CS229059B1 - Process for preparing bifunctional polymers - Google Patents

Abstract

The invention relates to a method for preparing bifunctional polymers by anionic polymerization of dilithium initiators in nonpolar solvents. As initiators, dilithium adducts of conjugated dienes prepared and dissolved in a mixture of methyl tert.butyl ether with tetrahydrofuran are used. With the help of these initiator solutions, homogeneous polymerization of hydrocarbons is possible without chain interruption by ether cleavage, whereby polymers with a functional group at each end of the chain, or block copolymers of the A-B-A type, can be advantageously prepared.

Description

The invention relates to a process for the preparation of bifunctional polymers by anionic polymerization of conjugated dienes and / or vinylaromatic monomers in non-polar solvents with dilithium compounds as initiators. These polymers are used for the synthesis of end-functional polymers and for the preparation of defined block copolymers of type A-B-A. The polymers have a predetermined molecular weight and molecular weight distribution.

It is known that such polymers can generally be prepared by anionic polymerization with dilithioorgano compounds in a stoichiometric controllable reaction (Faserforschung unfl Textiltechnik 25 (1974) 5, p. 191; U.S. Pat. No. 3,135,716, NSR-OS 24.25924; USSR 296 775).

However, to obtain monodisperse bifunctional living polymers, it is necessary that the anionic polymerization be carried out without chain interruption using soluble dilithium initiators. An ideal method for preparing narrow-molecular-weight functional polymers is homogeneous anionic polymerization with organolithium initiators in non-polar solvents.

However, bifunctional lithium initiators typically have very limited solubility in hydrocarbons. In various patents, particularly suitable initiators are dilithium adducts of conjugated dienes, in particular 1,3-butadiene, isoprene and 2,3-dimethyl-utadian having 1 to 7 diene units (NSR-PS 1 169 674; NSR-AS 1,170,645; NDR-WP 99,170).

The formation of these alkali metal adducts necessitates ether as the reaction medium, since they cannot be prepared in solvents with a lower dielectric constant, and in all known processes the ether is used at least in stoichiometric amounts based on lithium metal to achieve reasonable organodilithium yields. compound and ensure the solubility of the initiator.

When polymerizing with these ether-containing initiator solutions, it is very easy to reduce the initiation and polymerization activity due to ether cleavage, or the dilithium compounds are stable in polar solvents for only a very short time (NSR-0S 20.03384; US 3,388,178) Liebigs Ann. Chem., 747 (1971), pp. 70-3.

The known methods therefore assume that, prior to polymerization, the ether is completely or partially replaced by an apolar solvent (U.S. Pat. No. 3,377,404; U.S. Pat. No. 3,388,178; NSR-AS 1,768,188; NSR-OS 1,817,479). However, the conditions required for the removal of the ether often lead to the partial deactivation of the initiator by reaction with ether, so that the resulting solutions contain monolithium, dilithium and inactive initiator molecules. With these initiators, it is not possible to prepare end-functional polymers or block copolymers of type A-B-A.

Replacing one solvent with another before polymerization leads to additional operating costs. The resulting solutions also have the disadvantage that they are very viscous and contain some undissolved product, which is disadvantageous in terms of applicability as an initiator for the homogeneous anionic polymerization of conjugated dienes and vinyl-substituted aromatic monomers.

To maintain the solubility of the initiators in the hydrocarbon solvents, the chain of the organodilithium compound is often extended by adding a sufficient amount of conjugated diene. However, these initiators exhibit relatively high molecular weights and low initiator concentrations and are therefore useful for the synthesis of low molecular weight polymers.

Also, the addition of weakly solvating arylalkyl ethers, dieryl ethers and tertiary amines in the synthesis of initiators, resp. when solvent is exchanged as described in NSR-OS 21.48147 and FR 2 154 978, it is uneconomical in terms of the cost of the aromatic ether and causes difficulties in separating the high-boiling ether or amine from the final product, respectively.

These disadvantages are overcome by a process for preparing bifunctional polymers by anionic polymerization of conjugated dienes and / or vinylaromatic monomers in nonpolar solvents with di-thio compounds as polymerization initiators by using dilithium adducts of conjugated dienes, optionally substituted, containing up to 6 monomers, as initiator molecule prepared in a mixture of methyl tert-butyl ether with tetrahydrofuran in which the proportion of tetrahydrofuran was 5 to 30% by volume.

In particular, butadiene or isoprene may be used as the conjugated diene; the vinylaromatic monomer may in particular be styrene or alphamethylstyrene. The soluble organodilithium polymerization initiators used are prepared by reacting lithium with a conjugated diene containing from 4 to 12 carbon atoms per molecule, such as 1,3-butadiene, isoprene or 2,3-dimethyl-1,3-butadiene in the presence of catalytic amounts of polycyclic aromatic hydrocarbon such as naphthalene, anthracene, biphenyl or stilbene.

An advantage of the process of the invention is that the resulting dilithium adduct solutions of conjugated dienes are highly concentrated. They have a concentration of 1.6 to 2.6 grammoms of lithium per liter, of which 90 to 98% are in the form of a polymerically active C-Li bond.

Due to the high concentration of lithium and a small proportion of strongly polar solvents in the initiator solution, only a minimal amount of strongly polar solvent enters the polymerization system with the initiator, so that polymerization activity is not reduced by side reactions with ether.

