Silacyclobutane functional polymers and their production

The silacyclobutane functional polydiorganosiloxane copolymers of the invention have the following structure: ##STR1## wherein M is selected from ##STR2## wherein R.sup.a, R.sup.b, R.sup.c, R.sup.d, R.sup.e, and R.sup.f are independently monovalent radicals selected from the group consisting of hydrogen, hydrocarbon, or substituted hydrocarbon; m and x are integers of from 0 or more; n is equal to 1; and p is an integer greater than 0; with the proviso that there is at least one silacyclobutane group in the copolymer. The copolymer can be made by reacting a hydroxyl endblocked polydiorganosiloxane with either a difunctional chain extending silacyclobutane or with a monofunctional chain stopper, or a mixture of chain extender and chain stopper. The copolymer can be made into curable compositions by use of suitable catalyst.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to silacyclobutane functional siloxanes. 
2. Background information 
Silacyclobutane monomers are known and have been polymerized. To 
applicants' knowledge, however, stable silacyclobutane functional 
polyorganosiloxanes have not previously been made in high yield by a 
method which allows controlled design of the polymer structure. The 
polymers of the invention are useful intermediates for formulating room 
temperature vulcanizable and hot air vulcanizable silicone elastomers. 
The preparation of silacyclobutanes of the formula 
##STR3## 
where Y is chlorine or hydrogen, R' is hydrogen or methyl, and R is a 
monovalent hydrocarbon radical free of aliphatic unsaturation, and 
polymers derived therefrom, were revealed by Sommer in U.S. Pat. No. 
3,046,291, issued July 24, 1962. Polymerization was accomplished upon 
heating or simply standing and optionally in the presence of a catalyst 
from the group consisting of alkaline materials such as NaOH, KOH, LiOH; 
quaternary ammonium compounds; and metallic salts of sodium, aluminum, 
iron, cobalt, manganese, lead and zinc. 
Siloxane derivatives of silacycloalkanes of the formula 
##STR4## 
where n is 3, 4, or 5, and R is methyl, phenyl, or chlorine, were reported 
by Nametkin, Vdovin, and Babich in Khim. Geterotsikl. Soedin, (Chemistry 
of Heterocyclic Compounds) (1966) (4) 630. They were obtained by 
hydrolysis or cohydrolysis of silacycloalkanes with alkylsilanes having 
OH, ONa, or OAc groups at the silicon atom. 
Mixtures of siloxane derivatives of silacycloalkanes are prepared by this 
route and contain both desireable and undesirable species whose 
composition is dependent upon the reaction conditions employed. 
Preparation of siloxane derivatives of silacyclobutanes by a hydrolysis 
route is also undesirable as the silacyclobutane ring is known to react 
with water, thus opening the silacyclobutane ring and rendering it less 
reactive. 
U.S. Pat. No. 3,398,178, issued Aug. 20, 1968 to Nelson, teaches how 
silacyclobutanes react with a catalytic amount of halogenated silane, 
hydrohalic acid or aluminum halide to polymerize by opening the ring to 
form a polymer consisting essentially of 
##STR5## 
In U.S. Pat. No. 3,445,495, issued May 20, 1969, Nelson teaches the 
formation of similar polymers by polymerizing silacyclobutanes in the 
presence of a platinum catalyst, and, optionally, a silane monomer 
containing an SiH bond. 
Jonas and Owen show alkoxy and amino silacyclobutanes in U.S. Pat. No. 
3,687,995, issued Aug. 29, 1972, which they say may be reacted with 
organosilicon materials containing SiOH groups and therefore may be useful 
as cross-linking agents. This use is claimed in U.S. Pat. No. 3,694,427. 
These compositions have the disadvantage of undergoing gradual increase in 
viscosity with time, requiring the components to be stored separately if 
spontaneous thickening is undesirable. Further, these formulations emit 
volatile condensation byproducts. 
SUMMARY OF THE INVENTION 
Silacyclobutane functional polydiorganosiloxane copolymers which can be 
crosslinked to give a useful 3-dimensional network structure are prepared 
from a hydroxyl endblocked polydiorganosiloxane, a dihydrolyzable 
silacyclobutane, and a monohydrolyzable silane. 
