Siloxane organic hybrid polymers

Siloxane organic hybrid polymers and a method of making them by condensation polymerization reaction of organoalkoxysilane in the presence of organic film-forming polymers are disclosed.

FIELD OF THE INVENTION 
The present invention relates generally to the art of hydrolyric 
condensation polymers of organoalkoxysilanes, and also to the art of 
organic hybrid polymers of alkoxysilanes. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,405,679 to Fujioka et al discloses a coated shaped article 
of a polycarbonate type resin of improved abrasion resistance comprising a 
shaped polycarbonate substrate, an undercoat applied and cured on the 
substrate, and an overcoat applied and cured on the undercoat comprising a 
hydrolyzate of an epoxy-containing silicon compound, at least one member 
of the group of hydrolyzates of organic silicon compounds, colloidal 
silica and organic titania compounds, and a curing catalyst. 
U.S. Pat. Nos. 4,500,669 and 4,571,365 to Ashlock et al disclose 
transparent, abrasion-resistant coating compositions comprising a 
colloidal dispersion of a water-insoluble dispersant in a water-alcohol 
solution of the partial condensate of silanol wherein the dispersant 
comprises metals, alloys, salts, oxides and hydroxides thereof. 
In the Journal of Non-Crystalline Solids, Vol. 63, (1984), Philipp et al 
disclose in "New Material for Contact Lenses Prepared From Si- and 
Ti-Alkoxides by the Sol-Gel Process" that it is possible to combine 
inorganic and organic elements to develop materials with special 
properties. 
U.S. application Ser. No. 07/440,845 filed Nov. 24, 1989 now U.S. Pat. No. 
5,231,156 by Lin discloses organic-inorganic hybrid polymers prepared by 
polymerizing an organic monomer in the presence of an inorganic oxide sol 
comprising an organoalkoxysilane having an organic functional group 
capable of reacting with said organic monomer. 
SUMMARY OF THE INVENTION 
To combine the mechanical strength and stability of inorganic materials 
with the flexibility and film-forming ability of organic materials is an 
objective of this invention. Organic-inorganic hybrid polymers in 
accordance with the present invention are prepared by hydrolyric 
condensation polymerization of an organoalkoxysilane in the presence of a 
water soluble organic polymer such as polyvinylpyrrolidone. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Commercial abrasion-resistant coatings for stretched acrylic either contain 
colloidal silica and exhibit poor resistance to corrosion by solvents such 
as acetone and sulfuric acid, or are based on relatively soft organic 
polymer systems such as urethanes or melamines. 
The hydrolysis of silanes of the general formula R.sub.x Si(OR').sub.4-x, 
wherein R is an organic radical, R' is a hydrolyzable low molecular weight 
alkyl group and x is at least one and less than 4, such as 
methyltrimethoxysilane, dimethyldiethoxysilane and 
.gamma.-methacryloxypropyltriethoxysilane can be carried out under 
controlled conditions in the presence of appropriate additives and 
produces stable, clear solutions that exhibit excellent adhesion to 
unprimed stretched or cast acrylic. Cured coatings, preferably about four 
microns thick, typically exhibit Bayer abrasion results (i.e., percent 
haze after 300 cycles of one kilogram load) of 5-10 percent, have a stress 
crazing time of 17 minutes upon exposure to acetone and 30 minutes upon 
exposure to 75% sulfuric acid under 3000 pounds per square inch pressure, 
and remain crack-free for up to 1900 hours of ultraviolet radiation 
exposure. 
Preferably, the silane hydrolyric polycondensation is catalyzed by an 
appropriate acid which is volatile and which does not lower the pH of the 
solution excessively. Preferred catalysts include acetic acid and 
trifluoroacetic acid. The temperature of the hydrolyric polycondensation 
reaction must be controlled either by external cooling, or by adjusting 
the solvent and acid composition to control the reaction rate, preferably 
not to exceed 45.degree. C. A catalyst, preferably sodium acetate, is 
added to promote complete cure of the siloxane polymer at temperatures 
preferably in the range of 80.degree. C. A high molecular weight water 
soluble organic polymer, preferably polyvinylpyrrolidone having a 
molecular weight of at least 300,000, is added for optimum film formation. 
