WO1999063003A1

WO1999063003A1 - Low-outgassing, room temperature vulcanizing silicone compositions

Info

Publication number: WO1999063003A1
Application number: PCT/US1999/011885
Authority: WO
Inventors: Alfred A. Decato
Original assignee: Loctite Corporation
Priority date: 1998-06-04
Filing date: 1999-05-28
Publication date: 1999-12-09
Also published as: AU4217399A

Abstract

The invention relates to a low-outgassing, room temperature vulcanizing silicone composition, which includes the product of combining α, φ-di(aminoalkoxysilyl)polysiloxane and insoluble hydrophobic silica. The invention also relates to a process of sealing transportation headlamp assemblies with such a silicone composition, a step of which includes sealing a headlamp assembly with such a silicone composition. In addition, the invention relates to headlamp assemblies produced using such a composition in such a process.

Description

LOW-OUTGASSING, ROOM TEMPERATURE

VULCANIZING SILICONE COMPOSITIONS

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to Low-Outgassing,

Room Temperature Vulcanizing ("RTV ") Silicone Compositions, which are particularly well -suited for the sealing transportation headlamp assemblies.

Brief Description of Related Technology

One-part, moisture cure silicone sealants are used for many applications including preventing of water intrusion into electrical, mechanical and optical assemblies, such as transportation lights like automobile headlamps .

Conventional silicone sealants for prevention of water intrusion often contain a trialkoxy-terminated polydimethylsiloxane, a catalyst (such as a tin soap) , a non-reactive silicone plasticizer oil, silica and filler . One drawback with such silicone sealants is outgassing of organic ingredients that do not ultimately become part of the matrix when cured.

The outgassed material lost from these sealants includes lower molecular weight materials, such as methanol condensate from the curing reaction. Such lower molecular weight materials have too low a molecular weight to recondense on surfaces distant from the sealant. However, a fraction of the lower molecular weight materials yields non- volatile residues. Condensation of non-volatile residues on surfaces is particularly troublesome in optical assemblies, such as transportation lamps, that require beam definition. Too much residue condensation, irrespective of its transmissivity, on the inside surface of the lens of such an optical assembly will cause the beam to degrade and become more diffused. In addition, residue condensation on a reflective surface of the lens assembly will decrease luminosity.

The non-volatile residue in typical sealants result from catalyst, non-reactive fluid, lower molecular weight fractions of reactive fluid that have not been incorporated into the matrix prior to the reaction reaching infinite viscosity, and the like.

For uses other than as a water prevention sealant, such as coatings or pressure sensitive adhesives, certain known silicone compositions, which are moisture curable and are non- slump solids at ambient temperature but can be heated to a flowable liquid state and applied as such to substrates. These compositions include a hydroxyl- functional organopolysiloxane resin (which is soluble in the composition and ordinarily is solid at room temperature, but softens when heated) a diorganopolysiloxane polymer, and optionally, a hydrolyzable silane and catalyst. See U.S. Patent No. 5,302,671 (Cifuentes) . Accordingly, and notwithstanding the state-of -the- technology, it would be desirable for silicone sealants to be low outgassing so as to avoid the drawbacks to which reference was made above .

SUMMARY OF THE INVENTION

The invention relates to a low-outgassing, RTV silicone composition, which includes the product of combining α, co-di (aminoalkoxysilyl) polysiloxane and insoluble hydrophobic silica. The invention also relates to a process of sealing transportation headlamp assemblies with such a silicone composition, a step of which includes sealing a headlamp assembly with such a silicone composition. In addition, the invention relates to headlamp assemblies produced using such a composition in such a process.

The compositions of this invention are prepared from fewer different components, than known compositions to perform their intended function. As such, raw materials and processing time (and costs associated therewith) may be reduced as compared to conventional compositions, all else being equal. The compositions of this invention autocatalyze in the absence of a separate catalyst component, and even exudate of the reactive fluid component of the compositions may tend to polymerize prior to evaporating and condensing. Though, in the event that faster cure speeds are desired for a particular end-use application, the inventive compositions may further include a catalyst .

