A polymer of vinylacetate and a vinylalkoxysilane wherein the alkoxy groups of said vinylalkoxysilane are in a saponified form and the acetyl groups of said vinylacetate are at least partially saponified, the vinyl silane radicals of said copolymer having the formula ##STR1## WHEREIN R is hydrogen, aryl, cycloalkyl or a branched or unbranched saturated alkyl of 1 to 18 carbon atoms; PA0 Ma is an alkali metal, NH.sub.4 or H; PA0 n is 0 to 2; A process for preparing such a saponified copolymer by contacting a solution of vinylacetate-vinylalkoxysilane copolymer with an alcoholic solution of an alkali metal hydroxide, isolating a precipitated copolymer and dissolving said copolymer in an aqueous alkali metal hydroxide or aqueous ammonia solution; the use of said copolymer as a surface coating agent for inorganic silicaceous substrates.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to saponified copolymer of vinylacetate and a 
vinylalkoxysilane wherein the alkoxy groups of the silane are completely 
saponified and the acetyl groups of the vinylacetate are at least 
partially saponified. More especially, this invention relates to 
non-cross-linked copolymers of vinylacetate and vinylalkoxysilane and the 
use of aqueous solutions thereof in the treatment of inorganic silicatic 
substrates. 
2. Discussion of the Prior Art 
The polymerization of vinylacetate with other materials is well known. It 
is also known to form copolymers thereof with vinylalkoxysilanes. These 
copolymers can be formed for instance in solution by solution 
polymerization in the presence of an initiator. Azoisobutyronitrile, for 
example, can be used although other radically acting initiators can be 
employed. 
It has become desirable, however, to prepare non-cross-linked copolymers of 
vinylacetate and vinylalkoxysilanes additionally characterized by the fact 
that the alkoxy groups of the vinylalkoxysilanes are saponified and the 
acetyl group of the vinylacetate units are at least partially saponified. 
It has become particularly desirable to prepare aqueous solutions of these 
materials wherein the alkyl group of the alkoxy silane is replaced by an 
alkali metal, ammonium or hydrogen. It has become additionally desirable 
to provide aqueous solutions of such saponified non-cross-linked 
copolymers of vinylacetate and vinylalkoxysilane. 
SUMMARY OF THE INVENTION 
In accordance with this invention there is provided a copolymer of 
vinylacetate and a vinylalkoxysilane wherein the alkoxy groups of said 
vinylalkoxysilane are in a saponified form and the acetyl groups of said 
vinylacetate are at least partially saponified, the vinylsilane radicals 
of said formula 
##STR2## 
WHEREIN R is hydrogen, aryl, cycloalkyl or a branched or unbranched 
saturated alkyl of 1 to 18 carbon atoms; 
Me is an alkali metal, ammonium or hydrogen, m is 0 to 2. 
In accordance with this invention there are provided new copolymers which 
can have a wide variety of molecular weight. The copolymers of the present 
invention can have a low molecular or high molecular weight or a molecular 
weight intermediate thereof. Preferably, the copolymers of the present 
invention have molecular weights between 5,000 and 150,000. 
The novel copolymers of the present invention can additionally contain 
units of a monoethylenically unsaturated monomer which copolymerizes with 
vinylacetate. The copolymers are provided by polymerizing vinylacetate and 
vinylalkoxysilane in the known manner with the additional use, if desired, 
of a monoethylenically unsaturated monomer copolymerizable with 
vinylacetate. After the initial copolymer is performed it is subjected, in 
accordance with this invention, to a saponification or transesterification 
which is carried out by contacting the copolymer in solution with an 
alcoholic solution of an alkali metal hydroxide. This treatment effects 
precipitation of a copolymer which is thereafter contacted with an aqueous 
alkali lye or aqueous ammonia solution thereby providing the desired 
saponified vinylacetate-vinylalkoxysilane copolymer. The resultant 
copolymer is in a form characterized by an exceptionally low degree of 
cross-linking. Generally, the cross-linking content is no greater than 
about 5%. 
Mostly, the saponification or transesterification is followed by a washing 
and refinement of the copolymer before the material is subjected to 
treatment with the aqueous alkali lye or ammonia solution. If desired, and 
in one preferred mode of this invention, the aqueous solution of the 
copolymer formed upon treatment of the precipitated copolymer with the 
aqueous alkali lye or ammonia solution is treated with an acid until the 
pH of the solution drops to 7 or below, preferably between 1 and 4. By 
such acidification the alkali metal atoms which replaced the alkyl group 
of the alkoxy radical are themselves replaced by hydrogen as more fully 
described below. 