The coated sample is subjected to standard Bayer abrasion testing for 300 
cycles, and QUV-B exposure alternating 8 hours of ultraviolet irradiation 
at 60.degree. C. and 4 hours at 45.degree. C. and 100 percent relative 
humidity without ultraviolet irradiation. The above invention will be 
further understood from the description in the specific example which 
follows.

EXAMPLE I 
A solution is prepared comprising 3.0 grams of polyvinylpyrrolidone 
dissolved in a solvent comprising 50 grams of water, 50 grams of methanol 
and 2 grams of formaldehyde (37% solution). The polyvinylpyrrolidone has a 
molecular weight of about 630,000 and is commercially available as K-90 
from GAF Corp. A mixture of siloxanes comprising 80 grams of 
methyltrimethoxysilane and 8 grams of dimethyldiethoxysilane is added to 
the polyvinylpyrrolidone solution at room temperature, along with three 
drops of trifluoroacetic acid. After stirring the reaction mixture for two 
hours, 50 grams of isobutanol and 0.1 gram of sodium acetate trihydrate 
are added. After further stirring, the sol is filtered and applied to 
either stretched acrylic or cast acrylic by dip coating for five minutes 
at room temperature. No pretreatment of the acrylic surface is necessary. 
The coating is cured at 80.degree. C. for 16 hours. After 300 cycles of 
Bayer Abrasion testing, the coated acrylic exhibits only 13.7 percent 
haze, compared with 50 percent haze for uncoated acrylic after the same 
abrasion testing. 
EXAMPLE II 
A solution is prepared comprising 18 grams of polyvlnylpyrrolidone 
dissolved in a solvent comprising 330 grams of deionized water and 330 
grams of methanol. A second solution is prepared comprising 480 grams of 
methyltrimethoxysilane, 48 grams of dimethyldiethoxysilane and 24 grams of 
glacial acetic acid. The two solutions are combined, stirred for 2 hours 
at ambient temperature, and diluted with 300 grams of 2-propanol and 150 
grams of diacetone alcohol containing 1.8 grams of sodium acetate. A 
stretched acrylic substrate is dipped into this coating composition and 
dried in air at ambient temperature for 5 to 10 minutes before curing the 
coating at 80.degree. C. for 2 hours. After 300 cycles of Bayer Abrasion 
testing, the coated acrylic exhibits only 8 to 10 percent haze compared 
with 50 percent haze for uncoated acrylic after the same abrasion testing. 
EXAMPLE III 
Three grams of the polyvinylpyrrolidone of Example I are dissolved in a 
solution comprising 35 grams of deionized water and 35 grams of methanol. 
The solution is stirred for 15 minutes before adding 80 grams of 
methyltrimethoxysilane, 8 grams of dimethyldiethoxysilane and 4 grams of 
glacial acetic acid. The mixture is stirred for 2 hours at room 
temperature, after which 0.2 grams of sodium acetate is added and the 
mixture is diluted with 50 grams of 2-propanol. A stretched acrylic 
substrate is dip-coated into the above composition, and the coating is 
cured at 80.degree. C. for 4 hours. The cured coating is then subjected to 
Bayer Abrasion testing with the result of 3.5 percent haze after 300 
cycles. Ultraviolet radiation exposure testing (QUV-B) results in only 
light cracking of the coating after 1732 hours. 