DESCRIPTION OF THE INVENTION 
The silacyclobutane functional polydiorganosiloxane copolymers of the 
invention have the following structure: 
##STR6## 
wherein M is selected from 
##STR7## 
wherein R.sup.a, R.sup.b, R.sup.c, R.sup.d, R.sup.e, and R.sup.f are 
independently monovalent radicals selected from the group consisting of 
hydrogen, hydrocarbon, or substituted hydrocarbon; m and x are integers of 
from 0 or more; n is equal to 1; and p is an integer greater than 0; with 
the proviso that there is at least one silacyclobutane group in the 
copolymer. Generally, the copolymer will have an average molecular weight 
between 1,000 and 1,000,000. 
The silacyclobutane functional polydiorganosiloxane copolymers can be made 
by reacting a siloxane of the formula HO(R.sup.a.sub.2 SiO).sub.m H with 
either a chain extending silacyclobutane of the formula 
##STR8## 
or with a chain stopper selected from those of the formula 
##STR9## 
wherein Y is a radical or atom reactive with the SiOH group and selected 
from the group consisting of halogen, 
##STR10## 
or both chain extender and chain stopper, wherein R is independently a 
monovalent radical, as are R.sup.a, R.sup.b, R.sup.c, R.sup.d, R.sup.e, 
R.sup.f and R.sup.g, and wherein m is an integer sufficient to define a 
polydiorganosiloxane, i.e., 2 or more, n is an integer of from three to 
five and z is an integer of from one to three. 
Exemplary of suitable monovalent radicals for the R, R.sup.a, R.sup.b, 
R.sup.c, R.sup.d, R.sup.e, R.sup.f, and R.sup.g groups are hydrogen, the 
hydrocarbons, or substituted hydrocarbons. Thus, for example, these groups 
can be alkyl such as methyl, ethyl, propyl or octadecyl; substituted alkyl 
such as aminopropyl or thiopropyl; haloalkyl such as chloropropyl; aryl 
such as phenyl, xenyl or naphthyl; alkaryl such as tolyl or xylyl; aralkyl 
such as benzyl; unsaturated alkenyl such as vinyl, propenyl, or hexenyl; 
and unsaturated alkynyl such as acetylenyl or propynyl. R.sup.a, R.sup.e, 
and R.sup.f are preferably methyl, vinyl, phenyl, ethyl, hydrogen, or 
trifluoropropyl, and most preferably methyl. R.sup.d is preferably methyl, 
ethyl, vinyl, phenyl, or hydrogen, and most preferably methyl. R.sup.b, 
R.sup.c, and R.sup.g are preferably methyl or hydrogen and most preferably 
hydrogen. The cyclobutane ring containing the R.sup.b and R.sup.c radicals 
can be substituted or unsubstituted. The term "silacyclobutane" throughout 
this disclosure is intended to include either the unsubstituted 
cyclobutane ring or the substituted ring. 
Suitable halogens for Y are chlorine and bromine with the former preferred. 
Suitable RO- groups include CH.sub.3 O--, CH.sub.3 CH.sub.2 O--, and 
CH.sub.2 .dbd.C(CH.sub.3)O--. Suitable R.sub.2 N--groups include H.sub.2 
N--and (CH.sub.3 CH.sub.2).sub.2 N--. 
##STR11## 
It is preferred that the Y groups of the difunctional chain extender be the 
same as the Y group of the monofunctional endblocker. It is also most 
preferred that the Y group is Cl. The use of a difunctional chain extender 
is not necessary if a difunctional siloxane polymer endcapped with the 
silacyclobutane group is the desired product. Further, the use of a 
monofunctional endblocker is optional if the polymer composition is 
required to crosslink upon mixing of the silanol terminated polysiloxane 
and the difunctional silacyclobutane chain extender. The use of a 
monofunctional silacyclobutane endcapper is preferred if a room 
temperature stable, fluid polymer is desired. 
The polymers can be prepared by mixing the ingredients together at a mild 
temperature between about -50.degree. C. and about 100.degree. C., at 
atmospheric pressure and, optionally, with a solvent. Suitable solvents 
include toluene, tetrahydrofuran, diethyl ether, benzene, chloroform, and 
methylene chloride. For best results, the polydiorganosiloxane, 
HO(R.sup.a.sub.2 SiO).sub.m H, has a hydroxyl stoichiometry equivalent to 
or up to 10 percent less than the reactive groups (Y) on the 
silacyclobutane. When the silacyclobutane has one or more halogen groups, 
it is preferred to use a hydrogen halide acceptor in the reaction mixture. 
Typical hydrogen halide acceptors include: calcium carbonate, 
triethylamine, or pyridine. Any solid byproducts can be removed by 
filtration. 
The solvent and volatile byproducts can be removed by reduced pressure 
distillation and a fluid polymer recovered. It will be seen from the 
examples that, without an end blocker, a gel is formed as the polymer 
molecular weight is uncontrollable, and partial crosslinking may occur. 