DESCRIPTION OF SPECIFIC EMBODIMENTS 
In order to prepare the copolymers of the present invention the copolymer 
of the vinylalkoxysilane and vinylacetate must be initially formed. The 
vinylalkoxysilane utilized has the general formula 
##STR3## 
in which R represents hydrogen, an aryl especially phenyl, cycloalkyl, 
e.g., C.sub.5 -C.sub.7 cycloalkyl or arylalkyl or a branched or unbranched 
saturated alkyl radical of 1 to 18 carbon atoms, preferably 1 to 4 carbon 
atoms or Cl, R' represents identical or different saturated, branched or 
unbranched alkyl radicals of 1 to 18 carbon atoms. The alkyl radicals of 
R' can be ones wherein the chain of carbon atoms is interrupted by an 
oxygen atom such as a radical --CH.sub.2 --CH.sub.2 --O--CH.sub.2 
--CH.sub.3. In the formula n is 0 to 2. 
Examples of vinylalkoxysilanes are: vinyltrialkoxysilanes such as 
vinyltrimethoxysilane, vinyltriethoxysilane, 
vinyl-tris-(.beta.-methoxyethoxy)-silane and the like, and 
vinyldialkoxysilanes such as vinylisobutyldimethoxysilane, 
vinylmonochlorodimethoxysilane and the like. Vinyltrialkoxysilanes having 
C.sub.1 to C.sub.4 alkyl radicals are preferred. 
The vinylalkoxysilane is best used in a quantity amounting to 0.1 to 20, 
preferably 0.5 to 15, percent of the total weight of the monomers to be 
polymerized. 
Examples of additional comonomers which can be used owing to their ability 
to copolymerize with vinylacetate are: ethylene, propylene, acrylic esters 
and the like. It is desired to use the monomer in lesser amounts than the 
vinylacetate. For example, the vinylacetate content of the polymer can be 
replaced by approximately 30 to 40% by weight of comonomer. 
The copolymers obtained from copolymerization of vinylacetate and 
vinylalkoxysilane are those prepared in the known manner, preferably by 
solution polymerization in the presence of an initiator. 
Azoisobutyronitrile or another radically acting initiator can be employed 
for this purpose. The polymerization reaction is best performed with the 
substantial exclusion of moisture and oxygen. The reactants as well as the 
solvents should be dry and pure insofar as possible. An appropriate 
solvent for this polymerization, for instance, is ethyl acetate. After 
several hours of reaction at elevated temperature, e.g., at temperatures 
between 40.degree. C and the boiling temperature of the solvent, in an 
apparatus equipped with reflux condenser, the solvent is removed, for 
example, by use of a rotary evaporator and a copolymer is obtained which 
is the starting product for the preparation of the new copolymers of the 
present invention. 
The relative viscosities of these unsaponified copolymers which are 
utilized as starting materials of the present invention depend upon the 
molecular weight, polymerization, temperature and also upon the percentage 
of vinylalkoxysilane in the copolymer. If, for example, the monomeric 
component of the polymerization mixture comprises 0.5 weight percent of 
vinyltriethoxysilane and 99.5 weight percent vinylacetate, a copolymer is 
obtained having a relative viscosity (.eta..sub.rel) of 1.310 (determined 
in a 1 weight percent solution in ethyl acetate at 20.degree. C) at a 
polymerization temperature of 75.degree. C. If, however, the monomeric 
composition of the polymerization reaction mixture consists of 15 weight 
percent vinyltriethoxysilane and 85 weight percent vinylacetate a 
copolymer is obtained having a relative viscosity of 1.110 at the same 
polymerization temperature. Generally speaking, the copolymers which serve 
as starting materials of the present invention have a relative viscosity 
of between 1.05 and 6.0. 
In the saponification or transesterification procedure of the invention a 
10 to 50% by weight alcoholic solution of copolymer is reacted, with 
stirring, with between 0.2 and 2 weight percent of alkali hydroxide. The 
reaction is desirably accomplished at elevated temperature such as at a 
temperature between 30.degree. C and the boiling point of the reaction 
mixture. Usually the saponified copolymers precipitate out of the hot 
solution. They are thereafter separated from the liquid, washed with 
alcohol, for example, and, if desired, dried. 
