FIELD OF THE INVENTION
The present invention relates to core/shell vinyl polymers wherein an at least partially crosslinked core is formed from a monovinyl monomer and/or a di/tri/ or higher multivinyl monomer wherein the degree of crosslinking in the core ranges from slight to high depending on the ratio of monovinyl and/or di/tri/ or higher multivinyl monomers, and wherein the outer shell is formed from a monovinyl and/or a di/tri/ or higher multi-vinyl monomer that optionally may be crosslinked, and wherein the outer shell has on its surface linear or branched C3-C30 alkyl chains formed from substituted vinyl monomers.
BACKGROUND OF THE INVENTION
In recent years, environmental problems such as destruction of the ozone layer, global warming, environmental pollution, and air pollution are being increasingly addressed. At the same time, for environmental protection, the governments of many countries have imposed various controls, for instance, in the US the National VOC [Volatile Organic Compound] Emission Standard (Section 183 e), in the EU countries Council Directive (1999/13/EC) and in some accession countries, e.g. Hungary (10/2001 Governmental Decree), have been promulgated to regulate activities in areas of concern. In such circumstances, releasing organic solvents in the air has become a significant problem and, consequently an attempt to use less or no solvents has become increasingly common in many industries. Also in the coating industry, powder coatings are being tested as substitutes for conventional solvent-type coatings. Improvements in the coat film performance of high-solid, or advanced high-solid coatings are being developed to meet requirements of environmental protection and good technical applicability. The development of new polymers with designed structure and architecture has, consequently, become an intensively studied field of material science.
TECHNOLOGICAL BACKGROUND OF THE INVENTION
It is known in the art to use core/shell, star and microgel polymers to combine mechanical and thermal properties of polymeric particles. The core is formed by cross-linking mono- and/or di- or higher multifunctional vinyl monomers. Then in a second stage the outer shell is formed from monovinyl and di- and/or multi-vinyl monomers that optionally may be crosslinked. Macromolecules typically exist in a solution phase as a sol macromolecular colloid system. These systems are usually prepared in an aqueous medium as an emulsion polymerization. The polymerization of the monomers with multiple vinyl functionality results in gelation of the whole mixture.
The following patents further describe the technological background of the prersent invention.
 Fujii et al. in U.S. Pat. No. 5,298,559 describe a multi-layered polymer system polymer having core layer of an aromatic vinyl polymer, an intermediate layer of a butadienic rubbery polymer and an outer layer of an aromatic vinyl glassy polymer, that provides a thermoplastic resin composition excellent not only in impact strength, especially in impact strength at low temperatures.
2] Oshima et al. in U.S. Pat. No. 5,324,780 prepare core-shell polymers comprising a core phase which is a rubbery polymer and a shell phase which is a glassy polymer with an unsaturated dicarboxylic acid or its mono-alkyl ester as a constituent thereof, wherein the toluene-soluble fraction of the core-shell polymer accounts for not more than 10% by weight. The resin compositions and molded articles which comprise the core-shell polymer as an impact modifier have good features, especially a high impact strength at temperatures ranging from room temperature to −30° C.
 Eisenhart et al. in U.S. Pat. No. 5,451,641 describe a polymeric thickener which consists of multi-stage polymer particles comprising at least one hydrophobically-modified, ionically-soluble polymer stage polymerized from hydrophobic monomer and ethylenically-unsaturated monomers. The grafting monomer may be, among others, an unsaturated carboxylic acid allyl ester, such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, etc. In particular, allyl methacrylate is preferred. Such crosslinking monomer and grafting monomer are used each in an amount within the range of 0.01 to 5% by weight, preferably 0.1 to 2% by weight, based on the total monomer amount for the core.
 Takeuchi et al. in U.S. Pat. No. 5,453,458 describe a two and multistage polymerization forming a core-shell polymer which core is composed essentially of a cross-linked polymer of styrene. The core-shell polymer of the invention can be produced by a multi-stage seed emulsion polymerization method or a multi-stage suspension polymerization method. In the first-stage polymerization, they use a cross-linking monomer as a monomer in an amount of not more than 5% by weight, preferably in an amount of not more than 2% by weight, based on the total of the core forming monomers used in the first-stage polymerization. The polymerization described here gives only a lightly crosslinked core with a limited impact properties.
