PROCESSES FOR IMPROVING STABILITY OF LIVING POLYMERIZATION CHAIN ENDS

Abstract: Initiator compositions capable of imparting improved thermal stability of living polymerization chain ends and processes of using the same. The compositions include an alkyllithium initiator and a silyl ether. The silyl ether can be incorporated into the initiator (as a protected functionalized initiator), or as a separate small molecule added to the initiator solution.

Description: PROCESSES FOR IMPROVING STABILITY OF LIVING POLYMERIZATION CHAIN ENDS Field of the Invention This invention relates to novel compositions of anionic polymerization initiators which contain a silyl ether functionality, and processes which employ these compositions in the formation of living polymer anions which have improved thermal stability. Background of the Invention The thermal stability of living chain ends during an anionic polymerization is of importance, particularly on a commercial scale. If the chain ends are labile, the living chain ends will disproportionate to the corresponding olefin and alkane . The chain ends can also decompose by thermal elimination of lithium hydride, to also afford an olefin. Further, the elimination product olefin can then add an additional equivalent of living polymer to form unwanted dimers . For example, Fetters and Pennisi studied the thermal stability of poly (butadienyl) lithium at 75°C (R. . Pennisi and L. J. Fetters, acromolecules, 21 , 1094 (1988) . They found that 10 wt% of the polymer linked to form higher molecular weight products after only three hours at this temperature. After fourteen hours, 25 wt% of the polymer had linked. See Hsieh and Quirk (H. L. Hsieh and R. P. Quirk, Anionic Polymerization, Marcel Dekker, Inc., New York, 1996, p. 177-180) for additional discussion of the thermal stability of living polymer chain ends. Thermally stable polymer chain end are required for efficient formation of block copolymers, end group functionalization or coupling to form linear or radial (star) polymers. Summarv of the Invention The present invention provides novel compositions containing an anionic polymerization initiator and a silyl ether. The compositions of the invention include as a component one or more alkyllithium initiators, such as those represented by the formula RLi, wherein R represents an aliphatic, cycloaliphatic, or aryl substituted aliphatic radical. A currently preferred alkyllithium initiator is butyllithium. In addition, the compositions of the invention include one or more silyl ether compounds. The inventors have found that addition of one or more silyl ethers can provide enhanced thermal stability for living polymer anions, which in turn can afford higher yield in subsequent coupling or functionalization reactions . Exemplary silyl ether compounds include those of the formula R x R 2 R 3 Si -0-R 4 or R-.R 2 R 3 Si -0-R 5 -0-SiR 6 R 7 R 8 , wherein : R-,, R 2 , R 3 , R 6 , R 7 , and R 8 are each independently selected from the group consisting of hydrogen, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; R 4 is selected from the group consisting of C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; and R 5 is a branched or straight chain tether or connecting group containing 1-25 carbon atoms, optionally containing either as substituents on the tether, or as part of the tether backbone, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino groups, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl. Alternatively, the silyl ether can be incorporated into the living polymer backbone. In this embodiment, the silyl ether is derived from a protected functionalized initiator. The present invention also provides processes for preparing living polymer anions with enhanced thermal stability. Detailed Description of the Invention The compositions of the invention can include one or more alkyllithium initiators. Exemplary alkyllithium initiators include those represented by the formula RLi, wherein R represents an aliphatic, cycloaliphatic, or aryl substituted aliphatic radical. Preferably R is an alkyl or substituted alkyl group of 1-12 carbon atoms. Such initiators include, but are not limited to, methyllithium, ethyllithium, n- propyllithium, 2-propyllithium, n-butyllithium, s- butyllithium, t-butyllithium, n-hexyllithium, 2- ethylhexyllithium, and mixtures thereof. As used herein, alkyllithium initiators also include dilithium initiators as known in the art. See, for example, U.S. Patent Nos . 