Abstract: This invention relates to the use of copper and cobalt ions to control molecular weight in the aqueous polymerization of vinyl monomers. Incorporating catalytic amounts, generally from 1 to about 300 ppm of copper or cobalt ions, in aqueous polymerization reactions initiated with peroxides, preferably with partial neutralization of the monomers, provides for molecular weight control of the resulting polymers.

Abstract: The present invention provides a method of reducing the levels of protoanemonin present in aqueous monomer solutions by adding an effective amount of one or more para-phenylenediamines having the formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different radical selected from hydrogen, methyl, ethyl, n-propyl, iso-propyl, phenyl or methoxyphenyl with the proviso that at least one of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is hydrogen; R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are the same or different radical selected from hydrogen, methyl, ethyl, n-propyl, iso-propyl, methoxy or ethoxy with the proviso that at least one of R.sub.5, R.sub.6, R.sub.7 and R.sub.8 is hydrogen; and salts thereof.