Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-03-29
2003-01-07
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S504000, C524S505000, C524S507000, C524S801000, C524S804000, C524S819000, C524S832000
Reexamination Certificate
active
06503975
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to aqueous copolymer compositions and in particular to self-stabilized aqueous copolymer emulsions. The aqueous copolymer compositions are stabilized by block and/or graft copolymers derived from the copolymerization of a water soluble or dispersible macromonomer with a monomer or blend which is water insoluble.
Conventional emulsion copolymerization is a process in which a copolymer is formed directly in water using surfactants (i.e., compounds which are able to form micelles in the aqueous phase), which stabilize the copolymer particles in the emulsion. Surfactants may be non-ionic (e.g., alkyl or alkylphenol ethoxylated derivatives); anionic (e.g., salts of alkyl sulfates, phosphates or sulfonates); or cationic (e.g., quaternary ammonium salts of alkyl amines). Using such surfactants, which remain in the free form as a water soluble species in the emulsion, can cause problems when the emulsions are used as coating compositions, such as poor humidity and corrosion performance. It would therefore be an advantage if such copolymer emulsions could be prepared without the use of the monomeric, water sensitive surfactants.
U.S. Pat. No. 5,936,026 is directed to surfactant-free emulsions and coating compositions containing same. The emulsion is prepared by emulsion copolymerization of a monomer blend in the presence of a water soluble or water dispersible macromonomer with at least 10% of unsaturated monomers all having acid or all having amine groups in an ionized form. At least 2% and preferably 10-40% of macromonomer is needed to prepare stable emulsions, based on the overall ionized acid or amine content in the macromonomer. Such copolymer emulsions do still have a high overall level of water sensitive groups. The macromonomers do not form micelles like conventional surfactants, which is why the higher levels of macromonomer are needed to sufficiently stabilize the overall copolymer emulsion.
U.S. Pat. No. 5,362,826 discloses a method of preparing macromonomers from oligomers with a terminal unsaturated end-group. The oligomers are prepared by cobalt catalytic chain transfer polymerization as described in U.S. Pat. Nos. 4,680,352 and 4,722,984. There is no teaching in those references that the macromonomers can be used as surfactants in an emulsion copolymerization process. PCT/US95/00376 teaches aqueous branched copolymers having hydrophobic macromonomer arms and a hydrophilic backbone. These copolymers are prepared in solvent and then inverted into water. There is no teaching or suggestion that such copolymers are suitable for use in emulsion coatings.
U.S. Pat. No. 5,231,131 relates to pigment dispersions in an aqueous carrier containing a graft copolymer having a polymeric backbone which is hydrophobic in nature as compared to the side chains which are hydrophilic. The side chains consists of hydrophilic macromonomers with 20-50% of polymerized acid functional co-monomer which are neutralized with an amine or inorganic base. There is no teaching of using such graft copolymers as surfactants in an emulsion copolymerization.
SUMMARY OF THE INVENTION
An emulsion useful for forming coating compositions comprising
a) an aqueous carrier;
b) a polymer mixture comprising:
(1) 40-99.5% by weight of a copolymer with a weight average molecular weight of at least 3000; and
(2) 0.5-60% by weight of a stabilizing copolymer dispersed in water, said stabilizing copolymer comprising a hydrophobic portion and a hydrophilic portion, wherein said stabilizing polymer is selected from the group consisting of:
(i) polymers comprising 5-95% by weight of a hydrophilic macromonomer having at least 10% by weight of an acid functional monomer and 5-90% by weight of at least one hydrophobic monomer polymerized in the presence of the macromonomer;
(ii) polymers comprising 5-95% by weight of a hydrophobic macromonomer and 5-95% by weight of hydrophilic copolymer comprising at least 10% by weight of an acid functional monomer polymerized in the presence of the macromonomer.
The stabilizing copolymer can comprise a graft copolymer having a hydrophobic backbone with hydrophilic macromonomer arms, a hydrophilic backbone with hydrophobic macromonomer arms, or can comprise an AB block copolymer having a hydrophobic or hydrophilic macromonomer as the A block and a hydrophilic or hydrophobic copolymer as the B block.
The macromonomers preferably comprise the polymerization product of at least 50% by weight of monomers selected from methacrylate, methacrylonitrile, methacrylamide and derivatives and mixtures thereof with a weight average molecular weight of 500 to 10000 and prepared by cobalt catalytic chain transfer polymerization.
The process for making the emulsion and coating compositions based on the emulsion are also part of this invention.
In a most preferred embodiment, the acid value of the emulsion is less than 32.
DETAILED DESCRIPTION OF THE INVENTION
Emulsion copolymerization is a process of forming a copolymer from ethylenically unsaturated compounds directly in water. In the prior art, small amounts of surfactants were used in the process. By “surfactants” we mean organic compounds capable of forming micelles in water. These surfactants are monomer or low molecular weight derivatives which are water sensitive and can be non-ionic, anionic or cationic. Using the emulsion copolymers prepared in the presence of the surfactants in water borne coating formulations often led to problems such as poor humidity and corrosion resistance because of the presence of free surfactants which remain in the final film.
In an effort to solve these problems in the prior art, the present inventors discovered that certain structured polymers (i.e., polymers with a well defined architecture, such as AB block copolymers and graft copolymers) prepared by cobalt catalytic chain transfer polymerization act as surfactants in an emulsion copolymerization process by stabilizing the emulsion. However, unlike the surfactants used in prior art processes, the stabilizing polymers do not present disadvantages in coatings containing the emulsion and indeed can become part of the cross-linked network that forms the coating, depending on the functional groups present in the stabilizing polymer and the type of cross-linking agent used.
In the research leading up to the present invention, it was discovered that AB block copolymers prepared by the so-called Group Transfer Polymerization (“GTP”) process taught in Webster, U.S. Pat. No. 4,508,880, having at least 10% content in either block, were not as effective at stabilizing the emulsions. More specifically, the present inventor found that the GTP AB block copolymers with an acid content of at least 10% in either block were not able to stabilize emulsions with high solid content (i.e., greater than 25% solids), unless relatively large amounts of the GTP polymer were used. The increased amount of the GTP polymer needed to stabilize the high solids emulsions, in turn, raised the acid value of the overall emulsion to greater than 32.
Chain transfer agents employing cobalt II or III chelates such as disclosed in U.S. Pat. Nos. 4,680,352 and 4,694,054 allow the synthesis of low molecular weight (meth)acrylate based macromonomers with a terminally ethylenically unsaturated group. The term “macromonomers” as understood in the art and used herein means a polymer terminating at one end with —C—(COOR)═CH
2
. Low molecular weight oligomers prepared from such chain transfer agents act themselves as chain transfer agents for methacrylate monomers through an addition-fragmentation process allowing the synthesis of semi-block copolymers as disclosed in U.S. Pat. No. 5,371,151. The terminal unsaturated end group on the macromonomer can also co-polymerize with vinyl and acrylate type monomers to form a graft copolymer.
Block or graft copolymers can so be synthesized from a hydrophilic macromonomer via copolymerization of the macromonomer with hydrophobic co-monomers or from a hydrophobic macromonomer by copolymerization of the hydrophobic macromono
Benjamin Steven C.
Cain Edward J.
E. I du Pont de Nemours and Company
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