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to low-outgassing RTV silicone compositions, which are particularly attractive as sealants.

The compositions include α, ω- di (aminoalkoxysilyl)polysiloxane; and insoluble hydrophobic silica.

The reactive fluid, α, ω- di (aminoalkoxysilyl)polysiloxane, is the reaction product of an aminoalkoxysilane, and a silanol-terminated polydimethylsiloxane or polydimethyldiphenylsiloxane . These fluids may be prepared by reacting two moles of a silane such as 3-aminopropyltrimethoxysilane with one mole of a silanol-terminatedpolydimethylsiloxane to yield α, ω-di(3- aminopropyldimethoxysilyl) polydimethylsiloxane reactive fluid and two moles of methanol as condensate. Synthesis details for this class of compounds may be found in U.S. Patent Nos. 5,300,608, 5,302,671 and 5,534,610, the disclosures of each of which are hereby expressly incorporated herein by reference.

The silanol-terminated fluid should be silanol- terminated polydimethylsiloxane, although silanol-terminated polydimethyldiphenylsiloxane may be used, particularly in the event when enhanced low temperature performance is desired. The desirable viscosity of sealant grade silanol fluids should be in the range of about 700 to about 175,000 cPs, such as about 3,500 cPs .

The aminoalkoxysilane precursor should have an alkoxy functionality of at least two. Examples of such aminoalkoxysilanes include 3-aminopropyltrimethoxysilane, 3- aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, (aminoethylaminomethyl)phenethyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyltrimethoxysilane, N- (6- aminohexyl) aminopropyltrimethoxysilane, 3- (m- aminophenoxy) propyltrimethoxysilane, m- aminophenyltrimethoxysilane, p-aminophenyltrimethoxysilane, 3- (1-aminopropoxy) -3 , 3 -dimethyl -1-propenyltrimethoxysilane, 3-aminopropyltris (methoxyethoxyethoxy) silane, N- (2- aminoethyl) -3-aminopropylmethyldimethoxysilane, 3- aminopropylmethyldiethoxysilane , 3 - aminopropylmethyldimethoxysilane and mixtures thereof. After reaction with silanol fluid, these aminoalkoxysilane precursors should yield reactive fluids with the following respective terminal groups: 3- aminopropyldimethoxysilyl, 3-aminopropyldiethoxysilyl, 4- aminobutyldiethoxysilyl , (aminoethyaminomethyl) phenethyldimethoxysilyl, N- (2- aminoethyl) -3-aminopropyldimethoxysilyl, N- (6- aminohexyl ) aminopropyldimethoxysilyl , 3 - (m- aminophenoxy) propy1dimethoxysily1 , m- aminophenyldimethoxysilyl, p-aminophenyldimethoxysilyl, 3- (1-aminopropoxy) -3, 3 -dimethyl -1-propenyldimethoxysilyl, 3- aminopropylbis (methoxyethoxyethoxy) silyl, N- (2-aminoethyl) - 3 -aminopropylmethylmethoxysilyl , 3 - aminopropylmethylethoxysilyl, 3- aminopropylmethylmethoxysilyl and mixtures thereof.

The α, ω-di (aminoalkoxysilyl) polysiloxane prepared by reacting the above should be used in the inventive compositions within the range of about 5 to about 100% w/w.

This reactive fluid may then be mixed with an . insoluble hydrophobic silica for reinforcement purposes.

The insoluble hydrophobic silica should be a high surface area silica, such as fumed, colloidal and precipitated silicas. Most of the hydroxyl groups on these silicas have been capped by materials such as siloxane fluids, octyltrimethoxysilane, methyldimethoxysilane and the like, to prevent the pendant hydroxyl from inducing premature gelation and to improve compatibility, and hence, ease of incorporation of the silicas into the α, ω- di (aminoalkoxysilyl) polysiloxane .

