Uniform initiation of anionic polymerization using...

Details Uniform initiation of anionic polymerization using... Uniform initiation of anionic polymerization using...

2000-03-14

2002-09-24

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S176000, C526S177000, C526S178000

Reexamination Certificate

active

06455651

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the anionic polymerization of monomers utilizing organo-alkali metal initiators. More particularly, the invention relates to the uniform initiation of anionic polymerization for systems having little or no added accelerator/promoter and/or systems where a highly active structure modifier is used in relatively small amounts.
BACKGROUND OF THE INVENTION
Polymers of conjugated dienes and/or vinyl aromatic hydrocarbons have been produced by numerous methods. However, anionic polymerization of such monomers in the presence of an anionic polymerization initiator is a widely used commercial process. The polymerization is carried out in an inert solvent such as hexane, cyclohexane, or toluene and the polymerization initiator is commonly an organo-substituted alkali metal compound, especially aliphatic, cycloaliphatic, aromatic, and alkyl-substituted aromatic alkali metal compounds, and most especially alkyl lithium compounds such as sec-butyl lithium and n-butyl lithium. Another type of polymerization initiator, a protected functional initiator, has the structure
wherein R
1
, R
2
, and R
3
are independently selected from saturated and unsaturated aliphatic and aromatic radicals, A is a hydrocarbon bridging group containing from 1 to 25 carbon atoms, and B is an alkali metal. Other protected functional initiators with similar structures are known. Multifunctional organo-substituted alkali metal initiators are also used. For instance, a difunctional lithium initiator which is the sec-butyl lithium adduct of diisopropenylbenzene has been described in U.S. Pat. Nos. 5,554,696 and 5,750,055.
These anionic polymerizations are most often carried out in the presence of an accelerator/promoter for the polymerization process, such as diethyl ether. Alternatively, highly active microstructure modifiers such as diethoxypropane (DEP) or ortho-dimethoxybenzene (ODMB) are used to change the microstructure of the diene portion of the polymer produced. The most common initiators used in these processes have been sec-butyl lithium and n-butyl lithium and when they are used, with or without the accelerator/promoter or microstructure modifiers, the initiation of the polymerization proceeds very uniformly and at a reasonable rate. It has been found, however, that when other initiators are used and only low levels of accelerator/promoter or microstructure modifier are used, significant problems with the uniform initiation of the polymerization and with the rate of the polymerization are observed. For instance, when the sec-butyl lithium adduct of diisopropenylbenzene is used as a multifunctional initiator, problems with uniform initiation of polymerization are experienced when the accelerator/promoter (diethyl ether) is used in an amount of less than one equivalent of ether per equivalent of lithium initiator (in this case each molecule of initiator has two equivalents of lithium) and/or when the microstructure modifier (DEP or ODMB) is used in an amount wherein the molar ratio of modifier to lithium is less than 1:10.
It would be advantageous to provide a solution to this problem with initiation which did not involve the use of significant amounts of accelerator/promoter or microstructure modifier because both of those solutions promote the production of polymer with a high vinyl content. While having a high vinyl content in the polymer is often advantageous, it is not always the desired result and it would be advantageous to be able to achieve uniform initiation and still make a lower vinyl content polymer.
U.S. Pat. Nos. 5,554,696 and 5,750,055 describe one solution to this problem wherein the diinitiator is created in the presence of a tertiary amine and then is prereacted with a small amount of conjugated diene monomer to form a solution of a dilithio poly conjugated diene initiator. In the first patent, an aromatic ether activator is an additional component. The present invention provides an alternative solution to the problem which obviates the necessity of the tertiary amine, aromatic ether activator, and the prereaction step.
The term “vinyl content” refers to the fact that a conjugated diene is polymerized via 1,2-addition (in the case of butadiene—it would be 3,4-addition in the case of isoprene). Although a pure “vinyl” group is formed only in the case of 1,2-addition polymerization of 1,3-butadiene, the effects of 3,4-addition polymerization of isoprene (and similar addition for other conjugated dienes) on the final properties of the block copolymer will be similar. The term “vinyl” refers to the presence of a pendant vinyl group on the polymer chain. The purpose here is to introduce chain branching and to reduce the size of the main polymer backbone (since some of the carbons in the diene are in the pendant group) which reduces the end to end length of the molecule and, in turn, its viscosity in the cement.
SUMMARY OF THE INVENTION
The present invention is an improvement upon the known method of anionically polymerizing monomers by contacting the monomers with an anionic polymerization initiator which is an organo-substituted alkali metal compound in the presence of low amounts of an accelerator/promoter and/or a highly active microstructure modifier. The improvement comprises adding from 0.1 to 1.0, preferably 0.2 to 0.7, equivalents of a metal alkyl compound per equivalent of alkali metal initiator. The alkyl groups of the metal alkyl compound are chosen so that they will not exchange with the organo substituents of the alkali metal compound. Generally, this means that they are more basic and/or less bulky than the organo substituents of the alkali metal compound. The organo substituents of the alkali metal compound are aliphatic, cycloaliphatic, aromatic, or alkyl-substituted aromatic and include multi-functional initiators such as the sec-butyl lithium adduct of diisopropenyl benzene which is the preferred initiator for use herein. The preferred metal alkyl for use herein is triethyl aluminum.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to anionic polymers and processes for polymerizing them by anionic polymerization using mono- or 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 from any anionically polymerizable monomer, including random and block copolymers with styrene, dienes, polyether polymers, polyester polymers, polycarbonate polymers, polystyrene, acrylics, methacrylics, etc. Polystyrene polymers 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 polymerized simultaneously or sequentially with an anionic polymerization initiator such as group IA metals, their alkyls, amides, silanolates, naphthalides, biphenyls or anthracenyl derivatives. It is preferred to use an organo alkali metal (such as lithium or sodium or potassium) compound in a suitable solvent at a temperature within the range from about −150° C. to about 150° C., preferably at a temperature within the range from about −700° C. to about 100° C. Particularly effective anionic polymerization initiators are organo lithium compounds having the general formula:
RLi
n
wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to 20 about carbon atoms and n is an integer of 1 to 4. The organolithium initiators are preferred for polymerization at higher temperatures because of their increased stability at elevated temperatures.
Other initiators which can be used herein include multifunctional initiators. There are many multifunctional initiators that can be used herein. The di-sec-butyl lithium adduct of m-diisopropenyl benzene is preferred because of the relatively low cost of the reagents invol

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