Silylated derivatives of isobutene crosslinkable under ambient conditions, and process for preparing them

Isobutene is copolymerized with an unsaturated comonomer containing the chlorosilanic function, and the chlorosilanic function is subsequently transformed into an alkoxysilanic function by means of a reaction of alcoholysis, thus silylated copolymers of isobutene being obtained, which are crosslinkable under ambient conditions, suitable for use in sealants and paints.

FIELD OF THE INVENTION 
The present invention relates to a process for preparing silylated 
copolymers of isobutene, crosslinkable under ambient conditions of 
humidity and temperature, suitable for use in sealants and paints, as well 
as to said copolymers. 
BACKGROUND OF THE INVENTION 
In the art, elastomeric compositions are known, which contain polymers 
functionalized with reactive groups, which are fluids under ambient 
conditions, and are capable of crosslinking, due to the effect of 
atmosphere humidity, into solid and rubbery products, endowed with 
characteristics which make them useful in sealant compositions. 
U.K. Pat. No. 1,167,521 discloses a process for transforming polymers of 
hydrocarbon type, e.g., copolymers of isobutene with piperylene, into 
polymers crosslinking under the influence of the ambient humidity, by 
means of the grafting of a chlorosilane in the presence of catalysts. 
The disadvantage of the process consists in the severe grafting conditions: 
in fact, excess amounts of chlorosilane and free-radical catalysis are 
used, in as much as the milder catalysts based on platinum have resulted 
inefficacious. 
In Polymer Sci. Polymer Chem., 18th Ed., 1529 (1980) and Polym. Bull. 1 
575, (1979), Kennedy describes the preparation of 
.alpha.,.omega.-chlorosilane-derivatives of polyisobutenes, followed by 
the treatment with alcohols, to yield polymers containing the 
alkoxysilanic function, crosslinkable in the presence of ambient humidity. 
Such preparation is anyway difficultly applicable on an industrial scale, 
due to the complexity and of the high costs thereof. 
In U.S. Pat. No. 4,524,187, issued on June 18, 1985, a process is disclosed 
for preparing fluid silylated copolymers of isobutene, suitable for use in 
sealants, and crosslinkable under the influence of the ambient humidity. 
According to this process, particular copolymers of isobutene with 
1,3,7-octatriene or with 5-methyl-1,3,6-heptatriene are grafted with 
chlorosilanes, such as, e.g., HSiMeCl.sub.2 and HSiMe.sub.2 Cl. The 
alkoxysilanic functions necessary for the crosslinking are obtained by 
means of the subsequent treatment with alcohols. In this process, mild 
grafting conditions in the presence of platinum-based catalysts, or the 
like, are used. In U.S. Pat. No. 4,524,187 issued on June 18, 1985 the 
alkoxysilanic function is on the contrary directly grafted on copolymers 
of isobutene with 1,3,7-octatriene or 5-methyl-1,3,6-heptatriene, by means 
of the reaction with thiomercaptopropylalkoxysilanes in the presence of 
free-radical or anionic catalysts. 
The processes disclosed in said U.S. Patent is burdensome and shows the 
drawback that the special copolymers of isobutene with 1,3,7-octatriene or 
5-methyl-1,3,6-heptatriene must be produced according to a process wherein 
blends of (chlorinated/non-chlorinated) solvents are used, to secure the 
solubility of the catalyst, with this latter being furthermore used in 
large amounts, and that in the subsequent grafting reaction the solvent 
must be changed. 
SUMMARY OF THE INVENTION 
The present Applicant has found now that it is possible to overcome the 
drawbacks deriving from the present state of the art, by means of a 
process which makes it possible to obtain a silylated polyisobutene which 
crosslinks under ambient conditions of temperature and pressure, by means 
of the direct copolymerization of isobutene with a suitable comonomer 
containing the chlorosilanic function, and the subsequent conversion of 
the chlorosilanic bond into the alkoxysilanic bond by reaction with the 
corresponding alcohol. 
A purpose of the present invention is therefore a process for the 
preparation of fluid silylated copolymers of isobutene, crosslinkable 
under ambient conditions of humidity and temperature, suitable for use in 
sealants and paints. 
Another purpose of the present invention are said copolymers. 
A further purpose of the present invention are formulations suitable for 
use in the field of sealants and of paints containing said copolymers. 
