Dihydrobenzothiazine compounds and the preparation thereof

Abstract

The present invention relates to new dihydrobenzothiazine compounds, to the production thereof and to the use thereof as stabilizers and co-stabilizers against the oxidative and/or thermal degradation of organic polymers.

Description

This invention relates to new dihydrobenzothiazine compounds, to the production thereof and to the use thereof as stabilisers and co-stabilisers against the oxidative and/or thermal degradation of organic polymers.

It is known that many organic polymers, such as polyolefins, ABS-polymers and various rubber-like polymers, undergo degradation under the effect of heat, oxygen, ozone and/or light during storage and processing. Products produced from organic polymers of this type are similarly affected in practical applications. Such degradation gives rise to a deterioration in physical properties, for example to discolouration, clouding, surface crazing, and to a deterioration in mechanical properties, for example tensile strength. To avoid this, it is conventional practice to add stabilisers.

The most effective oxidation inhibitors are amine-based compounds, for example p-phenylene diamine derivatives or oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline. However, they discolour the products stabilised therewith and result in more or less pronounced contact discolouration (J. Voigt "Die Stabilisierung der Kunstoffe gegen Licht und Warme (The Stabilisation of Plastics against Light and Heat)," Springer-Verlag, Berlin/Heidelberg/New York, 1966, cf. in particular pages 279 to 316). For this reason, amine stabilisers may only be used to a limited extent in practice, for example in vehicle tyres, while the less effective phenolic stabilisers are used on a much wider scale.

Accordingly, there is a need for non-discolouring oxidation inhibitors comparable in effectiveness with amine-containing stabilisers.

In general, phenolic and amine-containing oxidation inhibitors adversely affect cross-linkable polymers because the radical cross-linking process is disturbed by the transfer of hydrogen atoms. This results in partial inactivation of the oxidation inhibitors. Added to this is the fact that cross-linked polymers are more sensitive to oxidation than uncross-linked polymers because they still contain long-lived radicals (which serve as starter radicals for the thermo-oxidative ageing process) and an increased concentration of readily oxidisable groups. Accordingly, although the effectiveness thereof is reduced by the cross-linking reaction, the oxidation inhibitors have to meet fairly stringent requirements. However, any increase in the concentration of oxidation inhibitor also leads to fairly serious interference with the cross-linking process with the result that it is difficult to produce adequately stabilised polymers characterized by a high degree of cross-linking.

The compounds corresponding to general formula (I) according to the present invention are non-discolouring stabilisers comparable in effectiveness with amine-containing oxidation inhibitors. They do not adversely affect the cross-linking of cross-linkable polymers, particularly polyolefins.

The compounds according to the present invention correspond to the following general formula (I): ##STR1## wherein R.sup.1 and R.sup.2, which may be the same or different, each represents hydrogen, lower alkyl containing from 1 to 4 carbon atoms, cycloalkyl containing from 5 to 8 carbon atoms, aralkyl containing from 7 to 11 carbon atoms or aryl or together represent a radical --(CH.sub.2).sub.m -- wherein m represents an integer of from 4 to 7;