Desirable treated silicas are hexamethyldisilazane ("HMDS") treated and polydimethylsiloxane ("PDMS") treated silicas . A particularly desirable HMDS-treated silica is R-

812S (available commercially from Degussa, Ridgefield Park, NJ) , which receives a double treatment of HMDS and has a surface area of 220 m²/g, and HDK H 20 (available commercially from Wacker-Chemie, Adrian, MI) , which is a hydrophobic silica having a surface area of 170 m²/g. Other HMDS-treated silicas include Tellenox 500, commercially available from Tulco. Inc. and HDK 2000, commercially available from Wacker-Chemie.

A particularly desirable PDMS-treated silica is Cab-O-Sil N70-TS (commercially available from the Cabot

Corporation) , which is reported to have a carbon content of 5 weight percent and a surface area of 70 m²/g. The product is the result of a process in which trimethylsilyl ("TMS") terminated silicone fluid is absorbed onto the fumed silica and treated at elevated temperatures (about 200°C) . The silanol groups on the silica are replaced by TMS terminated polydimethylsiloxane chains. The silicone fluid may be present predominantly as adsorbed silicone rather than as covalently bonded polymerfragments . AEROSIL R202, commercially available from Degussa, is believed to be a comparable treated silica product.

Another category of treated silicas suitable for use in the inventive compositions are those treated with trialkoxy alkyl silanes, an example of which is AEROSIL R805 (commercially available from Degussa) , which is a trimethoxyoctylsilane-treated silica having a surface area of 150 m²/gm. Examples of dimethyldichlorosilane-treated silicas include AEROSIL R972, AEROSIL R974 and AEROSIL R976, each of which are commercially available from Degussa.

The insoluble hydrophobic silica should be used in the inventive compositions at levels of up to about 50% w/w. Other optional components include catalyst, filler and crosslinker.

The optional catalyst may be chosen from a raft of commercial materials available, such as titanates like tetraisopropoxy titanate, tetrabutyl titanate, titanate chelates, carboxylic acid salts of tin like dibutyltindilaurate, dibutyl tin diacetate, tin octanoate, dibutyltindihydroxide, carboxylic acid salts of zinc like zinc octanoate, carboxylic acid salts of iron and mixtures thereof. When used, the catalyst may be included at levels of up to about 5% w/w.

The optional filler may be chosen from any filler material known to those persons of ordinary skill in the art. An example of a desirable filler is calcium carbonate. When used, the filler may be included at levels of up to about 70% w/w.

The crosslinker should be of the condensation type and, as described above, should be employed when the α, ω- di (aminoalkoxysilane) polysiloxane functionality is two. Examples of the crosslinker include vinyltrimethoxysilane, 1, 3-dimethyltetramethoxydisiloxane, tetraethoxysilane, tetramethoxysilane, tetra n-propoxysilane, methytrimethoxysilane, methyltriethoxysilane and mixtures thereof. The crosslinker should be selected with care so that the leaving groups thereon do not contribute to nonvolatile residue or interfere with the cure of the α, ω- di (aminoalkoxysilyl) olysiloxane. Accordingly, vinyltrimethoxysilane is a desirable choice. When used, the crosslinker should be included at levels of up to about 30% w/w.

The reactive fluid described above has a functionality of 4; if the silane precursor had been 3- aminopropyldimethoxymethylsilane, the functionality of the resulting fluid would be two and crosslinker would be required in order to form a thermoset . Therefore, crosslinker should be included when the alkoxy functionality of the α, ω-di (aminoalkoxysilyl) polysiloxane is two. While alkoxy leaving groups are desirable, the reaction product of an amino functional silane having at least two hydrolyzable groups generally and a silanol terminated polysiloxane is also an embodiment of the invention. Alternative hydrolyzable groups include ketoximes and the like.

