by the water/catalyst ratio is followed by a much slower rate; only the second slow stage appears to produce crystallizable polymer. At critical ratios of the water/catalyst concentrations, the system becomes heterogeneous and the initial rate falls sharply. In the bulk reaction, these two effects occur simultaneously at a ratio [H2O]/[Al2Me6] = 3:1. In solution, the rate falls at a ratio 0.4:1, and the reaction mixture becomes heterogeneous at a 1:1 ratio. Mechanisms are proposed for the various stages of the reaction, and a bridge‐bonded hydrolytic complex is suggested as the active catalyst for the stereospecific stage.
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