5,393,843 and 5,405,911. Dilithium initiators can be prepared by the reaction of two equivalents of an alkyllithium reagent, such as sec- butyllithium, with a compound having at least two independently polymerized vinyl groups, such as isomeric divinylbenzenes or isomeric diisopropenylbenzenes . The compositions of the invention further include one or more silyl ether compounds. Representative of such compounds include compounds of the formula R-.R 2 R 3 Si-0-R 4 or wherein: R- L , R 2 , R 3 , R 6 , R 7 , and R 8 are each independently selected from the group consisting of hydrogen, C1-C15 alkyl, substituted Cl-15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; R 4 is selected from the group consisting of C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; and R 5 is a branched or straight chain tether or connecting group containing 1-25 carbon atoms, optionally containing either as substituents on the tether, or as part of the tether backbone, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino groups, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl. Examples of silyl ether compounds useful for this invention include, but are not limited to, 1- (t- butyldimethylsilyloxy) propane, 1- (t- butyldimethylsilyloxy) butane, 1- (t- butyldimethylsilyloxy) hexane, 1- (t- butyldimethylsilyloxy) -2-ethylhexane, 1- (t- butyldimethylsilyloxy) octane, 2- (t- butyldimethylsilyloxy) propane, 2- (t- butyldimethylsilyloxy) butane, 2- (t- butyldimethylsilyloxy) hexane, 2- (t- butyldimethylsilyloxy) octane, 1,4- [bis- (t- butyldimethylsilyloxy) ] butane, 1,4- cyclohexanedimethanol- [bis- (t-butyldimethylsilyl) ] ether, 1, 4-cyclohexanedimethanol- [bis- (triisopropylsilyl) ] ether, 1,4- [bis- (t- butyldimethylsilyloxy) ] benzene, (triisopropylsilyloxy) ethane, 1- (triisopropylsilyloxy) propane, 1- (triisopropylsilyloxy) butane, 1, 6-bis- (triisopropylsilyloxy) hexane, 1- (triisopropylsilyloxy) heptane, (t- butyldiphenylsilyloxy) ethane, 1- (t- butyldiphenylsilyloxy) propane, 1- (t- butyldiphenylsilyloxy) butane, 1- (t- butyldiphenylsilyloxy) -2 , 2-dimethylpropane, 1- (t- butyldimethylsilyloxy) -2, 2-dimethylpropane, 1- (t- butyldimethylsilyloxy) -2, 2 -dimethylpropane, 1- (trimethylsilyloxy) -2, 2 -dimethylpropane, 1,3- [bis- (t- butyldimethylsilyloxy) ] -2 -methyl -propane, hexamethyldisiloxane, 1,1,3, 3-tetramethyldisiloxane, and the like and mixtures thereof. Other commercial silyl ethers useful in this invention include but are not limited to cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane , diphenyldimethoxysilane , ethyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane , octyltriethoxysilane , phenyltriethoxysilane, phenyltrimethoxysilane, n- propyltrimethoxysilane , tetra-n-butoxysilane , tetraethoxysilane , tetramethoxysilane , tetrapropoxysilane, and the like and mixtures thereof. Exemplary small molecule silyl ethers are commercially available, for example, organoreactive silanes from Dow Corning and from Hύls America Incorporated. It was discovered that the addition of a silyl ether improved the thermal stability of living polymerization chain ends. The more stable chain ends afforded higher conversions on subsequent functionalization reactions. The silyl ether can be added as part of the initiator composition, added to the polymerization reactor prior to the polymerization, as part of the monomer charge, or at the end of polymerization. In another embodiment of the invention, the silyl ether can be part of the living polymer backbone. In this embodiment, the silyl ether is derived from a protected functionalized initiator. The protected functionalized initiator has the formula: M-Q n -Z-0- (Si-R^R 3 ) wherein: M is an alkali metal selected from the group consisting of lithium, sodium and potassium; Q is an unsaturated or saturated hydrocarbyl group derived by incorporation of one or more conjugated diene hydrocarbons, one or more alkenylsubstituted aromatic compounds, or mixtures of one or more dienes with one or more alkenylsubstituted aromatic compounds into the M-Z linkage; Z is a branched or straight chain hydrocarbon connecting group which contains 3-25 carbon atoms, optionally substituted with C5-C25 aryl or substituted C5-C25 aryl; R 1 , R 2 , and R 3 are each independently selected from the group consisting of hydrogen, C1-C25 alkyl, substituted C1-C25 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl and substituted C5-C12 cycloalkyl ; and n is an integer f om 0 to 5. Examples of silyl ether containing functionalized initiators include, but are not limited to, 3- (t-butyldimethylsilyloxy) -1-propyllithium, 3-(t- butyldimethyl-silyloxy) -2-methyl-l-propyllithium, 