GB2083041A - Dilithium Adducts of Conjugated Diene Monomers and their use in Anionic Polymerisation - Google Patents

Abstract

An improved process for the preparation of difunctional "living" polymers by anionic polymerization of conjugated dienes and/or vinyl substituted aromatic compounds in the presence of dilithium organic compounds as initiators utilizes a dilithium adduct of conjugated dienes (e.g. 1,3 butadiene, isoprene or 2,3 dimethyl-1,3-butadiene) having 4 to 12 carbon atoms in a monomer molecule and 1 to 6 of such monomer units in a molecule of adduct. The adduct is prepared by reacting diene with 0.5 to 2 gram-atom of lithium per mole diene in 5 to 10 moles of a mixture of solvents wherein 70 to 95 volume percent is selected from toluene, benzene, diethyl ether and methyltertiary-butyl ether with the balance being tetrahydrofuran. The reaction is carried out in the presence of a polycyclic aromatic compound as promotor, preferably naphthalene, anthracene, biphenyl or stilbene. The terminal difunctional "living" polymers formed by the polymerization process can be further functionalized to telechelic polymers or used for preparation of A-B-A block polymers.

Description

SPECIFICATION Improved Process for Preparing Difunctional Polymers This invention relates to the preparation of difunctional "living" polymers by anionic polymerization of conjugated dienes and/or vinylsubstituted aromatic compounds with dilithium compounds as initiators.

Polymers of this type are used especially in the synthesis of polymers with terminal functional groups and A-B-A block polymer preparation.

These polymers have a pre-selected molecular weight and narrow molecular weight distribution.

It has already been described how to prepare such polymers by anionic polymerization in the presence of dilithium organo polymerization in the presence of dilithium organo compounds under stoichiometrically controlled reaction conditions (Faseforschung und Textiltechnik 25 (1974), 5, p.

191, U.S. Patent No. 3 135 716, West German published appln. No. 2 425 924, Soviet Union Patent 296 775).

To prepare monodisperse difunctional "living" polymers, it is necessary to carry out the polymerization without chain termination and to use soluble dilithium initiators. The ideal process for preparing difunctional polymers with narrow molecular weight distribution consists in a homogeneous anionic polymerization in the presence of organodilithium initiators in non-polar solvents. Difunctional lithium initiators have as a rule a very limited solubility in hydrocarbons.In a number of patents dilithium adducts of conjugated dienes, especially of 1,3-butadiene, isoprene, and 2,3-dimethyl-1 ,3-butadiene, having 1 to 7 monomer units in molecule are presented as the most suitable initiators (West German Patent No. 1 1 69 674, West German examined Appln. No. 1 170 645, German Democratic Republic Patent No. 99 170).

For preparation of these alkali metal adducts presence of a polar solvent in reaction medium is necessary, e.g. of an ether or amine, because preparation in solvents with a lower dielectric constant is impossible. To achieve reasonable yields of organo dilithium compounds at least the stoichiometric amount of ether is used, based on the amount of lithium metal. This also ensures solubility of the initiator. If polymerization is carried out in presence of these ether containing solutions, activity of initiator and polymer are diminished by ether splitting, so that stability of dilithium compounds is limited, when present in polar solvents. (West German published Appln.

No. 2 003 384, U.S. patent No. 3 388 178, Liebigs Ann. Chem. 747 (1971), pp. 70-83).

Therefore, in the known processes ether is substituted fully or partially by a non-polar solvent before polymerization (U.S. patent Nos. 3 377 404 and 3 388 178, West German examined Appln. No. 1 768 188, West German published Appln. No. 1 817 479).

Under conditions necessary for substitution of the ether partial de-activation of the initiator by a reaction with ether takes place. Therefore, the resulting solutions contain monolithium and dilithium as well as inactive molecules of initiator.

Well defined terminally difunctional polymers or block polymers of A-B-A type are not possible to prepare using these initiators.

The substitution of solvent by a different one brings about higher production costs. These solutions are also very viscous and contain undissolved product. This is a disadvantage in its use as initiator in homogeneous anionic polymerization of conjugated dienes or vinylsubstituted aromatic monomer. (West German published Appln. No. 2 148 147).

