Chemistry of carbon compounds – Miscellaneous organic carbon compounds – C-metal
Reexamination Certificate
1999-09-30
2001-04-17
Nazario-Gonzalez, Porfirio (Department: 1621)
Chemistry of carbon compounds
Miscellaneous organic carbon compounds
C-metal
Reexamination Certificate
active
06217798
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for making anionic polymers using dilithium initiators. More particularly, this invention relates to a method for making a dilithium diisopropenylbenzene-based initiator for use in such a process.
BACKGROUND OF THE INVENTION
Functionalized anionically polymerized polymers of conjugated dienes and other monomers wherein the functionalization is terminal and/or internal are known. Particularly, U.S. Pat. No. 5,393,843 describes poly-butadiene polymers having terminal functional groups. One of the methods described for making such polymers involves anionic polymerization utilizing a dilithium initiator such as the adduct derived from the reaction of m-diisopropenylbenzene with two equivalents of s-BuLi. Monomer is added to the initiator in hydrocarbon solution and anionic living polymer chains grow outwardly from the ends of the dilithium initiator.
U.S. Pat. No. 3,734,973 describes the production of multifunctional anionic polymerization initiators by reacting diisopropenylbenzene compounds with organo monolithium compounds. These two components are reacted in a molar range of 0.1:1 to 4:1 and the reaction is conducted in the presence of a polymerizable monovinyl-substituted aromatic compound employed as a solubilizing monomer and also in the presence of a hydrocarbon or polar diluent. For example, it describes the addition of butadiene to a mixture of diisopropenylbenzene and toluene and then adding secondary butyllithium to that mixture in solution in cyclohexane, after which time the reaction to form the dilithium initiator was carried out. The reaction was also carried out without the butadiene as a solubilizing agent and a precipitate formed. These initiators were used to carry out the anionic copolymerization of stryene and butadiene. They can also be used to make block copolymers of those monomers.
Unfortunately, the chemistry involved in the reaction of the diisopropenylbenzene and the lithium alkyl is prone to suffer from a competing side reaction which forms oligomers of diisopropenylbenzene. The oligomers consume diisopropenylbenzene and this limits the yield of the dilithium initiator. In addition and perhaps more importantly, the oligomers have more than two lithium centers per molecule. If all of the lithium centers in the oligomers initiate polymerization, a nonlinear, star, or radial polymer will result. This is undesirable if the desired polymer is a difunctional anionic polymer.
For these reasons, it can be seen that it is desirable to limit the level of oligomerization in the synthesis of the dilithium initiator from diisopropenylbenzene. We have discovered that combining the components in a particular order, carrying out the reaction within a narrow temperature range, and carrying out the reaction in the presence of the appropriate amount of diethyl ether provides the advantage of minimizing the oligomerization of the diisopropenyl-benzene.
SUMMARY OF THE INVENTION
This invention is a process for making a difunctional lithium initiator which comprises reacting a secondary or tertiary lithium alkyl with a diisopropenylbenzene compound in the presence of diethyl ether at a temperature of 25 to 50° C. wherein the molar ratio of the diethyl ether to the lithium alkyl is from above 0.1:1 to 2:1 and the diisopropenylbenzene compound and the diethyl ether are first mixed together and then added to the lithium alkyl. The molar ratio of the diisopropenylbenzene compound to the lithium alkyl should be as close to 0.5:1 as possible. Clearly, having an excess of diisopropenylbenzene compound is undesirable as it will promote the formation of oligomers. If there is not enough lithium alkyl to react with all of the isopropenyl centers, they will react with the newly formed benzyl lithium centers and in this way make oligomers. Having excess lithium alkyl, on the other hand, is only undesirable if the polymerization application cannot tolerate monoinitiated product. Monoinitiated product would arise from the excess lithium alkyl used in the preparation of the diinitiator. For some applications, a combination of monoinitiated and diinitated polymers will be preferred. For these applications, an excess of lithium alkyl should be used in the preparation of the diinitiator. It is preferred that the molar ratio of diethyl ether to lithium alkyl be as close to 1:1 as possible.