3- (t- butyldimethylsilyloxy) -2 , 2 -dimethyl -1-propyllithium, 4- (t-butyldimethylsilyloxy) -1-butyllithium, 5- (t- butyldimethyl-silyloxy) -1-pentyllithium, 6- (t- butyldimethylsilyloxy) -1-hexyllithium, 8- (t- butyldimethylsilyloxy) -1-octyllithium, 3- (t- butyldiphenylsilyloxy) -1-propyllithium, 3- (t- butyldiphenylylsiloxy) -2-methyl-l-propyllithium, 3- (t- butyldiphenylsilyloxy) -2 , 2 -dimethyl -1-propyllithium, 6- (t-butyldiphenylsilyloxy) -1-hexyllithium, 3- (triisopropylsilyloxy) -1-propyllithium, 3- (trimethylsilyloxy) -2 , 2-dimethyl-l-propyllithium, and the like and mixtures thereof. Chain extended analogues thereof can also be employed. These and other silyl ether compounds can be prepared according to standard literature and patent procedures, for example, as described in PCT Published Application No. WO 97/05176. Anionic polymerizations employing the silyl ether stabilization compounds in accordance with the present invention can be conducted in an inert solvent, preferably a non-polar solvent, optionally containing an ethereal modifier, using an olefinic monomer (s), as described below. The polymerization can be conducted under conventional conditions, for example, at a temperature of about -30°C to about 150°C. The polymerization can be conducted using conventional alkyllithium initiators and/or protected functional organolithium initiators known in the art. The polymers may have a molecular weight range of about 1000 to 200,000 but the molecular weight can be higher. Typically about .01 to about 10 equivalents silyl ether stabilizing compound per mole equivalent of polymer is used. The monomer to be polymerized is selected from the group consisting of conjugated diene hydrocarbons, such as butadiene and isoprene, and alkenylsubstituted aromatic compounds, such as styrene and alpha-methylstyrene . The monomers may be polymerized alone, or in admixture with one other to form random copolymers, or by charging monomer to the reaction mixture sequentially to form block copolymers. Examples of conjugated diene hydrocarbons include, but are not limited to, 1, 3 -butadiene, isoprene, 2,3- dimethyl-1, 3 -butadiene, 1 , 3-pentadiene, myrcene, 2- methyl-3 -ethyl- 1, 3-butadiene, 2 -methyl-3 -ethyl-1, 3- pentadiene, 1, 3-hexadiene, 2-methyl-l, 3-hexadiene, 1,3- heptadiene, 3 -methyl- 1, 3-heptadiene, 1, 3-octadiene, 3- butyl-1, 3-octadiene, 3 , 4 -dimethyl -1, 3-hexadiene, 3-n- propyl-1, 3-pentadiene, 4 , 5-diethyl-l, 3-octadiene, 2,4- diethyl-1, 3 -butadiene, 2 , 3-di-n-propyl-l, 3 -butadiene, 2-methyl-3-isopropyl-l, 3-butadiene, and the like and mixtures thereof . Examples of polymerizable alkenylsubstituted aromatic compounds which can be anionically polymerized include, but are not limited to, styrene, alpha- methylstyrene, vinyltoluene, 2-vinylpyridine, 4- vinylpyridine, 1-vinylnaphthalene, 2-vinylnaphthalene, 1-alpha-methylvinylnaphthalene, 2 -alpha- methylvinylnaphathalene, 1,2-diphenyl-4-methyl-1-hexene and mixtures of these, as well as alkyl, cycloalkyl, aryl, alkaryl and aralkyl derivatives thereof in which the total number of carbon atoms in the combined hydrocarbon constituents is generally not greater than 18. Examples of these latter compounds include without limitation 3 -methylstyrene, 3 , 5-diethylstyrene, 2- ethyl-4-benzylstyrene, 4 -phenylstyrene, 4-p- tolylstyrene, 2, 4-divinyltoluene and 4, 5-dimethyl-l- vinylnaphthalene. Reference is made to U.S. Patent No. 3,377,404 for disclosures of additional alkenylsubstituted aromatic compounds. When alkenylsubstituted aromatic compounds are employed as monomers or comonomers, at least a few mole percent (about 0.01 to about 10%) of a conjugated diene should be added at the end of the end of the polymerization. This can maximize thermal stability of the living chain end. The inert solvent employed during the polymerizations is preferably a non-polar solvent such as a hydrocarbon, since anionic polymerization in the presence of such non-polar solvents is known to produce polyenes with high 1,4 -contents from 1,3 -dienes. Inert hydrocarbon solvents useful in practicing this invention include but are not limited to inert liquid alkanes, cycloalkanes and aromatic solvents such as alkanes and cycloalkanes containing five to ten carbon atoms such as pentane, hexane, cyclohexane, methylcyclohexane, heptane, methylcycloheptane, octane, decane and so forth and aromatic solvents containing six to ten carbon atoms such as benzene, toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, n- propylbenzene, isopropylbenzene, n-butylbenzene, and