The initiator solutions themselves can be stored for 2-4 weeks without sacrificing initiation activity when stored below +5 ° C in an inert atmosphere.

After functionalization of the active polymers thus obtained, high functionality telechelic polymers can be prepared.

The monomers that can be polymerized in the 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, alphamethylstyrene, 1-vinylnaphthalene and 2-vinylnaphthalene.

The polymerization is carried out under such conditions as are known for anionic solution polymerization with organo-alkali metal initiators. Suitable solvents are aliphatic, cycloaliphatic and aromatic hydrocarbons such as benzene, toluene, n-hexane, n-heptane, cyclohexane or a gasoline fraction.

The polymerizations can be carried out at 198 to 423 ° K, preferably at 263 to 323 ° K, at atmospheric or elevated pressure.

Due to the use of conjugated diene dilithium adducts as initiators, the initiation delay is so small that the polymerization reaction begins almost immediately and the duration of the process is short. The polymerization time is generally 1 to 3 hours.

The amount of initiator used is determined by the desired molecular weight of the polymer, since it is not a stoichiometric polymerization. Homopolymers and copolymers of high molecular weight, e.g. 200,000, as well as very low molecular weight, e.g. 1,000 to 10,000, can be prepared.

The active strands of the resulting living polymers can be functionalized by known methods by end-capping electrophilic reagents such as carbon dioxide, alkylene oxide, epichlorohydrin or gamabutyrolactone, so that telechelic polymers having a functional group at each end of the chain are very preferably formed.

The process according to the invention is characterized in that it is possible to carry out a homogeneous anionic polymerization in hydrocarbons without the need for solvent exchange before the polymerization, and in that the polymerization does not interrupt the chain of reactions of active centers and ethers. obtain telechelic polymers with high functionality.

The examples given below explain the method according to the invention without representing its limits.

Example 1

A 0.5 L initiator solution containing 440 mmol of butadiene-1.3 dilithium adduct in a 75 volume mixture was charged to the reaction vessel. % methyl tert-butyl ether and 25 vol. % tetrahydrofuran, toluene (3.4 L) was added and a total of 880 g of butadiene was added over 2 hours at 283 ° K. Ethylene oxide functionalization was then carried out at 268 ° K. Hydrolysis of the gel formed was performed with aqueous NH 4 Cl solution.

Example 2

To a solution of 470 mmol of the isoprene dilithium adduct in 0.5 L of methyl tert-butyl ether-tetrahydrofuran mixture (90:10 v / v) was added 3.6 L of toluene and a total of 940 g of butadiene was gradually added at 293 ° C over two hours. After completion of the polymerization, ethylene oxide functionalization was performed. Further polymer processing was carried out analogously to Example 1.

The isolated polymer had an osmotically determined molecular weight of 2050 and a hydroxyl group content of 1.625%, giving a functionality of 1.96. '

Example 3.

The reaction vessel was charged with 30 mmol of the isithene dilithium adduct dissolved in 50 mL of methyl tert-butyl ether / tetrahydrofurene (10 vol% tetrahydrofuran) and 300 mL of toluene. The mixture was maintained under an argon atmosphere. To this solution was added a solution of 90 g of isoprene in 50 ml of toluene at 298 K over one hour. After the addition of isoprene was added, the mixture was stirred for 0.5 h and then polymerization was stopped by addition of 5.3 g of ethylene oxide. Then, the polymer was hydrolyzed with water and was obtained with a 100% yield of Polylsoprene with an average molecular weight of 3200. The molecular weight calculated from the monomer / initiator ratio was 3000. Acidometric titration determined a hydroxyl group content of 1.025%, corresponding to a functionality of 1.93.

Example á

To the reaction vessel of Example 3 was charged 416 mmol of the isithene dilithium adduct in 590 mL of methyl tert-butyl ether / tetrahydrofuran mixture containing 20 vol% tetra-. hydrofuran and 3.2 L of toluene. This mixture was polymerized at 293 K with 832 g of styrene for 2 hours. The living polymer was then reacted with 72 g of ethylene oxide and then hydrolyzed with water. In 100% yield, hydroxyl-terminated polystyrene was obtained having an average molecular weight. 2,100 (theoretically: 2,000), and an OH content of 1.60%, resulting in a functionality of 1.98,

Example 5

To a mixture of 50 mmol of butadiene 1,3 dilithium adduct dissolved in 85 ml of methyl tert-butyl ether / tetrahydrofuran mixture and 200 ml of toluene, a mixture of 50 g of butadiene -1.3 and 16.7 g of styrene was added over 2 hours in a 323 K autoclave. 9 g of ethylene oxide were then added and hydrolyzed with water. With a 100% yield, a styrene butadiene copolymer was obtained having a styrene content of 35 mol%, an average molecular weight of 1,500, a hydroxyl group content of 2.14% and a functionality of 1.89.

Claims (1)

. OBJECT OF THE INVENTION Process for preparing bifunctional polymers by anionic polymerization of conjugated dienes and / or vinylaromatic monomers in non-polar solvents with dilithium compounds as polymerization initiators, characterized in that dilithium adducts of conjugated dienes, optionally substituted, containing 1 to 6 monomer units per molecule, prepared in a mixture of methyl tert-butyl ether with tetrahydrofuran in which the proportion of tetrahydrofuran was 5 to 30% by volume.