There may be some unreacted hydroxyl groups present in the copolymer also, 
depending upon the ratio of the ingredients used in the preparation. 
The silacyclobutane functional polydiorganosiloxane copolymers of the 
invention may be cured to useful elastomers by vulcanization to cause ring 
opening polymerization of the silacyclobutane groups and formation of a 
crosslinked network of polydiorganosiloxanes. Generally, a temperature of 
greater than 150.degree. C. is required to crosslink the 
polydiorganosiloxane copolymers in a useful time of less than 1 day. A 
catalyst may be used to lower the cure temperature and accelerate the rate 
of cure. Useful catalysts include compounds and supported metals of the 
noble (platinum group) metals and compounds of aluminum, zinc and tin. 
Preferred are homogeneous compounds and supported heterogeneous metal 
catalysts of platinum, palladium, rhodium, ruthenium and iron, and most 
preferred are homogeneous and heterogeneous catalysts of platinum. Metal 
concentrations of from 0.1 to 1000 ppm may be used with a preferred range 
of 5 to 50 ppm metal. In the presence of this type of catalyst, the 
vulcanization time will vary with the form of catalyst, concentration of 
catalyst and temperature. Vulcanization temperatures of greater than 
100.degree. C. are preferred to cure the silacyclobutane functional 
polydiorganosiloxane copolymers in a useful time, but vulcanization can be 
slowly accomplished even at room temperature in the presence of a 
catalyst. 
The rate of vulcanization can be further accelerated by the addition of an 
organosilicon compound containing an SiH bond. Further, the degree of 
crosslinking and hence the physical properties of the cured elastomer can 
be predictably varied by adjusting the concentration of SiH functional 
material. Useful SiH organosilicon compounds may contain one or more 
silicon atoms and one or more SiH bonds. The concentration of the SiH 
functional organosilicon compound can be described by the ratio of SiH 
functionality to silacyclobutane group and may vary from greater than zero 
with no upper limit. A preferred SiH to silacyclobutane ratio is from 
0.001 to 2.0 and most preferred is a ratio of 0.1 to 0.5 with the 
understanding that the preferred ratio of SiH to silacyclobutane depends 
upon the degree of crosslinking required for the product elastomer. 
The preparation of polyorganosiloxane elastomers by vulcanization is 
generally accomplished in the art by heating the polymer formulation in 
the presence of organic peroxides or by heating a formulation of 
ethylenically unsaturated and SiH functional polyorganosiloxanes in the 
presence of a metal, preferably platinum, catalyst. For the latter, 
crosslinking is accomplished by the addition of the SiH bond to the 
unsaturated group, a reaction known as hydrosilation. For this cure 
system, the ratio of SiH to unsaturated groups is generally kept greater 
than 1. The vulcanization of silacyclobutane functional 
polydiorganosiloxanes with SiH functional materials thus requires the use 
of less SiH functional material than the vulcanization of unsaturated 
functional polydiorganosiloxanes. Additionally, the vulcanization of 
silacyclobutane functional polydiorganosiloxanes in the presence of SiH 
functional materials leads to a higher crosslink density than 
vulcanization of comparable vinyl functional polydiorganosiloxanes in the 
presence of SiH functional materials. 
The vulcanization of silacyclobutane functional polydiorganosiloxane 
copolymers may be performed in the presence of additives known in the art 
to improve the processing, cure and resultant physical properties of the 
material. Such additives include, but are not limited to, fillers such as 
fumed silica, carbon black, iron oxide and calcium carbonate; process aids 
such as silicone fluids; pigments; adhesion promoters; mold release 
agents; stabilizers such as metals and their oxides; and catalysts. 
Vulcanization of the silacylobutane functional polydiorganosiloxanes may be 
accomplished by heating in a mold or oven. Heating may also be performed 
by irradiation with infrared, ultraviolet, photomagnetic, or microwave 
radiation and, optionally, in the presence of a material which absorbs the 
incident radiation. Heating may also be performed inside an oscillating 
magnetic field in the presence of paramagnetic material, a process known 
as induction heating. 
The silacyclobutane group has been shown to be inert to free radicals in 
the condensed phase and at or near room temperature. Therefore, 
crosslinking of silacyclobutane functional polydiorganosiloxanes by 
ultraviolet irradiation in the presence of a photoinitiator or electron 
beam irradiation is not expected to occur. However, the silacyclobutane 
functional polydiorganosiloxanes were found to undergo crosslinking under 
ultraviolet light when a photoinitiator was present at rates slightly 
faster than in control experiments with polydiorganosiloxanes containing 
only methyl functionality. Similarly, the silacyclobutane functional 
polymers underwent electron beam curing at rates slightly faster than the 
polymers containing only the methyl group. 