the like. Polar solvents (modifiers) can be added to the polymerization reaction to alter the microstructure of the resulting polymer, i.e., increase the proportion of 1,2 (vinyl) microstructure or to promote functionalization or randomization. Examples of polar modifiers include, but are not limited to, diethyl ether, dibutyl ether, tetrahydrofuran, 2- methyltetrahydrofuran, methyl tert-butyl ether, 1,2- dimethoxyethane (glyme) , 1, 2-diethoxyethane, diazabicyclo [2.2.2] octane, triethylamine, tributylamine, N-methylpiperidine, N-methylpyrrolidine, and N,N,N' ,N' -tetramethylethylene diamine (TMEDA) . The amount of the polar modifier added depends on the vinyl content desired, the nature of the monomer, the temperature of the polymerization, and the identity of the polar modifier. The polar solvent (modifier) can be added to the reaction medium at the beginning of the polymerization as part of the solvent reaction medium or added during the polymerization. The enhanced thermal stability of the living polymer anions was determined as follows. Living polymer anions were generated by the anionic polymerization of 1, 3 -butadiene with various initiators. Samples of the living polymer anions were then placed in sealed ampoules in a constant temperature bath at 100°C. Periodically, the samples were withdrawn and analyzed by size exclusion chromatography (SEC) , UV-Vis spectroscopy, and double titration for active carbon-lithium species. The results are collected in the table below: Exp. # Initiator Additive Mn (calc.) Mn (obs.) Mw/Mn Concentration Active C-Li Active C-Li (mol/1) 50 hrs 100 hrs 1 s-Buli None 2000 2000 1.06 0.035 84% 58% 2 s-Buli A 2000 2000 1.06 0.035 97% 81% 3 B None 2000 2400 1.09 0.037 85% 68% 4 C None 2000 2300 1.08 0.033 98% 97% A = l-(t-Butyldimethylsilyloxy)-propane B = 3-(lJ-Dimethylethoxy)-l-propyllithium, chain extended with two equivalents of isoprene C = 3-(t-Butyldimethylsilyloxy)-l-propyllithium Excellent thermal stability was observed by titration for the two experiments that contained a silyl ether (Experiments 2 and 4) . For example, when 3-(t- butyldimethylsilyloxy) -1-propyllithium was employed as the initiator, essentially all of the living polymer chain ends were still present in solution after 100 hours at 100°C. Similarly, after 50 hours, no loss of chain ends was detected when 1- (t- butyldimethylsilyloxy) propane was added to a polymerization initiated by s-butyllithium. Similar increases in chain end stability were observed in the two experiments that contained a silyl ether by UN-Vis spectroscopy and SEC. Significantly less higher molecular weight fractions were detected by both analytical techniques. The present invention will be further illustrated by the following non-limiting examples. Example 1 Synthesis and Stability of Alpha- (t-Butyldimethylsilyloxy) -Poly (butadienyl) lithium A 1000 ml. glass reactor was equipped with one break-seal reagent ampoule, a sampling port attached with a Teflon ® stopcock, an inlet tube fitted with a septum cap, and a magnetic stir bar. This reactor was flame sealed to a high vacuum line, and evacuated at 120°C for 8 hours. The flask was refilled with dry argon, and allowed to cool to room temperature. 3- (t-Butyldimethylsilyloxy) -1- propyllithium 17.93 wt . % in cyclohexane, 3.60 grams (20 mmoles) was added to the reactor with a syringe via the inlet tube. Cyclohexane, 585 ml., was then vacuum distilled directly into the reactor. The flask was then removed from the vacuum line by a flame seal. The monomer, purified 1, 3 -butadiene, 40 grams (740 mmole) was added from the ampoule. The reaction mixture was then placed in a constant temperature bath at 30°C, until all of the 1 , 3-butadiene had been consumed, about 15 hours. A 2 ml . aliquot of the living polymer was withdrawn with a dry syringe through the sample port, quenched with degassed methanol, and analyzed by SEC. The resultant functionalized polymer was characterized by SEC, and had the following properties: M n = 2.00 X 10 3 g/mole M w = 2.16 X 10 3 g/mole M w /M n = 1.08 The stability of the living chain was determined in a separate experiment . A reactor was equipped with an ampoule containing an aliquot of the living polymer produced above, a UV cell, a splitting assembly, and a degassed methanol ampoule. This apparatus was connected to the vacuum line with a torch. The reactor was evacuated until high vacuum was achieved, then heat sealed from the vacuum line. The living, polymeric organolithium solution was charged into the reactor by breaking