DESCRIPTION OF THE INVENTION 
In accordance with the above purposes, according to the present invention 
silylated copolymers of isobutene, crosslinkable under ambient conditions 
of humidity and temperature, which are suitable for use in sealants and 
paints, are prepared by means of a process according to which: 
(a) isobutene is copolymerized with a silylated unsaturated comonomer 
defined by the formula: 
##STR1## 
wherein: R and R'=H, CH.sub.3 ; 
R"=an alkyl radical containing from 1 to 5 carbon atoms; 
X=Cl, Br; 
n=0, 1, 2; 
and the substituents on the benzene rings are in ortho, or meta, or para 
position, by operating in solution, in inert organic solvents, at a 
temperature comprised within the range of from -100.degree. C. to 
0.degree. C., in the presence of Lewis' acids catalysts, until copolymers 
with an Mn of from 2,000 to 50,000 are obtained, which contain percentages 
of from 0.1 to 10% by weight of the silylated comonomer; 
(b) the so-obtained copolymer is treated with an aliphatic alcohol of from 
1 to 5 carbon atoms, to yield an end polymer containing the alkoxysilanic 
function: 
##STR2## 
wherein: R, R', R", n have the above seen meaning; and 
R'"=an alkyl radical of from 1 to 5 carbon atoms; 
(c) the copolymer is recovered from the reaction mixture. 
According to the present invention, the unsaturated silylated comonomer (I) 
can be obtained by means of the hydrosilation of divinylbenzene (either 
pure, or as the commercial mixture of ethylvinylbenzene-divinylbenzene) or 
of dipropenylbenzene, with halosilanes of the type: 
##STR3## 
wherein R", X and n have the above seen meaning, in the presence of 
catalytic amounts of chloroplatinic acid. 
The reaction is carried out at a temperature of from 40.degree. to 
80.degree. C. and for a time of some hours under an atmosphere of an inert 
gas in an anhydrous environment. 
The preferred silylating agent is HSiMeCl.sub.2 (Me=CH.sub.3), but also 
HSiCl.sub.3, HSiMe.sub.2 Cl can be used. An advantage of the present 
invention is the fact that for the subsequent copolymerization with 
isobutene, the raw product coming from such a hydrosilation reaction can 
be used, without separating the pure comonomer (I) being necessary. 
The copolymerization of isobutene with the unsaturated silylated comonomer 
(I) (either in pure form, or as the raw material outcoming from the 
hydrosilation reaction) is carried out in solution, in inert, anhydrous, 
organic solvents, in particular, aliphatic hydrocarbons, such as, e.g., 
pentane, hexane, isopentane, heptane, kerosene, either pure or mixed with 
one another. 
As the copolymerization catalysts, Lewis' acids, are used, preferably 
AlCl.sub.3, which is charged to the copolymerization reaction as a 
suspension in hydrocarbons of particles having an average dimension of 
from 0.5 to 2.mu., at the concentration of from 0.1 to 2% by weight. 
The reaction temperature is comprised within the range of from -100.degree. 
C. to 0.degree. C. and preferably of from -60.degree. C. to 0.degree. C., 
and the reaction is carried out under an atmosphere of inert gas, in an 
anhydrous environment. 
By controlling the temperature within the above said range, it is possible 
to obtain copolymers having a desired molecular weight (Mn of from 2,000 
to 50,000, and preferably of from 2,500 to 20,000). 
For the purpose of regulating the molecular weight, chain transfer agents 
can be furthermore used, such as, e.g., tert.butyl chloride, allyl 
chloride and bromide, or, if one does not wish to use halogenated 
compounds, indene, cyclopentadiene, isooctene, and so forth, can be used. 
The unsaturated silylated comonomer is extremely reactive and copolymerizes 
to a complete extent, within a time comprised within the range of from 5 
to 30 minutes. 
The amounts of comonomer regarded as optimum in the copolymer are comprised 
within the range of from 0.1 to 10% by weight, or, preferably, from 1 to 
5% by weight. 
To the polymeric solution contained inside the polymerization reactor, an 
aliphatic alcohol of from 1 to 5 carbon atoms is added, in an amount from 
1.5 to 5 times as large as the amount required by the stoichiometry of 
alcoholysis of the Si--Cl and Al--Cl bonds, and an HCl-blocker is added, 
in a molar ratio of the HCl-blocker to the alcohol of from 3/1 to 4/1. 
This reaction occurs normally at a temperature comprised within the range 
of from room temperature (20.degree.-25.degree. C.) to approximately 
40.degree. C. 
Practically, the alcohol is added to the polymeric solution coming from the 
polymerization step at the polymerization temperature, and temperature is 
permitted to increase up to the indicated values. 
The preferred alcohol is methanol, due to its volatility, and the hydrogen 
chloride blocker is usually a low molecular weight epoxide, such as, e.g., 
propylene oxide or ethylene oxide, or an orthoformate, e.g., trimethyl 
orthoformate. 
The conversion of the chlorosilanic groups into alkoxysilanic groups is 
quantitative, and at the end of the reaction, the AlCl.sub.3 catalyst, 
which precipitates from the polymeric solution as Al(OR'").sub.3, can be 
removed by simple filtration or decantation. 