The silacyclobutane functional polydiorganosiloxane copolymers of the 
invention may also be crosslinked upon exposure to atmospheric moisture, a 
process known as room temperature vulcanization (RTV). This process can be 
accelerated in the presence of a nucleophilic or basic catalyst. 
Hydrolysis of the silacyclobutane group is thought to provide an n-propyl 
silanol which can undergo condensation to give a siloxane bond: 
##STR12## 
Thus, when the silacyclobutane groups are attached to a polymer chain, 
they can react with water and condense to form a siloxane bond between the 
polymer chains. This cure system has a distinct advantage over 
conventional RTV cure systems used in the art to crosslink silicones: no 
volatile condensation byproducts such as acetic acid, alcohol, ketone, 
oxime or amine are generated during curing and therefore no byproducts are 
released. An RTV silicone which does not release condensation byproducts 
is desireable in confined spaces where the byproduct cannot dissipate or 
in applications where the cure byproduct poses a safety, flammability, 
toxicity, irritation or environmental hazard. Additionally, a cure system 
which evolves no condensation byproduct is desired to give lower shrink 
upon exposure to moisture. 
The silacyclobutane functional polymers of the invention may be formulated 
into one part RTV sealants consisting of the following parts: 
A. The silacyclobutane functional polymer as defined previously 
B. Catalyst 
C. Optional filler and other additives 
The catalyst (B.) is HONR.sub.2 or diorganoaminoxy functional 
polyorganosiloxane such as R.sub.3 SiO(R.sub.2 SiO).sub.a (RXSiO).sub.b 
SiR.sub.3 or (RXSiO).sub.c (R.sub.2 SiO).sub.d where X is --ONR.sub.2, a 
and d are equal to or greater than 0, b is equal to or greater than 1, c 
plus d is equal to or greater than 3, and R is a monovalent radical. The 
preferred catalyst is diethylhydroxyl amine. The optional fillers include 
silica, alumina, metal carbonates and metal oxides. The sealant may be 
extruded and cured by atmospheric exposure.

The following examples will serve to illustrate the invention. All parts 
and percentages in said examples and elsewhere in the specification and 
claims are by weight unless otherwise indicated. 
EXAMPLE 1 
To a solution of 100 g HO(Me.sub.2 SiO).sub.x H, (0.23 percent OH by weight 
and a number average molecular weight (Mn) of 14,500, Polymer A) and 7.10 
g triethylamine in 100 g diethyl ether was added a solution of 1.80 g 
1-chloro-1-methylsilacyclobutane in 19 g diethyl ether. The polymer 
solution was stirred for 16 hours, filtered and stripped to 70.degree. C. 
and 1 mm Hg to give 95 g of clear polymer. The polymer was characterized 
by gel permeation chromatography. It had a weight average molecular weight 
(Mw) of 38,000, a number average molecular weight (Mn) of 15,000, and a 
dispersion ratio (Mw/Mn) of 2.5. 
Incorporation of the silacyclobutane group into the polymer was 
demonstrated by crosslinking of the polymer upon heating in the presence 
of a platinum catalyst. A catalyst was prepared from chloroplatinic acid 
complex of divinyltetramethyldisiloxane diluted with dimethylvinylsiloxy 
endblocked polydimethylsiloxane to provide 0.7 weight percent platinum. To 
1.02 g of the above polymer was added 2.0 milligrams of the above catalyst 
to give a concentration of 13 parts of platinum per million parts of 
polymer (ppm). An 8 mil film of the mixture was drawn onto an aluminum 
panel and the fluid film heated at 157.degree. C. for ten minutes to give 
a free standing elastomeric film. When polymer A, containing no 
silacyclobutane group, was similarly vulcanized with the platinum 
catalyst, it failed to undergo crosslinking, and an elastomer was not 
formed. 
