Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-05-04
2001-06-05
Lipman, Bernard (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...
C525S332800, C525S332900, C525S333100, C525S333200, C525S339000
Reexamination Certificate
active
06242538
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.
If the living carbon—alkali metal endgroups (chain ends) are first transformed to the “ate” complex (aluminate) by reaction with a trialkylaluminum compound, the addition of EO occurs nearly quantitatively, without the formation of gel. Addition of a trialkylaluminum compound can also dissipate a gel of this kind that has already formed. The molar ratio of the trialkyl aluminum compound to the polymer chain ends is generally at least 0.1:1, preferably 0.33:1 and most preferably 0.66:1 to 1:1 since this results in a freely flowing solution. Unfortunately, at the preferred aluminum levels, the hydrogenation activity of the Ni/Al catalysts that are often used in the hydrogenation of these polymers is poor. Substantially more catalyst and longer reaction time are required to reach an acceptable level of residual unsaturation in the trialkylaluminum—containing cements than in controls prepared in the absence of aluminum. The present invention provides a method whereby polymers using trialkylaluminum to mitigate the gel problem can be efficiently hydrogenated.
It is common practice to add an alkanol, such as methanol, to neutralize the basicity of the solution (known as the polymer cement) after the polymerization reaction prior to hydrogenation. Previously we found that addition of methanol at this point was preferable to omitting the alcohol or adding other alcohols, such as 2-ethylhexanol, but hydrogenation performance was poor compared to samples prepared without the added alkyl aluminum. We found that it was preferred to remove the aluminum and lithium by contact with aqueous mineral acid. This improvement resulted in a substantial improvement in both the rate of hydrogenation and the extent of hydrogenation at a given catalyst level. While this process represents a substantial improvement over the state of the art, it introduces an additional process step. It can be seen that it would be advantageous to accomplish the same result without the necessity of an additional process step.
SUMMARY OF THE INVENTION
This invention relates to a gel-free process for making functionalized polymers. In this second embodiment, the aluminum trialkyl may be 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). When multi-lithium initiators are used to make these polymers anionically, the process comprises anionically polymerizing at least one monomer with a multi-lithium initiator in a hydrocarbon solvent, functionalizing 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, resulting in a polymer gel, adding a trialkyl aluminum compound to the polymer gel, whereby the gel dissipates, adding a proton source to eliminate the gel-forming OLi wherein the proton source can be an organic acid with a pK
a
of 11 or less or a mixture of an alkanol and the organic acid, hydrogenating the polymer with a hydrogenation catalyst, optionally washing the polymer with aqueous acid to extract the lithium and catalyst residue, and optionally washing the polymer with water or aqueous base to extract the organic acid. In the reagent that is the proton source, there must be at least 1 mole of protons per mole of lithium ions in the polymer cement and at least 0.4 of those must come from the organic acid, preferably from 0.5 to 1. There must also be at least 2 moles of protons per mole of aluminum in the polymer cement. The organic acid can be a carboxylic acid such as citric acid, a mineral acid ester such as di-2-ethylhexylphosphoric acid, and an aromatic alcohol such as phenol since these are acids and have a pK
a
of 11 or less.
In a second embodiment, the present invention relates to a process for making such polymers which comprises anionically polymerizing them as described, adding to the polymer a trialkyl aluminum compound, and then adding the capping reagent, adding a proton source, and washing and hydrogenating the polymer as described above. In this second embodiment, the aluminum trialkyl may be 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.
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 di- or multi-alkali metal, generally lithium, initiators. Sodium or potassium initiators can also be used. For instance, polymers which can be made according the present invention are those made from any anionically polymerizable monomer, especially including terminal and internal functionalized polydiene polymers, including random and block copolymers with styrene. Styrene copolymers hereunder can be made in the same manner as the polydiene polymers and can be random or block copolymers with dienes.
In general, when solution anionic techniques are used, copolymers of conjugated diolefins, optionally with vinyl aromatic hydrocarbons, are prepared by contacting the monomer or monomers to be
Bening Robert Charles
Diaz Zaida
Wilkey John David
Willis Carl Lesley
Haas Donald F.
Lipman Bernard
Shell Oil Company
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