Additional additives include colorants such as carbon black, biocides, adhesion promoters, such functionalized silane, titanate and zirconate coupling agents, desiccants, such as molecular sieves and the like, and are typically present at levels of up to about 20% w/w. The present invention will be illustrated by reference to the following working examples.

EXAMPLES EXAMPLE 1

1000 grams of silanol-terminated polydimethylsiloxane having a viscosity of 3,500 cPs was heated to a temperature of about 120°C, stripped for a period of time of about two hours, and thereafter cooled to room temperature. 15.34 grams of aminopropyltrimethoxysilane and 0.9 ml of 1.6M n-butyl lithium was added with stirring and vacuum over the course of a period of time of about 1 hour. After the addition was complete, dry ice was added, the mixture was stirred for an additional 15 minute period of time, and then was degassed to obtain α, ω-di (3 - aminopropyldimethoxysilyl) polydimethylsiloxane .

EXAMPLE 2 A moisture cure one-part silicone sealant was prepared by combining the following ingredients: 348 grams (58 pbw) of α, ω-di(3- aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 48 grams (8 pbw) of insoluble hydrophobic silica (R-812S) , 18 grams (3 pbw) of vinyltrimethoxysilane, 180 grams (30 pbw) of calcium carbonate filler and 3.3 grams (0.5 pbw) of a tin soap catalyst (Fomrez UL-2, commercially available Witco Corp., Greenwich, CT) . More specifically, α, ω-di(3- aminopropyldimethoxysilyl) polydimethylsiloxane was charged to a mixer and vinyltrimethoxysilane was added and mixed under a vacuum for a period of time of about 15 minutes. Vacuum was broken with nitrogen, and insoluble hydrophobic silica was added and mixed under a vacuum with high shear for a period of time of about 20 minutes. Vacuum was again broken with nitrogen, and calcium carbonate was added and mixed under vacuum with medium shear for 30 minutes, keeping the temperature below about 100°F. Vacuum was broken with nitrogen, and the mixer was scraped down under nitrogen sparge . Then catalyst was added and mixed under vacuum for a period of time of about 15 minutes, while the mixture cooled to room temperature .

EXAMPLE 3 A moisture cure one-part silicone sealant was prepared using the process described in Example 2 by combining the following ingredients: 348 grams (52 pbw) α, co-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 60 grams (9 pbw) insoluble hydrophobic silica (R-812S) , 18 grams (3 pbw) vinyltrimethoxysilane, 240 grams (36 pbw) calcium carbonate filler and 3.3 grams (0.5 pbw) tin soap catalyst (Fomrez UL- 2) . EXAMPLE 4

A moisture cure one-part silicone sealant was prepared using the process described in Example 2 by combining the following ingredients: 416 grams (52 pbw) α, ω-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 72 grams (9 pbw) insoluble hydrophobic silica (R-812S) , 21.6 grams (3 pbw) vinyltrimethoxysilane, 286 grams (36 pbw) calcium carbonate filler, 4 grams (0.5 pbw) tin soap catalyst (Fomrez UL-2) and 0.16 grams (0.02 pbw) carbon black.

EXAMPLE 5

A moisture cure one-part silicone sealant was prepared using the process described in Example 2 by combining the following ingredients: 316 grams (53 pbw) α, ω-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 54 grams (9 pbw) insoluble hydrophobic silica (R-812S) , 12 grams (2 pbw) vinyltrimethoxysilane, 215g (36 pbw) calcium carbonate filler, 4 grams (0.5 pbw) dibutytin bis-neodecanoate catalyst and 0.12 grams (0.02 pbw) carbon black.

EXAMPLE 6 A moisture cure one-part silicone sealant was using the process described in Example 4 prepared and by combining the following ingredients: 11.6 Kg α, ω-di (3- aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 1.42 Kg insoluble hydrophobic silica (R-812S) , 0.495 Kg vinyltrimethoxysilane, 5.4 Kg calcium carbonate filler, 0.003 Kg carbon black and 0.075 Kg tin soap catalyst (Fomrez UL-2) .

