Polymer and polymer compositions
View Patent ↗A polyorganosiloxane polyoxyalkylene block copolymer having one or more polyorganosiloxane blocks and one or more polyoxyalkylene blocks linked to each other via divalent radicals which comprises at least two silicon-bonded alkoxy groups, preferably of the form PS (A PO) m (A PS) n , wherein PO is a polyoxyalkylene block, PS represents a polyorganosiloxane block, A is a divalent radical, m and n have independently a value of at least 1, comprising at least one alkoxy-substituted siloxane unit of the formula (R′) q (OR)—SiO 3−q/2 ′ , wherein R represents an alkyl group having 1 to 4 carbon atoms and each R′ represents an alkyl group having 1 to 6 carbon atoms, a phenyl group, or an alkoxy group of the formula —OR and q has a value of 0, 1 or 2, provided at least two silicon-bonded groups OR are present in the block copolymer. Also provided is a curable composition of the above which may comprise a condensation catalyst and a hydrophilic polymer network made from curing the composition in the presence of moisture, which exhibit interesting reversible hydrophilic properties.
1. A polymer composition curable to a water-insoluble hydrophilic polymer network, said composition comprising a polyorganosiloxane polyoxyalkylene block copolymer of the form
PS-(A-PO-A-PS) n , wherein
PS represents a polydimethylsiloxane block having from 4 to 40 siloxane units terminated with an alkoxy-substituted siloxane unit which is linked via oxygen to another silicon atom of the PS block and which has the formula
wherein R represents an alkyl group having 1 to 4 carbon atoms and each R′ represents an alkyl group having 1 to 6 carbon atoms, a phenyl group, or an alkoxy group of the formula —OR,
PO is a polyoxyalkylene block having the general formula —(C s H 2s O) t —where each s independently has a value of from 2 to 6 and t has a value of from 4 to 40, with the proviso that at least 50% of the polyoxyalkylene units in the polyoxyalkylene block are oxyethylene units,
A is a divalent radical having from 2 to 10 carbon atoms,
n has a value of at least 1, and
the molar ratio of oxyalkylene units to siloxane units in the polyorganosiloxane polyoxyalkylene block copolymer is in the range 0.05:1 to 0.5:1, and
a branched polyorganosiloxane cross-linking agent comprising one or more siloxane Q units of the formula (SiO 4/2 ), 0 to 250 D units of the formula R b 2 SiO 2/2 and M units of the formula R a 3 SiO 1/2 wherein the R a R b and R c substituents are selected from alkyl and alkoxy groups having 1 to 6 carbon atoms, at least three R a , R b and/or R c substituents being alkoxy units.
2. A curable polymer composition according to claim 1 , which further comprises a condensation catalyst selected from the group consisting of protic acids, Lewis acids, organic and inorganic bases, transition metal compounds, metal salts and organometallic complexes.
3. A curable polymer composition according to claim 2 , wherein the siloxane condensation catalyst comprises a compound of a transition metal selected from titanium, zirconium and hafnium.
4. A curable polymer composition according to claim 3 , wherein the catalyst is a titanium tetraalkoxide or chelated titanium alkoxide.
5. A curable polymer composition according to claim 2 , wherein the siloxane condensation catalyst comprises an organic compound of tin.
6. A curable polymer composition according to claim 1 , which further comprises a contain a filler selected from the group consisting of silica, fumed silica, fused silica, precipitated silica, barium sulphate, calcium sulphate, calcium carbonate, silicates, talc, feldspar, china clay, bentonite, and and solid silicone resins.
7. A curable polymer composition according to claim 1 , wherein the composition contains a siloxane condensation catalyst and in that the composition is packed in a moisture-proof container.