GB2306491A

GB2306491A - Low viscosity alkoxypolysiloxane compositions

Info

Publication number: GB2306491A
Application number: GB9617490A
Authority: GB
Inventors: Timothy Brydon Burnell; James Anthony Cella; Judith Stein
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1995-11-01
Filing date: 1996-08-21
Publication date: 1997-05-07
Also published as: GB9617490D0; DE19633413A1; FR2740464B1; FR2740464A1; JPH09165556A

Description

RD-24340 2306491 LOW VISCOSITY SILICONE COMPOSITIONS

Field of the Invention

This invention relates to novel compositions of matter. More particularly, the instant invention is directed to low viscosity silica filled compositions which may be used to protect surfaces from biofouling.

Background of the Invention

Structures exposed to water, whether fresh water or seawater, often become encrusted with many objects and organisms. Such structures often include, among other things, ship hulls, buoys, splash-zone surfaces of oil production platforms and inlets and outlets of power stations. They become encrusted with, for example, objects such as ice and organisms like barnacles, tube worms, algae and zebra mussels, all of which negatively impact the performance of the structures.

Moisture curable, 2-part silicone compositions have been employed as coatings to protect structures like the abovedescribed from being encrusted with objects and organisms.

However, the conventionally employed silicone compositions consist of high molecular weight polysiloxanes and have high viscosities in the uncured state, making them very difficult to handle and apply. Because of this, such silicone compositions are often thinned with environmentally unfriendly organic solvents, making them easier to handle and apply.

In an attempt to avoid the use of organic solvents, low viscosity compositions having low molecular weight silanol stopped RD-24340 polymers and non-reinforcing fillers have been made. However, these compositions are not desirable because they display poor physical properties in the cured state. In an attempt to increase their post-cure physical properties, these low viscosity compositions have been mixed with silica. The resulting mixtures, however, display a dramatic increase in pre-cure viscosities; in fact, the viscosities of the mixtures are higher than those displayed in compositions having high molecular weight polyorganosiloxanes.

The instant invention, therefore, is directed to low viscosity silica filled compositions that display favorable physical properties and foul release properties after curing.

Description of the Prior Art

Efforts have been described for preparing room temperature vulcanizable compositions. In commonly assigned U.S.

Patent 4,959,407, solventless organopolysiloxane compositions are described and the compositions comprise a bis(ureido)silane as a coupler and an aminoxysiloxane as a crosslinker.

Additionally, in U.S. Patent 4,965,367, a process for preparing silacyclobutanes is described and the process comprises the step of reacting a halogen substituted silacyclobutane with a silylating reagent.

Still other investigators have focused on the preparation of curable compositions. In U.S. Patent 3,694,427, compositions comprising a silacyclobutane and an organopolysiloxane are described.

Summary of the Invention

The instant invention is directed to a sprayable composition comprising:

(a) an alkoxysilane stopped polymer; (b) a silica based filler; and (c) a condensation catalyst, RD-24340 -3.

wherein the composition is volatile organic compound (VOC) free.

The compositions, unexpectedly, display a viscosity substantially identical to conventional low viscosity compositions such as those with low molecular weight silanol stopped polymers and non-reinforcing fillers like calcium carbonate. Moreover, they unexpectedly display viscosities which are at least about ten times and preferably at least about thirty times and most preferably at least about sixty times less than compositions with low molecular weight sHanol stopped polymers and silica based reinforcing fillers. Low viscosity, as used herein, is defined to mean less than about 30,000 cps, preferably less than about 20,000 cps and most preferably less than about 10,000 cps at ambient temperature. Low molecular weight, as used herein, is defined to mean a Mw of less than about 100,000 and preferably less than about 60,000 and most preferably less than about 45,000.

Still further, the compositions of the instant invention unexpectedly show favorable physical properties after curing in comparison to conventional low Viscosity compositions. The unexpected results of this invention are confirmed in the tables which follow below.