R.sup.3 and R.sup.4 which may be the same or different, each represents lower alkyl containing from 1 to 4 carbon atoms, optionally substituted cyclohexyl containing from 5 to 8 carbon atoms, aralkyl containing from 7 to 11 carbon atoms or aryl or together represent a radical --(CH.sub.2).sub.n -- wherein n represents an integer of from 4 to 7, or one of the radicals R.sup.3 or R.sup.4 together with R.sup.1 or R.sup.2 represents an alkylene radical containing from 3 to 6 carbon atoms; R.sup.6 and R.sup.8, which may be the same or different, each represents hydrogen, halogen, nitro, linear or branched alkyl containing from 1 to 12 carbon atoms, linear or branched alkenyl containing from 2 to 12 carbon atoms, aralkyl containing from 7 to 11 carbon atoms, cycloalkyl containing from 5 to 8 carbon atoms, and the radicals R.sup.5 are the same or different and represent hydrogen, halogen, nitro, linear or branched alkyl containing from 1 to 12 carbon atoms, linear or branched alkenyl containing from 2 to 12 carbon atoms, cycloalkyl containing from 5 to 8 carbon atoms, aralkyl containing from 7 to 11 carbon atoms, alkoxy, the radical ##STR2## wherein p represents an integer of from 0 to 20, preferably from 8 to 16 and A represents --(CH.sub.2).sub.q --, --O--(CH.sub.2).sub.q --, --NH--(CH.sub.2).sub.q -- or --S--(CH.sub.2).sub.q wherein q=0 to 4, preferably 0 or 1, or the radical ##STR3## wherein R.sup.1 to R.sup.6 and R.sup.8 are as defined above, while R.sup.9 and R.sup.10 represent the radicals defined below, and R.sup.9 and R.sup.10 independently represent hydrogen, optionally substituted aryl, linear or branched alkyl containing from 1 to 12 carbon atoms, cycloalkyl or cycloalkenyl containing from 5 to 8 carbon atoms or R.sup.9 and R.sup.10 together with the carbon atoms to which they are attached complete a cycloalkyl radical containing from 5 to 7 carbon atoms.

Independently of one another, R.sup.1 and R.sup.2 preferably represent hydrogen or a lower alkyl radical containing from 1 to 4 carbon atoms, R.sup.3 and R.sup.4 represent a lower alkyl radical containing from 1 to 4 carbon atoms and R.sup.5 to R.sup.8 represent hydrogen, R.sup.9 and R.sup.10 are as defined above.

More preferably, R.sup.1 and R.sup.2 independently represent hydrogen or methyl, R.sup.3 and R.sup.4 independently represent methyl and R.sup.5 to R.sup.8 independently represent hydrogen.

The following are examples of compounds corresponding to the present invention: ##STR4## di-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl-)-methane; di-(2,2,3,3-tetramethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane ##STR5## 2-methyl-1-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-1-[3,3-dimethyl-5-(2-methyl-1-propenyl)-2,3-dihydro-4H-1,4-benzothiazin-7-yl]-propane

di-(3-methyl-8-nitro-3-phenyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane di-(3,3-diethyl-2,3-dihydro-5-stearoyl-4H-1,4-benzothiazin-7-yl)-methane 1,1-di-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-cyclohexane ##STR6## 1-cyclohex-3-enyl-1,1-di-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane 1-(4-chlorophenyl)-1,1-di-(3,3-dimethyl-2-propyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane ##STR7## 2,2-di-(10a-methyl-1,2,3,4,4a,10a-hexahydrophenothiazin-7-yl)-propane ##STR8##1-(2,2,3,3-tetramethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-1-[2,2,3,3-tetramethyl-5-(2,2,3,3-tetramethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl-methyl)-2,3-dihydro-4H-1,4-benzothiazin-7-yl]-methane.

The compounds corresponding to general formula (I) according to the present invention may be produced by reacting a compound corresponding to the following general formula (II): ##STR9## wherein the substituents are as defined above; with a carbonyl compound corresponding to the following general formula (III): ##STR10## wherein the substituents are as defined above; in a molar ratio of from 10:1 to 1:1, optionally in an inert organic solvent and optionally in the presence of a catalyst at temperatures of from about 0.degree. to about 200.degree. C.

It is advantageous to use an acid catalyst, preferably a mineral acid. The reaction may be carried out in a solvent, such as ether, alcohol, toluene or carbon tetrachloride. The reaction may also be carried out in the absence of a solvent. The molar ratio between the compound (II) and the carbonyl compound (III) may vary from 10:1 to 1:1 and is preferably from 4:1 to 2:1. To shorten the reaction time, it is preferred to use elevated temperatures of from 50.degree. to 150.degree. C. or boiling temperature. For the same reason, it is advantageous in some cases to react the components under elevated pressure.