Alcohols which are useful solvents for the alkali metal hydroxides include 
methanol, ethanol, normal propanol, isopropanol, normal butanol and 
isobutanol. It should be understood that the concentration of the 
copolymer in its solution can be greater than 50% or lower than 10% and 
that the range of 10 to 50 weight percent represents a preferred range. 
The new modified copolymers of the invention are obtained if the saponified 
or transesterified copolymer is contacted thereafter with an aqueous 
alkali metal hydroxide or aqueous ammonia solution. The aqueous alkali 
metal hydroxides can be diluted alkali metal hydroxides such as 0.5 to 5 
weight percent solutions. The alkali metal hydroxides particularly 
suitable include sodium hydroxide and potassium hydroxide. Aqueous ammonia 
solutions can also be used. When an aqueous ammonia solution is used, a 
concentration of 15 to 25 percent by weight is desired. The new copolymers 
of the invention can, if desired, be treated with an acid to remove any 
alkali metal or ammonium with hydrogen. If an acid treatment is performed 
the acid is usually one of the following: HCl, H.sub.2 SO.sub.4, 
HNO.sub.3, H.sub.3 PO.sub.4, CH.sub.3 COOH and the like. 
The copolymers of the present invention can be formed in a water soluble or 
insoluble form depending upon the silane content. The copolymers tend to 
become more water insoluble as the specific silane content increases. This 
insolubility has been found to depend upon the amount of alkali metal 
hydroxide that remains in the saponified copolymer and thus the extent to 
which the copolymer is washed following the treatment with the alcoholic 
solution is relevant. The water-insoluble copolymers can be dissolved by 
aqueous alkali metal hydroxides or aqueous ammonia solutions, the 
solubility being promoted by increasing concentrations of alkali and 
ammonia in the aqueous solutions used. Moderately elevated temperatures 
also promote water solubility. In order to understand and fully appreciate 
the chemical phenomenon which is occurring by the subject process 
reference is made to the theoretical chemical formulas set forth below. 
##STR4## 
In the above formula Me represents an alkali metal or ammonium, x and y 
which may be equal or unequal to one another, each independently represent 
a whole number of 1 or more and up to 2,000. Preferably, x and y are whole 
numbers between 1 and 1,000. In the formulas, n is 0 to 2 while R has the 
same meaning as set forth in the abstract. 
If the aqueous solutions of the non-cross-linked polymer of formula II are 
acidified with dilute aqueous hydrochloric acid, for example, the reverse 
reaction to the product of formula I surprisingly does not take place as 
would be expected. It has been discovered that when the aqueous solution 
of the product of formula II is acidified the viscosity does not increase 
nor does any precipitation of the product of formula I occur. This means 
that no cross-linking takes place when the materials are in solution. 
Stated differently, no cross-linking takes place at certain polymer 
concentration levels. In the acid solution, the copolymer of formula II is 
transformed to the copolymer of the following structure. 
##STR5## 
If films are cast from aqueous acid solutions containing the copolymer of 
formula III and dried, a clear film is obtained which is insoluble in 
water. Solubility in water in this case is dependent on the pH of the 
casting solution. If the pH of the casting solution is 1 to 3 the dried 
film will be insoluble in water; at pH 4 to 6 it will be partially soluble 
in water, and at pH 7 it will be completely water soluble. Aqueous 
solutions of copolymers of formula III are stable at pH 1.0, i.e., no 
precipitation takes place at certain solid concentrations. In general, 
aqueous solutions of formula III are stable at pH 1 to 6 provided the 
concentrations of solids are less than 6% by weight. 
The stability of the solutions depends also on the molecular weight of the 
copolymer and on its silane content in addition to the concentration of 
solids. For example, an aqueous solution containing a copolymer of Formula 
III in a concentration of 5% by weight is stable for several weeks and 
longer at pH 1. A 6 weight percent solution of the same copolymer, 
however, will set in a short time at pH 1. The copolymer had been 
prepared by the saponification of a copolymer of 96 weight-parts of 
vinylacetate and 4 weight parts of vinyltriethoxysilane. It had a relative 
viscosity of 1.22, measured in a 1 weight percent solution in ethyl 
acetate at 20.degree. C. 
