# US 8,785,507 B2 · Viscoelastic silicon rubber compositions

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- Number: US 8,785,507 B2
- Document ID: US8785507B2
- Status: Granted
- Kind: B2
- Application number: 13/583,397
- Filed: 2011-03-09
- Published: 2012-12-27
- Granted: 2014-07-22
- Earliest claimed: 2010-03-09
- Assignees: University of Virginia Patent Foundation
- Applicants: Louis A. Bloomfield
- Inventors: Louis A. Bloomfield
- Web page: https://patentgrep.com/patent/US8785507B2

## CPC

- C08G 77/56: Boron-containing linkages
- C08G 77/16: to hydroxy groups
- C08K 3/38: Boron-containing compounds
- C08K 5/5415: containing at least one Si—O bond
- C08K 5/5419: containing at least one Si—C bond
- C08K 5/55: Boron-containing compounds {(C08K5/0091 takes precedence)}
- C08L 83/00: Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
- C08L 83/04: Polysiloxanes
- C08L 83/14: in which at least two but not all the silicon atoms are connected by linkages other than oxygen atoms (C08L83/10 takes precedence)
- C08G 2110/0016: semi-rigid
- C08K 2003/387: {Borates}
- C08K 2201/002: Physical properties
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)

## Abstract

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.

## Claims

### Claim 1

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; and
curing the mixture under conditions sufficient to form a viscoelastic silicone rubber composition,
wherein the boron-containing crosslinking agent is added in an amount up to 100% saturation.

### Claim 2 (depends on 1)

The method of claim 1, further comprising the step of:
mixing the silanol-terminated polyorganosiloxane base with a filler prior to reaction with a boron-containing crosslinking agent.

### Claim 3 (depends on 1)

The method of claim 1, further comprising, prior to or during the curing step, the steps of:
injecting a pressurized gas into the mixture; and
releasing the pressure to form a foamed viscoelastic silicone rubber composition.

### Claim 4 (depends on 1)

The method of claim 1, further comprising, prior to the curing step, the step of:
placing the mixture in a mold.

### Claim 5

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; and
curing the mixture under conditions sufficient to form a viscoelastic silicone rubber composition,
wherein the boron-containing crosslinking agent is added in an amount up to 100% saturation.

### Claim 6 (depends on 5)

The method of claim 5, further comprising the step of:
mixing the silanol-terminated polyorganosiloxane base with a filler prior to the combining step.

### Claim 7 (depends on 5)

The method of claim 5, further comprising, prior to or during the curing step, the steps of:
injecting a pressurized gas into the mixture; and
releasing the pressure to form a foamed viscoelastic silicone rubber composition.

### Claim 8 (depends on 5)

The method of claim 5, further comprising, prior to the curing step, the step of:
placing the mixture in a mold.