Compositions of hexamethoxymethyl melamine (HMMM)-ether polyol and acrylate can be cured by a hybrid polymerization comprising condensation polymerization and free-radical polymerization, in the presence of a latent acid catalyst at high temperature. It was found that the initiating free radical was derived from the decomposition of hydroperoxides, which was formed by the oxidation of active methylene groups catalyzed by HMMM. It was also found that strong acid could accelerate the free-radical polymerization in the hybrid system. To make the formulations more flexible, the activities of different types of methylene groups were investigated and two compounds with more active methylene groups and hydroxyl were synthesized, characterized, and used as crosslinker-initiators in the hybrid polymerization system.