This application describes methods of forming an object. The methods described include forming a mixture with i) one or more primary diamines, ii) one or more polymerizable monomers, iii) a formaldehyde-type reagent, and iv) a polymerization initiator; forming a gel by heating the mixture to a temperature of at least 50° C.; and curing the one or more polymerizable monomers by activating the polymerization initiator. The one or more primary diamines may include one or more amine functional oligomers and/or primary aromatic diamine small molecules. The one or more polymerizable monomers may include styrenics, acrylates, methacrylates, vinyl esters, unsaturated polyesters, and derivatives thereof. The gel is a polyhemiaminal (PHA), a polyhexahydrotriazine (PHT), and/or a polyoctatriazacane (POTA) polymer, and curing of the gel forms an interpenetrating network of the PHA/PHT/POTA and the polymer formed from the polymerizable monomers.