A composition of matter includes a polymerizable mixture comprising 1 to 99 weight percent of a first monomer and an initiator therefor, the first monomer being one of 1) at least one free-radically polymerizable monomer or 2) at least one cyanate ester monomer, and 99 to 1 weight percent of a second monomer and an initiator therefor, the second monomer being the member of 1) or 2) that is not selected as the first monomer, wherein the curative for the cyanate ester is a transition metal-containing organometallic compound curing agent and the curative for the free-radically polymerizable monomer is a free-radical generating curing agent or a transition metal-containing organometallic compound. The polymeric mixtures are useful, for example, in applications requiring high performance, such as high temperature performance; in composites, particularly structural composites; structural adhesives; vibration damping materials; electronic applications such as printed wiring boards, semiconductor encapsulants and electronic adhesives; photoresists; injection molding and prepregs; protective coatings; tough self-supporting films; and high performance binders. In addition, a curable composition including (1) an ethylenically unsaturated monomer or (2) an ethylenically unsaturated monomer and a cyanate ester monomer, and certain organometallic neutral compounds is useful in the graphic arts.