DETAILED DESCRIPTION OF THE INVENTION
The diisopropenylbenzene compounds which can be used according to the present invention are represented by the following formula
where two R's are isopropenyl radicals and each of the remaining R's is hydrogen, or an alkyl, or cycloalkyl radical, or combinations thereof, containing from one to six carbon atoms.
Exemplary compounds are 1,2-diisopropenylbenzene; 1,3-diisopropenylbenzene; 1,4-diisopropenylbenzene; 3,4,5,6-tetramethyl-1,2-diisopropenylbenzene; 2,4,5,6-tetraethyl-1,3-diisopropenyl-benzene; 2,3,5,6-tetra-n-hexyl-1,4-diisopropenylbenzene; 3,4-dicyclohexyl-1,2-diisopropenylbenzene; 5-(3-methyl-cyclopentyl)-1,3-diisopropenylbenzene; 3-cyclopentyl-methyl-6-n-propyl-1,4-diisopropenylbenzene; 4-(2-cyclo-butyl-1-ethyl)-1,2-diisopropenylbenzene; 3-(2-n-propylcyclopropyl)-1,4-diisopropenylbenzene; 2-methyl-5-n-hexyl-1,3-diisopropenylbenzene; 4-methyl-1,2-diiso-propenylbenzene; 5-ethyl-1,3-diisopropenylbenzene; 3-methyl-1,4-diisopropenylbenzene; and the like. 1,3-diisopropenylbenzene is preferred. The meta isomer gives the best product because it gives a faster rate of reaction with the lithium alkyl.
The organomonolithium compounds that are reacted with the diisopropenylbenzene compounds of this invention are represented by the formula R′Li, wherein R′ is a secondary or tertiary alkyl, preferably containing from 3 to 20, preferably 4 to 10, carbon atoms per molecule. Exemplary of these organomonolithium compounds are isopropyllithium, sec-butyllithium, tert-octyllithium, tert-butyllithium, and the like. sec-butyl and tert-butyllithium are preferred.
The dilithium initiators of this invention are prepared by reacting a lithium alkyl compound with a diisopropenylbenzene compound at a mole ratio of diisopropenylbenzene to lithium alkyl in the range of 0.4:1 to 0.6:1, preferably 0.45:1 to 0.55:1. Excess lithium alkyl may be used for applications where a mixture of diinitiator and monoinitiator is preferred. Diethyl ether is utilized in the reaction at a molar ratio of diethyl ether to lithium alkyl compound of above 0.1:1 to 1.5:1 for secondary lithium alkyls and 2:1 for tertiary lithium alkyls, preferably 0.4:1 to 1.1:1, and most preferably about 1:1 for secondary lithium alkyls and 2:1 for tertiary lithium alkyls because this ratio gives the best results with poorer results observed at both lower and higher ratios.
This reaction is carried out in a relatively narrow temperature range of 25 to 50° C. and in the case of secondary lithium alkyls, 40 to 50° C. Lower yields of the dilithium initiator and thus higher levels of oligomer will be obtained at higher and lower temperatures. If a dilithium initiator is prepared according to this invention at a lower temperature, heating it to a temperature within the above range will result in increased levels of the dilithium initiator.
The order of addition of the components of this reaction is very important to achieving the desired result of the minimization of the oligomers produced and the maximization of the production of the dilithium initiator. In order to accomplish this result, the diisopropenylbenzene compound and the diethyl ether are first mixed together. Then they are added to the lithium alkyl compound. It is highly preferred that this mixture be added to the lithium alkyl at a rate that allows control of the reaction temperature within the desired range.
Anionically polymerized polymers of conjugated dienes and/or vinyl aromatic hydrocarbons and/or other monomers can be made with the dilithium initiators according to conventional practice such as described in U.S. Pat. No. 3,734,973. Functionalized anionic polymers wherein the functi
Haddix Grant Wesley
Schisla David Karl
van der Steen Fred Hendrik
Willis Carl Lesley
Haas Donald F.
Nazario-Gonzalez Porfirio
Shell Oil Company
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