Highly functionalized polymers and a process for making the...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...

Reexamination Certificate

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C526S217000, C526S083000, C525S331900, C525S332800, C525S333600

Reexamination Certificate

active

06451935

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to highly functionalized polymers and processes for making the same. More particularly, the highly functionalized polymers of this invention are prepared by using anionic polymerization techniques and then the polymers are end-functionalized in the presence of stabilization compounds. More specifically, the highly functionalized polymers prepared according to this invention are end-functionalized in the presence of at least one lithium alkoxide compound.
BACKGROUND OF THE INVENTION
It is known to use organolithium initiators to polymerize conjugated diene, triene, and monovinyl aromatic monomers. These polymerizations proceed according to anionic polymerization mechanisms. That is, these polymerization reactions generally include the reaction of monomers by nucleophilic initiation to form and propagate a polymeric structure. Throughout the formation and propagation of this polymer, the polymeric structure is ionic or “living.” A living polymer, therefore, is a polymeric segment having a living or reactive end. For example, when a lithium containing initiator is employed to initiate the formation of a polymer, the reaction will produce a reactive polymer having a lithium atom at its living or reactive end.
Chain propagation of an anionically-polymerized polymer typically ceases when all available monomer is consumed or when the living end is quenched or terminated. Typically, termination occurs in the presence of an electrophilic reagent or proton donor. Also, living polymers can spontaneously terminate because their carbanion centers decay with time. Spontaneous termination is also prevalent at higher polymerization temperatures where inter-polymer coupling likewise occurs.
It is often desirable to synthesize polymers having relatively high molecular weights and relatively small molecular weight distributions. Accordingly, anionically polymerized polymers are commercially prepared in the presence of an excess of monomer and the chain propagation reaction is terminated with terminating agents after a desired chain propagation. Also, it is commercially desirable and economically efficient to prepare anionically-polymerized polymers with a minimal amount of solvent and thereby increase polymer production yield. This is especially true when continuous polymerization techniques are employed.
These high monomer concentrations, however, produce very exothermic reactions that result in very high reaction temperatures. This heat is believed to promote spontaneous termination and inter-polymer coupling, which results in the formation of low molecular weight polymers and a wide molecular weight distribution. Also, the efficacy of end-chain functionalizing reactions is reduced due to a reduction in living-polymer ends.
Accordingly, there is a need to run highly concentrated anionic polymerizations and thereby increase polymer production efficiency while maintaining the living ends of polymers until a desired end-funcitonalization is effected.
SUMMARY OF THE INVENTION
In general the present invention provides a process for preparing highly functionalized polymers comprising the steps of admixing anionically-polymerizable monomers and at least one anionic-polymerization initiator to form an admixture of living polymers, adding at least one lithium alkoxide stabilizer to the admixture of living polymers to form a stabilized admixture, and adding a functionalizing agent to the stabilized admixture.
The present invention also includes a method for functionalizing living polymers, the method comprising the steps of preparing a solution of living polymers, where the solution includes at least one lithium alkoxide stabilizer, and adding a functionalizing agent to the solution of living polymers.
The present invention further provides a highly functionalized polymer prepared by the steps comprising admixing anionically-polymerizable monomers and anionic-polymerization initiators to form an admixture of living polymers, adding at least one lithium alkoxide stabilizer to the admixture of living polymers to form a stabilized admixture, and adding a functionalizing agent to the stabilized admixture.
Advantageously, the process of the present invention overcomes many shortcomings of the prior art by end-functionalizing anionically-polymerized polymers in the presence of at least one stabilizer compound. As a result, the monomer concentration of a polymerization medium can be increased and highly functionalized polymers are obtained. Also, the amount of solvent needed to run anionic polymerizations in solution is reduced, thereby increasing the efficacy of continuous polymerization processes.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
It has now been found that highly functionalized polymers can be prepared by functionalizing living polymers in the presence of at least one stabilizer compound. These compounds are believed to stabilize the reactive or living nature of the polymer and thus, once reacted with a functionalizing agent, provide a polymeric composition having an increased number of functionalized polymers. The stabilizers that are useful in practicing this invention can generally be classified as lithium alkoxide compounds, and the practice of this invention is especially useful when preparing anionically-polymerized polymers by using organolithium initiators. In one embodiment of this invention, the highly functionalized polymers are extremely useful for fabricating tires.
According to a preferred embodiment of this invention, one or more lithium alkoxides are added to a polymerization-reaction medium prior to the attainment of a peak polymerization temperature. As noted above, the use of this stabilizer is particularly useful when using organolithium compounds as initiators. Those skilled in the art will appreciate that polymerization reactions of this type are exothermic and lead to increased reaction temperatures until a peak reaction temperature is achieved. Afterwards, the reaction medium naturally begins to cool. Therefore, the lithium alkoxide stabilizers employed in this invention can be added to a polymerization medium prior to initiating polymerization or after polymerization has begun, but preferably not later than when the peak polymerization temperature is achieved.
The amount of lithium alkoxide that is added to a polymerization medium according to this invention can vary depending on the amount of initiator, the concentration of the monomers, and the expected temperature profile. In a preferred embodiment, the ratio of lithium alkoxide to lithium-containing initiator is from about 0.5:1 to about 2:1, and more preferably from about 0.8:1 to about 1.2:1.
One or more lithium alkoxides can be added to a polymerization-reaction medium in a couple of ways. First, the compounds can be added directly to a polymerization medium. This can be accomplished by adding a solution that contains one or more lithium alkoxides that are dissolved or suspended therein. Or, a composition of matter that essentially includes lithium alkoxide compounds can be added. It should be understood that the foregoing solutions, suspensions, or compositions may include individual lithium alkoxide molecules, complexes of more than one lithium alkoxide compound, reaction products of lithium alkoxide compounds, solubilized ionic species of lithium alkoxide compounds, or mixtures thereof. Therefore, the term lithium alkoxide or lithium alkoxide compositions may simply be used to refer to all of these lithium alkoxide compositions.
Alternatively, the lithium alkoxide may be added to a polymerization medium by adding reactants that will ultimately form a lithium alkoxide composition. In other words, the lithium alkoxide is formed in situ within the polymerization medium. For example, alkyllithiums and alcohols react and form lithium alkoxide. Any reference to adding lithium alkoxide to a polymerization medium will therefore refer to the addition of a lithium alkoxide composition, as discussed above, and to the addition of reactants that will form li

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