the breakseal of the ampoule. The reactor was then placed in an oil bath equipped with a temperature controller and preheated to the desired temperature for thermolysis (100°C) . The changes in chain-end structure and living chain end concentration were monitored by UV-VIS spectroscopy as a function of heating time. Periodically, aliquots were removed via the splitting assembly for titration of carbon-bound lithium (modified Gilman titration) , and polymer characterization using size exclusion chromatography (SEC) . Example 2 Synthesis and Stability of Poly (butadienyl) lithium A 1000 ml. glass reactor was equipped with one break-seal reagent ampoule, a sampling port attached with a Teflon ® stopcock, an inlet tube fitted with a septum cap, and a magnetic stir bar. This reactor was flame sealed to a high vacuum line, and evacuated at 120°C for 8 hours. The flask was refilled with dry argon, and allowed to cool to room temperature. s-Butyllithium, 12.0 wt . % in cyclohexane, 1.28 grams (20 mmoles) was added to the reactor with a syringe via the inlet tube. Cyclohexane, 560 ml., was then vacuum distilled directly into the reactor. The flask was then removed from the vacuum line by a flame seal. The silyl ether compound, 1-t- butyldimethylsilyloxy- propane, 3.48 grams (20 mmole, 1.0 equivalent) was added from one break-seal ampoule. The monomer, purified 1, 3 -butadiene, 40 grams (740 mmole) was then added from the break-seal ampoule. The reaction mixture was then placed in a constant temperature bath at 30°C, until all of the 1,3- butadiene had been consumed, about 15 hours. A 2 ml . aliquot of the living polymer was withdrawn with a dry syringe through the sample port, quenched with degassed methanol , and analyzed by SEC . The resultant functionalized polymer was characterized by SEC, and had the following properties: M n = 2 . 00 X 10 3 g/mole M w = 2 . 12 X 10 3 g/mole M w /M n = 1 . 06 The stability of the living chain was determined in a separate experiment. A reactor was equipped with an ampoule containing an aliquot of the living polymer produced above, an ampoule which contained the silyl ether stabilizer, a UV cell, a splitting assembly, and a degassed methanol ampoule. This apparatus was connected to the vacuum line with a torch. The reactor was evacuated until high vacuum was achieved, then heat sealed from the vacuum line. The living, polymeric organolithium solution was charged into the reactor by breaking the breakseal of the ampoule. The reactor was then placed in an oil bath equipped with a temperature controller and preheated to the desired temperature for thermolysis (100°C) . The changes in chain-end structure and living chain end concentration were monitored by UV-VIS spectrospcopy as a function of heating time. Periodically, aliquots were removed via the splitting assembly for titration of carbon-bound lithium (modified Gil an titration) , and polymer characterization using size exclusion chromatography (SEC) . Example 3 Synthesis and Stability of Alpha- (t-Butyldimethylsilyloxy) -Poly (styryl) lithium A 1000 ml. glass reactor is equipped with two break-seal reagent ampoules, a sampling port attached with a Teflon ® stopcock, an inlet tube fitted with a septum cap, and a magnetic stir bar. This reactor is flame sealed to a high vacuum line, and evacuated at 120°C for 8 hours. The flask is refilled with dry argon, and allowed to cool to room temperature. 3- (t- Butyldimethylsilyloxy) -1-propyllithium 17.93 wt . % in cyclohexane, 3.60 grams (20 mmoles) is added to the reactor with a syringe via the inlet tube. Cyclohexane, 585 ml., is then vacuum distilled directly into the reactor. The flask is then removed from the vacuum line by a flame seal. The styrene monomer, 40 grams (384 mmole) is added from the ampoule. The reaction mixture is then placed in a constant temperature bath at 30°C, until all of the styrene is consumed, about 15 hours. Purified 1, 3 -butadiene, 3.25 grams (60 mmol) is then added from the second break seal ampoule. The reaction mixture is maintained in a constant temperature bath at 30°C, until all of the 1, 3 -butadiene is consumed, about 15 hours. A 2 ml . aliquot of the living polymer is withdrawn with a dry syringe through the sample port, quenched with degassed methanol, and analyzed by SEC. The resultant functionalized polymer is characterized by SEC, and has the following properties: M n = 2.00 X 10 3 g/mole M w = 2 . 16 X 10 3 g/mole M w /M n = 1 . 