Addition polymerization at constant temperature normally proceeds with reduction in the volume of the reactants. Polymerization shrinkage frequently diminishes the performance and durability of polymeric materials. In adhesives, coatings, and encapsulating materials, voids are created which serve as channels for the penetration of foreign substances and destructive agents. Matrix polymers in composite materials or surface coatings retract from reinforcing fibers and fillers, thereby reducing the bond area between them. In bulk polymers, shrinkage produces voids which reduce the strength and useful life of the end product, and molded products do not conform to molds or dies.