To maintain the initiator soluble, its molecular chain is made longer by addition of a sufficient amount of conjugated diene to dilithium organocompound. These initiators have a relatively high molecular weight and low active sites concentration, which limits their use in the synthesis of low molecular weight polymers. Also the addition of weakly solvating aryl-alkyl ethers, diaryl ethers and tertiary amines during initiator synthesis or solvent substitution respectively, is costly. Further they bring about difficulties in separation of ether or amine having a high boiling point from the end product.

All known methods need also a long reaction time for dilithio-oligodienes preparation or for ether separation. Disadvantages are also low reaction temperatures and that lithium has to be in a dispersion of sufficiently fine particle size to obtain satisfactory lithium turn-over.

According to the state of the art polycyclic aromatic hydrocarbons, as naphthalene, used as promoters, have to be added in high amounts, corresponding to the lithium amount used. This has a negative influence on applicability of the initiator.

It is an object of this invention to polymerize conjugated dienes and or vinyl aromatic monomers in presence of dilithium initiators to terminal difunctional "living" polymers having narrow molecular weight distribution that can be further functionalized to telechelic polymer or used for preparation of A-B-A block polymers.

It is another object of the invention to provide a new process whcih obviates or mitigates the above mentioned disadvantages.

According to the present invention there is provided a method of preparing a dilithium organo compound comprising forming dilithium adducts of conjugated diene monomers having from 4 to 12 carbon atoms per monomer molecule, wherein the adducts have from 1 to 6 monomer units per molecule, by reacting the diene monomer in the liquid phase at a temperature of from 243K to 323K (-30 to 500 C) for at least one hour with from 0.5 to 2 gram-atom of lithium per mole of diene, in from 5 to 10 moles of a mixture of 70 to 95 volume percent of a solvent selected from toluene, benzene, diethyl ether and methyltertiary-butyl ether, with 5 to 30 volume percent of tetrahydrofuran, in the presence of from 0.005 to 0.125 moles of a polycyclic aromatic compound per equivalent of lithium.

It has now been discovered that these "living" difunctional polymers of dienes can be prepared by anionic polymerization in presence of organodilithium polymerization initiators on the basis of substituted or unsubstituted conjugated dienes. The initiators have 1 to 6 monomer units in an initiator molecule. The monomers which can be employed in the preparation of the terminally reactive polymers include 1,3-butadiene or isoprene representing the family of dienes having 4 to 12 carbon atoms in molecule or vinyl aromatic monomers, e.g. styrene or alpha-methyl styrene.

The terminally reactive polymers are prepared by contacting the monomer or monomers desired to polymerize with an organo dilithium polymerization initiator. This organo dilithium polymerisation initiator is prepared by reaction for at least one hour of a conjugated diene having 4 to 12 carbon atoms in molecule with 0.5 to 2.0 gram-atom of lithium per mole of diene. This conjugated diene can be substituted and the most suitable dienes are 1 ,3-butadiene or isoprene or 2,3-dimethyl-1 ,3-butadiene.

The initiator is prepared in the presence of 0.005 to 0.125 mole of a polycyclic aromatic compound as a promoter, preferably selected from the group of naphthalene, anthracene, biphenyl or stilbene per equivalent of lithium.

The initiator is prepared in 5 to 10 moles of a mixture of solvents comprising 70 to 95 volume percent of toluene, benzene, diethyl ether or methyl tert. butyl ether and 5 to 30 volume percent of tetrahydrofuran. The initiator preparation is carried out at a temperature of from 243K to 323K (-30 to 500C), preferably 283K to 303K (10 to 300 C), The resulting dilithium adducts contain 1 to 6 monomer units per molecule and are completely soluble in the above mentioned mixture of solvents.

Conversion of lithium is 80 to 90 percent based on metallic lithium used. 90 to 95 percent of the converted lithium is in the form of the polymerization active C-Li bond. The solutions have a concentration of 1.6 to 2.6 gram-atom of lithium per litre and can be stored for 2 to 8 weeks without loss of initiating activity if stored at a temperature below 278K (50C) and under an inert atmosphere.

The amount of solvents is not critical. However, for attaining high concentration of lithium compounds together with solubility, 5 to 10 mole of solvents mixture per mole of diene is the optimum amount. High lithium concentration and minimum polar solvent in the initiator solution reduce the amount of polar solvent in the polymerization system so that loss of polymer activity due to side reactions with ether is not observed.