EXAMPLE 2 
To a solution of 50.2 g HO(Me.sub.2 SiO).sub.x H (1.82 percent OH by weight 
and a Mn of 2,400, Polymer B) and 32.5 g triethylamine in 153 g diethyl 
ether was added a solution of 6.04 g 1,1-dichlorosilacyclobutane in 20 g 
diethyl ether. After stirring for 10 minutes, a solution of 2.33 g 
trimethylchlorosilane in 20 g diethyl ether was added, and stirring 
continued for 135 minutes. The mixture was filtered, stripped to 
50.degree. C./0.4 mm Hg, redissolved in ether, pressure filtered through 
0.45 micron pore size membrane and stripped to 50.degree. C./0.4 mm Hg to 
give a clear colorless fluid having a Mw of 40,000, a Mn of 19,000, and a 
Mw/Mn of 2.1. This polymer was characterized by proton NMR, which showed a 
chemical shift of delta equal to 1.52 ppm for the silacyclobutane protons 
and 0.17 ppm for the methyl protons. Integration gave a ratio of one 
Si(CH.sub.2 CH.sub.2 CH.sub.2) group per 17 Si(CH.sub.3).sub.2 groups. 
The above polymer was vulcanized at room temperature by mixing in a 
catalytic amount of diethylhydroxylamine in the amount shown in Table I, 
pouring the catalyzed material into a 1 inch by 1 inch chase to a 
thickness of 0.15 inch, and then exposing to atmospheric moisture at 37 
percent relative humidity. The skin over time (SOT) and tack free time 
(TFT) were measured as the materials cured. The SOT is the time for a 
nonflowable skin to form over the surface. The TFT is the time required 
for the surface to reach a degree of cure such that a 1 inch wide strip of 
polyethylene film applied to the surface peels freely away without any 
material sticking to the film. 
TABLE I 
______________________________________ 
Polymer Et.sub.2 NOH 
SOT TFT 
Sample No. (grams) (gram) (hours) 
(hours) 
______________________________________ 
1 5.01 0.34 1.0 3.7 
2 5.01 0.084 1.0 4.5 
3 5.02 0.017 2.5 4.5 
4 7.32 0.0069 3.7 5.5 
5 5.0 0 did not cure 
______________________________________ 
Samples 1 through 4 were stored in aluminum tubes at least 4 months and 
were found to be stable in the absence of moisture. When exposed to 
moisture, they cured at a rate comparable to the initial rate shown in 
Table I. 
EXAMPLE 3 
To a solution of 150.7 g of HO(Me.sub.2 SiO).sub.x H, (0.14 percent OH by 
weight and a Mn of 24,000, Polymer C) and 2.54 g triethylamine in 350 g 
diethyl ether was added a solution of 0.16 ml 
1-chloro-1-methylsilacyclobutane and 0.72 ml 1,1-dichlorosilacyclobutane 
in 50 ml diethyl ether. The mixture was stirred for 3 hours, filtered and 
stripped to 75.degree. C./1.5 mm Hg to give a clear polymer having a Mw of 
582,000, a Mn of 127,000, and a Mw/Mn of 4.6. To 43 g of this polymer was 
milled in enough of the platinum catalyst of Example 1 to give 19 ppm 
platinum. The catalyzed gum cured to an elastomer upon standing at room 
temperature for one day. In the absence of catalyst, the gum remained 
fluid after two weeks. 
To 35 g of the polymer was added enough of the platinum catalyst to give 19 
ppm platinum. The product catalyzed gum was molded into a sheet and heated 
at 180.degree. C. for 20 minutes to give an elastomer with a tensile 
strength of 53 psi, an elongation of 509 percent, and a modulus at 200 
percent elongation of 22 psi. 
EXAMPLE 4 
This composition contained no endblocker and the composition formed was a 
crosslinked gel. To 150 g of Polymer C and 2.55 g of triethylamine in 352 
g of diethyl ether was added a solution of 0.80 ml 
1,1-dichlorosilacyclobutane in 50 g diethyl ether. After stirring for 21 
hours, the mixture was filtered and stripped to 75.degree. C. at 1.5 mm 
Hg. The clear colorless polymer exhibited viscous flow but gelled to a 
crosslinked elastomer upon standing for 11 days. 
EXAMPLE 5 
To 100 g of Polymer B was added 9.94 g 
##STR13## 
and 10 ml toluene. The solution was stirred for 15 days and then stripped 
to 81.degree. C. at 4 mm Hg to give a slightly hazy fluid. 
To 0.50 g of the product polymer was added 3.1 mg of a 0.4 percent solution 
of di-mu-chloro-dichlorobis(tri-n-butylphosphine)diplatinum in toluene to 
give 55 ppm platinum. The mixture was vulcanized at 135.degree. C. for 20 
minutes to give a hard crosslinked elastomer. 
