CS254630B1 - Process for the solution copolymerisation of conjugated dienes with vinylaromatic hydrocarbons - Google Patents

Abstract

Solution Copolymerization Method conjugated dienes such as butadiene or isoprene, with vinylaromatic hydrocarbons, such as styrene or alpha-methylstyrene, in which the copolymerization is carried out in methyl tert-butyl ether. The resulting copolymers may accordingly have whether the comonomers are added simultaneously or sequentially, statistical or block arrangement of comonomer units. Choosing reaction temperatures can be prepared by copolymers with a medium content (50%) of vinyl content units of incorporated polybutadiene. Copolymer initiator can be used use dilithiobutene prepared by reaction butadiene and lithium in methyl tert-butyl ether.

Description

The present invention relates to solution copolymerization of dienes with vinylaromatic hydrocarbons in the presence of organo-lithium initiators.

It is well known that in the anionic solution copolymerization of dienes such as 1,3-butadiene or isoprene with vinylaromatic hydrocarbons such as styrene or alpha-methylstyrene initiated by organolithium compounds or lithium metal, the nature of the polymer formed is dependent on the solvent used. Both random copolymers, where individual comonomers are incorporated into the macromolecule in random order, and block copolymers, wherein the macromolecules contain linked polymer chains composed of one type of monomer unit, find practical application. The choice of solvents for anionic copolymerization is limited to materials which do not contain groups that deactivate the polymer growth centers, usually saturated aliphatic, cycloaliphatic and aromatic hydrocarbons, some ethers and amines are used.

Pure non-polar hydrocarbon solvents such as hexane, cyclohexane or toluene give rise to polymers in which the diene hydrocarbon is predominantly incorporated by 1,4-addition. The copolymerization parameters between dienes and vinylaromates in these solvents favor the formation of block copolymers with preferential polymerization of the diene from the monomer mixture. The statistical copolymers required for some practical applications (SBR - rubber) can only be obtained here by special measures, such as copolymerization at extremely low diene concentration or addition of special randomizers (sodium, potassium alcoholates, ethers or amines strongly solvating lithium ion, etc.). High-styrene-containing copolymers may be insoluble in aliphatic hydrocarbons, which complicates the reaction.

In polar etheric solvents that solvate the metal counterion of the growth center, the diene hydrocarbon is incorporated into the polymer chain predominantly by 1,2-addition and copolymerization parameters with vinylaromatic hydrocarbons are beneficial for the formation of random copolymers with uniform loss of both monomers from the reaction mixture. The rate of polymerization in ether solvents is generally higher than that of hydrocarbon solvents. A disadvantage of ethers is their tendency to deactivate to some extent the growth centers of polymerization. This property, as well as the ability to influence the diene incorporation method and copolymerization parameters between dienes and vinylaromates, is closely related to the solvation power of the solvent against the lithium ion and is dependent on the ether structure. Such strongly solvating ethers are not used other than as hydrocarbon mixtures to reduce the degradation of growth centers and to adjust the balanced ratio between 1,2- and 1,4-diene addition.

Some organolithium initiators can only be successfully prepared in ethereal solvents. Here, too, the polarity of the environment is usually adjusted to the required extent by the addition of a hydrocarbon solvent to the polymerization batch, with some ethers (e.g., dimethyl ether) being almost completely removed prior to polymerization due to their too pronounced solvating effect.

Processes in which the solvent of the desired polarity is obtained by mixing the ether with a hydrocarbon, complicate the separation of the solvent mixture when recycled in production. Some ethers have unfavorable fire safety characteristics due to the low auto-ignition temperature (diethyl ether 180 ° C) and most of them form explosive peroxides with oxygen from the air.

The disadvantages of the known methods of solution copolymerization of conjugated dienes with vinylaromatic hydrocarbons in the presence of organolithium initiators eliminates the process according to the invention, in which the copolymerization is carried out in a medium of methyl tert-butyl ether. Particular preference is given to carrying out the process according to the invention in the presence of dilithiobutene prepared in methyl tert-butyl ether.

The polarity of methyl tert-butyl ether and its solvating ability against the lithium counterion of the growth centers of the anionic polymerization of dienes and vinylaromates is precisely such that by simply changing the reaction temperature the ratio between 1,2- and 1,4-addition can be influenced it is available only when mixed with hydrocarbons. For example, at temperatures of 40 to 60 ° C, up to 50% of butadiene is incorporated into the copolymers by addition of 1.2; SBR with this medium vinyl group content is, according to more recent opinion from tire manufacturers, the optimal basis for tread compounds with increased road adhesion. The stability of the growth centers in methyl tert-butyl ether is sufficiently high for the preparation of copolymers having a molecular weight of about 200,000. Block copolymers are formed separately when comonomers are added to the polymerization reaction mixture and statistical copolymers are formed when comonomers are added. The polymerization proceeds at a higher rate than in hydrocarbons, which is favorable for reactor throughput. The copolymers are soluble in the methyl tert-butyl ether throughout their composition, but the viscosity of the polymerization solutions is lower than that of aromatic hydrocarbons, making it possible to prepare more concentrated solutions, thereby increasing polymerization reactor throughput and reducing polymer isolation and solvent recovery costs.