Monomers polymerizable in presence of these initiator solutions are conjugated dienes, such as 1 ,3-butadiene, isoprene, 2,3-dimethyl-1,3- butadiene, and 1,3-hexadiene, as well as vinyl substituted aromatic compounds, such as styrene, alpha-methyl styrene, 1-vinylnaphthalene, and 2vinylnaphthalene.

Polymerization is carried out under the usual conditions for anionic polymerization with alkali metal organic initiators. Aliphatic, cycloaliphatic, and aromatic hydrocarbons, such as benzene, toluene, n-hexane, n-heptane, cyclohexane and/or their mixtures, as well as gasoline fractions can be used as solvents for polymerizations. The polymerization can be carried out at 1 98K to 423K (-75 to 1500 C), preferably at 263K to 323K (-10 to 500 C) under atmospheric or elevated pressure.

In the presence of oligomer dilithium adducts of dienes as polymerization initiators, the polymerization reaction starts practically immediately and the polymerization time is regulated from 1 to 3 hours. The initiator amount to be used relates to the polymer molecular weight desired as this polymerisation is a stoichiometric one. Homopolymers or copolymers having high molecular weight, e.g. 200 000 as well as very low molecular weight, e.g. 1000 to 10 000 can be prepared The reactive C-Li end groups of the "living" polymers, from this polymerization, can be functionalized by known processes in a reaction with electrophi!ic agents forming end groups.

Such agents are carbon dioxide, alkylene oxide epichlorhydrin or gamma-butyrolactone, etc.

Reactions result in telechelic polymers having a functional end group on each end of the molecule chain. Another use of the "living" polymers is preparation of A-B-A block polymers.

By the process of this invention concentrated stable solutions of dilithium organo compounds from lithium and 1,3-dienes can be prepared exhibiting high initiating activity. The dilithium adducts of dienes are prepared from easily available and relatively cheap raw materials.

Lithium can be used in pieces. The amount of promoter used is lower. The reaction is a one-step simple reaction exhibiting a reaction time in initiator preparation which is shorter than inknown processes. Relatively high temperatures can be used and good yields are achieved.

A homogeneous anionic polymerization in hydrocarbons directly without previous solvent substitution in the initiator solution is possible.

During the polymerization no chain splitting owing to reaction of active centres with ethers is observed. This enables the preparation of telechelic polymers with high functionality.

The invention will now be described by way of the following examples.

Example 1 A reactor equipped with a mixer, thermometer, jacket and dropping funnel, filled with argon atmosphere was charged with: lithium in pieces 23.10 g, naphthalene 28.16 g, toluene 935 ml, and tetrahydrofuran 1 65 ml. To this mixture 149.6 g isoprene, dissolved in 468 ml toluene and 82 ml tetrahydrofuran was added dropwise under mixing over a period of 2 hours. The reactions started at once. When reaction was completed, the unreacted lithium was filtered off.

Reaction temperature was 298K (250C). Lithium concentration in the initiator solution thus prepared was 1.8 gram equivalents per litre which corresponds to a lithium conversion of 90 percent. Activity (lithium to carbon bond content) was 96 percent. In the above mentioned reaction oligoisoprenyl dilithium was formed.

1.233 mole of oligoisoprenyl dilithium in this solution was dissolved in the second stage in 8.55 litre of toluene, in a polymerisation reactor, equipped with a mixer, temperature control and jacket, with an argon atmosphere. To this mixture 3.1 kg butadiene was added in doses over a period of 2 hours. Temperature was maintained at 283K (1 00C) and pressure was sufficient to keep all materials in liquid state. When the butadiene addition was finished the reaction mixture was mixed for another 0.5 hour, and then terminated with carbon dioxide addition. The carboxylates formed were transferred with gaseous hydrogen chloride in polybutadiene dicarboxylic acid, this acid precipitated with methanol and dried under vacuum at 323K (500C).

Molecular weight of polymer was determined by vapour pressure osmometry in methylethyl ketone, and corresponded to the calculated value of 2 500. Carboxyl content was determined by titration with an alcoholic solution of potassium hydroxide, and was 3.53 percent which corresponds to a functionality of 1.96.

