Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
1999-06-14
2001-03-20
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C252S183120
Reexamination Certificate
active
06204403
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improved process for the production of acrylamidoalkylalkoxysilanes which find use as coupling agents.
BACKGROUND OF THE INVENTION
Certain methacrylate-functional silanes have been known, including, for example, 3-methacryloxypropyltrimethoxysilane, which has uses in glass fiber-reinforced composites of various thermoplastics and in durable coatings for metallic substrates. There has been a continuing need for products with differentiated and improved performance in areas in which 3-methacryloxypropyltrimethoxysilane is used, whereby differences in molecular structure result in useful differences in silane performance in properties as diverse as rate of hydrolysis, aqueous solubility, low product color, processability of the substrate being treated from aspects of lubricity, static control, fiber strength, speed of fiber drawing, and the like. One class of structural variations which has become useful relative to 3-methacryloxypropyltrimethoxysilane is the class of methacrylamidoalkylalkoxysilanes. Prior to the present invention, the processes for the production of acrylamidoalkylalkoxysilanes have had at least one major deficiency.
One early disclosure for the preparation of acrylamidoalkylalkoxysilanes is U.S. Pat. No. 3,249,461, wherein aminopropyltrimethoxysilane is reacted with methacryloyl or acryloyl chloride in an inert solvent blend. The reaction generates an equimolar amount of hydrogen chloride by-product, which was removed by washing the product/by-product mixture with excess aqueous sodium carbonate. Deficiencies of this process include the use of solvents, which lowers yield based on unit volume of production equipment, the formation of hydrogen chloride by-product necessitating its removal, and the removal of hydrogen chloride by aqueous washing, which will hydrolyze a significant portion of the methoxysilane groups forming higher oligomeric or polymeric siloxanes.
The above process has been modified in U.S. Pat. No. 4,711,943 wherein the hydrogen chloride by-product has been handled by formation of tertiary amine hydrochloride salt, which can be removed by filtration or centrifugation. Solvent is still used, and the formation and removal of solid tertiary amine hydrochloride salts further reduces yield per unit volume, adds a difficult and time-consuming step, and generates an undesirable waste which must be disposed of or treated for recycle. U.S. Pat. No. 3,249,461 also discloses that the corresponding acid anhydride may be used in place of the acid chloride, and U.S. Pat. No. 3,900,679 discloses formation of methacrylamidoalkylalkoxysilanes by reaction of aminoalkylsilanes with methacrylic acid. Reaction of amines with acids, which would also be by-products of the acid anhydride route above, to form amide groups is accompanied by the formation of an equimolar amount of water. As is known in the art, water will hydrolyze two equivalent amounts of the alkoxysilane groups, forming siloxanes, which reduce product purity, and build molecular weight and viscosity, potentially to the point of gelation.
U.S. Pat. No. 4,990,641 teaches a hydrosilation route to structurally different methacrylamidoalkyl-bis-alkoxysilanes as well as an acid chloride route to similar structures. The hydrosilation route to methacrylamidoalkylalkoxysilanes may be complicated by cyclizations of the N-allyl(meth)acrylamide starting materials under reaction conditions (Chem. Abstr., 95, 94175r(1976)). Lastly, the reaction of silazacyclobutanes with acid chlorides is disclosed in U.S. Pat. No. 5,446,180 and the reaction of acid chlorides with silazacyclopentanes in U.S. Pat. No. 5,082,958. This approach is practical only for monofunctional alkoxysilanes, which are of less utility than the di- and trialkoxysilane derivatives. It also requires the intermediate preparation of the commercially unavailable silazacycloalkanes. Thus, while utility for methacrylamidoalkylalkoxysilanes has been increasing (see U.S. Pat. Nos. 4,243,426, 4,762,759, 5,008,349, and 5,372,841 among others), there is still a need for improved processes to make said methacrylamidoalkylalkoxysilanes.
While the reaction of aminoalkylsilanes with acrylate esters is known as disclosed in U.S. Pat. No. 4,209,455, which is incorporated herein by reference, the reaction conditions are such that Michael addition of the amine group to the acrylate double bond is the first reaction which occurs, and the products are devoid of (meth)acrylate functionality.
SUMMARY OF THE INVENTION
Acrylamidoalkylalkoxysilanes are prepared by reactions of aminoalkylalkoxysilanes containing at least one —NH— group and at least one alkoxy group on silicon with acrylate esters, in the presence of an effective amount of an amidation catalyst and an effective amount of an inhibitor system at an elevated reaction temperature. The reactions preferably are run in the absence of added solvents, including tertiary amines or water washes used in prior art processes to remove acid by-products.
DETAILED DESCRIPTION OF THE INVENTION
It is an objective of this invention to provide a process for the production of acrylamidoalkylalkoxysilanes which provides high yields per unit volume of production equipment, i.e., the majority of the occupied reactor volume is filled with product, and not with solvents, by-products, or water washes. Preferably, greater than 60% of the occupied volume in the reactor will be filled with product prior to and during purification, more preferably greater than 75%, and most preferably greater than 90%, i.e., preferably there is less than 25% by volume of solvent, and most preferably less than 10% by weight solvent. While the process of this invention does not require the use of solvents, solvents may be used to a limited extent if needed to control temperature or viscosity.
The process of this invention does not require the use of tertiary amines or aqueous washes to remove acid by-products. Preferably, the process is run under essentially anhydrous conditions, i.e., there is less than 0.1 wt % water throughout the entire process, and more preferably less than 0.01 wt % water.
It is a further objective of this invention to provide processes yielding acrylamidoalkylalkoxysilanes with high shelf stability toward acrylate polymerization, preferably at least three months, more preferably six months, and most preferably, at least one year, and high process reproducibility, including avoidance of polymerization during the preparation and purification steps. It is another objective of this invention to provide purified acrylamidoalkylalkoxysilanes, having low color, i.e., less than 100 on the platinum/cobalt scale as described in ASTM Method D-1209, so that said silanes do not contribute undesired color to the products in which they are used. It is a further objective of this invention to provide processes for the production of acrylamidoalkylalkoxysilanes, which employ readily available raw materials, intermediates, and production equipment and which allow for easy purification of the silanes to high purities, i.e., greater than 95%, by standard means, as by simple distillation.
The process of the present invention involves the reaction of an aminoalkylalkoxysilane, containing at least one primary or secondary amine group with an acrylate ester in the presence of an effective amount of an amidation catalyst and an effective amount of an inhibitor system at a relatively high reaction temperature. For the purposes of the present invention an acrylate ester includes, but is not limited to, methacrylate esters, or esters which have alkyl substituents on the unsaturated carbons which are alpha and/or beta to the carboxylate.
The process is represented by the reaction shown:
where each R is a lower alkyl group of one to ten carbon atoms, R
1
is a linear, branched, cyclic, or substituted divalent hydrocarbon radical of one to twelve carbon atoms which may include heteroatoms, R
2
is hydrogen, R, or a monovalent aromatic hydrocarbon radical of six to twelve carbon atoms, an aminoalkyl group or a sily
McMullen Anne Kathryn
Pepe Enrico J.
Turner Scot M.
Weller Keith J.
Crompton Corporation
Ma Shirley S.
Shaver Paul F.
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