Compounds corresponding to general formula (I) wherein R.sup.5 represents C.sub.1 -C.sub.12 alkyl or C.sub.7 -C.sub.11 aralkyl may also be produced by alkylating compounds (I) wherein R.sup.5 represents hydrogen by reaction with olefins, styrene derivatives, alkyl halides, aralkyl halides, alcohols and the like in the presence of a Lewis acid catalyst. The reaction may be carried out in the absence of a solvent or in an inert solvent, such as ether, benzene, toluene, chlorobenzene, chloroform or carbon tetrachloride. Preferred Lewis acids are aluminium trichloride, boron trifluoride, anhydrous zinc chloride and concentrated sulphuric acid. The catalyst may be used in a quantity of from 0.001 to 110 mole percent, preferably from 0.1 to 10 mole percent. The temperature is from 20.degree. to 200.degree. C., preferably from 80.degree. to 130.degree. C. At relatively high temperatures in particular, it is preferred to carry out the reaction in the absence of oxygen.

Compounds corresponding to general formula (I) wherein R.sup.5 represents an acyl radical are similarly obtained by acylating compounds (I) wherein R.sup.5 represents hydrogen with carboxylic acid halides, anhydrides or with free carboxylic acids, but containing from 2 to 22, preferably from 10 to 18, carbon atoms, in the presence of a Lewis acid catalyst.

The compounds according to the present invention are suitable for stabilising organic polymers against thermo-oxidative degradation, particularly plastics, such as polyolefins, ABS-polymers, high-impact polystyrene, polyesters, polyamides, polycarbonates, polyurethanes, natural rubber, synthetic rubbers, such as butadiene-styrene copolymers, polybutadiene, polyisoprene, ethylene-propylene-diene terpolymers (EPDM-rubbers), butyl rubber, chlorinated and chlorosulphonated polyethylene and nitrile rubber.

One preferred application for the present compounds is in radically cross-linked polymers, particularly cross-linked polyethylene, but also ethylene/propylene copolymers and EPDM-rubbers, chlorinated and chlorosulphonated polyethylene.

The compounds according to the present invention are generally used in quantities of from 0.001 to 20%, preferably from 0.05 to 5%, based on the total weight of the polymer to be stabilised. The compounds may be introduced directly or through a master batch containing, for example, from 30 to 90% of a compound corresponding to general formula (I). The method of using master batches is known. The stabilised organic materials may only contain compounds corresponding to general formula (I) or additionally other auxiliaries for improving the properties thereof. Such auxiliaries are, for example, other stabilisers or co-stabilisers against deterioration under the effect of heat and oxygen or UV-light. Examples of co-stabilisers of this type are dilauryl and distearyl thiodipropionate, 2-mercaptobenzimidazole, 2,6-di-t-butyl-p-cresol, o-hydroxybenzophenone and the like. Other additives, such as anticorrosives and rust-proofing agents, dispersion aids, emulsifiers, plasticisers, lubricants, flameproofing agents and anitozonants, metal deactivators, blowing agents, coupling agents, dyes, pigments, fillers, carbon black, accelerators and cross-linking agents, may also be present.

The present invention also relates to the organic materials containing a compound corresponding to general formula (I) according to the present invention and also to an agent containing a compound corresponding to general formula (I).

The present invention is illustrated by the following Examples.

EXAMPLES

EXAMPLE 1

2.869 kg (16 moles) of 3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazine, 5 kg of methanol and 46 g (0.45 mole) of concentrated sulphuric acid are initially introduced, followed by the dropwise addition at 30.degree. C. of 327 g (4 moles) of a 37% aqueous formaldehyde solution. After refluxing for 1.5 hours, 40 g (1 mole) of sodium hydroxide are added, followed by refluxing for another 3 hours. After cooling, the product is filtered under suction, the residue is washed with methanol and water and is dried in a recirculating air cabinet.