Detailed Description of the Preferred Embodiments

There is no limitation with respect to the alkoxysilane stopped polymers which may be employed in this invention. C)fte however, they are represented by the formula 1 F ' r_ 0 R. 'OR n wherein each R is independently a Cl-10 alkyl group, Cl-10 alkoxy group, substituted or unsubstituted aromatic radical including a phenyl group, cyanoalkyl group including cyanoethyl, tdhaloalkyl RD-24340 group including trifluoropropyl or a vinyl group. Each R' is independently a C1.10 alkyl group or substituted or unsubstituted radical. Preferably, however, each R is a methyl group and each R1 is a methyl group. n is an integer from about 25 to 5,000 and preferably has a value such that the viscosity of the alkoxysilane stopped polymers is about 100 to about 20,000 and preferably from about 200 to about 15,000 and most preferably from about 1,000 to about 10,000.

Such alkoxysilane stopped polymers are commercially available and produced, for example, by reacting a silanol stopped polyorganosiloxane with a tri or tetrafunctional alkoxysilane in the presence of a capping catalyst.

There is essentially no limitation with respect to the silica based fillers that may be employed in this invention. Often, however, commercially available fumed silica is preferred.

There is also essentially no limitation with respect to the condensation catalysts which may be employed in this invention. Often they include salts of cerium, zinc and lead, including carboxylic acids thereof. The preferred catalysts are those which contain titanium or tin, including dibutyltin-bis-acetylacetonate, dib utyltin di lau rate and di-isopropoxybis-2,4-bis-pentanedionato titanium(IV).

The compositions of this invention may be prepared, for instance, in any mixing vessel capable of mixing the alkoxysilane stopped silanol polymer, silica based filler and condensation catalyst. The order in which the reagents are mixed is generally not limited. Often, however, it is preferred to form a premix with the alkoxysilane stopped silanol polymer and silica based filler prior to adding the condensation catalyst.

In a preferred embodiment of this invention, R is desirable to add crosslinkers to accelerate curing. There is no limitation with respect to the crosslinkers which may be employed in the instant invention other than that they are capable of crosslinking alkoxysilane stopped polymers to produce a cured compositions. The RD-24340 wherein each X1 is independently a C1.10 hydrocarbon and preferably a methyl group and each Z is independently an alkoxy group including a methoxy group, aminoxy groups, dialkylamino groups including dimethylamino groups, oxime groups or alkoxy groups including methoxy groups and q is 3 or 4.

Such crosslinkers are typically added to the abovedescribed premix or to the condensation catalyst and can be prepared for instance by reacting a hydroxyamine or an alcohol with a silicone hydride. An additional description of crosslinker production may be found in commonly assigned U.S. Patent 4,959,407, the disclosure of which is incorporated herein by reference.

It is further within the scope of the instant invention to employ any conventional additives known in the art. Such additives include, for instance, oils, group IIA carbonates and sulfates like calcium carbonate and calcium sulfate, transition metal oxides like titanium and ferric oxides, carbon black, diatomaceous earth, alumina, hydrated alumina, glass microspheres, quartz, organic fillers as well as reinforcing and nonreinforcing fillers.

Additionally, K is within the scope of the instant invention to employ any of the conventional adhesion promoters known in the art. Such adhesion promoters include, for instance, nitrogen containing silanes such as 3-aminopropyftrimethoxysilane, 3aminoethyltriethoxysi lane and W(2-aminoethyl-3aminopropyi)trimethoxysilane, epoxide containing silanes such as 3- (glycidioxoxypropyi)trimethoxysi lane and cyanurate containing silanes such as 1,3,5-tris (3-trimethoxys ilylpropyl) isocyan u rate.

There is no limitation with respect to the use of the novel compositions described in the instant invention; in fact, they may be employed, for example, as protective coatings and/or caulks/sealants.

often preferred crosslinkers employed in this invention are trifunctional organopolysilanes having the formula X1(4-q)-Si-Zq, RD-24340 6- Further, they may be applied via any conventional method including spraying, brushing and troweling.

