Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-11-24
2001-08-28
Dawson, Robert (Department: 1712)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C525S384000, C556S401000, C526S082000, C528S010000
Reexamination Certificate
active
06279632
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method for controlling the increase in Mooney viscosity during aging of siloxane-modified polymers. More particularly, the invention relates to a method for stabilizing and slowing substantially the rise in Mooney viscosity at any given level upon aging of these siloxane-modified polymers.
BACKGROUND OF THE INVENTION
Elastomeric polymers such as styrene-butadiene rubbers having a styrene content of from about 20 percent to about 35 percent are commonly produced in inert organic solvents such as hexane. These polymers can be terminated by a number of different compounds including silane containing compounds to yield silane end-capped polymers. This siloxane termination can also result in an increase in the Mooney viscosity of the treated polymer similar to the increase that occurs during tin coupling. However, upon subsequent desolventization of the siloxane-terminated polymer through the use of either steam or heated water, an even larger increase in Mooney viscosity often occurs during the hydrolysis of siloxane groups such as pendant —SiOR groups on the siloxane end groups thereby leading to coupling of the polymer via formation of Si—O—bonds between two siloxane end groups.
Thus, a process utilizing steam or heated water in the desolventization of siloxane end-capped polymers containing hydrolyzable groups such as pendant —SiOR groups has always been accompanied by an increase in the Mooney viscosity of the polymers due to hydrolysis and subsequent coupling that occurs between the terminal siloxane groups.
Various attempts have been made to overcome this hydrolysis and coupling problem. For example, U.S. Pat. No. 5,659,056 discloses the use of acids such as C
1
to C
12
aliphatic and C
6
to C
12
cycloaliphatic and aromatic carboxylic acids including acetic acid, propionic acid, butyric acid, decanoic acid, cyclohexanoic acid, benzoic acid and the like, as well as acyl halides thereof, as viscosity stabilizing agents to treat the polymer prior to desolventization. These viscosity stabilizing agents do not react with the siloxane terminal end groups of the polymer, but rather serve to neutralize the by-product lithium compounds in admixture with the polymer, thereby preventing the formation of low boiling alcohols during desolventization at the rate normally produced. Thus, the rate of the hydrolysis reaction and, therefore, the rate of coupling of the polymer which, in turn, correlates to the increase in Mooney viscosity of the siloxane terminated polymer having at least one hydrolyzable substituent on the siloxane end group during contact with water or steam, is slowed substantially. The Mooney viscosity of the polymer can therefore be controlled not only during the desolventization process, but also during subsequent storage of the polymer for a limited period of time where the polymer may be subjected to hydrolysis in the form of moisture in the air or in some other manner.
Other attempts at controlling the Mooney viscosity of siloxane terminated polymers have included the use of alkyl alkoxysilanes such as octyl triethoxysilane as viscosity stabilizing agents. These viscosity stabilizing agents are also added prior to desolventization but, unlike the acids set forth in U.S. Pat. No. 5,659,056, react with the siloxane-terminated polymers. Moreover, these viscosity stabilizing agents, i.e., alkyl alkoxysilanes, have the ability to eliminate, not just slow down, any increase in the Mooney viscosity for a period of time. The successful use of these viscosity stabilizing agents however is extremely concentration dependent. That is, the number of —SiOR groups available from the addition of the viscosity stabilizing agent must be such that any Si—O—Si bonds formed are between the hydrolyzable siloxane terminated polymer and the viscosity stabilizing agent, not between the polymers themselves. Furthermore, alkyl alkoxysilanes are relatively expensive compared to many other materials.
Therefore, the need continues to exist for alternative methods for stabilizing and controlling the rate of increase in Mooney viscosity of siloxane-terminated polymers. Such methods preferably would not be dependent upon the concentration of the added viscosity stabilizing agent and would not affect the pH of the polymer.
SUMMARY OF INVENTION
In general the present invention provides a method for stabilizing the Mooney viscosity of a siloxane-terminated polymer having at least one hydrolyzable substituent on the siloxane end group by adding, after the polymerization but still in the presence of an inert solvent, a viscosity stabilizing effective amount of a long chain alcohol, prior to contacting the polymer with water. For purposes of this disclosure, a “long chain alcohol” can be defined as any monohydric or polyhydric alcohol of the formula R
1
OH wherein R
1
is a moiety containing a hydrocarbon that may or may not include additional —OH groups, does not include a C═O group next to the —OH group and, therefore, is not an acid, and includes more than the number of carbon atoms found in the siloxane termination group —SiOR of the polymer. More preferably, the long chain alcohol can be selected from the group consisting of aliphatic, cycloaliphatic, and aromatic alcohols having at least 6 carbon atoms and fatty acid esters of hydrogenated and non-hydrogenated C
5
and C
6
sugars.
The present invention also includes a moisture stabilized polymer comprising the hydrolysis reaction product of a siloxane terminated polymer reacted with a long chain alcohol. More preferably, the alcohol can be selected from the group consisting of aliphatic, cycloaliphatic, and aromatic alcohols having at least 6 carbon atoms and fatty acid esters of hydrogenated and non-hydrogenated C
5
and C
6
sugars.
The present invention further includes a tire comprising an elastomeric compound containing the moisture stabilized polymer comprising the hydrolysis reaction product of a siloxane terminated polymer reacted with a long chain alcohol. More preferably, the alcohol can be selected from the group consisting of aliphatic, cycloaliphatic, and aromatic alcohols having at least 6 carbon atoms and fatty acid esters of hydrogenated and non-hydrogenated C
5
and C
6
sugars.
By using a long chain alcohol to react with the siloxane termination on the polymer, the hydrolyzable substituent on the siloxane end groups is made longer and becomes more difficult to hydrolyze, thereby slowing the rate of coupling of the polymer which, in turn, slows and stabilizes the foreseen increase in Mooney viscosity of the siloxane polymer. The reaction, however, is not concentration dependent to the extent that any added long chain alcohol will provide at least some affect in decreasing the rate of hydrolysis and, in turn, the rate of increase in Mooney viscosity.
EMBODIMENTS OF THE INVENTION
As noted hereinabove, the present invention is directed toward a method for controlling and stabilizing, and more particularly, to substantially slowing the increase in Mooney viscosity, particularly during aging, of siloxane-modified polymers. The present invention succeeds in controlling and stabilizing Mooney viscosity by adding an effective amount of a long chain alcohol, preferably having at least 6 carbon atoms, to the siloxane-terminated polymer prior to desolventization or other contact with water such that the alcohol (R
1
OH) will react with the hydrolyzable substituent (R) of the pendant —SiOR group of the siloxane-terminated polymers and form new, preferably more hydrophobic —SiOR
1
groups on the siloxane terminated polymers rather than having the siloxane-terminated polymers couple.
Siloxane-terminated polymers are well known in the art and have been prepared in U.S. Pat. No. 3,244,664 to Zelinski et al. and U.S. Pat. No. 4,185,042 to Verkouw, both of which are herein incorporated by reference. The process of the present invention is particularly applicable to any elastomer having a siloxane-functionalized end group having a hydrolyzable substituent which, when hydrolyzed, is
Hergenrother William L.
Hogan Terrence E.
Lin Chen-Chy
Bridgestone Corporation
Dawson Robert
Hornickel John H.
Palmer Meredith E.
Peng Kuo-Liang
LandOfFree
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