PROCESS FOR THE ANIONIC POLYMERIZATION OF ACRYLIC MONOMERS

Abstract: A polymer or copolymer having a low polydispersity is formed by an anionic polymerization process. The process comprises the steps of: forming a polymerization initiator medium; and rapidly adding an acrylic or methacrylic monomer to the polymerization initiator medium and polymerizing the acrylic or methacrylic monomer to form the polymer or copolymer having a low polydispersity.

Description: PROCESS FOR THE ANIONIC POLYMERIZATION OF ACRYLIC MONOMERS FIELD OF THE INVENTION The invention relates to the polymerization of acrylic monomers, optionally using vinyl comonomers in the presence of an anionic initiator to form polymers or copolymers having a narrow molecular weight distribution. BACKGROUND OF THE INVENTION The polymerization of acrylic or methacrylic monomers, such as, for example, alkyl acrylates and methacrylates as well as the copolymerization of acrylic or methacrylic monomers with vinyl comonomers in the presence of anionic polymerization initiators is generally known. Initiators having the general formula: R - M in which denotes an alkali metal or an alkaline earth metal and R denotes a straight-chain or branched alkyl containing 2 to 6 carbon atoms or an aryl have been employed. Examples of such initiators include sec- butyllithium, naphthalenesodium, 1,4-disodio-l,1,4,4- tetraphenyl butane, diphenylmethyl potassium, diphenylmethyl sodium, 1 ' -methylstyryllithium, 1,1- diphenyl-3-methylpentyllithium and others such as tertiary alcoholates of lithium and compounds containing trimethylsilyl groups. It is advantageous for various applications of acrylate or methacrylate polymers or copolymers that there be a narrow range of molecular weight distribution of the polymers or copolymers. In some cases, polymers have been prepared having a wide range of molecular weight distribution and this polymer composition is physically treated to form a material in which the polymer molecular weights fall within some narrower range. Additionally, it has been found that various additives including non- nitrogenous complexing agents can be added to the anionic polymerization reaction mixture so as to obtain polymers having relatively low polydispersity (see U.S. Patent No. 4,927,703 and U.S. Patent No. 4,826,941). In general, there are numerous publications and patents in the general area of acrylates or methacrylates prepared by anionic polymerization. U.S. Patent No. 4,927,703, U.S. Patent No. 4,826,941 and Fayt et al. , Macromolecules vol. 20(b), 1442-1444 (1987) are illustrative. These citations disclose the use of lithiu chloride and crown ethers to prepare narrow polydispersit poly(meth)acrylates. For example, at page 1443 of Fayt e al. it is noted that by the use of lithium chloride one can prepare polymethacrylates with a polydispersity of 1.2-1.6 as compared to 3.61 without lithium chloride. it is an object of the present invention to provide a polymerization or copolymerization process for the preparation of polymers or copolymers acrylates and methacrylates in which the polymers or copolymers produce have a narrow molecular weight distribution. SUMMARY OF THE INVENTION The present invention relates to an improved process for the anionic polymerization or copolymerizatio of acrylates and methacrylates wherein the monomers and comonomers are added to the anionic polymerization reaction medium either at once or in very fast continuous manner. More specifically, the instant process comprises the steps of preparing an anionic polymerization initiation system and adding the monomers to be polymerized or copolymerized to the initiation system either at once or in a rapid continuous manner. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the anionic polymerization of acrylate and methacrylate monomers optionally with vinyl comonomers. Acrylic and methacrylic monomers which are polymerized in the present invention include acrylic acid, acrylic acid esters, acrylonitriles, acrylamides, methacrylic acid, methacrylic acid esters, methacrylonitriles, and methacrylamide. The preferred acrylic and methacrylic monomers are alkyl acrylates or alkyl methacrylates wherein the alkyl group contains from 1 to 18 carbon atoms. The alkyl radical can be either unsubstituted or substituted. Examples of such acrylates and methacrylates include methylacrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butylmethacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, isopropyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate and stearyl methacrylate. Vinyl comonomers include, for example, butadiene, isoprene, styrene, alpha methyl styrene, vinyl toluene, t-butyl styrene, chlorostyrene, vinylnaphthalene, 2-vinylpyridine, 4-vinylpyridine and the like. Initiators useful in the present invention include initiators of the formula: R - M in which M is an alkali metal or an alkaline earth metal and R is a straight-chain or branched alkyl or cyclo-alkyl preferably having from 1 