A method of forming a three-dimensional object (e.g. comprised of polyurethane, polyurea, or copolymer thereof) is carried out by: (a) providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween; (b) filling the build region with a polymerizable liquid, the polymerizable liquid comprising a mixture of: (i) a light polymerizable liquid first component, and (ii) a second solidifiable component that is different from the first component; (c) irradiating the build region with light through the optically transparent member to form a solid blocked polymer scaffold and advancing the carrier away from the build surface to form a three-dimensional intermediate having the same shape as, or a shape to be imparted to, the three-dimensional object, with the intermediate containing the second solidifiable component; and then (d) contacting the three-dimensional intermediate to water to form the three-dimensional object.