The disclosed subject matter relates to method for increasing the molecular weight of a polymer material during an additive manufacturing process. The method can comprise disposing a first layer of the polymer material at a target surface; exposing the first layer of the polymer material to an energy source for a sufficient period of time to sinter or melt and undergo a condensation reaction at least at a portion of the polymer material; controlling the condensation reaction to allow a desired increased number average molecular weight of the polymer material; and repeating the method steps to form an object in a layerwise fashion. Controlling the condensation reaction can comprise controlling and/or adjusting an energy 10 source-related parameter, a polymer-related parameter, a temperature related parameter, a vacuum related parameter, a process duration, a processing gas, an air flow volume and/or speed, or a combination thereof.