Dow Corning S.a.

Brian R Trego

Hans-Juergen Wessely

Michelle M Berthet

The specification describes and claims filled compositions, e.g. moisture curable sealant compositions which comprise 100 parts by weight of polymeric material comprising a mixture and/or a reaction product of a polydiorganosiloxane having silicon-bonded hydroxyl groups with a compound containing silicon-bonded alkoxy or alkoxyalkoxy groups, 50 to 200 parts by weight of finely divided filler and an additive which is a reaction product of an organic amine, an oxide, hydroxide, carbonate, bicarbonate or a mixture thereof with a sulphonic acid of the formula RSO.sub.3 H in which R represents a hydrocarbon group which may be halogenated. The additive is preferably a reaction product of the sulphonic acid and an oxide, hydroxide, carbonate or bicarbonate of magnesium, or calcium and the acid is preferably one in which R represents a group R'C.sub.6 H.sub.4 wherein R' represents an alkyl group having 6 to 18 carbon atoms, for example dodecylbenzenesulphonic acid. The filler is preferably an oxide, hydroxide, carbonate or bicarbonate of calcium, magnesium, barium or zinc or a mixture thereof and has a particle size in the range 0.05 to 5 microns.

Filled compositions

The specification discloses a curable composition comprising 100 parts by weight of polysiloxane, 50 to 200 parts by weight of finely divided filler having an average particle size greater than 0.05 micron and not less than 0.5 parts by weight per 100 parts by weight of the filler of an additive which is a reaction product of an organic amine, or an oxide, hydroxide, carbonate, or bicarbonate or a mixture thereof with a sulphonic acid of the formula RSO.sub.3 H in which R represents a hydrocarbon group which may have halogen or amino substituents and which contains not less than six carbon atoms. Preferred additives are reaction products of the sulphonic acid and an oxide, hydroxide, carbonate or bicarbonate of sodium, magnesium, zinc, calcium, barium, aluminium or a mixture thereof. The group R of the sulphonic acid may be R'C.sub.6 H.sub.4 where R' represents an alkyl group having 6 to 18 carbon atoms and a preferred acid is dodecylbenzenesulphonic acid. The filler is preferably basic and may be oxide, hydroxide, carbonate or bicarbonate of calcium, magnesium, barium or zinc or a mixture thereof. Preferably the polysiloxane corresponds to a mixture and/or a reaction product of a polydiorganosiloxane HO(R'.sub.2 SiO).sub.x H with a compound containing silicon-bonded groups which are reactive therewith under the influence of moisture.

The specification discloses a method of preparing a polysiloxane by chain extension of a silicon compound having chain terminating units including a silicon-bonded hydroxyl group which comprises bringing about condensation of the silicon-bonded hydroxyl groups at a temperature of less than 50.degree. C. in presence of an acidic condensation catalyst of the formula RSO.sub.3 H and water, to an extent of less than 7 moles per mole of acidic condensation catalyst. The silicon compound may comprise a hydroxyl end-blocked polydimethylsiloxane having a viscosity at 25.degree. C. in the range 30 to 100,000 mm.sup.2 /s, and it may be polymerized to provide an .alpha.,.omega. dihydroxy polydimethylsiloxane having a viscosity in the range 1,000 mm.sup.2 /s to 100,000 mm.sup.2 /s or more. Preferred acidic condensation catalysts are those in which R is an alkyl group having a chain of 6 to 18 carbon atoms or a group R'C.sub.6 H.sub.4 where R' represents a hydrogen atom or an alkyl group having a chain of 6 to 18 carbon atoms. The preferred catalyst is dodecylbenzenesulphonic acid. A basic material may be added to the reaction mixture to neutralize said catalyst for example calcium carbonate or magnesium carbonate. The reaction mixture may be compounded to provide a curable composition, for example a moisture curable sealant composition comprising a mixture and/or a reaction product of the polysiloxane and a curative, a catalyst and finely divided filler.

Preparation of hydroxy terminated polysiloxanes

The specification describes a method of preparing a polysiloxane including at least one siloxane unit having a silicon-bonded group --OX in which X is a saturated or unsaturated hydrocarbon group, for example methyl, alkenyl or alkynyl. The method comprises bringing about chemical reaction between a polymer having at least one siloxane unit having a silicon-bonded hydroxyl group and an alcohol of the general formula HOX in presnece of an acidic condensation catalyst of the formula (i) RSO.sub.3 H in which R represents an alkyl, aryl or alkaryl group which may be halogenated at a temperature of less than 50.degree. C. under conditions to cause condensation reaction between hydroxyl groups of the siloxane units and the alcohol. Preferred polymers are polyorganosiloxanes comprising predominantly dimethyl siloxane units especially those prepared by polymerization of a precursor siloxane comprising at least two siloxane units which have a silicon-bonded hydroxyl group in presence of an acidic condensation catalyst of the formula (i). Preferably the group R of the acidic condensation catalyst is an alkyl group having a chain of 6 to 18 carbon atoms or a group R'C.sub.6 H.sub.4 where R' represents an alkyl group having 6 to 18 carbon atoms, for example dodecylbenzenesulphonic acid. Water may be present in the reaction mixture to an extent of not more than 7 moles per mole of acidic condensation catalyst. A basic material, e.g. calcium carbonate or magnesium carbonate may be added to the reaction mixture to neutralize the catalyst. Also disclosed are curable compositions including a polysiloxane made according to the invention.

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Dinas Powys, United Kingdom

Brian R Trego