To another 0.5 g of the product polymer was added 5.5 mg of a 5.0 percent 
solution of tris(triphenylphosphine)rhodium chloride in toluene to give 60 
ppm rhodium. The mixture was heated at 205.degree. C. for 20 minutes to 
give a hard crosslinked elastomer. In the absence of a catalyst, the 
polymer showed no sign of crosslinking after heating at 205.degree. C. for 
2 hours. In the absence of catalyst, the product polymer remained fluid 
after 16 months. 
EXAMPLE 6 
To a solution of 50.0 g Polymer B in 100 g toluene was added a solution of 
2.06 g 
##STR14## 
in 15 ml toluene. The mixture was stirred 20 minutes at 25.degree. C., 
then 16 hours at 70.degree. C., then 72 hours at 25.degree. C. Enough 
toluene was added to give 167 g total solution which was divided as 
follows: A. To 55.4 g of the solution was added 0.24 g 
##STR15## 
in 10 ml toluene. 
The mixture was stirred at 70.degree. C. for 7.5 hours, then at 25.degree. 
C. for 20 hours. The mixture was stripped to 75.degree. C./1 mm Hg to 
yield 17.0 g viscous fluid with a slight haze having a Mw of 21,000, a Mn 
of 7,000, and a Mw/Mn of 3. To 2 g of the product polymer was added 64 mg 
of the catalyst of example 1 to give 200 ppm platinum. The mixture was 
poured into an aluminum cup and heated 10 minutes at 150.degree. C. to 
give a hard elastomer. The product polymer did not cure after 30 minutes 
at 200.degree. C. in the absence of catalyst. 
B. As a comparative example, no endblocker was added to a portion of the 
solution and solvent removal as above gave a crosslinked gel. The 
remainder of the solution was stripped to 75.degree. C. at less than 1 mm 
of Hg to give a clear, viscous fluid. The fluid gelled to a crosslinked 
solid after 24 hours. 
EXAMPLE 7 
To a mixture of 75.0 g of Polymer A, 3.16 g of triethylamine and 10.2 g of 
anhydrous magnesium sulfate in 227 g diethyl ether was added 1.53 ml 
1-acetoxy-1-methylsilacyclobutane. This mixture was stirred 48 hours, 
filtered and stripped to 73.degree. C. and 0.6 mm Hg to give 73.5 g of 
clear colorless fluid having a Mw of 39,000, a Mn of 22,000, and a Mw/Mn 
of 1.8. 
To 1 g of this polymer was added 1.9 mg of the catalyst of Example 1. The 
mixture was poured into an aluminum cup and heated at 155.degree. C. for 5 
minutes to give a crosslinked elastomer. In the absence of catalyst, the 
polymer failed to cure upon heating for 20 minutes at 180.degree. C., but 
cured to a weak elastomer upon heating for 20 minutes at 202.degree. C. 
EXAMPLE 8 
To a mixture of 152 g Polymer C and 15.3 g anhydrous magnesium sulfate in 
352 g diethyl ether was added a solution of 0.197 g 
1-acetoxy-1-methylsilacylobutane and 1.15 g 1,1-diacetoxysilacyclobuane in 
50 ml diethyl ether. The mixture was stirred for 3 hours, filtered and 
stripped to 75.degree. C./1.5 mm Hg to give 149.2 g of clear colorless 
copolymer having a Mw of 340,000, a Mn of 88,000, and a Mw/Mn of 3.9. 
To 47 g of the product polymer was milled in 0.14 g of the catalyst of 
Example 1 to give 20 ppm platinum. The catalyzed gum was heated at 
180.degree. C. for 22 minutes in an electric press to yield an elastomer 
with tensile strength of 31 psi, elongation of 266 percent, and modulus at 
200 percent elongation of 21 psi. 
EXAMPLE 9 
To 10 g Polymer A was added 0.09 g 1,1-diacetoxysilacyclobutane and 0.04 g 
trimethylsilylacetate. Following mixing and 23 hours in a vacuum chamber 
to remove volatiles, the product copolymer was a clear colorless fluid 
having a Mw of 561,000, a Mn of 110,000, and a Mw/Mn of 5.1. To 1 g of the 
product polymer was added 1.9 mg of the catalyst of Example 1 to give 11 
ppm platinum. The mixture was poured into an aluminum cup and heated at 
156.degree. C. for 20 minutes to give a crosslinked elastomer. 
EXAMPLE 10 
This formulation contained no end blocker and gave a crosslinked elastomer. 
To 10.1 g Polymer A was added 0.11 g 1,1-diacetoxysilacyclobutane. The 
mixture was placed in a vacuum chamber to remove volatiles and solidified 
to an elastomeric foam after 23 hours. 
