CS237589B1 - Method of polymerization polyfunctional starters preparation containing lithium - Google Patents

Description

The present invention relates to a process for preparing lithium-containing polyfunctional polymerization initiators by reacting divinylbenzene with a monoalkyllithium compound, in particular with secondary butyllithium in hydrocarbon solvents.

These initiators are suitable for anionic polymerization to telechelic homopolymers and copolymers, in particular conjugated dienes and vinyl-substituted aromatic compounds.

Multifunctional soluble organoalkalometallic initiators are suitable for the synthesis of star-branched polymers and for the preparation of end-functional polymers having a functionality greater than 2.

Most bifunctional and multifunctional organolithium compounds are insoluble in hydrocarbons and even many can only be prepared in strongly polar solvents. When polymerization is carried out with a solution of such initiators, e.g. containing ether, side reactions such as chain breaking, chain transfer and ether cleavage occur very easily.

This is associated with a greater or lesser decrease in the content of active Li-C bonds. This results in lower functionality, higher molecular weight and greater molecular weight distribution, as well as lower initiator efficiency.

It is known that hydrocarbon-soluble lithium polymerization initiators can be prepared by reaction of divinylbenzene with a monoalkyllithium, in particular butyllithium, in inert organic solvents.

As a rule, m-divinylbenzene is used for this, since it has less tendency to polymerize in metallation reactions than other divinylbenzene isomers. For example, the preparation of organolithium initiators by the reaction of m-divinylbenzene with alkyllithium compounds in a molar ratio of 1 · 2 in the presence or absence of tertiary amines has been described / Plaste und KAUTSCHUK 26/1979/5, pp. 263-264 | Compt. Rend. Hebd. Seances Acad. Sci., Ser. OJ C 283/1976/4, pp. 123-125; U.S. 3,725,368; U.S. 3,862,251; NSR-DOS 2,063,642 /.

In all cases, however, only dilithium compounds are formed. Multifunctional lithium initiators cannot be obtained.

Multifunctional lithium initiators can be prepared by reacting alkyllithium compounds with divinylbenzene in a molar ratio of 1: 0.1 to 1: 2 in the presence of solvent-acting monomers as conjugated dienes or monovinylaromates, wherein the molar ratio of alkyllithium compound to solvent-acting monomers is 1: 2 to 1: 15.

A disadvantage of these initiators is that their polymerizable monomer in which they dissolve must be added during the synthesis of the initiators (NSR-dAS 2 003 384 and US 3 644 322 and US 3 787 510).

These initiators themselves have a high molecular weight and are therefore not suitable for the synthesis of low molecular weight polymers. The functionality of the multilithium initiators can only be controlled via the number of vinyl groups of polyvinylaromates or the excess polyvinylaromate, and there is a risk of crosslinking, i.e. gel formation from the initiator.

Moreover, recovering m-divinylbenzene from the tie mixture is a demanding and expensive process (Chem.). Techn. 30/1978/3, p. 144 and 30 (1978) (7), p.

According to US 3,734,973 and US 3,652,516 it is preferable to replace m-divinylbenzene with diisopropylbenzene, since its upper limit temperature is substantially lower. However, obtaining diisopropylbenzene is even more expensive than m-divinylbenzene.

These disadvantages are overcome by the process for preparing lithium-containing polyfunctional polymerization initiators by reacting divinylbenzene with a monoalkyllithium compound, in particular secondary butyllithium, in hydrocarbon solvents according to the invention, in which a solution of alkyllithium in a hydrocarbon solvent, particularly benzene or toluene up to 60 minutes at a temperature of 268 to 303 K of a mixture of meta and paradivinylbenzene at a molar ratio of divinylbenzene to alkyllithium of n: n + 1, n being any number greater than or equal to two, optionally in the presence of a tertiary amine, especially triethylamine, dimethylaniline; mixtures thereof, wherein the molar ratio of lithium to tertiary amine is 1: 1 to 1: 1.5.

Suitable hydrocarbon solvents are aliphatic and aromatic hydrocarbons, aromatic hydrocarbons such as benzene or tluene being more suitable. Tertiary amines can be added to increase the reactivity of alkyllithium. ,

The ratio of meta to paradivinylbenzene is not critical to the reaction, but it is preferable to use mixtures which can be isolated from the technical mixture of divinylbenzene after alkylation of benzene.

The resulting initiator solutions are soluble polyfunctional organolithium compounds. The number of lithium atoms is determined by the molar ratio of divinylbenzene to alkyl lithium and corresponds to n + 1. Thus the functionality of the initiator can be consciously controlled.

The initiators of the invention are linear, non-crosslinked, low molecular weight, organolithium compounds.

An advantage of the process of the invention is that soluble, low molecular weight, polyfunctional, organolithium compounds can be prepared from readily accessible raw materials. The disadvantages of the known methods of preparation are avoided. '

Mixtures of meta and paradivinylbenzene may be used without prior separation of the individual isomers. Paradivinylbenzene can also be used for the synthesis.

The invention is further elucidated on the basis of several examples of specific embodiments, which are not to be construed as limiting.

Example 1 '

A 500 ml sulfonation flask was charged with 61.5 ml of a 0.98 molar solution of secondary butyllithium in benzene, 4 ml of triethylamine, 4 ml of dimethylaniline and 50 ml of benzene. To this mixture was added a mixture of meta and paradivinylbenzene in 20 mL of benzene at 298 K over 30 minutes.

This solution was added from a dropping funnel with stirring. After the addition of divinylbenzene was complete, the mixture was stirred for 2 hours at 298 K. A homogeneous dark red initiator solution was obtained, which was functionalized with ethylene oxide to determine the degree of metalation.

After hydrolysis of the reaction product with 30 ml of water, the solution was centrifuged and from the organic phase the solvent was removed on a vacuum rotary evaporator at 323 K. From the isolated divinylbenzene oligomer the molecular weight was determined by vapor phase osmosis in benzene and the hydroxyl content was determined by acidometric titration.

The product had an average molecular weight M _{n of} 760 and a hydroxyl group content of 6.75%, corresponding to a functionality of 3.02.

Example 2

To a mixture consisting of 20 ml of a 1.4 molar solution of secondary butyllithium in benzol (28 mmol), 5 ml of triethylamine and 30 ml of benzene was added dropwise a solution of 21 mmol of a mixture of meta and paradivinylbenzene in 20 ml of benzene at 278 K.

The mixture was then stirred at the same temperature for 2 hours. The homogeneous reaction solution was further processed as in Example 1. The isolated product had an average molecular weight M _{n of} 870 and a hydroxyl group content of 8.36%.

From this, the functionality 4.28 can be calculated.

Claims (1)

SUBJECT OF THE INVENTION A process for preparing lithium-containing polyfunctional polymerization initiators by reacting divinylbenzene with a monoalkyllithium compound, in particular with secondary butyllithium, in hydrocarbon solvents, characterized in that it is added to a solution of alkyllithium in a hydrocarbon solvent, especially benzene or toluene, at 15 to 60 minutes. up to 303 K solution of a mixture of meta and paradivinylbenzene at a molar ratio of divinylbenzene to alkyllithium n: n + 1, n being any number greater than or equal to two, optionally in the presence of a tertiary amine, especially triethylamine, dimethylaniline or mixtures thereof; The lithium to the tertiary amine is 1: 1 to 1: 1.5.