Gel-free process for making functionalized anionically...

Details Gel-free process for making functionalized anionically... Gel-free process for making functionalized anionically...

1999-01-20

2002-10-08

Teskin, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S330300, C525S333100, C525S333200, C525S333300, C525S344000, C525S361000, C525S375000, C525S383000, C525S385000, C525S409000, C525S415000, C525S461000, C526S173000

Reexamination Certificate

active

06462143

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a gel-free process for making functionalized polymers, primarily functionalized anionic polymers which are made using multi-lithium initiators. More particularly, this invention relates to a gel-free process for making polydiene diols.
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 polybutadiene 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. These polymers are then capped to form functional end groups as described in U.S. Pat. Nos. 4,417,029, 4,518,753, and 4,753,991. Of particular interest herein are terminal hydroxyl, carboxyl, sulfonate, and amine groups.
It has been observed that when the living polymer is reacted with the commonly available “capping” agents, the polymer in the hydrocarbon solution forms a gel. For purposes of this invention, a polymer gel is defined as a blend of a polymer and a hydrocarbon solvent that has a yield stress, that is, it will not flow unless it is acted on by at least some critical stress. A polymer gel as defined herein will require a significant application of force in order to initiate flow through an orifice. Of particular interest are gels that will not flow under the force of their own weight. The presence of gel that will not flow under the force of its own weight is readily detected by visual observation. This effect is observed by inverting a bottle containing the solution to see whether it flows to the bottom of the inverted flask. Gelled solutions will not readily flow to the bottom of the bottle.
The physical characteristics of these gels make them more difficult to handle in equipment which is designed for moving, mixing, or combining freely flowing liquids, i.e. materials without a significant yield stress. Pumps, reactors, heat exchangers, and other equipment that are normally used for making polymer solutions that can be characterized as viscous fluids are not typically suited to handling polymer gels. Thus, one would expect that processing equipment likely to be found at a manufacturing location that is designed to handle liquid polymer solutions, as defined above, would be ill suited to handling gels of this nature.
Without limiting the invention thereto, we offer the following theory as to why this gelation occurs. We believe that gelation results from the strong association of the “capped” polymer chain ends in the hydrocarbon solvents used, i.e., cyclohexanesldiethylether. In the case of an ethylene oxide capping agent, the polymer chain ends would be lithium alkoxides. In essence, these very polar lithium alkoxide sites interact strongly as they are formed and, in the nonpolar solvent, self-assemble into aggregates having multiple alkoxide centers. The association of alkoxide ends from multiple chains in a single aggregate provides a mechanism for network formation. Since the polymer chains each have two alkoxide ends, having the ends anchored in different aggregates leads to elastic properties, creating a gel as defined herein.
A suggested mechanism for the formation of a strongly associating gel in the case of a polybutadiene diol is as follows:
Li—Li+Butadiene→Li—CH
2
PolymerCH
2
—Li
Li—CH
2
PolymerCH
2
—Li+2(ethyleneoxde)→
The dilithium initiation technology discussed above has advantages over other technologies used to make functionalized anionically polymerized polymers including polydiene diols and polyols. For instance, U.S. Pat. No. 5,416,168 describes a process which utilizes a monolithium initiator which contains a protected functional center (Protected Functional Initiator) to make a polybutadiene mono-ol. The preparation of the initiator is complicated by the fact that the precursor to the initiator must contain the functional center that is desired in the final polymer and further that this center must be derivatized to make it inert to the chemistry used in making the C—Li bond in the initiator. Once the Protected functional initiator is prepared, it may be used to polymerize a suitable monomer such as butadiene. This process leaves the protected functional initiator on one end of the polymer chain and a living C—Li center on the other end of the chain. Optionally, the “living” end of the polymer chain may be reacted with a capping agent. If ethylene oxide is used as the capping agent, then a polybutadiene mono-ol is the product. These steps are then followed by a step of deprotecting the first functionalized polymer chain end. This chemistry frees the functionality on the other end of the polymer chain. Finally, the polymer product must be washed to remove the residue of the protecting agent and the residues of the reagent that were used to remove it.
It can be seen that a dilithium initiation process would be highly advantageous over such a protected functional initiator process in terms of elimination of process steps, cost, etc. The invention described herein is a process for producing terminally functional polymers using the di- or multi- organo alkali metal initiator method. This process for making terminally functional polymers avoids gel formation through the addition of “screening agents” which block or weaken the association of the polar functional moieties.
SUMMARY OF THE INVENTION
This invention relates to a gel-free process for making functionalized polymers. When multi-organo alkali metal initiators are used to make these polymers anionically, the process comprises anionically polymerizing at least one monomer with a multi-organo alkali metal initiator in a hydrocabon solvent and then capping the polymer by adding to the polymer a capping agent that reacts with the ends of the polymer chains such that strongly associating chain ends are formed wherein a polymer gel is formed. The important characteristic of the capping agent herein is that it caps the living polymer and adds a functional group to the polymer chain end which will be strongly associating in the hydrocarbon solvent. The result of the association of the chain ends is that the solution will gel. The final step of the process is adding a trialkyl aluminum compound to the polymer gel which results in a freely flowing solution.
In a second embodiment, the present invention relates to a process for making such polymers which comprises anionically polymerizing them as described and then capping the polymer by adding the above-described capping agent. An aluminum trialkyl is added before or during polymerization or before or with the capping agent (i.e., before a gel can form—prior to any reaction of the alkali metal with the gel-forming functionality).
In the first embodiment, a gel is formed and then removed. In the second embodiment, the gel never is formed because of the presence of the trialkyl aluminum compound.
In a third embodiment, an unfunctionalized polymer is functionalized by lithiation and reaction with a capping agent of this invention, whereby a strongly associating gel is formed. A promoter such as triethylamine or tetramethylethylenediamine is necessary. In a fourth embodiment, an already functionalized polymer is reacted with RLi
n
(or an active Na or K compound) in order to convert to a different functionality. In both embodiments, the gel can be broken by addition of trialkyl aluminum to the gel or prevented by addition thereof prior to the reaction of Li (or Na or K) with the gel-forming functionality.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to functionalized polymers and processes for avoiding gel formation, especially when such polymers are made by anionic polymerization using d

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