CS196011B1 - Process for the stabilization of phenolic monomers - Google Patents

Description

The invention relates. stabilization of enolic monomers, used in particular for the preparation of polyphenylene oxides by oxidative polycondensation.

Phenol, cresols and xylenols are very easily subject to thermooxidation, accelerated by the presence of metal, such as class 11 material - steel.

The result is the formation of colored, non-volatile oxidation-condensation products, whose amount increases rapidly (up to one percent) with increasing temperature, and exposure time, and thus depreciates the raw material often so much that re-purification, for example by distillation, is necessary choose special construction materials which are not catalysts of thermo-oxidative reactions.

Phenol instability is caused by the oxidative lability of the phenolic group - OH. The resulting phenoxyraical is capable of damaging substituents on the one hand and leads to the formation of quinone structures. Oxidative condensation, quinone ring cleavage and other reactions Polyconjugated products with molecular weights of the order of 1θ are formed. The presence of quinones is particularly detrimental in the production of polyphenylene oxides, where these impurities substantially impair the mechanical properties of the product.

The technical solution to this problem is not yet desirable. Oxidation condensation reactions can generally be prevented by the addition of suitable stabilizers. For phenolocylene monomers, the choice of stabilizer is limited by the condition that the stabilizer used must not impair the desired homeland.

196 011 to prevent the course of oxidative polycondensation.

It was. It has been found that the desired effect is obtained by means of thermo-oxidizing stabilizers based on organic phosphorus compounds.

SUMMARY OF THE INVENTION The present invention provides a process for stabilizing phenolic monomers such as 2,6 dimethylphenol against thermo-oxidative aging by adding 0.1-5% by weight of a phosphite of the formula

wherein n is 1 or 2, R1 is alkyl of 4 to 20 carbon atoms, aryl optionally substituted with p alkyl of 4 to 20 carbon atoms or styryl, R is two mutually identical or different substituents R ^, wherein R ^ has the above or tetramethylene methane.

Phosphites are used as thermo-oxidizing stabilizers for plastics, mostly in synergistic combinations with substituted phenols, which are themselves effective thermo-oxidizing stabilizers, especially polyolefins.

It has been found that the formation of undesired oxidation products is substantially reduced when phosphites are added to phenolic monomers. The amount of these products can be quantified spectroscopically; suitably the degree of deterioration of the polymer can be characterized by, for example, an absorption peak in the region of 320 to 340 mm. The absorbance of the phenol solution is then proportional to the amount of non-volatile condensation products. In this way, the efficacy of thermo-oxidative stabilizers based on organic phosphorus compounds on polycondensation can also be evaluated by preparing polyphenylene oxide under comparable conditions. Possible phosphite residues in the product cannot be impeded, as these phosphites are used as stabilizing additives in polyphenylene oxide, where these residues are desirable.

The invention is illustrated by the following non-limiting examples. Example 1

Steel chips and varying amounts of triphenyl 90 styrylphosphite were added to the 2,6-xylenol melt. The mixture was exposed to 70 ° C for 120 hours. Monitored color changes are listed in the table:

% phosphite (% by weight) relative change in absorbance at 330 nm 0 1 0.1 0.35 0.2 0.21 0.3 0.20 0.4 0.05 3 0 5 0

198 011

Example 2 ml of a solution of 15 g of 2,6-xylenol in an azeotropic mixture of ethyl alcohol-benzene (64: 36% by volume) was metered into a 100 ml solution of 225 mg of copper (II) chloride dihydrate and 3 ml of morpholine in azeotropic mixture. The mixture was bubbled with oxygen and the reaction terminated 33 minutes after the start of dosing. The resulting polymer was filtered and washed with an azeotropic mixture and dried.

The product of the reaction was 13.5 g of poly (2,6-dimethyl-1,4-phenylene oxide) having a molecular weight of 51,000.

Example 3

The polymerization was carried out according to Example 2, and 0.75 g (5%) triphenylstyrylphosphite was added to the reaction mixture. The reaction product was 13.2 g of polyphenylene oxide having a molecular weight of 49,000. The presence of 5% phosphite did not affect the polycondensation reaction.

Example 4

The conditions were the same as in Example 1 and in the amount of 0.2% and 3% various osphites were added to the xylenol. The following table shows the effect of these foefits on the relative color changes of 2,6-xylenol.

phosphite. · Relative absorbance change

/ 340 nm / addition 0.2% 3.0% - 1 1 triieodecylfošfit 0.37 0.20 di (nonylphenyl) phenylphosphite 0.20 0.15 tri (nonylphenyl) phosphite 0.20 0.10 diisodecylphenylphosphite 0.16 0,15 ' tri (styrylphenyl) phosphite 0.10 0.09 diphenylisodecyl phosphite 0.06 0.05 d i / 2-ethylhexyl / penta erythrit from if os f it 0.03 0.03 triiaurylphosphite 0 0 triphenylphosphite 0 0

object of the invention

Claims (1)

A process for stabilizing phenolic monomers such as 2,6-dimethylphenol against thermo-oxidative aging, characterized in that 0.1-5% by weight of a phosphite of the general formula [ ^R1 where n is 1 or 2, R1 is an alkyl of 4, up to 20 carbon atoms, aryl optionally substituted By C 4 -C 20 alkyl or styryl, R denotes two identical or different substituents R ¹ , where R ¹ is as defined above, or tetramethylmethane.