Example 1
Production of an End-Equilibrated, Acetoxy-Terminated, Linear Polydimethylsiloxane
In a 1000 ml four-necked flask fitted with a KPG stirrer, an internal thermometer and a reflux cooler 77.3 g (0.757 mol) of acetic anhydride together with 732.8 g (1.98 mol) of decamethylcyclopentasiloxane (D5) and 24.3 g of acetic acid (3.0 percent by weight based on the total mass of the reactants) are initially charged with stirring and admixed with 1.62 g (0.88 ml) of trifluoromethanesulfonic acid (0.2 percent by mass based on the total batch) and swiftly heated to 150° C. The initially slightly cloudy reaction mixture is left at this temperature for 4 hours with continued stirring.
After cooling of the batch a colorless, clear, mobile liquid is isolated, whose 29Si-NMR spectrum demonstrates the presence of Si-acetoxy groups in a yield of about 93% based on employed acetic anhydride corresponding to an α,ω-diacetoxypolydimethylsiloxane having an average total chain length of about 14.
Conversion of the α,ω-Diacetoxypolydimethylsiloxane into the Corresponding α,ω-Diisopropoxypolydimethylsiloxane for Analytical Characterization
Immediately after the synthesis in a 250 ml four-necked round-bottomed flask fitted with a KPG stirrer, an internal thermometer and a reflux cooler 50.0 g of this trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxane are mixed together with 11.3 g of a molecular sieve-dried isopropanol by stirring at 22° C. Gaseous ammonia (NH3) is then introduced to the reaction mixture until alkaline reaction (moist universal indicator paper) and the mixture is then stirred at this temperature for a further 45 minutes. The precipitated salts are removed using a fluted filter.
A colorless, clear liquid is isolated, whose accompanying 29Si-NMR spectrum demonstrates the quantitative conversion of the α,ω-diacetoxypolydimethylsiloxane into an α,ω-diisopropoxypolydimethylsiloxane.
An aliquot of this α,ω-diisopropoxypolydimethylsiloxane is withdrawn and analysed by gas chromatography. The gas chromatogram shows the following contents (reported in percent by mass):
Example 2
a) Pretreatment of the Trifluoromethanesulfonic Acid-Acidified, End-Equilibrated α,ω-Diacetoxypolydimethylsiloxane
In a 250 ml four-necked flask fitted with a KPG stirrer, a contact thermometer and a gas introduction tube 100 g of the trifluoromethanesulfonic acid-acidified, end-equilibrated, acetoxy-terminated, linear polydimethylsiloxane produced in example 1 are subjected to a moderate ammonia stream at 22° C. for 30 minutes with stirring and a salt precipitation is observed. Once gas introduction is complete and the stirrer is switched off a sample of the clear supernatant is withdrawn and characterized using 29Si-NMR analysis. The integral intensity over the signal layers characteristic for short-chain α,ω-diacetoxysiloxanes have markedly reduced compared to the 29Si-NMR spectrum of the non-pretreated, end-equilibrated, acetoxy-terminated, linear polydimethylsiloxane and altogether represent only about 27% of the Si-bonded acetoxy groups originally appearing in this shift range in the starting spectrum. Calculating the average chain length based on the integral intensities of the new spectrum results in a length of about N=15. A pleated filter is used to separate the mixture from the precipitated salts and the α,ω-diacetoxypolydimethylsiloxane is isolated.
b) Reacting the α,ω-Diacetoxypolydimethylsiloxane Resulting from a) with Polyether Diol in the Presence of Ammonia as the Base
In a 250 ml four-necked flask fitted with a KPG stirrer, a contact thermometer and a water separator 56.1 g (0.02 mol) of a polyether diol constructed from ethylene oxide and propylene oxide units and having an average molar mass of about 2800 g/mol and a propylene oxide proportion of 40 percent by mass are admixed with 91.3 g of toluene and subjected to azeotropic drying at 120° C. After cooling 35.2 g (0.029 mol) of the α,ω-diacetoxypolydimethylsiloxane from step a) are added and then a moderate stream of dry ammonia is introduced at 22° C. over 3 hours with stirring. The resulting salts are subsequently separated using a filter press. The obtained clear filtrate is concentrated to about 75% of its original volume in a rotary evaporator at a bottom temperature of 150° C. and an applied auxiliary vacuum of <1 mbar and then mixed with 91.3 g of a butanol-started polyetherol consisting solely of propyleneoxy units having an average molar mass of 700 g/mol before distillation under the previously chosen conditions is continued until volatiles no longer pass over. Cooling affords a clear, colorless, high viscosity material whose 29Si-NMR spectrum verifies quantitative conversion.