The amount of alkoxysilane stopped silanol polymer, silica based filler and condensation catalyst employed in this invention is limited only to the extent that a curable composition is produced. Often, however, no more than about 20 parts by weight and preferably no more than about 15 parts by weight and most preferably no more than about 10 parts by weight of alkoxysilane stopped silanol polymer are employed for every part by weight of silica based filler.

Additionally, no more than about 10 parts and preferably no more than about 5 parts and most preferably no more than about 1 part by weight of catalyst is employed for every 100 parts of premix (mixture of alkoxysilane stopped silanol polymer and silica based filler) employed.

The following examples further illustrate and facilitate an understanding of the instant invention. The products obtained may be confirmed by conventional techniques such as proton and carbon- 13 nuclear magnetic resonance spectroscopy, mass spectroscopy, infrared spectroscopy and GPC analysis.

Example 1

A mixing vessel was charged with 500g of a silane stopped polydimethyisifoxane (3000 centipoise at ambient temperature), 20g of methyltrimethoxysilane, 1.Og of sec-butylamine and 0.5g of acetic acid. The resulting mixture was heated to WC for 1 hour and cooled to about 45C at which point 2.5g of hexamethyidisilazane were added as a methanol scavenger. The resulting polymer was an alkoxysilane stopped polymer, yield approximately 95%.

RD-24340 Example 2

A mixing vessel was charged with 10.09 of the alkoxysilane stopped polymer produced in Example 1 and 0. 1 g of dibutyltindilau rate. The resulting mixture was exposed to atmospheric moisture under ambient conditions, became tack free within 1 hour and cured to an elastomeric: state after 10 hours.

Example 3

Example 3 was conducted in a manner similar to the one described in Example 2 except that di-isopropoxybis-2,4-bispentanedionato titanium(IV) was used in lieu of dibutyltindilau rate. The resulting composition because tack free within 1 hour and cured to an elastomenc state after 10 hours.

Example 4

A mixing vessel was charged with 434.59 of methyitrimethoxysilane stopped polydimethylsiloxane (3000 centipoise at ambient temperature) and 1319 of hexamethyidisilazane and octamethylcyclotetrasiloxane treated silica which was added with stirring over five increments. When all of the silica was added, another 434.5g of methyltrimethoxysilane stopped polydimethylsiloxane were added. The resulting mixture was subjected to vacuum for about 5 minutes and subsequently a high shear mixer for approximately 2000 cycles. The resulting composition was a low viscosity composition (about 7000 centipoise at ambient temperature) with a silica based reinforcing filler.

Example 5

Example 5 was prepared in a manner similar to the one described in Example 4 except that calcium carbonate was used in RD-24340 A mixing vessel was charged with 1009 of alkoxysilane stopped as produced in Example 4, 3.Og of totraethylorthosilicate and 0.65g of dibutyitin-bis- acetylacetonate. After mixing, the resulting composition was degassed by centrifugation, poured into molds and 10 cured for analysis.

lieu of silica. The resulting composition had a viscosity of about 7000 centipoise at ambient temperature.

Example 6

Example 7

Example 7 was prepared in a manner similar to the one described in Example 4 except that approximately 10% by weight of the composition included silicon oil (polydimethylsiloxane, 20 centipoise at ambient temperature). The composition was sprayed onto a solid substrate and cured to an elastomer displaying favorable film properties.

The data in Table 1 is provided to demonstrate the low viscosities of the compositions of this invention in comparison to the conventional compositions with silanol stopped polymers. All compositions were prepared in a manner similar to those described in the examples.

Table 1

Polymerb Entry Polymera viscosity Compositionb Filler viscosity 1 X 3,000 CaC03 7,000 2 X 3,000 Silica 460,000 3 y 3,000 Silica 7,000 ax = silanol stopped polydimethylsiloxane; y = alkoxysilane stopped polydimethylsiloxane.

bCentipoise at ambient temperature.