The silylated copolymers obtained by means of the process of the present 
invention are characterized in that they contain at least one molecule, 
and preferably two molecules, of silylated comonomer, per each 
macromolecule, and have an Mn comprised within the range of from 2,000 to 
50,000, and preferably of from 2,500 to 20,000, and can be used in the 
field of the sealants and of the paints, wherein a low permability to 
water, a considerably high resistance to oxidation and to the chemical 
agents, excellent electrical properties are required. 
Such copolymers can be used as such, or to them diluents and/or plastifiers 
can be added, and they can be used in formulations containing crosslinking 
catalysts, siliceous materials, mineral fillers, dyeing agents, UV 
absorbers, and so forth. 
The catalysts are generally constituted by salts and organic compounds of 
heavy metals, such as, e.g., dibutyltin dilaurate or titanium 
tetrabutoxide and/or by aliphatic amines, such as, e.g., laurylamine. 
Among the siliceous materials, in particular amorphous silica can be used. 
The advantages achieved with the preparation of said fluid silylated 
copolymers of isobutene according to the process disclosed in the present 
invention are numerous. 
First of all, the preparation of the copolymer containing the chlorosilanic 
function can be carried out in one single step only, and the subsequent 
transformation of the chlorosilanic function into the alkoxysilanic 
function can be carried out inside the same reactor, and with the same 
solvent. 
The efficacy, then of the alkoxysilanic function introduced is such that, 
for copolymers having an Mn comprised within the range of from 2,000 to 
50,000, amounts of comonomer of from 0.1 to 2% by weight in the copolymer 
are enough to cause the same copolymer to crosslink due to the effect of 
the ambient humidity and at ambient temperature, with amount of end gel 
larger than 60% by weight, relatively to the weight of the crosslinked 
material. 
The silylated copolymers obtained by the process disclosed in the present 
invention show, after the crosslinking, excellent mechanical properties, 
higher than of the polymers of the prior art, with the molecular weight 
and the crosslinking function being the same (ultimate tensile strength of 
from 3 to 10 kg/cm.sup.2, elongation at break from 200 to 800%), combined 
with a considerable adhesion to many substrates such as, e.g., glass and 
concrete, without the aid of primers or of adhesion promoters. 
Such copolymers are furthermore endowed with the excellent properties of 
chemical resistance and of barrier for gases, which is typical of 
isobutene polymers. 
Because of the total absence of unsaturations, said copolymers are endowed 
with chemical-physical characteristics better than any other polymers 
which can be obtained by direct silylation, of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following examples are illustrative and not limitative of the same 
invention. 
Example 1 
To a reaction tube perfectly dry, and equipped with a side stopcock and 
screw cover, under a nitrogen atmosphere 18 g of commercial divinylbenzene 
(mixture of 45% by weight of ethyldivinylbenzene), 16.6 g of 
methyldichlorosilane and 4.10.sup.-5 mol of H.sub.2 PtCl.sub.6 (as a 0.73M 
solution in isopropanol) are charged. 
The reaction tube, perfectly sealed, is heated in an oil bath at 60.degree. 
C. for 4 hours, with magnetic stirring. After the contents being cooled 
down to room temperature, they are stripped under vacuum, to remove 
unreacted chlorosilane. The obtained product is not furthermore purified, 
but is used as such in the copolymerizations with isobutene. 
On the basis of the gas-chromatographic analysis, it is possible to 
determine that the product mixture is constituted by 86% of monosilylated 
products, with the balance to 100% being mainly constituted by unreacted 
ethylvinylbenzene. 
Example 2 
To a glass reactor of 400 ml of capacity, perfectly dry, equipped with 
mechanical stirrer, nitrogen inlet and low-temperature thermometer, 150 ml 
of anhydrous hexane is charged. 
The reactor is then cooled to the temperature of -60.degree. C. with a dry 
ice-ethanol bath. 
To such reactor, 25 ml of anhydrous isobutene and 1 g of comonomer (I), 
prepared as in Example 1, are added. 
The operations are all carried out under an inert atmosphere of nitrogen. 
To the reaction mixture, cooled to the temperature of -50.degree. C. and 
kept stirred, during a time of approximately 15 minutes 6 ml of an hexanic 
suspension of AlCl.sub.3 at 1.5% by weight is added, while the temperature 
is controlled to remain within the range of from -55.degree. C. to 
-45.degree. C. 
When the addition of the suspension of AlCl.sub.3 is complete, the reaction 
mixture is maintained at -50.degree. C. for a 30-minute time. To the 
polymerization reactor, 5 ml of a methanol/propylene oxide, in a molar 
ratio of 1/4 to each other, is then added. 
At the end of the addition, the temperature is allowed to increase up to 
room values (20.degree.-25.degree. C.). 
