Calcium-based catalyst system

Abstract

The process and catalyst system of this invention can be utilized to synthesize a highly random styrene-butadiene rubber having a high trans content by solution polymerization. The styrene-butadiene rubber made by the process of this invention can be utilized in tire tread rubbers that exhibit improved wear characteristics. This invention more specifically reveals a catalyst system for use in isothermal polymerizations which consists essentially of (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. The subject invention further discloses a process for synthesizing a random styrene-butadiene rubber having a low vinyl content by a process which comprises copolymerizing styrene and 1,3-butadiene under isothermal conditions in an organic solvent in the presence of a catalyst system which consists essentially of (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. An amine can also be added to the catalyst system to increase the molecular weight (Mooney viscosity) of the rubber.

What is claimed is:  
     
         1 . A catalyst system which consists essentially of (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide.  
     
     
         2 . A catalyst system as specified in  claim 1  wherein the molar ratio of the lithium alkoxide to the calcium alkoxide is within the range of about 1:1 to about 20:1.  
     
     
         3 . A catalyst system as specified in  claim 4  wherein the molar ratio of the alkyl lithium compound to the calcium alkoxide is within the range of about 1:1 to about 6:1.  
     
     
         4 . A catalyst system as specified in  claim 5  wherein the calcium alkoxide is selected from the group consisting of calcium dimethoxide, calcium diethoxide, calcium diisopropoxide, calcium di-n-butoxide, calcium di-sec-butoxide, calcium di-t-butoxide, calcium di(1,1-dimethylpropoxide), calcium di(1,2-dimethyl-propoxide), calcium di(1,1-dimethylbutoxide), calcium di(1,10-dimethylpentoxide), calcium di(2-ethyl-hexanoxide), calcium di(1-methylheptoxide), calcium diphenoxide, calcium di(p-methylphenoxide), calcium di(p-octylphenoxide), calcium di(p-nonylphenoxide), calcium di(p-dodecylphenoxide), calcium di(α-naphthoxide), calcium di(β-naphthoxide), calcium (o-methoxyphenoxide), calcium (o-methoxyphenoxide), calcium di(m-methoxyphenoxide), calcium di(p-methoxy-phenoxide), calcium (o-ethoxyphenoxide) and calcium (4-methoxy-1-naphthoxide) and calcium tetrahydrofurfurylate.  
     
     
         5 . A catalyst system as specified in  claim 6  wherein the organolithium compound is an organomonolithium compound.  
     
     
         6 . A catalyst system as specified in  claim 7  wherein the molar ratio of the lithium alkoxide to the calcium alkoxide is within the range of about 5:2 to about 10:1.  
     
     
         7 . A catalyst system as specified in  claim 8  wherein the molar ratio of the alkyl lithium compound to the calcium alkoxide is within the range of about 3:2 to about 4:1.  
     
     
         8 . A catalyst system as specified in  claim 9  wherein the lithium alkoxide is made by reacting an organolithium compound, metallic lithium or lithium hydride with an alcohol selected from the group consisting of methanol, ethanol, normal-propyl alcohol, isopropyl alcohol, t-butanol, sec-butanol, cyclohexanol, octanol, 2-ethylhexanol, p-cresol, m-cresol, nonyl phenol, hexylphenol, tetrahydrofuryl alcohol, furfuryl alcohol, 3-methyltetrahydrofurfuryl alcohol, oligomer of tetrahydrofurfuryl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, N,N-diphenylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine, N-phenyldiethanolamine, N,N-dimethylpropanolamine, N,N-dibutylpropanolamine, N-methyldipropanolamine, N-ethyldipropanolamine, 1-(2-hydroxyethyl)pyrrolidine, 2-methyl-1-(2-hydroxyethyl)pyrrolidine, 1-piperidineethanol, 2-phenyl-1-piperidineethanol, 2-ethyl-1-piperidinepropanol, N-β-hydroxyethylmorpholine, 2-ethyl-N-8-hydroxyethylmorpholine, 1-piperazineethanol, 1-piperazinepropanol, N,N′bis(β-hydroxyethyl)piperazine, N,N′-bis(Y-hydroxypropyl)-piperazine, 2-(β-hydroxyethyl)pyridine and 2-(γ-hydroxypropyl)pyridine.  
     
