Process for the Degassing of Polymers of a beta-Lactone

1,197,366. Degassing #-lactone polyesters. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 26 Aug., 1968, No. 40714/68. Heading C3R. A polyester obtained by the melt polymerization of a #-lactone is freed from volatile impurities by subjecting the polyester in the liquid state to a pressure of at least 1¢ atmospheres (absolute) in contact with a space of lower pressure into which the volatile products enter. Preferably the process is effected in a single- or multiple-screw extruder in which (a) the depth or pitch of the screw(s) decreases in the direction of the discharge side and/or (b) a die with one or more small openings is provided at the discharge side. One or more venting sections to the atmosphere or a vacuum apparatus are attached to the extruder. The polyester may have been obtained by polymerization of the #-lactone in a wiped film reactor, a screw pump or a gear pump and may have been first degassed at atmospheric pressure and thereafter solidified. It may contain a stabilizer or a nucleating agent of which very many are specified. The example describes the degassing of poly-(pivalolactone).