EXAMPLE 11 
To 10.1 g of Polymer A was added 0.185 g 
1-methyl-1-(N-methylacetamido)silacyclobutane, 
##STR16## 
to give a hazy fluid having a Mw of 38,000, a Mn of 19,000, and a Mw/Mn of 
2. To 1.1 g of the product polymer was added 2.4 mg of the catalyst 
prepared in Example 1 to give 14 ppm platinum. The mixture was poured into 
an aluminum cup and heated at 157.degree. C. for 20 minutes to yield a 
weak elastomer. 
EXAMPLE 12 
To a mixture of 189 g Polymer C and 19.8 g anhydrous magnesium sulfate in 
353 g of tetrahydrofuran was added a solution of 1.60 g 
1,1-bis(N-methylacetamido)silacyclobutane 
##STR17## 
and 0.26 g 1-methyl-1(N-methylacetamido)silacyclobutane in 50 ml 
tetrahydrofuran. The mixture was stirred for 41 hours, filtered and 
stripped to 75.degree. C. at 0.8 mm Hg to give 165 g of hazy viscous fluid 
having a Mw of 183,000, a Mn of 95,000, and a Mw/Mn of 1.9. Into 23 g of 
the product polymer was milled 7.7 mg of the catalyst of Example 1 to give 
20 ppm platinum. The mixture was heated at 180.degree. C. for 20 minutes 
to yield a weak elastomer. The catalyzed polymer cured to an elastomer 
after five months at room temperature. The uncatalyzed polymer remained a 
viscous fluid after six months. 
EXAMPLE 13 
To 10 g of Polymer A was added 0.047 g 
N-methyl-N-(trimethylsilyl)acetamide. After stirring, 0.416 g of a 22.56 
percent by weight solution of 1,1-bis(N-methylacetamido) silacyclobutane 
in chloroform was stirred in to give a viscous fluid having a Mw of 
147,000, a Mn of 61,000, and a Mw/Mn of 2.4. To 1.1 g of the product 
polymer was added 7.9 mg of the catalyst of Example 1 to give 47 ppm 
platinum. The mixture was heated at 157.degree. C. for 20 minutes to yield 
a weak elastomer. 
EXAMPLE 14 
To a mixture of 10 g Polymer A and 0.184 g Me.sub.3 SiO(Me.sub.2 SiO).sub.3 
H was stirred in 0.854 g of a 22.56 percent by weight solution of 
1,1-bis(N-methylacetamido)silacyclobutane in chloroform to give a viscous 
fluid having a Mw of 106,000, a Mn of 44,000, and a Mw/Mn of 2.4. To 1.1 g 
of the product polymer was added 6.7 mg of the catalyst of Example 1 to 
give 39 ppm platinum. The mixture was heated at 157.degree. C. for 20 
minutes to give a crosslinked gel. 
EXAMPLE 15 
This composition contained no endblocker and gave a crosslinked elastomer. 
To 10 g of Polymer A was added 1.13 g of a 22.52 percent solution of 
1,1-bis(N-methylacetamido) silacyclobutane in dimethylformamide. Upon 
stirring, the composition gelled to a weak elastomer. 
EXAMPLE 16 
To a solution of 50 g of Polymer B and 32.5 g triethylamine in 152 g of 
diethyl ether was added a solution of 6.05 g 1,1-dichlorosilacyclobutane 
in 20 g of diethyl ether. After stirring the mixture for 30 minutes, a 
solution of 2.59 g of 1-chloro-1-methylsilacyclobutane in 14 g diethyl 
ether was added and stirring continued for 140 minutes. The mixture was 
then stripped to 50.degree. C. at 0.4 mm Hg pressure, redissolved in 
ether, twice pressure filtered through 0.45 micron pore size membrane, and 
stripped to 50.degree. C. at 0.4 mm Hg pressure to give a clear colorless 
fluid. The fluid had a Mw of 28,400, Mn of 12,200, and a Mw/Mn ratio of 
2.3. 
The above polymer was vulcanized and tested as in Example 2 with the 
results shown in Table II. 
TABLE II 
______________________________________ 
Sample Polymer Et.sub.2 NOH 
SOT TFT 
No. (grams) (gram) (Hour) 
(Hours) 
______________________________________ 
1 5.0 0.52 1 1.6 
2 5.0 0.14 1 1.6 
3 5.0 0 did not cure 
______________________________________ 
EXAMPLE 17 
A silacyclobutane functional polymer was prepared, formulated with silica 
filler, process aids, catalyst, and crosslinker. Test samples of cured 
elastomer were prepared and tested. 
