Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-03-31
2001-08-28
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S204000, C526S209000, C526S217000, C526S227000, C526S230000, C526S232100, C526S236000, C526S319000, C526S320000, C526S328000, C526S341000, C526S343000, C526S344000, C526S346000
Reexamination Certificate
active
06281311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the application of new nitroxides in the controlled free radical polymerization of a thermoplastic resin or resins. More particularly, the invention relates to a controlled free radical polymerization process wherein piperazinone and morpholone based nitroxides as well as their adducts are used to provide styrene and (meth)acrylate homopolymers and block copolymer resin products characterized by high monomer to polymer conversion and possessing narrow polydispersity properties.
2. Description of the Prior Art
Stable Free Radical Polymerization (SFRP) refers to a free radical polymerization in the presence of a stable free radical such as a nitroxide. The nitroxide traps carbon-centered radicals to form adducts. The trapping is reversible but the equilibrium is such that most (99%) polymer chains are dormant and only a very small fraction is dissociated. Thus, the concentration of free radicals is effectively lowered at all times in the polymerization as shown below, wherein P• represents the growing polymer radical, •ON represents the nitroxide, and M represents a monomer.
This in turn affects propagation and transfer rates but has an even greater effect on termination, since the latter is second order in radical concentration.
Thus, stable free radical polymerization minimizes chain termination reactions, while improving molecular weight and polymer architecture control. On the other hand, the SFRP technology slows down the polymerization process.
In U.S. Pat. No. 5,412,047, issued May 2, 1995 to Georges, et al., processes for the preparation of homopolymers of (meth)acrylic monomers and copolymers containing (meth)acrylate segments by nitroxide mediated polymerization are shown. The polymerization process comprises heating a mixture of a free radical initiator and an oxo-nitroxide, specifically 4-oxo-TEMPO (4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy), as a stable free radical agent, at least one polymerizable (meth)acrylate monomer compound, and optionally a solvent, to form a homopolymeric (meth)acrylate containing thermoplastic resin or resins with a high monomer to polymer conversion and a narrow polydispersity.
Examples of other stable free radical compounds said to be suitable for use in the '047 Patent include: 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO); 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy free radical; 2,2,5,5-tetramethyl-1-pyrrolidinyloxy; 3-carboxy-2,2,5,5-tetramethyl-1 pyrrolidinyloxy; and ditert-butyl nitroxide. As noted in the '047 Patent, though, surprisingly and unexpectedly, the aforementioned stable free radical compounds, and related derivatives, while said to be quite satisfactory for the purpose of moderating the polymerization of a wide variety of different monomer types and comonomers, are completely ineffective when used in homopolymerizations of (meth)acrylate monomers. That is to say, no homopolymeric product formation could be detected by GPC when a mixture of n-butyl acrylate, a free radical initiator such as benzoyl peroxide or AIBN, and a stable free radical compound of the type listed in the '047 Patent were heated for about 10 hours at about 140° C.
A solution to the problem of forming (meth)acrylate copolymers and copolymers was said to be achieved in the '047 Patent by substituting, for example, the carbonyl containing stable free radical 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (4-oxo-TEMPO) in place of the aforementioned ineffective stable free radical compounds. However, 4-oxo-TEMPO is not a stable free radical when heated above 100° C. in the presence of carbon radicals. Under these conditions it is known by those skilled in the art that 4-oxo-TEMPO decomposes rapidly to phorone and other non-radical compounds as set out in Volodarsky, L. B. et al., “Synthetic Chemistry of Stable Nitroxides”, p. 50 (CRC Press 1993) and Yoshioka, T., Higa Shida, S., Morimura, S., and Murayama, K., 44 Bull. Chem. Soc. Jpn., Volume 44, pp. 2207-2210 (1971).
All nitroxides based on TEMPO and its derivatives and used by the inventors of the '047 Patent, including 4-oxo-TEMPO, are problematic, particularly when used in the synthesis of (meth)acrylate homopolymers, styrene-n-butyl acrylate block copolymers, and n-butyl acrylate-styrene block copolymers, in that the polymers can not be synthesized in a controlled fashion with high yields. Further, these nitroxides are undesirable for various practical reasons—that is, the nitroxides cannot be synthetically modified easily. Nor do the nitroxides have a long shelf-life.
Thus, there remains a need for a controlled free radical polymerization process, which can be used to simply and economically synthesize high yields of (meth)acrylate homopolymers as well as styrene-n-butyl acrylate or n-butylacrylate-styrene block copolymers. In this regard, a need also exists for a stable free radical nitroxide for use in the polymerization process, which can be easily synthesized and stored over long periods of time.
INCORPORATION BY REFERENCE
U.S. Pat. Nos. 5,412,047, 4,914,232, 4,466,915, 5,401,804, and 4,581,429 are incorporated by reference herein as background information with respect to the present invention.
BRIEF SUMMARY OF THE INVENTION
We have discovered that piperazinone and morpholone based nitroxides as well as their adducts can be used in the (meth)acrylate polymerization processes of the '047 Patent with unexpectedly high efficiencies. These nitroxides are advantageous in that they are easily synthesized, particularly with regard to tailoring the nitroxide structure to improve reaction rates, introduce functionality, and tailor solubility. Further, these nitroxides have an improved shelf-life stability, since they are highly crystalline and can be stored indefinitely at room temperature or higher.
In addition, these nitroxides, quite unexpectedly, can be used to efficiently make high yields of styrene-n-butyl acrylate or n-butyl acrylate-styrene block copolymers with narrow polydispersities (1.0-3.0) simply and economically, while controlling both molecular weight and composition. Indeed, when used in the preparation of these styrene-block-acrylate copolymers, high yields of styrene or (meth)acrylate prepolymer are obtained in the first step of the polymerization process, thus enabling high yields of the styrene-block-(meth)acrylate copolymers in the second step of the polymerization process.
Block copolymers made in the presence of stable free radicals have been claimed in U.S. Pat. Nos. 5,322,912, 5,401,804, 5,449,998 and 5,545,504 but have only been reduced to practice for a styrene-styrene sulfonate diblock copolymer. We have found that (meth)acrylate containing block copolymers cannot be made using the nitroxides claimed in the aforementioned patents.
In addition, use of our nitroxides for styrene or (meth)acrylate homopolymerization showed a distinct rate advantage over TEMPO and its derivatives.
The present invention, then, provides an improvement in the process for the stable free radical polymerization by using new nitroxides to make homopolymers of (meth)acrylate monomers and copolymers containing (meth)acrylate segments by nitroxide mediated polymerization.
According to a first aspect of the invention, a free radical polymerization process for the preparation of a thermoplastic resin or resins is disclosed, which comprises heating from about 80° C. to about 160° C. a mixture of a free radical initiator, at least one polymerizable monomer compound, and a stable free radical agent comprising a nitroxyl radical to form the thermoplastic resin or resins having a polydispersity from about 1.0 to about 3.0. The nitroxyl radical has the following formula:
wherein X is CH
2
or C═O, Y is O or N—R, R, R
1
, R
2
, R
3
, and R
4
are independently selected from the group consisting of aryl, alkyl having from 1 to about 24 carbon atoms, cycloalkyl having from 5 to about 7 carbon atoms, aralkyl having from 7 to about 20 carbon atoms, cyanoalkyl having from 2 to abo
Lai John Ta-Yuan
Masler William F.
Nicholas Paul Peter
Pourahmady Nasar
Puts Rutger D.
Dunlap Thoburn T.
Moxon II George W.
PMD Holdings Corp.
Zitomer Fred
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