Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-10-03
2003-07-15
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C526S064000, C366S341000, C366S336000, C366SDIG001, C366SDIG002, C366SDIG003, C528S031000, C528S032000, C556S444000, C556S445000, C556S446000
Reexamination Certificate
active
06593436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a the manufacture of siloxane-oxyalkylene copolymers. The present invention relates to a process for the continuous production of silicone-containing copolymers with polyalkoxy substituent chains, and to the products produced by the process.
2. Description of Related Art
The reaction of hydrosilatable olefins, such as allyl-terminated polyalkyleneoxides with hydrogen siloxanes such as polydimethyl methylhydrogen siloxanes in the presence of an appropriate catalyst to produce silicone copolymers is known. There is interest in finding improved modes of carrying out the hydrosilation reaction. Improvements are elusive because of the variety of byproducts that typically are formed, their properties, and the need to control their formation and to remove those that do form from the desired siloxane copolymer product. In addition, the hydrosilation reaction itself is sensitive to a number of conditions such that it becomes necessary to balance competing effects and to accept non-optimum results.
The efficient manufacture of silicone copolymers via hydrosilation is desired for two primary reasons: 1) lower cost, and 2) less waste. Although the second factor inherently impacts the first, the relative significance on cost may be low; but the impact of waste on the environment, and consequently on the waste-treatment facilities which must be installed to prevent the copolymer from unintentionally reaching the environment, is large. Hence, a method or process of manufacture which is inherently more efficient is of considerable utility. If, in addition, the equipment needed for that method or process is less costly to construct, such method or process will be inherently attractive to manufacturers.
Chemical reactions may be conducted in a batch fashion, in a continuous fashion, or in hybrid fashion (partially batch or partially continuous). For example, the reactants necessary to prepare a silicone-containing copolymer are a silicone methyl hydrogen fluid (hereinafter referred to as a hydrogen siloxane), and an olefinically-terminated polyether or other olefinically terminated compound (hereinafter referred to as an olefinic reactant). The two components are mixed together, in appropriate amounts, with a noble metal catalyst added. A vigorous reaction ensues, and the olefin, by hydrosilation, becomes chemically attached to the silicone.
Traditional batchwise manufacturing operations produce a crude product containing the desired silicone copolymer in a mixture with by-products and one or more reactants. This crude product needs to be treated in order to recover the desired silicone copolymer in a subsequent step. Furthermore, this crude product most likely needs to be stored prior to purification. Storage of the crude product poses a risk of degrading the desired silicone copolymer as well as a risk of the crude product undergoing cross-reaction with potentially hazardous and even explosive effect. Also storing crude product within the manufacturing scheme represents an accumulated inventory of material which raises the overall cost of the process.
The reaction between the raw materials need not be conducted in a purely batch fashion. For example, if the reactivity of the hydrogen siloxane fluid is very high, the olefinic reactant may be charged to the reactor in its entirety, a fraction of the hydrogen siloxane fluid may be charged, the reaction catalyzed by adding a noble metal catalyst solution, and the remaining hydrogen siloxane fluid added subsequently and at such a rate, after the initial reaction exotherm has begun to subside, to keep the reaction under control. This process is sometimes called semi-batch, or (incorrectly) semi-continuous. If both the hydrogen siloxane fluid and the polyether or olefin are added only in part initially, and then all components added continuously after the reaction initiated, and added until the reactor were full, this fashion of reaction would be called (correctly) semi-continuous.
Inherently, continuous systems are much smaller than batch reactor systems, and are thus less costly. But more importantly from an operating perspective, they contain much less product, and are thus much easier to clean. Thus, less waste is generated, if cleaning is implemented between two different products, and less material is lost from equipment “holdup”, so overall efficiency is higher. From an operating perspective, they are also more “controllable”, in the sense that the extent or degree of reaction is primarily determined by the reactor or equipment design, as opposed to a batch reactor system, wherein the extent or degree of reaction is primarily determined by elapsed time, which factor can be enormously influenced by a multitude of variables such as purity of raw materials, temperature, material of construction, and others.
There are, in a general sense, two types of continuous reactors which are conceptually suitable for copolymer formation: continuous stirred tank reactors (CSTRs); and plug-flow reactors. A CSTR is simply a tank, usually vigorously agitated, into which the reactants and catalysts—all the components of a batch reaction—are fed continuously, and product is withdrawn continuously and at the same total rate as reactants are added. It is inherent, however, in this type of reactor, that not all of any of the reactants can be completely consumed. Because the system is vigorously agitated, fresh reactants, just momentarily previously introduced into the system, have a finite probability of exiting the reactor by withdrawal of the contents, along with old reactants which have spent much longer time in the tank—i.e., they have reacted, and, hence, have become crude product. A silicone-containing copolymer containing unreacted hydrogen siloxane fluid is well known in the art to be totally unsuitable for making certain polyurethane foams; for example, it collapses flexible/slab-stock foam.
In the simplest version of a plug-flow reactor, all reactants are introduced into the front end of a pipe of sufficient length to ensure reaction completion. The pipe is usually maintained at the temperature of reaction, and reaction ensues along the length of the pipe. The length of the pipe is determined by the time necessary to cause the reaction to proceed to completion—i.e., at least one of the reactants has been completely consumed. The above described problem of unreacted hydrogen siloxane fluid exiting a CSTR reactor might be circumvented by the use of a plug flow reactor, were it not that without continued mixing, an immiscible hydrogen siloxane fluid and olefinic reactant will phase-separate very rapidly subsequent to initial mixing, thus causing reaction to proceed more and more slowly. In fact, the reaction ceases rapidly without ongoing agitation, and then fails to proceed, even upon renewed agitation, which effect is believed to be caused by gradual, irreversible deactivation of the noble metal catalyst.
Thus, neither of the two standard continuous reactor systems alone are effective for manufacture of silicone-polyether copolymers, or any other silicone-containing copolymer for which the reactants are immiscible.
U.S. Pat. No. 5,986,022 to Austin, et al. which issued on Nov. 16, 1999, and assigned to the assignee of the present invention, is directed to the reaction of hydrogen siloxane fluids with polyalkyleneoxides in the presence of platinum catalyst in a continuous fashion employing stirred tank reactors in combination with plug flow reactors. Multiple reactors are required prior to the use of a non-agitated plug flow reactor, otherwise phase separation of the reactants is likely to occur and will cause potential performance problems in the product. And although potentially beneficial, slightly different molecular weight distributions of copolymer products are obtained using this method when compared to batchwise processing.
U.S. Pat. No. 6,015,920 to Schilling, et al. which issued on Jan. 18, 2000, and assigned to the assignee of the present invention, disclos
Austin Paul E.
Davis David B.
Heisler Ladislau
Crompton Corporation
Dawson Robert
Dilworth Michael P.
Peng Kuo-Liang
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