08 The stability of the living chain is determined in a separate experiment, utilizing the same protocol as detailed in Example 1. Comparative Example Synthesis and Stability of Alpha- (1, 1-Dimethylethyloxy) -Poly (butadienyl) lithium A 1000 ml. glass reactor was equipped with one break-seal reagent ampoule, a sampling port attached with a Teflon ® stopcock, an inlet tube fitted with a septum cap, and a magnetic stir bar. This reactor was flame sealed to a high vacuum line, and evacuated at 120°C for 8 hours. The flask was refilled with dry argon, and allowed to cool to room temperature. 3- (1, 1-Dimethylethyloxy) -1-propyllithium chain extended with two moles of isoprene, 15.8 wt . % in toluene, 5.16 grams (20 mmoles) was added to the reactor with a syringe via the inlet tube. Cyclohexane, 515 ml., was then vacuum distilled directly into the reactor. The flask was then removed from the vacuum line by a flame seal. The monomer, purified 1, 3 -butadiene, 40 grams (740 mmole) was added from the break-seal ampoule. The reaction mixture was then placed in a constant temperature bath at 30°C, until all of the 1, 3-butadiene had been consumed, about 15 hours. A 2 ml . aliquot of the living polymer was withdrawn with a dry syringe through the sample port, quenched with degassed methanol, and analyzed by SEC. The resultant functionalized polymer was characterized by SEC, and had the following properties: M n = 2.00 X 10 3 g/mole M w = 2.18 X 10 3 g/mole M w /M n = 1.09 The stability of the living chain was determined in a separate experiment, utilizing the same protocol as detailed in Example 1. Comparative Example Synthesis and Stability of Poly (butadienyl) lithium A 1000 ml. glass reactor was equipped with one break-seal reagent ampoule, a sampling port attached with a Teflon ® stopcock, an inlet tube fitted with a septum cap, and a magnetic stir bar. This reactor was flame sealed to a high vacuum line, and evacuated at 120°C for 8 hours. The flask was refilled with dry argon, and allowed to cool to room temperature. s-Butyllithium, 12.0 wt . % in cyclohexane, 1.28 grams (20 mmoles) was added to the reactor with a syringe via the inlet tube. Cyclohexane, 560 ml., was then vacuum distilled directly into the reactor. The flask was then removed from the vacuum line by a flame seal. The monomer, purified 1, 3 -butadiene, 40 grams (740 mmole) was added from the break-seal ampoule. The reaction mixture was then placed in a constant temperature bath at 30°C, until all of the 1,3- butadiene had been consumed, about 15 hours. A 2 ml . aliquot of the living polymer was withdrawn with a dry syringe through the sample port, quenched with degassed methanol , and analyzed by SEC . The resultant functionalized polymer was characterized by SEC, and had the following properties: M n = 2.00 X 10 3 g/mole M w = 2.12 X 10 3 g/mole M w /M n = 1.06 The stability of the living chain was determined in a separate experiment, utilizing the same protocol as detailed in Example 1. The foregoing examples are illustrative of the present invention and are not to be construed as limiting thereof.

Claims: THAT WHICH IS CLAIMED IS: 1. An initiator composition providing enhanced thermal stability to living polymer anions, comprising one or more alkyllithium initiators and one or more silyl ether compounds. 2. The composition of Claim 1, wherein said one or more silyl ether compounds comprise one or more compounds of the formula R-.R 2 R 3 Si-0-R 4 or R 1 R 2 R 3 Si-0-R 5 -0- SiR 6 R 7 R 8 , wherein: R l f R 2 , R 3 , R 6 , R 7 , and R 8 are each independently selected from the group consisting of hydrogen, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; R 4 is selected from the group consisting of C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; and R 5 is a branched or straight chain tether or connecting group containing 1-25 carbon atoms, optionally containing either as substituents on the tether, or as part of the tether backbone, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino groups, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl. 3. The composition of Claim 2, wherein said one or more silyl ether compounds comprise one or more compounds of the formula R 1 R 2 R 3 Si -0-R 4 wherein R 4 is Cl - C15 alkyl or substituted C1 - C15 alkyl . 