DE1745297C3 - Process for the homopolymerization of chloroprene - Google Patents

Description

Table I.

One of the possible processes for the production of chloroprene is by dehydrohalogenation of 3,4-Dichlorbutcn-l produced. This process is described in US Pat. No. 2,038,538. It however, it has been found that at least some polymer blends based on chloroprene are deficient exhibit. For example, the solution adhesives based on chloroprene polymers are unstable, and the The extrusion properties of the polymer blends are unsatisfactory. It was·; now found that this Deficiencies can be remedied by taking measures to reduce the level of 4-chlorobuladiene-1,2 to eliminate or reduce in the intermediate dichlorobutene, there otherwise butatriene is formed with the chloroprene and even very small amounts of, for example 150 ppm butatriene can adversely affect the properties of the chloroprene polymers obtained. It is difficult to determine the cause of the above deficiency. Butalriene is among these Difficult to identify conditions. It is surprising that the presence of these small amounts of butatriene is responsible for the mentioned deficiency. It is also surprising that the presence these small amounts of 4-chlorobutadiene-1,2 in dichlorobutene lead to deficiencies in the final polymer leads.

The invention accordingly provides a process for the homopolymerization of chloroprene in aqueous alkaline emulsion in the presence of an alkyl mercaptan serving as a modifying agent, using a chloroprene obtained in a known manner by dehydrochlorination of 3,4-dichlorobutene- (l) , which is characterized in that a chloroprene is used which is derived from a 3,4-dichlorobutene (l) which contains 4-chlorobutadiene- (l, 2) has been reduced to less than 0.1 percent by weight by fractional distillation.

The dichlorobutene can be obtained by fractional distillation, especially at very low levels Press, in a column, e.g. B. a packed column or a S ebbodenkolonne purified will. The purified dichlorobutene is drawn off at the bottom, while the 4-chlorobutadiene-1,2 and others Skip materials at the head.

component

Raw refined

3,4-dichlorobutene-l 93.4 96.82

1,4-trans-dichlorobutene-2 0.28 0.37

1,4-cis-dichlorobutene-2 0.08 0.11

dichlorobutane 0.92 0.96

4-chlorobutadiene-1,200.56 0.05

Other impurities:

Chloroprene

«■ -chloroprene, chlorobutenes,

Toluene 4.77 1.69

The refined material is placed in a stirred reaction vessel maintained at 103 ° C introduced and with a residence time of 2 minutes with 7 times the amount of aqueous sodium hydroxide (4.9% NaOH) converted to chloroprene. The product stream is distilled with steam and the organic phase (which contains about 40% chloroprene) cooled, separated from the entrained water and

4s approximately in the middle (between floors 4 and 6 | a packed column with about 10 theoretical plates, where it is below 175 mm Hg absolute in the presence of 250 parts per million parts of phentiazine (Polymerization inhibitor) is distilled at a reflux ratio of 0.36. The chloroprene is withdrawn at the top of the column and contains about 70 parts per million parts of butatriene. It will fed to a conventional polymerization process for the production of Polycnloroprene. That did not convert

ys dc! te 3,4-dichlorobutene-1 is at the foot of the column recovered and along with the refined material from the 18-stage 3,4-dichlorobutene-1 fractionation column returned to the reaction vessel provided for the production of chloroprene.

no It should be noted that the circulation of the in the production of chloroprene unreacted dichlorobutene from an economic point of view of great Meaning can be.

The following comparison numbers suggest some advantages

hs parts of chloroprene polymers made according to the invention have been prepared, against chloroprene polymers recognized by known methods have been produced, d. H. made of chloroprene, that

Contains larger amounts of butalriene mentioned in the tables.

Λ. Two samples of a rapidly crystallizing polychloroprene are obtained by polymerizing chloroprene at! (J C in the presence of a modifying agent serving alkyl mercaptan essentially according to that in Example 1 (A) British Patent 10 94 321 Process made. 100 parts of each sample are mixed with 4 parts of magnesium oxide and 5 parts of zinc oxide on a rubber mixing mill mixed at 50 C.

B. 4 parts of magnesium oxide and 45 parts of a phenol-formaldehyde resin are added to 474 parts of a solvent (from equal parts by volume toluene, η-hexane and ethyl acetate) and on a Roller mixer worked for 24 hours at room temperature.

64 parts of each sample A are mixed with 285 parts of sample B in glass vessels and placed on one Roller mixer processed to dissolution. The samples obtained are during the period in Table II mentioned time kept in glass flaps in a heating cabinet kept at 50 C. The viscosities are measured with a Brookfield Viscometer using a # 4 spindle at 60 rpm (ASTM D 1084-63, method B). Before measuring the viscosities, the samples are left for 15-30 minutes kneaded on the mixing roll mill and left to stand for 4 hours at room temperature. In table II each is Viscosity expressed as a percentage of the original viscosity.

Table Π Brookfield Viscosity Jer
Mixes after weeks
0 12 3 94
79 96
82 104
90 4th Bulatriengchalt
of chloroprene 100
100 112
gelled 0.0058%
0.0180%

Two polychloroprene samples are prepared essentially according to the process described in US Pat. No. 2,494,087 at a polymerization temperature of 40 ° C. and a mercaptan concentration of about 0.15%, based on chloroprene. After the samples have been aged at 56 ° C. for the time specified in Table III, the Mooney viscosities (ASTM D-1646) are measured using the large rotor at 100 ° C. after a warm-up time of 1 minute and a running time of 2.5 minutes.

Table III

Butatriene content
of chloroprene

Mooney viscosity des
Polymers after weeks

0 1 2

0.0050%
0.0157%

100
100

102
124

105

105
128

The Mooney viscosities are also given as a percentage of the original viscosities.

Claims (1)

Claim: Process for the homopolymerization of chloroprene in an aqueous alkaline emulsion in the presence of a modifying agent Alkylmcrcaptans, wherein a known manner by dehydrochlorination of 3,4-Diehlorbut-l obtained chloroprene is used, thereby gckennzeichn c t that a chloroprene is used which is produced from a 3,4-dichlorobutene-l whose content of 4-chlorobutadiene-l, 2 by fractional distillation was reduced to less than U, I wt .- "/, has been reduced. The invention is illustrated by the following example, in which all amounts are given refer to the weight, unless otherwise stated. B e i s ρ i e! Crude 3,4-dichlorobutene-1 is obtained by chlorination of 1,3-butadiene and fractionation to remove the 1,4-dichlorobutene-2-isomer. 130 parts of this raw material are fed to the middle of the column every hour. A nickel column filled with Berl saddles, which has about 18 theoretical plates, is used as the fractionation column. The return ratio is about 6.4, the pressure 130 mm 11 g absolute. The temperatures are 87 C at the bottom, 82 C in the middle and 38 C at the head. Every hour 122 parts of refined material are withdrawn from the base of the column. The composition of these materials is given in Table I below.