This invention discloses a process for producing a polymer by controlled polymerization which comprises polymerizing at least one monomer in the presence of a free radical controi agent of the stxuctural formula: (Z)-(R.sup.1).sub.n, wherein n represents an integer from 1 to about 6; wherein Z represents an aromatic or aliphatic moiety containing from 1 to about 20 carbon atoms; wherein R.sup.1 represents a moiety of the structural formula: ##STR00001## wherein R.sup.2 represents a moiety selected from the group consisting of alkyl groups, alkenyl groups, alkynyl groups, aryl groups. heteroaryl groups, and alkaryl groups; wherein the alky groups, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, and alkaryl groups can be substituted, unsubstituted, linear, branched or cyclic; and wherein Ar represents a p-alkoxyphenyl group having an alkoxy moiety that contains from 1 to 8 carbon atoms.