The units given in formulas I and II are to be interpreted as monomer units 
in the polymer. The polymers can, as described above, contain other 
monomer units in addition thereto. They can also have branches and can 
contain acetyl groups. The acetyl group content amounts generally to about 
2 to 30% by weight. 
The new copolymers are used for the coating of inorganic silicatic 
substrates. In the cross-linked state in accordance with formula I they 
exhibit strong adhesion to sheet glass, for example, when they are applied 
in the form of an aqueous, acidic solution in accordance with formula III. 
After the evaporation of the water, a polymer film forms pursuant to 
formula I. Other examples of inorganic silicatic substrates are glass 
filaments, glass wool, glass fabrics, and inorganic silicatic building 
materials. They are also suitable as thickening agents, as for example in 
paints for the protection of structures. For example, aqueous solutions of 
formula II in concentrations exceeding 6 weight percent, for example, 10 
to 20 weight percent can be prepared without being excessively viscous. 
The addition of acids changes the viscosity markedly, so that a gel is 
obtained. 
If aqueous ammonia solution is used instead of alkali lyes for the purpose 
of transforming the saponified copolymers to polymers of Type II, 
solutions of the copolymer are then obtained which are much more viscous 
than solutions prepared with alkali metal hydroxides. 
The new copolymers can also be used, for example, as suspension vehicles in 
polymerization reactions. For example, substances which are to be kept in 
finely divided form can be dispersed in aqueous solutions of copolymers of 
the formula II type and afterward, by the acidification of the solution, 
can be kept in finely divided form, even without continued stirring, since 
the viscosity is greatly increased upon acidification provided certain 
concentrations are present, depending on the molecular weight. 
The required amount of alkali hydroxide or ammonium hydroxide, as the case 
may be, depends on the silane content. For example, a saponification 
product of a copolymer of 95 weight percent vinylacetate and 5 weight 
percent vinyltriethoxysilane requires at least 0.75 weight percent of NaOH 
with respect to 100 parts of copolymer by weight. The saponification 
product of a copolymer of 85 weight percent vinylacetate and 15 weight 
percent vinyltriethoxysilane requires at least 10 weight percent of NaOH 
with respect to 100 parts of copolymer by weight. Although the critical 
figures regarding solid content, the required amount of alkali or ammonia 
etc, cannot be given for all cases, they are easy to determine by 
experiment in the individual case. 
In order to more fully illustrate the nature of the invention and the 
manner of practicing it the following examples are presented:

EXAMPLES 
A. Preparation of copolymers of vinylacetate and vinyltriethoxysilane 
720 g of distilled vinylacetate, 30 g of vinyltriethoxysilane and 750 g of 
acetic acid ethyl ester were placed under nitrogen in a 3-liter 
three-necked flask equipped with stirrer, thermometer, reflux condenser 
and nitrogen supply tube and exhaust tube. The mixture was heated with a 
water bath, with stirring, to 75.degree. C. Then 0.750 g of azoisobutyric 
acid dinitrile (commercially obtainable under the name "Porofor N") were 
added to the mixture. Another 0.750g of azoisobutyric acid dinitrile was 
added after two hours of heating at 75.degree. C, and another after three 
more hours of heating at 75.degree. C. After a total reaction time of 7.5 
hours, 375 g of acetic acid ethyl ester was added drop by drop to the 
batch over a period of one-half hour. This made the viscosity of the 
solution such that it could be handled easily. The acetic ester was 
removed in a rotatory evaporator and 745 g of a glass-clear polymer was 
obtained whose relative viscosity, measured in a 1 weight percent solution 
in acetic ester at 20.degree. C, amounted to 1.220. 
The relative viscosities reported herein were measured in the Hoppler 
viscosimeter and calculated by the following formula: 
##EQU1## 
t being the pouring time, using a 1 weight percent solution of polymer in 
acetic acid ethyl ester at 20.degree. C. 
On the basis of the above formula (composition from Example 5) additional 
copolymers were prepared from vinyl acetate and vinyl triethoxysilane, 
except that the percentage content of the vinyl triethoxysilane in the 
monomeric component was varied. 
As Table I shows, the relative viscosities depend on the weight-percentage 
of the monomeric vinyl triethoxysilane in the monomeric component, at 
constant polymerization temperature. 