To a solution of 900 g of polymer C, 40 g of magnesium sulphate, and 27.4 g 
of triethylamine in 900 g of diethyl ether was added 10.1 g of 
1-chloro-1-methylsilacyclobutane. The solution was stirred for 24 hours, 
filtered, stripped to 80.degree. C. at 1 mm Hg pressure, and further 
stripped for 15 hours at 95.degree. C. in a vacuum oven, to give polymer 
17A. 
A second, lower molecular weight polymer was similarly prepared. To a 
solution of 200 g of polymer A, 10 g magnesium sulphate, and 9.44 g 
triethylamine in 200 g diethyl ether was added 3.34 g 
1-chloro-1-methylsilacyclobutane. The solution was stirred for 23 hours, 
filtered, stripped to 83.degree. C. at 2 mm Hg pressure, and further 
stripped for 3 days at 95.degree. C. in a vacuum oven, to give polymer 
17B. 
A silica filler was prepared by mixing 600 g of fumed silica having a 
surface area of about 250m.sup.2 /g, 60 g of phenyltrimethoxysilane and 
0.6 g hexamethyldisilazane for one hour. 
A liquid silicone rubber base was prepared by mixing 358 g of polymer 17A, 
275 g of the above treated filler, and 27.5 g of hydroxyl endblocked 
polydimethylsiloxane, having about 7.3 weight percent hydroxyl, for 1 hour 
at 87.degree. C. and 16 inches of vacuum. The mixture was cooled and mixed 
with 258 g of polymer 17A and 170 g of polymer 17B for one hour to give 
polymer 17C. 
Part 1 of a two part system was prepared by mixing 210 g of polymer 17C and 
0.46 g of the catalyst of Example 1 for 2 minutes in a dental mixer. A 
series of part 2 were prepared by mixing polymer 17C and crosslinker 
material which was a trimethylsiloxy endblocked polydiorganosiloxane 
having an average of five methylhydrogensiloxane units and three 
dimethylsiloxane units per molecule with a silicon-bonded hydrogen atom 
content in the range of about 0.7 to 0.8 weight percent together in the 
amounts shown as follows: 
______________________________________ 
Polymer 17C Crosslinker 
mole SiH 
Part 2 (grams) (gram) mole SCB 
______________________________________ 
2a 30.0 0.16 0.25 
2b 30.1 0.24 0.375 
2c 30.1 0.32 0.50 
2d 30.1 0.46 0.75 
2e 30.1 0.61 1.00 
2f 25.0 0.62 1.25 
2g 30.1 0.91 1.50 
______________________________________ 
SCB = silacyclobutane 
Parts 1 and 2 were injected into adjacent sides of dual side-by-side 
extrusion tubes, centrifuged to remove air, and coextruded in equal 
amounts through a static mixing nozzle into a chase, where it was formed 
into a test sheet and cured as shown in Table III. The cured test sheet 
was then cut into test samples and the physical properties of the samples 
measured in accordance with ASTM D 412with the results as shown in Table 
III. 
TABLE III 
______________________________________ 
Tensile Strength 
Elongation 
200% Modulus 
Part 2 
Cure (psi) (percent) 
(psi) 
______________________________________ 
a a 820 326 410 
b b 988 396 363 
c a 795 337 365 
d b 813 359 341 
e a 996 442 296 
f b 903 411 300 
g b 1026 527 226 
______________________________________ 
cure a was 15 min. at 150.degree. C. 
cure b was 10 min. at 150.degree. C. 
EXAMPLE 18 
A silacyclobutane functional polydimethylsiloxane was generated as follows: 
To 100 g of Polymer A and 4.86 g triethylamine in 100 g ether was added a 
solution of 0.79 g 1,1-dichlorosilacyclobutane and 
1-chloro-1-methylsilacyclobutane in 21 g ether. The polymer solution was 
stirred for 16 hours, filtered, stripped to 70.degree. C. at 1 mm Hg 
pressure, and filtered through 0.65 micron pore membrane filter, to give a 
polymer having a Mw of 122,600, and a Mn of 44,000. 
A composition was formulated by mixing 0.76 g of this polymer, 0.0017 g of 
the platinum catalyst of Example 1, and 0.085 g of carbon black. A slab of 
this composition was irradiated on a glass plate inside a commercial 
kitchen microwave oven for 1 minute to give a strong, cured elastomer.