The sealant produced had the following properties: a durometer of 44 Shore A, an elongation to failure of 187+4%, a skin-over time of 45 minutes, tear strength, Die B of 38±3 psi, boeing sag @ 2 minutes of 1.3 inches and the following extrusion rates @ 90 psi, 1/8" orifice: Day 1, 130 gpm; Day 2, 114 gpm; Day 3, 160 gpm; Day 6, 196 gpm; Day 10, 150 gpm; Day 13, 159 gpm; Day 15, 154 gpm; Day 17, 156 gpm; Day 20, 212 gpm.

The sealant also possessed a tensile strength of 360±5 (psi) , and a modulus @ 50% of 158±8 and a modulus @ 100% 257±8.

EXAMPLE 7

A moisture cure one-part silicone sealant was prepared using the process described in Example 4 and by combining the following ingredients: 3.3 Kg (50.68 phr) α, ω-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 0.618 Kg (9.5 phr) insoluble hydrophobic silica (R-812S) , 0.215 Kg (3.3 phr) vinyltrimethoxysilane, 2.44 Kg (36 phr) calcium carbonate filler, 0.0013 Kg (0.02 phr) carbon black and 0.0033 Kg (0.5 phr) tin soap catalyst (Fomrez UL-2) .

The sealant produced had the following properties : a durometer of 44 Shore A, an elongation to failure of 148±20%, a skin-over time of 28 minutes and the following extrusion rates @ 90 psi, 1/8" orifice: Day 1, 100 gpm; Day 2, 73 gpm; Day 5, 65 gpm; Day 6, 196 gpm; Day 9, 70 gpm; Day 12, 59 gpm; Day 14, 60 gpm; Day 16, 56 gpm; Day 19, 52 gpm; Day 32, 53 gpm; Day 73, 47 gpm.

The sealant also possessed a tensile strength of 438±8 (psi) , and a modulus @ 50% of 246±12 and a modulus @ 100% of 366±18.

EXAMPLE 8

A moisture cure one-part silicone sealant was prepared by combining the following ingredients : 7.93 Kg (52.88 phr) α, ω-di (3- aminopropyldimethoxysilyl) polydimethylsiloxane as prepared in Example 1, 1.28 Kg (8.5 phr) insoluble hydrophobic silica (R-812S) , 510 Kg (3.4 phr) vinyltrimethoxysilane, 5.25 Kg (35 phr) calcium carbonate filler, 0.003 Kg (0.02 phr) carbon black and 0.030 Kg (0.2 phr) tin soap catalyst (Fomrez UL-2) . More specifically, vinyltrimethoxysilane was added to α, ω-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane (as prepared in Example 1) in a Myers mixer under nitroged, and mixed at slow speed for a period of time of about 5 minutes. The treated fumed silica was then added, and mixing at high shear was allowed to continue for a period of time of about 10 minutes. The calcium carbonate filler, and carbon black were next added, and mixing with high shear under nitrogen for a period of time of about 20 minutes, while maintaining the temperature at less than about 105°F. After this time, the mixer was scraped down, and the catalyst was added with mixing under a vacuum for a period of time of about 15 minutes while the mixture cooled to room temperature . The sealant produced had the following properties: a durometer of 50 Shore A, an elongation to failure of 148+20%, a skin-over time of 12 minutes, a tear strength (Die B) of 56±9 psi (62, 46, 61, and 46 nicked, 61 and 62 without nicking), a weight per gallon of 11.08 pounds, a boeing sag @ 2 minutes of 0.75 inches, an elongation to failure of 178±6% and the following extrusion rate @ 90 psi, 1/8" orifice: Day 1, 100 gpm; Day 2, 50 gpm; Day 5, 55 gpm; Day 8, 57 gpm; Day 13, 84 gpm; Day 17, 89 gpm; Day 34, 65 gpm; Day 58, 116 gpm. The sealant also possessed a tensile strength of

406±8 (psi) , and a modulus @ 50% of 189±2 and a modulus @ 100% of 311+1.