Example 2 The reactor used in Example 1 was filled with 18.82 g lithium in chips, 22.94 g naphthalene, 650 ml diethylether and 280 ml tetrahydrofuran.

122 g isoprene dissolved in 330 ml diethylether and 140 ml tetrahydrofuran was admixed to this mixture dropwise over a period of 2 hours at 293K (20 OC). Other conditions were the same as in Example 1. Lithium conversion was 80 percent, lithium concentration 1.48 gram equivalent per litre and activity 95.4 percent.

This solution of 1.035 mole oligoisoprenyl dilithium in 1.4 litre diethyl ether/tetrahydrofuran mixture was mixed with 9.9 litre n-hexane and then 2.6 kg butadiene was added dropwise over a period of 2 hours. Temperature was maintained at 288K (15 C) with the same pressure as in Example 1. When polymerization was completed the polymer was functionalized with ethylene oxide, and hydrolysed with water.

The separated polymer exhibited a molecular weight, determined by vapour pressure osmometry, of 3 000 and a hydroxyl content of 1.09 percent which gives a functionality of 1.93.

Example 3 607 g of liquid butadiene was added dropwise over a period of 2 hours at 298K (250C) to a mixture of 4.5 litre methyl tertiary-butyl ether, 1.5 litre tetrahydrofuran, 84 g lithium in chips and 102.4 g naphthalene. When the reaction was completed the unreacted lithium was filtered off.

Lithium conversion was 88.7 percent, activity 97.6 percent and the solution contained 1.75 gram-atom lithium per litre.

0.5 litre of this solution, containing 6.11 g of active lithium, was used for polymerization of butadiene. Initiator solution was added to a polymerization reactor, 3.4 litres of toluene added, and 880 g butadiene admixed dropwise over a period of 2 hours at 283K (10"C). The polymer obtained was functionalized with ethylene oxide at 268K (-50C). The gel formed was hydrolyzed with an aqueous solution of NH4CI, stabilized with 1% of Jonol ). The polymer solution which formed the organic phase was separated in a centrifuge and solvents evaporated from polymer in a vacuum rotary evaporator.

The separated polymer exhibited a molecular weight of 2100 (theoretically 2000), a hydroxyl content of 1.59 percent, and a functionality of 1.97.

Claims (10)

Claims

1. A method of preparing a dilithium organo compound comprising forming dilithium adducts of conjugated diene monomers having from 4 to 1 2 carbon atoms per monomer molecule, wherein the adducts have from 1 to 6 monomer units per molecule, by reacting the diene monomer in the liquid phase at a temperature of from 243K to 323K (-30 to 500 C) for at least one hour with from 0.5 to 2 gram-atom of lithium per mole of diene, in from 5 to 10 moles of a mixture of 70 to 95 volume percent selected from toluene, benzene, diethyl ether and methyl-tertiary-butyl ether, with 5 to 30 volume percent of tetrahydrofuran, in the presence of from 0.005 to 0.125 moles of a polycyclic aromatic compound per equivalent of lithium.

2. A method according to claim 1 wherein the conjugated diene is selected from 1,3-butadiene, isoprene and 2,3-dimethyl-1 ,3-butadiene.

3. A method according to claim 1 or claim 2 wherein the lithium is introduced to the mixture in the form of pieces or chips.

4. A method according to claim 1 or claim 2 or claim 3 wherein the polycyclic aromatic compound is selected from naphthalene, anthracene, biphenyl and stilbene.

5. A method according to any one of the preceding claims wherein the reaction is carried out at a temperature of from 283K to 303K (10 to 300 C).

6. A dilithium organo compound whenever prepared by a method according to any one of claims 1 to 5.

7. A process for the preparation of difunctional "living" polymers by anionic polymerization of conjugated dienes and/or vinyl substituted aromatic compounds wherein the anionic polymerization is initiated by a dilithium organo compound prepared by a method according to any one of claims 1 to 5.

8. A process for the preparation of difunctional "living" polymers according to any one of the Examples 1,2 and 3 hereinbefore.

9. Difunctional "living" polymers whenever prepared by a process according to either one of claims 7 or 8.

10. Telechelic polymers and A-B-A block polymers whenever prepared by a process according to either one of claims 7 or 8 above.