to 6 carbon atoms or an aryl. Examples of such initiators include, for example, hydrocarbyllithium initiators such as alkyllithium compounds, preferably methyl lithium, n-butyllithium, sec- butyllithium, cycloalkyllithium compounds, preferably, cyclohexyllithium and aryllithium compounds, preferably, phenyllithium, 1-methylstyryllithium, p-tolyllithium, naphyllithium and 1,l-diphenyl-3- methylpentyllithium. Also useful initiators include, naphthalene sodium, 1,4-disodio-l,1.4,4-tetraphenylbutane diphenylmethyl-potassium and diphenylmethylsodium. Tertiary alcoholates of lithium and compounds containing trimethylsilyl groups may also be employed. The instant process is preferably carried out i the absence of moisture and oxygen and in the presence of at least one inert solvent. Preferably, the polymerization is conducted in the absence of any impurit which is detrimental to an anionic catalyst systems. The inert solvent is preferably a hydrocarbon, an aromatic solvent or an ether. Suitable solvents include isobutane, pentane, cyclohexane, benzene, toluene, xylene, tetrahydrofuran, diglyme, tetraglyme, orthoterphenyl, biphenyl, decalin or tetralin. The polymerization or copolymerization temperature useful in the present process varies between about 30°C and about -78°C, preferably between about 0°C and -78°C. The present process preferably employs 1,1- diphenylethylene in the initiator system for the anionic polymerization. 1,1-diphenylethylene has relatively high electro-affinity and does not homopolymerize. The instant process enables the preparation of a whole range of homopolymers and copolymers including block copolymers wherein the number average molecular weight range of about 500 to about 1,000,000 preferably from about 1,000 to about 500,000, most preferably from about 1,000 to about 200,000 (number average m.w.) and a polydispersity index of about 1.0 to about 2.0, preferably from about 1.0 to about 1.5. The polymers and copolymers prepared in the present process have various known uses including, for example as lubricant additives. In the instant process, the polymerization is generally carried out in an inert atmosphere, for example under a nitrogen, argon, etc. atmosphere. Equipment used in the polymerization reaction should be carefully dried such as by drying at about 150°C for several hours. Solvents and reagents are also carefully dried. As an example if tetrahydrofuran (THF) is used as the polymerization medium, the THF can be freshly distilled over sodium-benzophenone (from a characteristic purple color) . Acrylic or methacrylic or other monomers or comonomers can be purified by passing the monomer or comonomer through neutral alumina. Diphenyl ethylene (DPE) can be dried over molecular sieve. The metallic initiators are normally used as received. It is important in achieving the desired polydispersity for the polymers or copolymers produced in the instant process that the monomers and comonomers be added to the polymerization reactor in a particular manner. Addition to the reactor containing reaction medium and initiator should be conducted in a rapid manner. Either the monomers and/or comonomers are added in one-shot (at once) as a single amount or rapidly added as a continuous stream. Dropwise addition cannot be used. The reaction is quite fast and is normally complete within a few seconds. Conversion is also quite good in the instant process and is generally approximately 100% conversion. The following examples are provided as being illustrative and are not intended to be in any way limiting on the scope of the present invention. EXAMPLES Experimental Procedure In the following examples, polymerizations were carried out in resin kettles under nitrogen atmosphere. The resin kettles were equipped with mechanical stirrers and polymerizations were carried out in THF. The sequence of addition/preparation for the polymerizations in the examples was as follows: 1. The required amount of distilled THF was charged to a dry resin kettle; 2. The THF was degassed by nitrogen for about 5 to 10 minutes with stirring; 3. The required amount of diphenylethylene wa charged to the resin kettle; 4. The polymerization system was titrated wit sec. butyllithium to a red endpoint (process for cleaning the impurities) ; 5. The required amount of sec. butyllithium was charged (solution became deep red) ,* 6. Monomer was added either slowly (comparative examples 1, 2 and 3) or at once (very fast) (invention examples 4 to 15) ; 7. The prepared polymer was recovered and the molecular weights and distributions were determined by Ge Pemeation Chromotograph (GPC) using polystyrene and/or polymethylmethacrylate calibration. Examples 1 to 15 were conducted in the manner discussed hereinabove at a temperature of -30°C. The relevant data for these examples is shown in the following Table: Example DPE* THF z-BuLi LMA** Mn M Mw/Mn 1 II mole ml mole mole g/mole 1 0.001 100 0.00039 0.034 21,200 72,000 3.4 1 2 0.001 100 0.00019 0.034 46,900 156,180 3.4 