     
         9 . A catalyst system as specified in  claim 10  wherein the organolithium compound is selected from the group consisting of ethyl lithium, isopropyl lithium, n-butyllithium, sec-butyllithium, tert-octyl lithium, phenyl lithium, 2-naphthyllithium, 4-butylphenyllithium, 4-tolyllithium, 4-phenylbutyllithium, cyclohexyl lithium and hexyl lithium.  
     
     
         10 . A catalyst system as specified in  claim 11  wherein the molar ratio of the lithium alkoxide to the calcium alkoxide is within the range of about 3:1 to about 5:1.  
     
     
         11 . A catalyst system as specified in  claim 12  wherein the molar ratio of the alkyl lithium compound to the calcium alkoxide is within the range of about 2:1 to about 3:1.  
     
     
         12 . A catalyst system which consists essentially of (a) an organometallic compound of a metal selected from the group consisting of lithium, potassium, magnesium, sodium, aluminum, zinc and tin, (b) a calcium compound and (c) a lithium alkoxide.  
     
     
         13 . A catalyst system as specified in  claim 21  wherein said calcium compound is selected from the group consisting of calcium carboxylates, calcium phenolates, calcium amines, calcium amides, calcium halides, calcium nitrates, calcium sulfates, calcium phosphates, calcium alcoholates and calcium ditetrahydrofurfurylate.  
     
     
         14 . A catalyst system as specified in  claim 22  wherein said organometallic compound is selected from the group consisting of organolithium compounds, organopotassium compounds, organomagnesium compounds and organosodium compound.  
     
     
         15 . A catalyst system as specified in  claim 23  wherein the calcium compound is selected from the group consisting of calcium alcoholates, calcium carboxylates and calcium phenolates.  
     
     
         16 . A catalyst system as specified in  claim 24  wherein the organometallic compound is an organolithium compound.  
     
     
         17 . A catalyst system as specified in  claim 23  wherein the calcium compound is a calcium alcoholate.  
     
     
         18 . A catalyst system as specified in  claim 21  wherein the molar ratio of the lithium alkoxide to the calcium compound is within the range of about 2:1 to about 20:1; and wherein the molar ratio organometallic compound to the calcium compound is within the range of about 1:1 to about 6:1.  
     
     
         19 . A catalyst system as specified in  claim 22  wherein the molar ratio of the lithium alkoxide to the calcium compound is within the range of about 5:2 to about 10:1; and wherein the molar ratio organometallic compound to the calcium compound is within the range of about 3:2 to about 4:1.  
     
     
         20 . A catalyst system as specified in  claim 23  wherein the molar ratio of the lithium alkoxide to the calcium compound is within the range of about 3:1 to about 5:1; and wherein the molar ratio organometallic compound to the calcium compound is within the range of about 2:1 to about 3:1.  
     
     
         21 . A process for the preparation of a calcium alkoxide which comprises reacting calcium hydroxide with an alcohol at a temperature which is within the range of about 150° C. to about 250° C. to produce the calcium alkoxide.  
     
     
         22 . A process as specified in claim  35  wherein the reaction is carried out in the presence of an excess of the alcohol.  
     
     
         23 . A process as specified in claim  36  wherein the alcohol is of the formula ROH wherein R represents a moiety selected from the group consisting of 2-ethylhexyl groups, nonylphenyl groups, dodecylphenyl groups, tetrahydrofurfuryl groups and furfuryl groups.  
     
     
         24 . A process as specified in claim  37  which further comprises removing the excess alcohol by distillation after the completion of the reaction.  
     
     
         25 . A process as specified in claim  38  wherein said reaction is carried out at a temperature which is within the range of about 175° C. to about 200° C.  
     
     
         26 . A process as specified in claim  38  herein said reaction is carried out at a temperature which is above the boiling point of the alcohol.  
     
     
         27 . A process as specified in claim  40  which further comprises recovering the calcium alkoxide by dissolving it in an organic solvent.  
     
     
         28 . A process as specified in claim  41  wherein the organic solvent is selected from the group consisting of ethyl benzene, toluene and xylene.  
     
     
         29 . A process as specified in  claim 1  wherein said catalyst system is further comprised of an amine.