Di-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane melting at from 179.degree. to 181.degree. C. is obtained in a yield of 1.26 kg. The mass spectrum shows a molecular ion at 370 (100% relative intensity) and as main fragments 355 (90%), 192 (23%), 170 (20%) (stabiliser A).

EXAMPLE 2

The procedure is as in Example 1, except that isobutyraldehyde is added dropwise instead of formaldehyde. 2-methyl-1-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-1-[3,3-dimethyl-5-(2-methyl-1-propenyl)-2,3-dihydro-4H-1,4-benzothiazin-7-yl]-propane is obtained in the form of a tough resin. The mass spectrum shows a molecular ion at 466 (24% relative intensity) and as main fragments 423 (74%), 412 (14%), 369 (100%), 272 (19%), 178 (7%) (stabiliser B).

EXAMPLE 3

8.2 g of di-(2,2,3,3-tetramethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane are obtained as in Example 1 from 12 g of 2,2,3,3-tetramethyl-2,3-dihydro-4H-1,4-benzothiazine and 2.4 g of 37% formaldehyde solution. Its mass spectrum shows a molecular ion at 426 (94% relative intensity) and as main fragments 411 (18%) and 383 (100%). In addition, the product also contains small quantities of compounds containing 3 and 4 (2,2,3,3-tetramethyl-2,4-dihydro-4H-1,4-benzothiazine)-nuclei with molecular weights of 645 and 864.

EXAMPLE 4

90 g (0.5 mole) of 3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazine, 500 ml of toluene, 3.2 g of concentrated sulphuric acid and 27.5 g (0.25 mole) of tetrahydrobenzaldehyde are refluxed for 5 hours, washed with water, the organic phase dried and the solvent removed in vacuo. Unreacted 3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazine is distilled off under a high vacuum, leaving as residue 1-cyclohex-3-enyl-1,1-di-(3,3-dimethyl-2,3-dihydro-4H-1,4-benzothiazin-7-yl)-methane in the form of a dark brown brittle resin.

The mass spectrum shows a molecular ion at 450 (26% relative intensity) and as main fragments 370 (27%), 369 (100%) (stabiliser C).

EXAMPLE 5

Example 5 shows that the compounds according to the present invention are superior to phenolic stabilisers in natural rubber and are comparable in stabilising effect with the amine-containing anti-ager 2,2,4-trimethyl-1,2-dihydroquinoline oligomer.

The following mixture was prepared on mixing rolls:

______________________________________ Parts, by weight______________________________________Light crepe 100.0Zinc oxide 10.0Stearic acid 1.0Titanium dioxide 10.0Blank fix 60.0Tetramethyl thiuram disulphide 0.5Sulphur 2.0Stabiliser as indicated in Table 1.______________________________________

The mixture was press-vulcanised for 15 minutes at 130.degree. C. The vulcanisate obtained was aged in an oxygen cylinder (according to Bierer-Davis) at 70.degree. C. under an oxygen pressure of 21 bars (DIN 53 508).

The results are set out in Table 1 below.