EXAMPLE 9 The sealant prepared in Example 2 was applied to the sealing channel of an automotive foglamp. This assembly includes two parts: a plastic housing and a polycarbonate lens. After applying the sealant, the parts were mated and conditioned at a temperature of about 25°C and 50% RH for a period of time of about 5 days, allowing the material to fully cure.

Similar assemblies were sealed with LOCTITE 5900 and 5699, both of which are commercially available from Loctite Corporation, Rocky Hill, CT, and GE 1458 RTV, commercially available from General Electric, Waterford, NY, and conditioned in the same manner.

Halogen lamps were placed in the assemblies and lit by a 12V DC power supply for a period of time of about 2 hours. When the assemblies returned to room temperature, all of the lamps, with the exception of the assembly prepared with the sealant of Example 2 , exhibited a fogging of the reflective surface inside the housing. The fogging was observed visually to be as fine, white particulates that appear as a haze or diffuse coating. In the assembly prepared with the sealant of Example 2, the metallized surface remained clear and very reflective.

While the present invention has been described and exemplified above in terms of certain desirable embodiments, various other embodiments may be apparent to those skilled in the art. Accordingly, the invention is not limited to the embodiments specifically described and exemplified, but variations and modifications may be made therein and thereto without departing from the spirit of the invention, the full scope of which is delineated by the claims.

Claims

What is Claimed is;

1. A low-outgassing room temperature vulcanizing silicone compositions, comprising the product of combining:

(a) α, ω-di (aminoalkoxysilyl) polysiloxane; and

(b) insoluble hydrophobic silica.

2. The composition according to Claim 1, wherein the aminoalkoxysilyl group is selected from the group consisting of 3 -aminopropyldimethoxysilyl, 3- aminopropyldiethoxysilyl , 4 -aminobutyldiethoxysilyl ,

(aminoethyaminomethyl)phenethyldimethoxysilyl, N- (2- aminoethyl) -3 -aminopropyldimethoxysilyl, N- (6- aminohexyl) aminopropyldimethoxysilyl , 3 - (m- aminophenoxy) propyldimethoxysilyl , m- aminophenyldimethoxysilyl, p-aminophenyldimethoxysilyl, 3- (1-aminopropoxy) -3 , 3 -dimethyl-1-propenyldimethoxysilyl, 3- aminopropylbis (methoxyethoxyethoxy) silyl , N- (2-aminoethyl) - 3-aminopropylmethylmethoxysilyl , 3 - aminopropylmethylethoxysilyl, and 3- aminopropylmethylmethoxysilyl .

3. The composition according to Claim 1, wherein the α, ω-di (aminoalkoxysilyl) polysiloxane is the reaction product of an aminoalkoxysilane and a silanol-terminated polydimethylsiloxane, wherein the silanol terminated polydimethylsiloxane has a viscosity of about 700 to about 175,000 cPs.

4. The composition according to Claim 3 , wherein the silanol- terminated polydimethylsiloxane has a viscosity of about 3,500 cPs .

5. The composition according to Claim 1, wherein the α, ω-di (aminoalkoxysilyl) olysiloxane is the reaction product of an aminoalkoxysilane and a silanol-terminated polydimethyldiphenylsiloxane .

6. The composition according to Claim 1, further comprising a catalytically effective amount of catalyst.

7. The composition according to Claim 6, wherein the catalyst is selected from the group consisting of titanates, carboxylic acid salts of tin, dibutyltindihydroxide, carboxylic acid salts of zinc, carboxylic acid salts of iron and mixtures thereof.

