disclosed is a tuneable microwave apparatus useful in carrying out chemical and physical processes on a sample , particularly including polymerization . the apparatus includes a cavity in which the sample is disposed , a microwave supply , microwave power meter and sensor , means for sensing the temperature in the cavity , means for varying the volume of the chamber within the cavity wherein the sample is disposed , means for measuring microwave reflection from the sample , and computer - controlled means operatively associated with the foregoing to vary the microwave power and the size of the chamber . openings are provided within the chamber to permit removal of vapor generated during expousre of the sample to the microwave radiation .