Preparation and characterization of polydimethylsiloxanes with narrow molecular weight distribution |
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Authors: | HJ Hölle BR Lehnen |
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Institution: | Institute of Physical Chemistry, Joh. Gutenberg-University, Sonderforschungsbereich “Makromoleküle”, Mainz/Darmstadt, West Germany |
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Abstract: | The preparation of polydimethylsiloxanes (PDMS) of narrow molecular weight distribution (MWD) by anionic polymerization of hexamethylcyclotrisiloxane (D3) in an improved polymerization apparatus is described. Using (CH3)2Si(OLi)2 as initiator and (CH3)3SiCl (TMCS) as terminating agent, polymers with only methyl groups were obtained with molecular weights ranging from 2 × 103 to 2 × 106. Kinetic investigations were performed only so far as necessary for controlling the polymerization under the chosen experimental conditions (solvent: n-hexane, solvating agent: hexamethylphosphortriamide (HMPT), polymerization temperature: 25°). The molecular weights of the polymers were determined by light-scattering and, after calibration, by viscometry and GPC. The non-uniformities of the samples with symmetrical MWD were estimated using the 4σ-method. The GPC apparatus had been calibrated with polystyrene and poly-α-methylstyrene samples of extremely small non-uniformity. |
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