 Chandran et al. in U.S. Pat. No. 6,165,563 describe star-branched polymers containing pendent olefinic groups which have been crosslinked using actinic radiation, and the use of these polymers in adhesives and coating applications.
 Letchford et al. in U.S. Pat. No. 6,221,991 disclose an anionic polymerization to provide novel polar polymers, including functionalized, telechelic, heterotelechelic, and multi-branched or star methacrylate and acrylate polymers, and processes for preparing the same. The novel polymers have applications in a variety of areas, including use in low VOC coatings, adhesives, and as viscosity index (V.I.) improvers for lubricants. The invention also provides processes for anionic polymerization of polar monomers to produce the polymers of the invention. These polymers are prepared from protected functionalized initiators which are reacted with an appropriate diaryl alkenyl group, such as 1, 1-diphenylethylene, to provide a stabilized carbanion. A polar monomer, preferably methyl methacrylate, is polymerized in the presence of the initiator to provide a living anion.
 Blankenship et al. in U.S. Pat. No. 6,252,004 disclose a process for preparing emulsion polymer particles providing an aqueous emulsion of a multistage core-shell polymer with a hydrophilic core. The process produces multistage polymers having low dry-bulk density useful in coating compositions such as paints and paper coatings.
 Solomon et al. in U.S. Pat. No. 6,300,443 describe a process for preparing polymeric microgels comprising reacting an alkoxyamine with an unsaturated monomer composition comprising a cross-linking agent comprising at least two double bonds and optionally one or more further monomers selected from monounsaturated monomers and conjugated diene monomers.
 Lubnin et al. in U.S. Pat. No. 6,316,107 disclose an emulsion or suspension polymer comprising a vinyl chloride polymeric core and an acrylic ester-acrylonitrile polymeric shell. The emulsion polymer was preferably prepared using a two-stage process. In the first stage, a vinyl chloride monomer was polymerized or copolymerized to form a first phase of a polymeric hard core having a relatively high chlorine content. In a second stage, the soft acrylic ester-acrylonitrile copolymer was made in situ in a reaction mixture comprising the first phase. The product provides both flame retardancy and low minimum film-forming temperature (MFFT), and is useful in a variety of coating and binding applications.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide novel core/shell compositions that are useful in forming surface coatings. Another object is to provide novel core/shell compositions for use in surface coatings having improved film forming properties. A further object is to provide novel core-shell compositions that form surface coatings having improved adhesion, hardness, and flexibility. Still another object is to provide novel core/shell compositions that have increased cross-linking, but which do not form gels. Yet another object is to provide novel core/shell compositions wherein the shell has attached to its surface a linear or branched alkyl chain having a terminal group adapted to react with predetermined groups, or to provide better film formation and adhesion properties. Another object is to provide methods for preparing these compositions. These and other objects of the present invention will be apparent from the following description.
SUMMARY OF THE INVENTION
The present invention relates to composite particle dispersions and, more particularly, it relates to core/shell polymers. The crosslinked polymeric core is formed from a linear vinyl polymer that has been at least partially crosslinked with a mono/di/tri/ and/or higher multifunctional monomer copolymerizable therewith. The polymeric outer shell is formed from mono/di/tri/ and/or higher multi-vinyl monomer that can be linear, branched, or crosslinked, or a mixture of two or more of the foregoing. The outer shell has on its surface a plurality of linear or branched alkyl chains formed from a vinyl monomer or a mixture thereof containing a terminal group adapted to react with at least one predetermined chemical group, or to provide better film formation and adhesion properties. The core, the outer shell, and the surface linear chains can be formed independently to be hydrophobic or hydrophilic. The polymerization can take place in a single stage process or in a multi-step process. In the single stage process, the core first is formed as a crosslinked seed wherein, due to sterical hindrance, adjacent linear or branched chains are formed. When the polymerization is performed in two or more stages, the formation of the primary crosslinked core is followed by formation of a covalently attached shell. Such polymers demonstrate increased cross-linking, improved film forming properties, and improved solubility in organic solvents.