4. The composition of Claim 1, wherein said one or more silyl ether compounds comprise one or more compounds selected from the group consisting of 1- (t- butyldimethylsilyloxy) propane, 1- (t- butyldimethylsilyloxy) butane, 1- (t- butyldimethylsilyloxy) hexane, 1- (t- butyldimethylsilyloxy) -2 -ethylhexane, 1- (t- butyldimethylsilyloxy) octane, 2- (t- butyldimethylsilyloxy) propane, 2- (t- butyldimethylsilyloxy) butane, 2- (t- butyldimethylsilyloxy) hexane, 2- (t- butyldimethylsilyloxy) octane, 1,4- [bis- (t- butyldimethylsilyloxy) ] butane, 1,4- cyclohexanedimethanol- [bis- (t-butyldimethylsilyl) ] ether, 1, 4-cyclohexanedimethanol- [bis- (triisopropylsilyl) ] ether, 1,4- [bis- (t- butyldimethylsilyloxy) ] benzene, (triisopropylsilyloxy) ethane, 1- (triisopropylsilyloxy) propane, 1- (triisopropylsilyloxy) butane, 1, 6-bis- (triisopropylsilyloxy) hexane, 1- (triisopropylsilyloxy) heptane, (t- butyldiphenylsilyloxy) ethane, 1- (t- butyldiphenylsilyloxy) propane, 1- (t- butyldiphenylsilyloxy) butane, 1- (t- butyldiphenylsilyloxy) -2 , 2-dimethylpropane, 1- (t- butyldimethylsilyloxy) -2 , 2 -dimethylpropane, 1- (t- butyldimethylsilyloxy) -2 , 2 -dimethylpropane, 1- (trimethylsilyloxy) -2 , 2 -dimethylpropane, 1,3- [bis- (t- butyldimethylsilyloxy) ] -2 -methyl-propane, hexamethyldisiloxane, 1,1,3, 3-tetramethyldisiloxane, cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, ethyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, octyltriethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, n- propyltrimethoxysilane, tetra-n-butoxysilane, tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, and mixtures thereof. 5. The composition of Claim 1, wherein said one or more alkyllithium initiators comprise one or more alkyllithium initiators represented by the formula RLi, wherein R represents an aliphatic, cycloaliphatic, or aryl substituted aliphatic radical . 6. The composition of Claim 5, wherein R is alkyl or substituted alkyl having 1 to 12 carbon atoms. 7. The composition of Claim 6, wherein said one or more alkyllithium initiators are selected from the group consisting of methyllithium, ethyllithium, n- propyllithium, 2-propyllithium, n-butyllithium, s- butyllithium, t-butyllithium, n-hexyllithium, 2- ethylhexyllithium, and mixtures thereof. 8. The composition of Claim 1, wherein said one or more alkyllithium initiators comprises one or more dilithium initiators. 9. The composition of Claim 1, wherein said one or more silyl ether compounds comprise one or more protected functionalized initiators of the formula: M-Q n -Z-0- (Si-R^R 3 ) wherein: M is an alkali metal selected from the group consisting of lithium, sodium and potassium; Q is an unsaturated or saturated hydrocarbyl group derived by incorporation of one or more conjugated diene hydrocarbons, one or more alkenylsubstituted aromatic compounds, or mixtures of one or more dienes with one or more alkenylsubstituted aromatic compounds into the M-Z linkage; Z is a branched or straight chain hydrocarbon connecting group which contains 3-25 carbon atoms, optionally substituted with C5-C25 aryl; R 1 , R 2 , and R 3 are each independently selected from the group consisting of hydrogen, C1-C25 alkyl, substituted C1-C25 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl and substituted C5-C12 cycloalkyl; and n is an integer from 0 to 5. 10. An initiator composition providing enhanced thermal stability to living polymer anions, comprising n-butyllithium initiator, s-butyllithium initiator or a mixture thereof, and 1- (t- butyldimethylsilyloxy) propane . 11. A process for preparing living polymer anions having improved thermal stability, comprising anionically polymerizing one or more monomers in the presence of one or more alkyllithium initiators and one or more silyl ethers. 12. The process of Claim 11, wherein said one or more silyl ethers comprise one or more compounds of the formula R 1 R 2 R 3 Si-0-R 4 or -O-R.-.-O- SiRgR.-R g , wherein: R lf R 2 , R 3 , R 6 , R 7 , and R 8 are each independently selected from the group consisting of hydrogen, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; R 4 is selected from the group consisting of C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl; and R 5 is a branched or straight chain tether or connecting group containing 1-25 carbon atoms, optionally containing either as substituents on the tether, or as part of the tether backbone, C1-C15 alkyl, substituted C1-C15 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino groups, C5-C12 cycloalkyl, and substituted C5-C12 cycloalkyl. 13. The process of Claim 12, wherein said one or more silyl ethers comprise one or more compounds of the formula R 1 R 2 R 3 Si-0-R 4 wherein R 4 is C1-C15 alkyl or substituted C1-C15 alkyl. 