VOLUME 33, NO. 5, MAY, 1956
LOW-TEMPERATURE POLYMERIZATION
A Laboratory Demonstration I. T. JENKINS The Chemstrand Corporation, Decatur, Alabama
THEexperiment described in this paper is designed for a classroom discussion demonstration or as part of a laboratory course in polymerization reactions. The use of a low-temperature redox system for suspension polymerization of various monomers is demonstrated. The experiment can be safely used to illustrate certain polymerization stages. It consists of polymerization of vinyl type monomers that are partially water soluble in the presence of a persulfate type oxidizing agent (initiator) and titanous sulfate reducing agent (activator). Vinyl type monomers that can be readily polymerized include acrylonitrile, vinyl acetate, ethyl methacrylate, etc. From two to five minutes are required for the usual experiment; however, it can be modified to cover a longer period of time. The importance of redox-initiated polymerizations was discovered by accident in England and Germany about the same time. The discovery was made through the use of reducing agents to offset the inhibiting effect of oxygen. In this way the inhibition periods were eliminated and a t the same time the rate of polymerization was increased. Bacon1 carried out the earliest systematic study of the rates of polymerization of a number of monomers in aqueous solution. The work carried out in Germany during the war is summarized by Kern.2 Kolthoff and othersa. have made a fairly complete study of the efficiency of various types of redox systems. The experiment outlined here has added interest because it deals with ~olvmerizationa t a BACON, R., Trans. Faraday Soe., 42, 140 (1946). 'KERN,W., Makmmol. Chem., I,199 (1948). 'KOLTHOFF,I. M., AND A. I. MEDALIA,J . Polvmer Sci., 5, 391 (1950).
' KOLTHOFF, MEDALLA, AND M. YOUSE,J. Polmer Sci., 6, 93
(1951).
convenient temperature using materials that are relatively safe and easy to handle. This demonstration can be carried out on any desired scale from test tube up. Large amounts, however, should be cooled to prevent excessive temperature build-up. Test tuhe amounts are suggested. Materials. (1) Vinyl monomers: acrylonitrile, vinyl acetate, ethyl methacrylate, etc. It is not necessary to purify any of the above monomers. Caution should be exercised in handling any vinyl monomer, i. e., avoid inhaling and spilling on the skin. (2) Potassium persulfate: the desired quantity can be weighed directly into the reaction vessel or an aliquot taken from a standard solution. (3) Titanous sulfate: a 30 per cent solution is available commercially. The following procedure is satisfactory: Twenty grams of distilled water are measured into a test tube. Vinyl monomer is then added to give a ten-to-one water/ monomer ratio. Persulfate oxidizing agent (0.5 per cent based on monomer weight) is added by direct weighing or aliquot. The mixture is slowly but thoroughly stirred and titanous sulfate solution added dropwise until 0.5 per cent based on monomer weight has been introduced. Continuous stirring should be maintained. Within a few seconds after the addition of titanous sulfate, opalescence in the tuhe indicates that active polymerization has started. This is followed by the appearance of an emulsion. It breaks in a short time and polymer precipitates from the solution. Polymerization continues for a short period of time. The reaction can be stopped a t any time either by diluting with ice water or by the addition of an inhibitor such as hydroquinone.