DETAILED DESCRIPTION OF THE INVENTION
The polymeric compositions of the present invention can be prepared by polymerizing vinyl monomers by free radical polymerization. The vinyl monomers are acrylic and methacrylic derivatives, preferably ester derivatives, and aromatic vinyl derivatives with one or more vinyl groups. Free radical polymerization is initiated by substituted peroxides or preferably by azo compounds. The core of the core/shell vinyl polymers of the present invention is formed from a linear vinyl polymer that is at least partially crosslinked, preferably with a mono/di/tri/ and/or higher multifunctional monomer copolymerizable therewith, which may be saturated or unsaturated, hydrophobic or hydrophilic, and a polymeric outer shell that is formed from a mono/di/tri and/or multi-vinyl monomer that optionally can be linear, branched, or crosslinked, or a mixture of two or more of the foregoing, and wherein the outer shell has on its surface a plurality of linear or branched C3-C30 alkyl chains optionally having a terminal group adapted to react with at least one predetermined chemical group, or adapted to provide better film formation and adhesion properties. Alkyl groups lacking reactive groups act to modify physical properties (e.g., glass transition temperature (Tg), solubility, etc.) of the polymer. Alkyl groups having a terminal group adapted to react with at least one predetermined chemical group serve to form crosslinked coatings which have excellent physical and chemical resistance.
A detailed listing of Examples of specific monovinyl monomers are disclosed below under the heading “Polymerizable Vinyl Componds: A. Monovinyl Monomers.” The following compounds are illustrative of this group: 2-hydroxyethylacrylate, 2-hydroxyethyl(meth)acrylate, 3-hydroxypropylacrylate, 3-hydroxypropyl(meth)acrylate, glycidylacrylate, glycidyl(meth)acrylate, caprolactone 2-(methacryloyloxy)ethyl ether, ethyl(meth)acrylate, propyl(meth)acrylate, and 2-ethylhexyl(meth)acrylate.
The degree of crosslinking in the core can vary from as little as about 1% to about 99%, depending upon the pendent double bonds in the di-, tri, and/or higher multifunctional monomers. The polymerization reaction is controlled by the conditions of reaction (e.g., concentration, temperature, solvent, etc.) to obtain either a very slightly crosslinked core wherein the porosity is very high, or to obtain a very highly crosslinked core wherein the porosity is very low. The degree of crosslinking is in the range of from about 5% to about 95%, preferably from about 20% to about 70%, and more preferably from about 30% to about 50%. When the core contains unreacted double bonds, that is, when it is slightly or not highly crosslinked, a postpolymerization reaction is used to convert it to a very highly crosslinked core having the degrees of crosslinking indicated above. Linear chains may be attached to the surface of the shell optionally containing reactive groups, preferably, hydroxy or epoxy, or containing less reactive groups, e.g. aliphatic groups, for better film formation and adhesion properties.
The composition of the shell depends on the type and number of monomers as described below. If the core contains unreacted double bonds, that is, when the core is slightly or even highly cross-linked, the shell is attached to the core by covalent bonds. If the core is largely saturated, the shell is physically attached to the shell by secondary bonds, or aggregation due to particle-particle interaction between the core and molecules in the shell. If the shell is composed of di/tri/ and/or higher multi-vinyl monomers it has a crosslinked structure. According to the core/shell polymers of the present invention, the core comprises from about 5 weight % to about 95 weight % of the total weight of the polymer, the shell comprises from about 1% to about 99% of the total weight of the polymer, and the alkyl chains comprise from about 1% to about 10% of the total weight of the polymer.
The porosity of the core and of the shell depends on the ratio of mono- and di- and multivinyl monomers. Both the core, the shell, and the linear chains on the surface of the shell, can be formed independently from hydrophobic or hydrophilic chains. As a result, the nature of the core-shell compositions of the present invention can be varied in many ways as illustrated by the following table.