Rb-24340 -g- The data in Table 11 is provided to demonstrate the postcure favorable properties of the compositions of this invention. All compositions were prepared in a manner similar to those described in the examples.

Table 91

Filler,b TearI Tensilef Tensilef Shore Af Entrya amount strength Ibslin stress psi strain % hardness 1 None 4.4 24.2 23.7 15 2 CaCO15% 7.70 0.4 48.5 69.5 18 3 CaCO19% 8.07 1.96 82.0 130.0 18 4 CaC03,13% 9.73 0.85 94.2 131.0 18 CaC03, 29% 13.7 0.61 175.9 154.0 30 6 Silica 5% 11.5 102.9 120.0 21 7 Silica 9% 14.7 0.99 306.0 214.0 27 8 Silica 13% 21 0.91 396.4 203.0 30 9 Silica Mc 1.23 0.53 206.0 163.0 23 Silica Md 25.3 1.4 296.0 204.0 32 11 Silica Mc 28.4 3.73 296.0 196.0 28 aAll entries prepared with alkoxysilane stopped silanol polymer as prepared in Example 1.

bAmount = weight % based on total weight of composition.

cSilicon oil added, 20% based on total weight of the composition.

do.1 gram of di-isoproxybis-2,4-bis-pentanedionato tdanium(IV) added as in Examle 2.

eCoupler employed = 1,1-dimethoxysilacyclopentane.

fAll pursuant to ASTM standards.

Rb-24340 CIAM:

1. A sprayable composition comprising:

(a) an alkoxysilane stopped polymer; (b) a silica base tiller, and (c) a condensation catalyst, wherein the composition is volatile organic compound free and has a viscosity of less than about 30,000 centipoise at ambient temperature.

2. A composition in accordance with claim 1 wherein said alkoxysilane stopped polymer has the forTnula 1 r p R'O-rl- i-0 i-OR' wherein each R is independently a Cl-10 alkyl group, alkoxy group, substituted or unsubstituted aromatic radical, cyanoalkyl group, trihaloalkyl group or a vinyl group and each R1 is independently a Cl-10 alkyl group or substituted or unsubstituted radical and n is an integer from about 25 to 5,000.

3. A composition in accordance with claim 2 wherein each R is a methyl group and each R1 is a methyl group.

4. A composition in accordance with claim 1 wherein said silica based filler is a fumed silica.

5. A composition in accordance with claim 1 wherein said condensation catalyst comprises titanium or tin.

6. A composition in accordance with claim 5 wherein said titanium comprising catalyst is di-isopropoxybis-2,4pentanedionato titanium(IV) and said tin comprising catalyst is dibutyltin-bis-acetylacetonate or dibutyltindilau rate.

7. A composition in accordance with claim 1 wherein said composition has a viscosity of less than about 20,000 centipoise at ambient temperature.

8. A composition in accordance with claim 1 wherein said composition further comprises a crosslinker.

t FiD-24340 - 11.

9. A composition in accordance with claim 8 wherein said crosslinker is a trifunctional organopolysilane having the formula X1(4-q)-Si-Zq 9 wherein X1 is a C1.10 hydrocarbon and each Z is independently an alkoxy group, aminoxy group, dialkylamino group, oxime group or alkoxy group and q is 3 or 4.

10. A composition in accordance with claim 1 wherein said composition further comprises additives.

11. A composition in accordance with claim 10 wherein said additives are oils, Group JIA carbonates and sulfates, transition metal oxides, carbon black, diatomaceous earth, alumina, hydrated alumina, glass microspheres, quartz or organic fillers.

12.. A composition in accordance with claim 1 wherein said composition further comprises adhesion promoters.

13. A composition in accordance with claim 12 wherein said adhesion promoters are 3-aminopropyftdmethoxysilane, 3aminoethyltriethoxysilane W(2-aminoethyl-3aminopropyi)trimethoxysilane, 3(giycidioxoxypropyi)trimethoxysilane 5 or 1,3,5-tris(3trimethoxysilylpropyi) isocyanurate.