Dilithiobutene-type two-center initiators can also be prepared in methyl tert-butyl ether, which can be advantageously used directly in this solvent for the two-stage copolymerization of butadiene with styrene to form an SBS block copolymer.

Methyl tert-butyl ether has a high auto-ignition temperature (more than 400 ° C) and does not form peroxides with oxygen.

Various variants of the process of the invention are shown in the following examples.

He did

10 kg of azeotropic-dried toluene, 1 kg of butadiene, 0.5 kg of styrene and 20 mmol of a 2.2 molar solution of n-butyllithium in hexane were charged to a stainless steel reactor equipped with a stirrer and jacket for tempering. The reaction mixture was tempered to 60-70 ° C, first by heating with steam and then cooling with water. After 100 minutes the development of polymeric heat ceased. The mixture was stirred for a further 30 minutes and then 80 ml of methanol was metered into the reactor. The conversion to the copolymer was 100%, determined from the evaporator of the polymer solution. The copolymer was stabilized by the addition of 0.5% by weight of the antioxidant Irganox 565 to the solution and de-solvented by evaporation first under normal pressure and then under vacuum. Mean values of molecular weights M _n - 110 000 and - 140 000 g.mol were found by gel chromatography 1. Analysis of polystyrene bound after decomposition of polydiene chain by means of osmium tetroxide showed that all polystyrene was incorporated in block (M PS -1). _v , ⁿ - 19,000 g.mol). This example demonstrates that a random butadiene-styrene copolymer is not formed in the hydrocarbon solvent with the use of both monomers.

Example 2

The procedure of Example 1 was repeated except that methyl tert-butyl ether was used instead of toluene and the reaction mixture was heated to 60-65 ° C. The development of polymerization heat ceased after 40 minutes. A polymer isolated in the same manner as in Example 1 had

- 90,000 and - 102,000. After the polybutadiene units were split, polystyrene with a higher molecular weight than 600 g / mol could not be found. This indicates a random arrangement of comonomer units.

Example 3

10 liters of methyl tert-butyl ether, mmol of dilithiobutene as a suspension in methyl tert-butyl ether at a concentration of 0.95 mmol Li / g, were charged to the same reactor as in Example 1. The reaction mixture was heated to 60 ° C and at this temperature butadiene was gradually added to the reactor up to a total amount of 1.4 kg. After the polymerization, which lasted 20 minutes, was sampled from the reactor, the polybutadiene of - 75,000 was recovered, and

- 92,000 g / mol. According to IR spectroscopy analysis, the microstructure of this polybutadiene was: trans / cis / vinyl-33/22/45%. The reactor was then charged with 0.74 kg of styrene. The polymerization took place in 8 minutes to 100% conversion. The isolated copolymer had a block structure of SBS as confirmed by determining the molecular weight of the polystyrene blocks (M 2 - 27,000) after polybutadiene cleavage.

Example 4

10 L of methyl t-butyl ether, a mixture of 0.66 kg of butadiene with 0.33 kg of styrene and 20 mmol of dilithiobutene as a suspension in 0.95 mmol of Li-tert-butyl ether were charged to the same reactor as in Example 1. G. The reaction mixture was tempered to 60-65 ° C and after 12 minutes at which time the polymerization heat ceased, a mixture of 0.66 kg butadiene and 0.33 kg styrene was added to the reactor. After 15 minutes of further polymerization heat development, the reaction mixture was stirred for 15 minutes at 50 ° C and the polymerization was then stopped by adding 80 mmol of methanol to the reactor. The isolated copolymer had a styrene-butadiene random arrangement of comonomer and molecular weight - 110,000 and _Mw - 132,000.

Example 5

To a 1.5 L sulfonation flask equipped with a stirrer and an immersion condenser was charged 700 mL of methyl tert-butyl ether 53 mmol of the dilithiobutene suspension. Within 73 minutes at ^{0, O} C were successively added 132 g of styrene; followed by the addition of 130 g of butadiene gas over 250 minutes. The organometallic content characterizing the deactivation rate was 92.2 before the addition of the monomers and 91.7% at the end of the polymerization. (Determined by Gilman double titration method with alkyl bromide as organometallic remover). The isolated block copolymer of the BSB type was semi-solid at room temperature, having a molecular weight of M _n -4 300 and M _w -4 590.

Example 6

To a 1.5 liter sulfonation flask as in Example 5 was added 800 mL of methyl tert-butyl ether and 1.1 mmol of a suspension of dilithioisopentene in methyl tert-butyl ether, prepared by reacting isoprene with lithium in the presence of naphthalene. At 45 ° C, 100 g of isoprene was added dropwise over 3 hours. The mixture was stirred for a further 30 minutes, then 10 g of alpha-methylstyrene was added at 0 ° C and the mixture was stirred for 5 hours. The polymerization was terminated by addition of 10 ml of water. The polymer was isolated by precipitation into ethanol in a semi-solid consistency yield of 4,450 at a distribution width of Μ / M - 1.21.

Claims (2)

SUBJECT OF THE INVENTION A process for the solution copolymerization of conjugated dienes with vinylaromatic hydrocarbons in the presence of organolithium initiators, characterized in that the copolymerization is carried out in a medium of methyl tert-butyl ether. 2. A process according to claim 1, wherein the initiator is dilithiobutene prepared in methyl tert-butyl ether.