SynopsisThe course of intermolecular reactions induced by peroxide decomposition in linear polyethylene has been determined and compared with similar reaction systems in which the substrate is a lowmolecular-weight alkane. Efficiency of intermolecular coupling is 40% for an alkane and 25-30% for the polymer system. Competing reactions, which reduce coupling efficiency, are mainly disproportionation of the initially formed radicals and to a minor extent further reactions involving the products from the peroxide decomposition. The low efficiencies found are similar to those well studied when initial radicals are produced by radiolysis in polymer and alkane systems.
retardation-namely, by the use of mixtures of normal and tertiary mercaptans and by an increase in the sodium hydroxide content of the system.The role of mercaptan in a recipe, such as given in Table I, is a dual one.It acts both as a chain initiator and as a chain transfer agent. The data in Table VI suggest that a DDM content of from 0.075 to 0.2 part should be sufficient to function as an initiator and that a tertiary mercaptan could then be used as modifier. This was verified in pilot plant experiments and found to be a practical method of overcoming retardation by ammonia. Measurements of Mooney viscosity of rubbers produced with ammoniaretarded recipes indicated that ammonia has little if any effect on the modifier activity of tertiary mercaptans. Thus, it appears that retardation affects initiation and not chain transfer.The effect of increasing the sodium hydroxide content of the recipe above that required to give a pH of 10 is interesting. Without ammonia (part A, Table VIII), the conversion is quite constant up to a sodium hydroxide content of 0.50 part. Some precoagulum appeared in the reaction vessel at higher conversions with the highest alkali concentration. In the presence of 200 p.p.m. ammonia, however, the increase in rate of conversion was very marked. At 16 hours, with 0.512 part sodium hydroxide, a conversion of 90.0% was obtained (Figure 4). This is about 15% higher than was expected without ammonia. The results indicate that, under these conditions, ammonia is a polymerization accelerator rather than a retarder. To verify this rather surprising observation the experiments reported in part C of Table VIII were conducted. The ammonia content was varied in two series of experiments, one with, and the other without, sodium hydroxide. The now familiar retardation was observed in the absence of sodium hydroxide but an increase in rate with increase of ammonia up to 200 p.p.m., followed by an extremely pronounced retardation, was obtained in the presence of sodium hydroxide. The data are plotted in Figure 5.
LITERATURE CITED(1) Baker, W. O., Bell Laboratories, to Office of Rubber Reserve, private communication, 1942. (2)
I he emulsion copolymerization of methyl isopropenyl ketone with butadiene has been investigated to determine the effects of emulsifier, modifier, temperature, ratio of monomers,
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