TABLE 1__________________________________________________________________________ Mixture of 2,2,4-trimethyl- Without alkyl and 1,2-dihydroquin- stabiliser aralkyl phenols oline oligomer (Comp. 1) (Comp. 2) (Comp. 3) A B C__________________________________________________________________________Parts, by weight -- 1 1 1 1 1Before ageingStrength (MPa) 22.7 23.1 23.8 20.4 21.5 23.3Elongation (%) 730 730 710 730 780 720Modulus at 450% 8.1 8.0 9.6 5.9 6.9 9.0Elongation (MPa)Elasticity (%) at 20.degree. C. 74 74 75 69 69 72 at 70.degree. C. 79 81 81 72 75 77Hardness (Shore A) at 20.degree. C. 52 52 54 47 47 52 at 70.degree. C. 52 52 53 47 44 52After ageing for 7 daysStrength (MPa) 5.0 14.6 16.8 -- 16.8 16.3Elongation (%) 470 600 580 -- 650 590Modulus at 450% -- 8.9 11.5 -- 8.9 10.5Elongation (MPa)Elasticity (%) at 20.degree. C. -- 65 72 -- 63 63 at 70.degree. C. 50 69 79 -- 70 71Hardness (Shore A) at 20.degree. C. 47 52 56 -- 48 54 at 70.degree. C. 35 50 55 -- 47 51After ageing for 14 daysStrength (MPa) destroyed 9.3 14.4 13.4 13.5 12.7Elongation (%) 560 570 570 620 580Modulus at 450% elongation 7.1 10.4 8.3 8.9 9.3(MPa)Elasticity at 20.degree. C. 47 66 60 58 57 at 70.degree. C. 56 75 70 66 70Hardness (Shore A) at 20.degree. C. 46 54 48 47 52 at 70.degree. C. 38 53 46 45 50After ageing for 21 daysStrength (MPa) destroyed destroyed 11.9 10.5 11.4 8.0Elongation (%) 540 550 600 520Modulus at 450% elongation 9.8 7.0 7.7 7.1(MPa)Elasticity (%) at 20.degree. C. destroyed destroyed 55 57 51 49 at 70.degree. C. 63 66 58 58Hardness (Shore A) at 20.degree. C. 53 49 45 49 at 70.degree. C. 50 47 -- 40__________________________________________________________________________

Vulcanisates containing comparison substances 1 and 2 of Table 1, 2,2'-methylene-bis-6-t-butyl-4-methylphenol (comparison 4) and stabiliser A did not show any discolouration before exposure to the light, while vulcanisates containing comparison substance 3 had already turned pink. After 2 months in daylight, the vulcanisates containing comparison substances 1 and 2 had remained white, the vulcanisate containing stabiliser A had turned pale cream, the vulcanisate containing comparison substance 4 had turned pink, while the vulcanisate containing comparison substance 3 had turned light brown. Accordingly, the compounds according to the present invention are equivalent to the phenolic antioxidants (comparison substances 1, 2 and 4) in the extent to which they discolour the vulcanisates and cause distinctly less discolouration of the vulcanisates than amine-containing anti-agers (comparison substance 3).

EXAMPLE 6

EPDM cable mixtures having the following compositions were prepared:

TABLE 2______________________________________ Parts, by weight______________________________________EPDM-rubber.sup.(1) 50 50EPDM-rubber.sup.(2) 50 50Kaolin 150 150Vinyl silane 1 1Polyethylene anti-ozonant wax 10 102,2,4-trimethyl-1,2-dihydroquinoline, 1 --polym.Stabiliser A -- 1Paraffin 5 5Mineral oil plasticiser 30 30Triallyl cyanurate 1.5 1.5Zinc oxide 5 5Dicumyl peroxide, 40% 5 5Before ageing:Strength (MPa) 7 6.1Breaking elongation (%) 310 300Modulus at 100% elongation (MPa) 3 3.1Modulus at 300% elongation (MPa) 7 6.1Hardness at 20.degree. C. (Shore A) 72 69After ageing for 10 days in hot airat 100.degree. C.Strength (MPa) 6.9 6.3Breaking elongation (%) 310 300Hardness at 20.degree. C. (Shore A) 70 69After ageing for 7 days in hot airat 135.degree. C.Strength (MPa) 8.8 7.5Breaking elongation (%) 330 290Hardness at 20.degree. C. (Shore A) 77 74______________________________________ .sup.(1) Statistical EPDM containing ethylidene norbornene as the ter component and having a Mooney viscosity ML 1 + 4 at 100.degree. C. of 70. .sup.(2) Sequential EPDM containing ethylidene norbornene as ter componen and having a high crude polymer strength and a Mooney viscosity ML 1 + 4 at 100.degree. C. of 85.

It may be seen from Table 2 that stabiliser A is as effective as an anti-ager as the slightly discolouring 2,2,4-trimethyl-1,2-dihydroquinoline oligomer.

