초록 ▼

This invention relates to viscoelastic silicone rubber compositions that are the products of the reaction of: (a) a silanol-terminated polyorganosiloxane base; (b) a boron-containing crosslinking agent; and (c) a siloxane bond-forming crosslinking agent. In a viscoelastic silicone rubber composition

This invention relates to viscoelastic silicone rubber compositions that are the products of the reaction of: (a) a silanol-terminated polyorganosiloxane base; (b) a boron-containing crosslinking agent; and (c) a siloxane bond-forming crosslinking agent. In a viscoelastic silicone rubber composition of the invention some of the crosslinks, the siloxane crosslinks, are permanent and others of the crosslinks, the boron-containing crosslinks, are temporary. Because a fraction of its crosslinks can come apart and then reform, a viscoelastic silicone rubber composition of the invention can relax stress in response to strain and thus adapt to new shapes. The composition has sufficient permanent crosslinks, however, to establish a permanent equilibrium shape to which the composition will eventually return when not subject to any imposed stress. A viscoelastic silicone rubber composition has sufficient temporary crosslinks to give the composition a stiffness that is greater on short timescales than it is on longer timescales.

대표청구항 ▼

1. A viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polyorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition

1. A viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polyorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shape,wherein the boron-containing cross/inking agent is present in an amount sufficient to, when subject to a strain, give the viscoelastic silicone rubber composition a stiffness that is greater on short timescales than it is on longer timescales. 2. A viscoelastic silicone rubber composition of claim 1, further comprising a filler. 3. A viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polyorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shape, wherein:the silanol-terminated polyorganosiloxane base comprises silanol-terminated polyorganosiloxane polymers of formula (I) having a molecular weight ranging from 400 to 50,000 Dalton and a viscosity ranging from 10 to 10,000 cSt and preferably from about 15 to 1,000 cSt and wherein “m” is 1 or greater and represents the number of the repeating units in parentheses to give the molecular weight of the particular polymer; the boron-containing crosslinking agent is selected from boric acid, trimethyl borate, triethyl borate, and tri-isopropyl borate; andthe siloxane bond-forming crosslinking agent is selected from a polydiethoxysilane, polydimethoxysilane, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, and methyltriethoxysilane. 4. The viscoelastic silicone rubber composition of claim 3, further comprising a filler. 5. The viscoelastic silicone rubber composition of claim 4 wherein the filler is silica, clay particles, glass beads, microspheres, or a mixture thereof. 6. A viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shape, wherein:the boron-containing crosslinking agent is present in an amount ranging from 20% to 200% saturation; andthe siloxane bond-forming crosslinking agent is present in an amount ranging from 20% to 100% saturation. 7. The viscoelastic silicone rubber composition of claim 1, wherein the composition's Shore Hardness at t=0 is greater than composition's Shore Hardness at t=60 seconds. 8. A viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polyorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shape, wherein the rubber composition is a foamed rubber composition. 9. A method of making a viscoelastic silicone rubber composition comprising the steps of: reacting a silanol-terminated polyorganosiloxane base with a boron-containing crosslinking agent under conditions to produce a borosilicone compound,adding a siloxane bond-forming crosslinking agent, a catalyst, an optional filler, and an optional foaming agent to the borosilicone compound to form a mixture; andcuring the mixture under conditions sufficient to form a viscoelastic silicone rubber composition,wherein the siloxane bond-forming crosslinking agent is present in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shape, and wherein the boron-containing cross/inking agent is present in an amount sufficient to, when subject to a strain, give the viscoelastic silicone rubber composition a stiffness that is greater on short timescales than it is on longer timescales. 10. The method of claim 9, further comprising the step of: mixing the silanol-terminated polyorganosiloxane base with a filler prior to reaction with a boron-containing crosslinking agent. 11. The method of claim 9 or 10, further comprising, prior to or during the curing step, the steps of: Injecting a pressurized gas into the mixture; andreleasing the pressure to form a foamed viscoelastic silicone rubber composition. 12. The method of claim 9 or 10, further comprising, prior to the curing step, the step of: placing the mixture in a mold. 13. A method of making a viscoelastic silicone rubber composition comprising the steps of: combining a silanol-terminated polyorganosiloxane base with a siloxane bond-forming crosslinking agent, a catalyst, an optional filler, and an optional foaming agent to form a mixture;adding a boron-containing crosslinking agent to the mixture; andcuring the mixture under conditions sufficient to form a viscoelastic silicone rubber composition. 14. The method of claim 13, further comprising the step of: mixing the silanol-terminated polyorganosiloxane base with a filler prior to the combining step. 15. The method of claim 13 or 14, further comprising, prior to or during the curing step, the steps of: injecting a pressurized gas into the mixture; andreleasing the pressure to form a foamed viscoelastic silicone rubber composition. 16. The method of claim 13 or 14, further comprising, prior to the curing step, the step of: placing the mixture in a mold. 17. A shaped article comprising a cured viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polyorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shapewherein the boron-containing cross/inking agent is present in an amount sufficient to, when subject to a strain, give the viscoelastic silicone rubber composition a stiffness that is greater on short timescales than it is on longer timescales. 18. A shaped article comprising a cured viscoelastic silicone rubber composition comprising the reaction product of: (a) a silanol-terminated polyorganosiloxane base;(b) a boron-containing crosslinking agent; and(c) a siloxane bond-forming crosslinking agent in an amount sufficient to give the viscoelastic silicone rubber composition an equilibrium shape, wherein:the silanol-terminated polyorganosiloxane polymer base comprises polymers of formula (I) having a molecular weight ranging from 400 to 50,000 Dalton and a viscosity ranging from 10 to 10,000 cSt and preferably from about 15 to 1,000 cSt and wherein “m” is 1 or greater and represents the number of the repeating units in parentheses to give the molecular weight of the particular polymer; the boron-containing crosslinking agent is selected from boric acid, trimethyl borate, triethyl borate, and tri-isopropyl borate; andthe siloxane bond-forming crosslinking agent is selected from a polydiethoxysilane, polydimethoxysilane, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, and methyltriethoxysilane. 19. A shaped article of claim 18, wherein the article's Shore Hardness at t=0 is greater than the article's Shore Hardness at t=60 seconds.