In situ chemical modification during additive manufacturing

An additive manufacturing method comprising:

• depositing a first build material from a first deposition nozzle to a surface to form a first layer having a first layer depth, the depositing taking place in a deposition chamber that contains an atmosphere comprising a pressure that is increased above atmospheric pressure by about 7 kilopascal or more;
• contacting the first layer with a reactive agent, wherein upon the contact, the reactive agent causes a modification to a chemical structure of a polymer of the first build material, the modification being carried out from a surface of the first layer to a depth of about 300 nm or more of the first layer depth, the modification extending through only a portion of the first layer such that the first layer exhibits a gradation of the modification across the first layer depth, wherein the reactive agent comprises a gas phase reactive agent.