EXAMPLE 7

The following natural latex mixture was prepared:

______________________________________ Parts, by weight______________________________________Natural latex 1673-benzyl-4-hydroxybiphenylpolyglycol ether, 120%Zinc oxide, active 2.5Colloidal sulphur 1.8______________________________________

The dispersion was prepared using either a ball mill or an "Ultraturax." The sample was vulcanised for 15 minutes at 110.degree. C. and then aged in hot air at 100.degree. C. The results are set out in Table 3.

TABLE 3__________________________________________________________________________ Comp. Comp. Comp. Comp. Example Example Comp. Comp. 1 2 3 4 A B 5 6__________________________________________________________________________2,2,4-trimethyl-1,2-dihydro 1 1 0.5 0.5 -- -- -- --quinoline (parts, by weight)2-mercaptobenzimidazole (parts, by weight) -- -- 0.5 0.5 0.5 0.5 -- --Stabiliser A -- -- -- -- 0.5 0.5 -- --Styrenised diphenylamine -- -- -- -- -- -- 1 --(parts, by weight)Dispersion using a ball mill + - + - + - + +Dispersion using an "Ultraturax" - + - + - + - -Stability of the mixture in slightly slightly thixo- thixo- satis- sediments satis- satis-storage after 14 days speckly speckly tropic tropic factory after factory factory and stirring slightly slightly speckly specklyBefore ageingTensile strength (Kp/cm.sup.2) 193 240 187 242 204 199 234 195Breaking elongation (%) 685 695 760 705 745 710 695 720Modulus at 500% elongation (Kp/cm.sup.2) 52 50 27 40 39 41 44 29After ageing for 3 daysTensile strength (Kp/cm.sup.2) 47 25 100 77 55 78 34 8Breaking elongation (%) 430 465 555 430 565 485 555 260Modulus at 500% elongation (Kp/cm.sup.2) -- -- 41 -- -- -- -- --After ageing for 6 daysTensile strength (Kp/cm.sup.2) 10 8 21 13 36 17 10 7Breaking elongation (%) 140 90 270 195 380 305 190 70Modulus at 500% elongation (Kp/cm.sup.2) -- -- -- -- -- -- -- --__________________________________________________________________________

Table 3 demonstrates the superiority of the compound according to the present invention (stabiliser A) over the comparison compounds in terms of its anti-ageing effect and dispersibility in the latex.

EXAMPLE 8

The quantities of stabiliser indicated in Table 5 were additionally worked by means of a 3 kg laboratory internal kneader of the Banbury type into an ABS commercial product normally stabilised for standard applications in which the monomer ratio of acrylonitrile to butadiene to styrene was 20:32:48% by weight and in which the SAN-resin phase had an average molecular weight of from 110,000 to 160,000. Standard small test bars were then injection moulded from the thus-obtained mixture.

Impact strength a.sub.n was measured in accordance with DIN 53 453 before and after heating from 4 minutes by the heating unit of a hot vacuum forming machine (Illig U 60; distance from the surface of the standrad test bars to the IR lamp=15 cm). Notched impact strength was also measured before the heat treatment. The results set out in Table 4 demonstrate the good stabilising effect of the compound according to the present invention.

TABLE 4______________________________________ Notched Impact strength a.sub.n impact before after strength a.sub.kTest Stabiliser ageing under heat (KJ/m.sup.2)______________________________________A -- unbroken 37 KJ/m.sup.2 17B 0.2% of 2,2'-dihydroxy- " unbroken 20 3,3'-dicyclohexyl-5,5'- dimethyl diphenyl methane (prior art)C 0.5% of 2,2'-dihydroxy- " " 18 3,3'-dicyclohexyl-5,5'- dimethyl diphenyl methane (prior art)D 0.2% of stabiliser A " " 19E 0.5% of stabiliser A " " 19______________________________________

EXAMPLE 9

After the indicated quantities of stabiliser together with 1.5% of di-t-butyl peroxide had been worked into a high-pressure polyethylene base resin for LPDE cable insulation (MI=2.6 g/10 mins at 190.degree. C.; d=0.922 g/cc), 1 mm thick sheets were produced by moulding and cross-linked at 135.degree. C. S2 standard bars were then punched out and subjected to ageing in hot air at 150.degree. C.