|TABLE I |
|Examples of Various Combinations of Hydrophilie and |
|Hydrophobic Components |
| ||EX. ||CORE ||SHELL ||LINEAR CHAINS |
| || |
| ||A. ||Hydrophilic ||Hydrophilic ||Hydrophilic |
| ||B. ||Hydrophilic ||Hydrophilic ||Hydrophobic |
| ||C. ||Hydrophilic ||Hydrophobic ||Hydrophobic |
| ||D. ||Hydrophilic ||Hydrophobic ||Hydrophilic |
| ||E. ||Hydrophilic ||Hydrophobic ||Hydrophobic |
| ||F. ||Hydrophobic ||Hydrophobic ||Hydrophilic |
| ||G. ||Hydrophobic ||Hydrophilic ||Hydrophobic |
| ||H. ||Hydrophobic ||Hydrophobic ||Hydrophobic |
| || |
The core/shell particles of the present invention, which are usefull for application to different substrates, e.g. ceramics, glass, leather, metal, paper and paper products, plastics, stone, textiles, wood, etc., have the following characteristics:
|Morphology: ||Spherical macromolecular particles |
|Particle size: ||35-150 nm |
|Functionality: ||Hydrophilic (OH, COOH, amine, epoxy, etc.) |
| ||Hydrophobic (alkyl, aromatic. etc.) |
|Porosity: ||Variable |
The morphology of a representative hydrophobic core and of a core/shell nanoparticle with attached alkyl chains (hydrophilic structures and mixed hydrophobic/hydrophilic components are obvious variants) is shown below:
Morphology of Core and Core/Shell Nanoparticles
Structure: for Hydrophobic Components
The polymeric macromolecular structures preferably are synthesized by a novel three-step process that produces spherical nanometer-sized core-shell particles wherein the polymeric core is produced from suitable mono/di/tri and/or higher multifunctional vinyl monomers, wherein the polymeric core is copolymerized with the other shell monomers to produce desired modifications of properties, and is at least partially surrounded by the shell which comprises covalently or physically bonded chains. The first step is the formation of the core with at least some crosslinked chains; the second step is post-polymerization to increase the density of crosslinking in the core; and the third step is to link the shell to the core.
The shell polymer is formed by applying a coating of a vinyl monomer to the surface of the core polymer. This surface coating is then polymerized using, in general, the same conditions as used to form the core polymer. The structure and composition of the shell polymer attached to the core can differ from the structure and composition of the core portion of the macromolecule
Polymerization, according to techniques used heretofore, using a di- or higher multifunctional reactants, provides a crosslinked polymeric material in a sol macromolecular colloid state. The crosslinking reactions form primary or secondary cycles in the polymeric chain. The growth of the polymeric chain is instantaneous up to formation of clusters or formation of a macroscopic gel. The reaction conditions applied according to the present invention result in the formation of macromolecules in a range of 1,000 to 30,000,000 Daltons wherein gel formation of the polymer is avoided and the solution shows rheological properties associated with Newtonian liquids.
Examples of some Suitable Polymerizable Vinyl Compounds
A. Monovinyl Monomers
Specific examples of suitable core co-monomers that are useful to form a linear vinyl monomer include the following: (meth)acrylate esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, isoamyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, 2-sulfoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, glycidyl (meth)acrylate, benzyl (meth)acrylate, allyl (meth)acrylate, 2-n-butoxyethyl (meth)acrylate, 2-chloroethyl(meth)acrylate, sec-butyl-(meth)acrylate, tert-butyl (meth)acrylate, 2-ethylbutyl(meth)acrylate, cinnamyl(meth)acrylate, crotyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, furfuryl (meth)acrylate, hexafluoroisopropyl (meth)acrylate, methallyl (meth)acrylate, 3-methoxybutyl(meth)acrylate, 2-methoxybutyl (meth)acrylate, 2-nitro-2-methylpropyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, phenyl(meth)acrylate, propargyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, norbornyl(meth)acrylate, tetrahydropyranyl (meth)acrylate, vinyl acetate, (meth)acrylonitrile, vinylpropionate, vinylidene chloride, (meth)acrylamide, N-methylolacrylamide, acrylic and methacrylic acids, ethyl acrylate, ethyl methacrylate, benzyl acrylate, benzyl methacrylate, propyl acrylate, propyl methacrylate, iso-propyl acrylate, iso-propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, octadecyl methacrylate, octadecyl acrylate, lauryl methacrylate, lauryl acrylate, hydroxyethyl acrylate, hydroxyethylmethacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, hydroxyoctadecyl acrylate, hydroxyoctadecyl methacrylate, hydroxylauryl methacrylate, hydroxylauryl acrylate, phenethyl acrylate, phenethyl methacrylate, 6-phenylhexyl acrylate, 6-phenylhexylmethacrylate, phenyllauryl acrylate, phenyllauryl methacrylate, 3-nitrophenyl-6-hexyl methacrylate, 3-nitrophenyl-18-octadecyl