3 0.001 100 0.00017 0.034 54,100 291,300 5.4 4 0.001 100 0.00017 0.034 52,400 68,800 1.3 5 0.001 100 0.00039 0.034 63,800 82,600 1.3 6 0.001 100 0.00039 0.034 32,800 41,100 1.2 7 0.003 300 0.0013 0.102 23,100 28,300 1.2 8 0.003 300 0.0013 0.102 23,100 29,500 1.2 9 0.001 100 0.00039 0.034 30,311 42,000 1.2 10 0.0015 300 0.00065 0.204 76,000 100,500 1.3 11 0.001 300 0.00039 0.034 24,900 32,400 1.3 12 0.001 100 0.00026 0.034 36,600 48,400 1.3 13 0.001 100 0.00039 0.017 13,600 18,300 1.3 14 0.005 100 0.00195 0.068 10,400 15,000 1.4 15 0.0275 300 0.156 0.170 2,750 3,695 1.3 (MMA***) * Diphenylethylene ** Laurylmethacxγlate *** Methylmethacrylate Results The conversions in all of the examples (1 to 15 were about 100% and the initiating efficiencies were clos to about 100%. In examples 1, 2 and 3 where monomer addition was slow, the polymers produced have broad polydispersity (3.4 - 5.4). In examples 4 to 15 (the present invention) , monomer addition was very fast (at once) and the polymers produced have a fairly narrow polydispersity in the range of about 1.2 - 1.4. The possible reason for this surprising result might be explainable based upon the mechanism of initiation and propagation of methacrylates by anionic polymerization. The specific embodiments of the invention as given in the examples are illustrative and not limiting. The artisan can easily determine various improvements or modifications which will fall within the scope of the present invention. Specific reaction conditions and reaction parameters for any specific monomer or comonomer can be determined with either no experimentation or with not undue amount of experimentation.

Claims: WE CLAIM: 1. A process for the polymerization of acrylic or methacrylic monomers to form a polymer or copolymer comprising the steps of: a) forming a polymerization initiator medium containing an initiator having the formula R - M in which M is an alkali metal or an alkaline earth metal and R is a straight-chain or branched alkyl or cyclo-alkyl preferably having from 1 to 6 carbon atoms or an aryl and diphenylethylene in an inert solvent; b) rapidly adding the acrylic or methacrylic monomer to the polymerization initiator medium formed in step a) and polymerizing the acrylic or methacrylic monomer to form the polymer or copolymer having a polydispersity of between about 1.0 and about 2.0; and c) recovering the polymer or copolymer. 2. A process according to claim 1, wherein the acrylic or methacrylic monomer is added as a single one- shot dosage to the polymerization initiator medium. 3. A process according to claim 1, wherein the acrylic or methacrylic monomer is added in a rapid continuous manner to the polymerization initiator medium. 4. A process according to claim 1, wherein the process is carried out in an inert atmosphere. 5. A process according to claim 1, wherein the reaction medium is a hydrocarbon, an aromatic solvent or an ether. 6. A process according to claim 5, wherein the reaction medium is iβobutane, pentane, cyclohexane, benzene, toluene, xylene, tetrahydrofuran, diglyme, tetraglyme, orthoterphenyl, biphenyl, decalin or tetralin 7. A process according to claim 1, wherein th polymer or copolymer has a polydispersity of from about 1.0 to about 1.5. 8. A process according to claim 1, wherein th polymerization reaction is carried out at a temperature o between about 30°C and about -76°C. 9. A process according to claim 1, wherein th initiator is a hydrocarbyllithium compound. 10. A process according to claim 9, wherein th hydrocarbyl- lithium compound is an alkyllithium compound a cycloalkyllithium compound or an aryllithium compound. 11. A process according to claim 1, wherein th acrylic or methacrylic monomer is acrylic acid, acrylic acid esters, acrylonitriles, acrylamides, methacrylic acid, methacrylic acid esters, ethacrylonitriles, and methacrylamide. 12. A process according to claim 1, further comprising adding a vinyl comonomer with the acrylic or methacrylic monomer to the polymerization reaction medium. 13. A process according to claim 1, wherein th number average molecular weight of the polymer or copolymer is from about 500 to about 1,000,000. 14. A process according to claim 11, wherein the acrylic and methacrylic monomers are alkyl acrylates or alkyl methacrylates wherein the alkyl group contains from 1 to 18 carbon atoms and alkyl can be either unsubstituted or substituted. lδ. A process according to claim 14, wherein the acrylates and methacrylates are methylacrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butylmethacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, isopropyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate and stearyl methacrylate.

Inventors: JUNG ALFRED KARL, MISHRA MUNMAYA KUMAR, SHIRODKAR SHAILAJA MADHUSUDHAN, JUNG, ALFRED, KARL, MISHRA, MUNMAYA, KUMAR, SHIRODKAR, SHAILAJA, MADHUSUDHAN
Applicants: TEXACO DEVELOPMENT CORP, TEXACO DEVELOPMENT CORPORATION
Application year: 1996
Main classification: C08F20
IPC codes: C08F4, C08F20