The results are set out in Table 5 and demonstrate the advantage of the compound according to the present invention.

TABLE 5__________________________________________________________________________ Before ageing After at 150.degree. C. 10 20 40 100 days__________________________________________________________________________0.3% of 2,2,4-trimethyl-1,2- tensile 21.4 10.3 6.2 destroyed destroyeddihydroquinoline oligomer strength (MPa)(Comparison 1)Gel content: 91% elongation (%) 445 218 -- -- --1.5% of 2,2,4-trimethyl-1,2- tensile 18.9 14.2 12.9 4.8 destroyeddihydroquinoline oligomer strength (MPa)(Comparison 2)Gel content: 92% elongation (%) 457 406 316 32 --0.3% of stabiliser A tensile 27.8 20.2 17.4 9.5 8.4 strength (MPa)Gel content: 89% elongation (%) 580 494 462 95 920.5% of stabiliser A tensile 26.5 21.2 18.4 12 9 strength (MPa)Gel content: 85% elongation 582 519 484 347 136__________________________________________________________________________

The following results were obtained in the so-called "hot set test" according to VDE 0472:

______________________________________Sample containing 0.5% 150.degree. C./0.2 MPa: 68% elongationof stabiliser A 200.degree. C./0.2 MPa: 70% elongationSample containing 0.5% 150.degree. C./0.2 MPa: 39% elongationof 2,2,4-trimethyl-1,2- 200.degree. C./0.2 MPa: 26% elongationdihydroquinoline oligomer(Comparison)______________________________________

In this test, too, the compound according to the present invention shows a considerably better effect.

EXAMPLE 10

0.5% of the stabiliser indicated was worked into an ethylene/vinyl acetate copolymer base resin for LDPE cable insulations (MI=25 g/10 mins. at 190.degree. C.; d=0.930 g/cc; vinyl acetate content 9%) and 1 mm thick sheets were moulded from the resulting compound. The thus-produced sheets were then cross-linked using a van-der-Graaf generator (radiation dose 20 Mrad), after which S2 standard bars were punched out and subjected to ageing in hot air at 150.degree. C.

The results set out in Table 6 demonstrate the advantages of the compound according to the present invention.

TABLE 6______________________________________ After 0 20 60 days' ageing______________________________________0.5% of 2,2,4-trimethyl- tensile 28 2.9 destroyed1,2-dihydroquinoline strengtholigomer (comparison) (MPa)Gel content: 75% elongation 499 6 -- (%)0.5% of stabiliser A tensile 26.9 8.5 7.1 strength (MPa)Gel content: 78% elongation 549 209 80 (%)______________________________________

The compound according to the present invention is also superior in the hot set test according to VDE 0472:

______________________________________LDPE containing 0.5% of 150.degree. C./0.2 MPa 105% elongationstabiliser A 200.degree. C./0.2 MPa 65% elongation______________________________________

EXAMPLE 11

0.5% of stabiliser, 1.5% of vinyl trimethoxy silane, 0.15% of dicumyl peroxide and 0.05% of dibutyl tin dilaurate were worked into a high pressure polyethylene base resin for LDPE cable insulations and 1 mm thick sheets were moulded from the resulting compound. After cross-linking under the effect of boiling water for 3 hours, S2 standard bars were punched out and subjected to ageing in hot air at 150.degree. C.

The results set out in Table 7 demonstrate the effectiveness of the compound according to the present invention.