acrylate, ethyleneglycol dicycopentyl ether acrylate, vinyl ethyl ketone, vinyl propyl ketone, vinyl hexyl ketone, vinyl octyl ketone, vinyl butylketone, cyclohexyl acrylate, 3-methacryloxypropyldimethylmethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylpentamethyldisiloxane, 3-methacryloxypropyltris(trimethylsiloxy)silane, 3-acryloxypropyldimethylmethoxysilane, acryloxypropylmethyldimethoxysilane, trifluoromethyl styrene, trifluoromethyl acrylate, trifluoromethyl methacrylate, tetrafluoropropyl acrylate, tetrafluoropropyl methacrylate, heptafluorobutyl methacrylate, N,N-dihexyl acrylamide, N,N-dioctyl acrylamide, aminoethylacrylate, aminoethyl methacrylate, aminoethyl butacrylate, aminoethylphenyl acrylate, aminopropyl acrylate, aminopropyl methacrylate, aminoisopropyl acrylate, aminoisopropylmethacrylate, aminobutyl acrylate, aminobutyl methacrylate, aminohexyl acrylate, aminohexyl methacrylate, aminooctadecyl methacrylate, aminooctadecyl acrylate, aminolaurylmethacrylate, aminolauryl acrylate, N,N-dimethyl-aminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate, piperidino-N-ethyl acrylate, vinyl propionate, vinylacetate, vinyl butyrate, vinyl butyl ether, and vinyl propyl ether, styrene and alkyl derivatives
B. Examples of Some Suitable Di- and Multivinyl Monomers
Crosslinking monomers suitable for use as the cross-linker in the core polymer are known to those skilled in the art, and are generally di- and higher multifunctional monomers copolymerizable with the other core monomers, as for example, glycol dimethacrylates and acrylates, triol triacrylates and methacrylates and the like. The preferred crosslinking monomers are butylene glycol diacrylates. When a crosslinking monomer is employed, it is preferably used at levels of from about 0.05% to about 50%, more preferably 0.5 to about 20%, and most preferably from about 5% to about 15%, based on the total weight of the core monomer before cross-linking.
Some specific examples of crosslinking monomers are: N,N′-methylene-bis-acrylamide, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, polypropylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, dipropylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, butanediol dimethacrylate, hexanediol dimethacrylate, trimethylolethane trimethacrylate, trimethylolpropane trimethacrylate. divinyl benzene, allyl methacrylate (ALMA), ethylene glycol dimethacrylate (EGDMA), trimethylolpropane trimethacrylate (TMPTMA), divinyl benzene (DVB), glycidyl methacrylate, 2,2-dimethylpropane 1,3 diacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, polyethylene glycol 200 diacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate, polyethylene glycol 600 dimethacrylate, poly(butanediol) diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, trimethylolpropane triethoxy triacrylate, glyceryl propoxy triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, and dipentaerythritol monohydroxypentaacrylate.
As further crosslinking monomers there may be mentioned, for example, aromatic divinyl monomers, such as divinylbenzene, bisphenol A di(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate, and alkane polyol acrylates and alkane polyol methacrylates, such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diacrylate, butylene glycol dimethacrylate, hexanediol diacrylate, hexanediol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate. Particularly preferred are butylene glycol diacrylate, hexanediol diacrylate and dipropylene glycol di(meth)acrylate.
The highly crosslinked core of the core/shell polymers of the present invention imparts good physical properties such as hardness, adhesion and viscosity lowering properties. The linear chains attached to the shell allow connecting monomers holding functional groups that facilitate adhesion to a metal surface, and/or crosslinking with one or more other functional groups such as, for example, amines, carboxylic acids, epoxy compounds and isocyanates. The core/shell polymers of the present invention have enhanced solubility in esters, ketones and aromatic solvents.
The following Examples illustrate the present invention without, however, limiting the same thereto. Testing of the physical properties of several durable, film-forming, polymers was performed and compared to prior art polymers. The tests involved a film-forming test, and a measurement of the glass transition temperature, Tg. Composition was determined by NMR spectroscopy. Molecular weight was determined by SEC method. Hydrodynamic volume of macromolecules was calculated on the basis of Laser light scattering measurements. Viscosity was measured by rotational viscometer.
(1) Film Forming Test. The core/shell polymer of the present invention was cast on a glass or aluminum substrate and allowed to dry at ambient conditions for several hours.
(2) Measurement of Tg. The glass transition temperature was measured by Differential Scanning Calorimetry, using a DSC available from Mettler-Toledo.