The catalyst, which has precipitated as Al(OMe).sub.3, is filtered off, and 
the solvent is eliminated by stripping under vacuum. 
The polymer is obtained with a conversion yield of 90%. 
The polymer shows the following characteristics: 
viscosity at 50.degree. C. (.eta..sup.50): 10.sup.4 Pa.s; 
number average molecular weight (Mn): 10,000. 
The polymer, after the addition to it of 1% of usual stabilizers, and of 1% 
of laurylamine and dibutyltin dilaurate as crosslinking catalysts, is used 
to spread a film of 2 mm of thickness, for the purpose of evaluating the 
parameters relating to the crosslinking under room conditions. The 
following results are obtained: 
time to touch dry: 1-2 hours 
Gel % after 10 days: 80%. 
On the crosslinked material, after that constant values of gel % are 
reached, mechanical tests for tensile strength are carried out. The 
following results are obtained in accordance with ASTM D-412: 
modulus at 100%: 2.92 kg/cm.sup.2 
ultimate tensile strength: 7.01 kg/cm.sup.2 
elongation at break: 430% 
elastic recovery (after 5 minutes): 98% 
Example 3 
By following the same operating modalities as of Example 2, to the reactor 
250 ml of anhydrous hexane, 20 g of anhydrous isobutene and 0.5 g of 
comonomer (I), prepared as in Example 1, are added. 
For the polymerization, 8 ml is used of hexanic suspension of AlCl.sub.3, 
and in the following reaction of alcoholysis, 5 ml of methanol/propylene 
oxide mixture in the mutual ratio of 1/4 is added. 
The polymer is obtained with a conversion yield of 90%, and shows the 
following characteristics: 
viscosity at 50.degree. C. (.eta..sup.50): 3.10.sup.4 Pa.s; 
number average molecular weight (Mn): 11,000. 
The polymer, after the addition to it of 1% of usual stabilizers, and of 1% 
of laurylamine and dibutyltin dilaurate as the crosslinking catalyst, is 
spread as a film of 1.5 mm of thickness, and the following results are 
obtained: 
time to touch dry: 1-2 hours 
Gel % after 10 days: 75%. 
On the crosslinked material, after that constant values of gel % were 
obtained, mechanical tests for tensile strength were carried out. The 
following results were obtained in accordance with ASTM D-412: 
modulus at 100%: 0.89 kg/cm.sup.2 
ultimate tensile strength: 3.25 kg/cm.sup.2 
elongation at break: 650% 
Example 4 
By following the same operating modalities as of Example 2, to the reactor 
250 ml of anhydrous hexane, 20 g of anhydrous isobutene and 2 g of 
comonomer (I), prepared as in Example 1, are added. 
The polymerization is carried out at -30.degree. C., making sure that 
during the addition of 4 ml of hexanic suspension of AlCl.sub.3 the 
temperature remains within the range of from -35.degree. to -25.degree. C. 
For the following reaction of alcoholysis, 10 ml of methanol/propylene 
oxide in the mutual ratio of 1/4 is used. 
The polymer is obtained with a conversion yield of 85%, and shows the 
following characteristics: 
viscosity at 50.degree. C. (.eta..sup.50): 450 Pa.s; 
number average molecular weight (Mn): 4,000. 
The polymer is treated as in Example 3, and the characteristics of the film 
are: 
time to touch dry: 36 hours 
Gel % after 9 days: 70%. 
The mechanical tests for tensile strength, carried out on the crosslinked 
material, after that constant values of gel % were obtained, gave the 
following results, in accordance with ASTM D-412: 
modulus at 100%: 1.73 kg/cm.sup.2 
ultimate tensile strength: 4.30 kg/cm.sup.2 
elongation at break: 289% 
Example 5 
In this Example, the polymer was prepared by following the same modalities 
as reported in Example 3, both as relates the proportions of the 
reactants, and as relates to the temperature of polymerization. The 
so-obtained polymer was used for preparing a formulation having the 
following percent composition by weight: 
polymer: 60.6% 
plasticizer (Vistanex polybutenes): 15.1% 
solvent (toluene, xylene): 15.1% 
SiO.sub.2 : 7.5% 
antioxidant: 0.8% 
U.V. stabilizer: 0.8% 
To the formulation, 0.5% of laurylamine and 1% of dibutyltin dilaurate were 
added, and the formulation was made crosslink in the air, as in the 
preceding Example. The following results were obtained: 
time to touch dry: 1-2 hours 
Gel % after 30 days: 54%. 
The mechanical tests for tensile strength, carried out on the crosslinked 
material, after that constant values of gel % were obtained, gave the 
following results, in accordance with ASTM D-412: 
modulus at 100%: 0.60 kg/cm.sup.2 
ultimate tensile strength: 4.77 kg/cm.sup.2 
elongation at break: 720%