TABLE 7______________________________________ After 0 10 30 days' ageing______________________________________0.5% of 2,2,4-trimethyl- tensile 15 15.3 6.71,2-dihydroquinoline strengtholigomer (comparison) (MPa) elongation 310 353 12 (%)0.5% of stabiliser A tensile 18.2 17 6 strength (MPa) elongation 510 430 35 (%)______________________________________

Claims

1. A compound of the formula ##STR11## wherein R.sup.1 and R.sup.2, which may be the same or different, each represents hydrogen, lower alkyl containing from 1 to 4 carbon atoms, cycloalkyl containing from 5 to 8 carbon atoms, aralkyl containing from 7 to 11 carbon atoms or carbocyclic aryl having 6 carbon atoms or together represent a radical --(CH.sub.2).sub.m -- wherein m represents an integer of from 4 to 7;

R.sup.3 and R.sup.4 which may be the same or different, each represents lower alkyl containing from 1 to 4 carbon atoms, cyclohexyl, aralkyl containing from 7 to 11 carbon atoms or carbocyclic aryl having 6 carbon atoms or together represent a radical --(CH.sub.2).sub.n -- wherein n represents an integer of from 4 to 7, or one of the radicals R.sup.3 or R.sup.4 together with R.sup.1 or R.sup.2 represents an alkylene radical containing from 3 to 6 carbon atoms;

R.sup.6 and R.sup.8, which may be the same or different, each represents hydrogen, halogen, nitro, linear or branched alkyl containing from 1 to 12 carbon atoms, linear or branched alkenyl containing from 2 to 12 carbon atoms, aralkyl containing from 7 to 11 carbon atoms, cycloalkyl containing from 5 to 8 carbon atoms, and the radicals R.sup.5 are the same or different and represent hydrogen, halogen, nitro, linear or branched alkyl containing from 1 to 12 carbon atoms, linear or branched alkenyl containing from 2 to 12 carbon atoms, cycloalkyl containing from 5 to 8 carbon atoms, aralkyl containing from 7 to 11 carbon atoms, alkoxy, the radical ##STR12## wherein p represents an integer of from 0 to 20, preferably from 8 to 16, and

A represents --(CH.sub.2).sub.q --, --O--(CH.sub.2).sub.q --, --NH--(CH.sub.2).sub.q -- or --S--(CH.sub.2).sub.q

q=0 to 4, preferably 0 or 1, or the radical ##STR13## wherein R.sup.1 to R.sup.6 and R.sup.8 are as defined above, while R.sup.9 and R.sup.10 represent the radicals defined below, and R.sup.9 and R.sup.10 independently represent hydrogen, carbocyclic aryl having 6 carbon atoms, linear or branched alkyl containing from 1 to 12 carbon atoms, cycloalkyl or cycloalkenyl containing from 5 to 8 carbon atoms or R.sup.9 and R.sup.10 together with the carbon atoms to which they are attached complete a cycloalkyl radical containing from 5 to 7 carbon atoms.

2. A compound of claim 1 wherein R.sup.1 and R.sup.2 are hydrogen or a C.sub.1 -C.sub.4 -alkyl radical; R.sup.3 and R.sup.4 are a C.sub.1 -C.sub.4 -alkyl radical; R.sup.5, R.sup.6 and R.sup.8 are each hydrogen and R.sup.9 and R.sup.10 are as defined in claim 1.

3. A compound of claim 1 wherein R.sup.1 and R.sup.2 are each hydrogen or methyl; R.sup.3 and R.sup.4 are each methyl; R.sup.5, R.sup.6 and R.sup.8 are each hydrogen and R.sup.9 and R.sup.10 are as defined in claim 1.

4. The compound ##STR14##

5. A process for the production of a compound of claim 1 wherein a compound of the formula ##STR15## wherein R.sup.1 to R.sup.6 and R.sup.8 are as defined in claim 1 is reacted with a compound of the formula ##STR16## wherein R.sup.9 and R.sup.10 are as defined in claim 10 in a molar ratio of from 10:1 to 1:1 at a temperature of from 0.degree. to 200.degree. C.

6. The process of claim 5 wherein said reaction is carried out in the presence of a catalytic amount of an acid catalyst.

7. The process of claim 5 wherein said reaction is carried out in an inert solvent.