Abstract: A method of radically (co)polymerizing vinyl ester, vinyl halide, diene, acrylonitrile and .alpha.-olefin monomers, optionally with one or more ethylenically unsaturated monomers, with a polymerization initiator in the presence of an amount of at least one peroxyacid chain transfer agent effective to reduce the molecular weight of the (co)polymer in comparison to a (co)polymer made by the same process without chain transfer agent, is disclosed. Also disclosed are (co)polymers produced by the method and the use of particular peroxyacids as chain transfer agents in the radical polymerization of one or more ethylenically unsaturated monomers. These peroxyacids give a significant molecular weight reduction, and are useful with a variety of different polymerization initiators.

Abstract: This disclosure relates to novel peroxy esters carrying a t-alkenyl, e.g. 2-methyl-3-butene-2-yl, peroxy group. These peroxy esters have shorter half-life periods of decomposition and are more reactive polymerization initiators and unsaturated polyester resin curing agents than the corresponding prior art peroxy esters carrying a t-alkyl, e.g. t-amyl, peroxy group.