ANTISTRUCTURE AGENTS FOR CURABLE ORGANOPOLYSILOXANE COMPOSITIONS

摘要

1497455 Hydroxy - methoxy - trisiloxane mixtures; silicone rubber antistructure additives SWS SILICONES CORP 18 June 1975 [20 June 1974] 25939/75 Heading C3T An antistructure additive for silicone rubbers consists of hexamethyl-trisiloxane-1,5-diol and 1 - methoxy - hexamethyl - trisiloxane - 5 - ol, and optionally one or more linear polydimethylsiloxanes having 4-6 Si atoms and OH or OMe end-groups, or one or more cyclic polydimethylsiloxanes having 3-6 Si atoms, the mixture containing at least 5 wt. per cent of Sibound OH groups. Preferably it contains 5-11 wt. per cent of OH groups, 2-4 wt. per cent of OMe groups and has 2À5-7 OH groups per OMe group. The mixture is obtained by hydrolysis of hexamethyl cyclotrisiloxane in water/methanol at pH 2-7, preferably using 0À5-2 mols of water per mol of trisiloxane and 3-10 mols of methanol per mol of water or trisiloxane, whichever is present in the greater amount. In Examples 1 and 4 hexamethyl cyclotrisiloxane, methanol and water in 1 : 5 : 1 molar ratio are heated ipo 0À1 moles of formic acid for 1 hour at 58-65‹ C or refluxed (68À5‹ C) ipo 0À1 mole of acetic acid for 17 hours. Cold water is added, and the siloxane layer removed and extracted with 5% aqueous NaHCO 3 then 5% NaCl (Ex. 1) or five times with 5% NaCl. In Example 5 8 phr of the product of Ex. 1 are added to polydimethylsiloxane gum having 0À2 mol per cent MeViSiO units with 40 phr of fume silica and 1À4 phr of bis (2,4- dichlorobenzoyl) peroxide.