8. The composition according to Claim 7, wherein the titanate is selected from the group consisting of tetraisopropyl titanate, tetrabutyl titanate, titanate chelates and mixtures thereof .

9. The composition according to Claim 7, wherein the carboxylic acid salts of tin are selected from the group consisting of dibutytin bis-neodecanoate, dibutyltindilaurate, dibutyl tin diacetate, tin octanoate and mixtures thereof .

10. The composition according to Claim 7, wherein the carboxylic acid salt of zinc is zinc octanoate.

11. The composition according to Claim 1, further comprising a crosslinker.

12. The composition according to Claim 11, wherein said cross-linker is selected from the group consisting of vinyltrimethoxysilane, 1,3- dimethyltetramethoxydisiloxane, tetraethoxysilane, tetramethoxysilane, tetra n-propoxysilane, methytrimethoxysilane, methyltriethoxysilane, and mixtures thereof .

13. The composition according to Claim 1, comprising the product of combining:

(a) α,ω-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane ; (b) insoluble hydrophobic silica;

(c) vinyltrimethoxysilane;

(c) filler; and

(d) a catalytically effective amount of tin soap catalyst.

14. The composition according to Claim 1, comprising the product of combining:

(a) about 58 pbw α, ω-di (3- aminopropyldimethoxysilyl) polydimethylsiloxane;

(b) about 8 pbw insoluble hydrophobic silica;

(c) about 3 pbw vinyltrimethoxysilane;

(d) about 30 pbw calcium carbonate filler; and

(e) about 0.5 pbw tin soap catalyst.

15. The composition according to Claim 1, comprising the product of combining:

(a) about 52 pbw α, ω-di (3- aminopropyldimethoxysilyl) polydimethylsiloxane ;

(b) about 9 pbw insoluble hydrophobic silica;

(c) about 2 pbw vinyltrimethoxysilane;

(d) about 36 pbw calcium carbonate filler; and

(e) about 0.5 pbw tin soap catalyst.

16. A process for sealing transportation headlamp assemblies with a sealant, comprising sealing a headlamp assembly with a sealant comprising α, ω- di (aminoalkoxysilyl) polysiloxane .

17. The process according to Claim 16, wherein the sealant further comprises insoluble hydrophobic silica.

18. The process according to Claim 16, wherein the sealant comprises the product of combining:

(a) α, ω-di (3 -aminopropyldimethoxysilyl) polydimethylsiloxane;

(b) insoluble hydrophobic silica;

(c) vinyltrimethoxysilane (d) filler; and

(e) a catalytically effective amount of tin soap catalyst.

19. The process according to Claim 16, wherein the sealant comprises the product of combining:

(a) about 58 pbw α, ω-di (3- aminopropyldimethoxysilyl ) polydimethylsiloxane ;

(b) about 8 pbw insoluble hydrophobic silica;

(c) about 3 pbw vinyltrimethoxysilane;

(d) about 30 pbw calcium carbonate filler; and

(e) about 0.5 pbw tin soap catalyst.

20. The process according to Claim 16, wherein the sealant comprises the product of combining:

(a) about 52 pbw α, ω-di (3- aminopropyldimethoxysilyl ) polydimethylsiloxane ;

(b) about 9 pbw insoluble hydrophobic silica;

(c) about 2 pbw vinyltrimethoxysilane;

(d) about 36 pbw calcium carbonate filler; and

(e) about 0.5 pbw tin soap catalyst.

21. A headlamp assembly produced by the process according to Claim 16.

22. A low-outgassing room temperature vulcanizing silicone composition, comprising the product of combining:

(a) the reaction product of an amino functional silane having at least two hydrolyzable groups and a silanol-terminated polysiloxane; and

(b) insoluble hydrophobic silica.

23. A process for sealing transportation headlamp assemblies with a sealant, comprising sealing a headlamp assembly with a sealant comprising the reaction product of an amino functional silane having at least two hydrolyzable groups and a silanol terminated polysiloxane.