EXAMPLE IV 
Three grams of the polyvinylpyrrolidone of the previous examples is 
dissolved in 55 grams of deionized water and 55 grams of methanol. After 
stirring the solution for 15 minutes, 80 grams of methyltrimethoxysilane, 
8 grams of dimethyldiethoxysilane and 4 grams of glacial acetic acid are 
added to the polyvinylpyrrolidone solution. After stirring the sol for 2 
hours, 0.2 grams of sodium acetate is added, and the sol is diluted with 
50 grams of 2-propanol. A stretched acrylic substrate is dip-coated into 
the sol, and the coating is cured at 80.degree. C. for 4 hours. The cured 
coating is subjected to Bayer Abrasion testing with a result of 3.2 
percent haze after 300 cycles. In QUV-B testing at 60.degree. C. the 
coating shows some debonding only after 1184 hours. 
EXAMPLE V 
Three grams of the polyvinylpyrrolidone of the previous examples are 
dissolved in 75 grams of deionized water and 75 grams of methanol. After 
stirring the solution for five minutes, 80 grams of 
methyltrimethoxysilane, 8 grams of dimethyldiethoxysilane and 4 grams of 
glacial acetic acid are added. After stirring for 2 hours at room 
temperature, 0.2 grams of sodium acetate and 50 grams of isopropanol are 
added. A stretched acrylic substrate is dip-coated into the above 
composition, and the coating is cured at 80.degree. C. for 4 hours. The 
cured coating is subjected to Bayer Abrasion testing and shows 3.9 percent 
haze after 300 cycles. 
EXAMPLE VI 
Three grams of the polyvinylpyrrolidone of the previous examples are 
dissolved in 55 grams of deionized water and 55 grams of methanol. After 
stirring the solution for 15 minutes, 60 grams of methyltrimethoxysilane, 
6 grams of dimethyldiethoxysilane and 4 grams of glacial acetic acid are 
added. After stirring for 2 hours at room temperature, 0.2 grams of sodium 
acetate and 50 grams of 2-propanol are added. A stretched acrylic 
substrate is dip-coated into the above composition, and the coating is 
cured at 80.degree. C. for 4 hours. The cured coating is subjected to 
Bayer Abrasion testing with a result of 8.4 percent haze. The coating is 
also subjected to QUV-B exposure, and shows a few cracks after 1328 hours. 
EXAMPLE VII 
Three grams of the polyvinylpyrrolidone of the previous examples are 
dissolved in 55 grams of deionized water and 55 grams of methanol. After 
stirring the solution for 15 minutes, 78.5 grams of methyltriethoxysllane, 
7.8 grams of dimethyldiethoxysilane and 4 grams of glacial acetic acid are 
added. After stirring at room temperature overnight, 0.2 grams of sodium 
acetate and 50 grams of 2-propanol are added. A stretched acrylic 
substrate is dip-coated into the above composition, and the coating is 
cured at 80.degree. C. for 4 hours. The coating shows some cracks after 
642 hours of QUV-B exposure. 
EXAMPLE VIII 
Eighteen grams of the polyvinylpyrrolidone of the previous examples are 
dissolved in 330 grams of deionized water and 330 grams of methanol. After 
stirring the solution for 15 minutes, 480 grams of methyltrimethoxysilane, 
48 grams of dimethyldiethoxysilane and 24 grams of glacial acetic acid are 
added. After stirring at room temperature for 2 hours, 0.2 grams of sodium 
acetate, 300 grams of 2-propanol and 125 grams of diacetone alcohol are 
added. A stretched acrylic substrate is dip-coated into the above 
composition, and the coating is cured at 80.degree. C. for 2 hours. The 
cured coating subjected to Bayer Abrasion testing shows 5.5 percent haze 
after 300 cycles, and has a few craze lines after 1406 hours of QUV-B 
exposure. 
The above examples are offered to illustrate the present invention. The 
composition and concentration of the silane, constitution of the alcohol 
diluent, concentration and type of the acid catalyst, water content, 
organic polymer and proportion, and other reaction conditions may be 
varied in accordance with the present invention. The abrasion resistant 
siloxane organic hybrid polymer coating of the present invention may be 
used on other substrates. The scope of the present invention is defined by 
the following claims.