Table 1 
______________________________________ 
Wt.-percentage of vinyltriethoxy- 
Examples silane in the polymerization mixture 
n.sub.rel 
______________________________________ 
1 0.5 1.310 
2 1.0 1.301 
3 2.0 1.247 
4 3.0 1.235 
5 4.0 1.220 
6 5.0 1.200 
7 10.0 1.150 
8 15.0 1.110 
______________________________________ 
If a monomeric component composed of 0.5 wt.-% vinyl triethoxysilane and 
99.5 wt.-% vinyl acetate is used (Example 1), the relative viscosity 
amounts to 1.310. As the amount of vinyl triethoxysilane increases, the 
relative viscosity diminishes down to 1.110 (Example 8). 
The copolymers dissolved in acetic ester can be cross-linked by the 
addition of 0.5 wt.-% hypophosphoric acid with respect to the copolymer, 
which shows that they are true copolymers. As it can be seen from Table 2, 
the cross-linked percentage increases with the percentage of the vinyl 
triethoxysilane in the monomeric component. 
Table 2 
______________________________________ 
Cross-linked per- 
Example Wt.-% silane centage by weight 
______________________________________ 
1 0.5 75.0 
2 1.0 83.2 
3 2.0 92.8 
4 3.0 95.0 
5 4.0 98.8 
______________________________________ 
B. Preparation of the polymers of the invention 
Saponification of the polymers described under A: 50 ccm of 1 wt.-% 
methanolic NaOH was placed in a 500 ccm three-necked flask equipped with 
stirrer, reflux condenser and dropping funnel. The contents of the flask 
were heated with stirring to 50.degree. C. Over a period of 30 minutes, 15 
g of a copolymer of vinyl acetate and vinyltriethoxysilane from Examples 
A-1 to A-8 was let in through the dropping funnel. Then the mixture was 
stirred for 30 additional minutes at 50.degree. C. The saponified product 
that precipitated was washed with methanol and dried. 
The saponified specimens were insoluble in water to a degree relating to 
their residual alkali content. However, they were soluble in dilute 
aqueous soda lye at 50.degree. C and they remained soluble even after 
cooling down to 20.degree. C. The required amount of NaOH depends upon the 
silane content of the monomeric component that was used in the preparation 
of the copolymers in accordance with Examples A-1 to A-8. For example, a 
saponification product of a copolymer of 95 wt.-parts of vinyl acetate and 
5 wt.-parts of vinyl triethoxysilane requires at least 0.75 wt.-% of NaOH. 
The saponification product of a copolymer of 85 wt.-% vinyl acetate and 15 
wt.-% vinyl triethoxysilane required at least 10 wt.-% of NaOH, each with 
respect to the saponified copolymer. 
In Table 3 are given the relative viscosities of the saponified copolymers 
dissolved in alkali lyes, as measured on solutions of 1% by weight in 
water at 20.degree. C, with respect to the starting copolymers. 
Table 3 
______________________________________ 
Example Weight-% Silane n.sub.rel 
______________________________________ 
1 0.5 1.575 
2 1.0 1.480 
3 2.0 1.310 
4 3.0 1.230 
5 4.0 1.200 
6 5.0 1.195 
7 10.0 1.135 
8 15.0 1.105 
______________________________________ 
If the relative viscosities of the saponified and unsaponified specimens 
are compared (Tables 3 and 1), the viscosities of the saponified and 
unsaponified copolymers are of the same order of magnitude. The 
saponification of copolymers of vinyl acetate and vinyl triethoxysilane is 
thus a reaction analogous to polymerization. 
If sheets are cast from the product from Example B-5, Table 3, with varying 
pH, specimens are obtained which have varying solubility in water. Table 4 
shows the solubilities. 
The aqueous casting solutions contained 5 wt.-% of the copolymer of Example 
B-5, Table 3. If the pH is varied from 7.0 to 1, no substantial change in 
the viscosity occurs. This shows that the polymer of Formula II becomes a 
polymer of Formula III, and that siloxane bonds in accordance with Formula 
I occur only to a slight extent or not at all. 
Table 4 
______________________________________ 
pH Solubility in wt.-% in H.sub.2 O 
______________________________________ 
1.0 0 
2.0 0 
3.0 0 
4.0 6 
5.0 20 
6.0 90 
7.0 100 
______________________________________