Room temperature curable hybrid silicones

Details Room temperature curable hybrid silicones Room temperature curable hybrid silicones

1999-07-28

2001-06-26

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S479000, C427S387000, C528S015000, C528S019000, C528S031000

Reexamination Certificate

active

06251993

ABSTRACT:

BACKGROUND OF THE INVENTION
Silicones have become important commercial polymers because of a combination of properties, including high thermal stability, Noll, W., “Chemistry and Technology of Silicones”, Academic Press, New York, N.Y., 1968, 388; low surface tension, Voronkov et al, “The Siloxane Bond”, Consultants Bureau, New York, N.Y., 1978; low glass transition temperature, optical transparency, Lewis, F. M. in “High Polymers”, Vol. XXIII Pt. 2, Kennedy, J. P. and Tornquist, E. G. M., eds, Ch.8, Interscience, New York, N.Y., 1969; and low dielectric constant. These materials, however, have relatively poor mechanical strength, Polmanteer, K. E. J. Elastoplastics, 1970, 2, 165 and Yilgor, I. et al, Adv. Polym. Sci.1988, 86, 1-86; generally requiring high filler loading to obtain acceptable properties. The poor strength is usually attributed to flaws or microcracks that grow readily because of the high mobility of the chains, Smith, T. L., Rubber Chem. Technol. 1978, 51, 225.
An alternative approach to the preparation of silicones with improved mechanical strength has been to attach difunctional silanes, such as hydride-terminated polydimethylsiloxanes, to high molecular weight polyolefins, such as polybutadiene, by hydrosilylation. To prevent premature crosslinking and gelation, the reactions were carried out in dilute solution. Under these conditions, after one end of a polysiloxane chain attaches to an olefin site, the other end tends to attach to a nearby olefin site on the same polybutadiene molecule forming a silicone side-loop on a hydrocarbon backbone. The side-loops provide the desirable surface properties of silicones, and the hydrocarbon backbone contributes to mechanical strength. This technology have been described in Baum, K., U.S. Pat. No. 5,703,163; Baum, K., U.S. Pat. No. 5,811,193 and Baum, K. et al, J. Am. Chem. Soc. 1998, 120, 2993-2996. This reaction is depicted in the following scheme.
The loop polymers have been used in the preparation of coatings. The dilute hydrolylation solution was concentrated, and the concentrate was applied to a surface. Small amounts of unreacted hydrido groups then reacted with olefinic groups to give crosslinked coatings. However, reaction temperatures of 50-150° C. were generally required to provide desirable cure rates. While these elevated temperature conditions are acceptable for many coating applications, they are not practical for other applications, such as ship hull coatings.
This invention relates to novel room temperature curable coatings. The room temperature curable coatings of this invention are particularly useful as ship hull coatings.
SUMMARY OF THE INVENTION
Briefly, this invention comprises novel moisture curable polymer composition comprising, in combination, a member selected from the group consisting of a polydiolefin polymer containing olefinic unsaturation in either the main polymer backbone or in pendent side chains and a loop polymer having a polymeric backbone and a plurality of olefinic groups which have been converted to closed loops by reaction with difunctional organic compounds reactive with said olefinic groups, said olefinic groups from which the loops are formed may either be present within the backbone and/or pendent from the polymeric backbone; and a silicon cross-linking compound containing at least one easily hydrolyzed substituent and at least one hydride substituent.
The invention further comprises exposing the above-described combinations of polymer and crosslinker to moisture to cross link, preferably at or around room temperature.
Still further the invention includes a substrate, usually steel or other metal, coated with the above-described combinations of polymer and cross linker, and cross linked by exposure to atmospheric moisture to form an adherent protective coating.
The polydiolefin polymers may be polybutadiene, polyisoprene, polychloroprene and the like.
The loop polymers are generally prepared by reacting a polyunsaturated material, such as polybutadiene, with a dihydrido silicon compound, such as hydride terminated polydimethyl-siloxane, in an inert solvent, such as toluene, in the presence of a hydrosilylation catalyst. The completion of the hydrosilylation reaction can be observed by the loss of silicon hydride absorption in the infrared spectrum.
The loop polymers may also have hydroxy or carboxy groups which can be capped with diisocyanates or epoxies, respectively.
The polydiolefins and the loop polymers may have molecular weights on the order of 1000 or 100,000 or more.
The present invention provides coatings in which hydrolytic type cures take place at or around room temperature, although temperatures of from about 0° F. to 100° F. are contemplated.
The cross-linking agents are silicon compounds with easily hydrolyzed substituents, such as halogens, alkoxy groups or acyloxy groups. When coatings containing these materials are exposed to the atmosphere, atmospheric moisture causes hydrolysis, forming silanol groups that are converted to siloxanes cross-links. Catalysts such as tin compounds are frequently used.
The cross-linking according to this invention can be general illustrated by the following reactions:
Cross linking agents contain one or more silicon atoms, with one or more easily hydrolyzable groups on silicon, and one or more hydrido functions on silicon. The hydrolyzable groups can be, but are not limited to, alkoxy groups, halogens or acyloxy groups.
The cross-linking agents are typically comprise from 1 to 100 mole % of the olefinic double bonds present in the polydiolefin or loop polymers.
These cross linking agents in one preferred class, can be depicted as follows:
wherein X is a hydrolyzable group such as chloro, alkoxy or acyloxy, and Y may be either aryl, alkyl or one of said hydrolyzable groups. The aryl and alkyl groups may be substituted or unsubstituted. Suitable substituents include halogens, alkyls, etc. The y groups can be the same or different from each other.
The aforementioned alkoxy, acyloxy, aryl and alkyl groups typically contain from 1 to about 20 carbon atoms.
Dimethylethoxysilane and dimethylchlorosilane are readily available compounds that meet these criteria, and are preferred cross linking agents. When loop polymers are used, the cross linking agent can be added to the hydrosilylation mixture after the loop formation is complete, although the point at which it is added is not critical. The cross linking agent adds to double bonds of the polybutadiene or other polydiolefin by hydrosilylation. Variation of the amount of the cross linking agent will vary the physical properties of the finished product.
After the hydrosilylation is complete, solvent may be removed to give a material with a concentration and viscosity suitable for application as a coating. Optionally, other components and catalysts may be added to vary the properties of coatings. For example, tetraethyl orthosilicate may be added to increase the cross-link density, and alkoxy terminated polydimethylsiloxane, to increase toughness.
When the invention is practiced using polydiolefins, the above-described cross linking agents, for example dimethylethoxysilane, are reacted directly with polybutadiene or other polydiolefin, omitting the step in which a difunctional hydrosilane is used to form side-loops.
In a further preferred embodiment of the invention, when a polydiolefin without side loops is used, an additional polymeric component can be used. The additional polymeric component is a polysiloxane terminated with hydrolyzable groups, such as ethoxy or chloro terminated polydimethylsiloxane. The poly siloxane terminated with hydrolyzable groups is essentially free of Si—H groups. The additional polymeric compound is added before or after enough solvent is removed to give a concentration suitable for application as a coating. After the material is applied to a substrate, co-hydrolysis of the two types of ethoxysilanes can give coatings with similar overall composition as those obtained using the side-loop method, but possibly with fewer loops and more silicone bridges

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