Cyclic distribution in dimethylsiloxanes

Gas–liquid chromatography was used to determine the amounts of cyclic molecules present in an equilibrium polymerization mixture of high polymer and cyclic dimethylsiloxane molecules. The study was carried out as a function of polymerization temperature. For [(CH 3 ) 2 SiO] 4–10 the equilibrium concentration is shown to be independent of temperature. The change in cyclic concentration as a function of n for [(CH 3 ) 2 SiO] 4–10 does not follow the theoretical Stockmayer‐Jacobson distribution. The concentrations of [(CH 3 ) 2 SiO] 3,4 are qualitatively predictable by the Stockmayer‐Jacobson theory and by the model proposed by Carmichael and Kinsinger. For [(CH 3 ) 2 SiO] 4 , K exp = 0.74 mole SiO/l. The model calculations yield 0.12 (Stockmayer‐Jacobson) and 0.36 Carmichael‐Kinsinger. For [(CH 3 ) 2 SiO] 3 , K exp = 0.024 mole SiO/l. Model calculations yield 0.017–0.16 (Stockmayer‐Jacobson) and 0.056–0.52 (Carmichael‐Kinsinger). The range of values rises because of uncertainty in the cyclic strain energy.