14. The process of Claim 11, wherein said one or more silyl ethers comprise one or more compounds selected from the group consisting of 1- (t- butyldimethylsilyloxy) propane, 1- (t- butyldimethylsilyloxy) butane, 1- (t- butyldimethylsilyloxy) hexane, 1- (t- butyldimethylsilyloxy) -2-ethylhexane, 1- (t- butyldimethylsilyloxy) octane, 2- (t- butyldimethylsilyloxy) propane, 2- (t- butyldimethylsilyloxy) butane, 2- (t- butyldimethylsilyloxy) hexane, 2- (t- butyldimethylsilyloxy) octane, 1,4- [bis- (t- butyldimethylsilyloxy) ] butane, 1,4- cyclohexanedimethanol- [bis- (t-butyldimethylsilyl) ] ether, 1 , 4-cyclohexanedimethanol- [bis- (triisopropylsilyl) ] ether, 1,4- [bis- (t- butyldimethylsilyloxy) ] benzene, (triisopropylsilyloxy) ethane, 1- (triisopropylsilyloxy) propane, 1- (triisopropylsilyloxy) butane, 1,6-bis- (triisopropylsilyloxy) hexane, 1- (triisopropylsilyloxy) heptane, (t- butyldiphenylsilyloxy) ethane, 1- (t- butyldiphenylsilyloxy) propane, 1- (t- butyldiphenylsilyloxy) butane, 1- (t- butyldiphenylsilyloxy) -2 , 2 -dimethylpropane, 1- (t- butyldimethylsilyloxy) -2 , 2 -dimethylpropane, 1- (t- butyldimethylsilyloxy) -2 , 2 -dimethylpropane, 1- (trimethylsilyloxy) -2 , 2-dimethylpropane, 1,3- [bis- (t- butyldimethylsilyloxy) ] -2 -methyl-propane, hexamethyldisiloxane, 1,1,3, 3-tetramethyldisiloxane, cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, ethyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, octyltriethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, n- propyltrimethoxysilane, tetra-n-butoxysilane, tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, and mixtures thereof. 15. The process of Claim 11, wherein said one or more alkyllithium initiators comprise one or more alkylithium initiators represented by the formula RLi, wherein R represents an aliphatic, cycloaliphatic, or aryl substituted aliphatic radical. 16. The process of Claim 15, wherein R is alkyl or substituted alkyl having 1 to 12 carbon atoms. 17. The process of Claim 16, wherein said one or more alkyllithium initiators are selected from the group consisting of methyllithium, ethyllithium, n- propyllithium, 2-propyllithium, n-butyllithium, s- butyllithium, t-butyllithium, n-hexyllithium, 2- ethylhexyllithium, and mixtures thereof. 18. The process of Claim 11, wherein said one or more alkyllithium initiators comprises one or more dilithium initiators. 19. The process of Claim 11, wherein said one or more silyl ethers comprise one or more protected functionalized initiators of the formula: M-Q n -Z-0-(Si-R 1 R 2 R 3 ) wherein: M is an alkali metal selected from the group consisting of lithium, sodium and potassium; Q is an unsaturated or saturated hydrocarbyl group derived by incorporation of one or more conjugated diene hydrocarbons, one or more alkenylsubstituted aromatic compounds, or mixtures of one or more dienes with one or more alkenylsubstituted aromatic compounds into the M-Z linkage; Z is a branched or straight chain hydrocarbon connecting group which contains 3-25 carbon atoms, optionally substituted with C5-C25 aryl; R 1 , R 2 , and R 3 are each independently selected from the group consisting of hydrogen, C1-C25 alkyl, substituted C1-C25 alkyl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C25 aryl, substituted C5-C25 aryl containing one or more lower C1-C10 alkyl, lower alkylthio, and lower dialkylamino, C5-C12 cycloalkyl and substituted C5-C12 cycloalkyl ; and n is an integer from 0 to 5. 20. A process for preparing living polymer anions having improved thermal stability, comprising anionically polymerizing one or more monomers in the presence of n-butyllithium initiator, s-butyllithium initiator or a mixture thereof, and 1- (t- butyldimethylsilyloxy) propane . 21. A process for preparing living polymer anions having improved thermal stability, comprising anionically polymerizing one or more monomers in the presence of n-butyllithium initiator, s-butyllithium initiator or a mixture thereof, and 3-(t- butyldimethylsilyloxy) -1-propyllithium. 22. A process for preparing living polymer anions having improved thermal stability, comprising anionically polymerizing one or more monomers in the presence of one or more protected functionalized initiators which contain a silyl ether.

Inventors: BURBA JOHN L, JANG SUNG HOON, LETCHFORD ROBERT J, QUIRK RODERIC P, SCHWINDEMAN JAMES A, BURBA, JOHN, L., JANG, SUNG, HOON, LETCHFORD, ROBERT, J., QUIRK, RODERIC, P., SCHWINDEMAN, JAMES, A.
Applicants: BURBA JOHN L, FMC CORP, JANG SUNG HOON, LETCHFORD ROBERT J, QUIRK RODERIC P, SCHWINDEMAN JAMES A, BURBA, JOHN, L., FMC CORPORATION, JANG, SUNG, HOON, LETCHFORD, ROBERT, J., QUIRK, RODERIC, P., SCHWINDEMAN, JAMES, A.
Application year: 1998
Main classification: C08F4
IPC codes: C08F4, C08F12, C08F36, C08F297