The invention relates to diamines of the formula

The invention also relates to polyamides and polyimides based on these diamines. Because of the presence of the sterically hindered t-butyl group in the diamines according to the invention such polymers display little tendency to crystallize.

A diamine which contains aromatic amide groups and may be used as a raw material in the preparation of polyamides is known from US 3 049 518. The diamine described herein is N,N'-bis(3-aminophenyl )- isophthalamide. Its reaction with difunctional acid derivatives generates crystalline polymers. They form a class of polymers different from the amorphous polyamides generated from diamines according to the invention.

A major advantage of the diamines according to the invention is the possibility of preparing amorphous polymers having a relatively high glass transition temperature (Tg) . Such polymers may be prepared by reacting a diamine according to the invention with aromatic difunctional acid derivatives. A polyamide is then formed which has a relatively high Tg because of the rigid aromatic polymer chains but is amorphous on account of being interrupted reiteratively, and thus more readily processable from solution.

Such polymers are especially suited to be used in the electronics industry, since in this industry resistance to a brief high thermal load (soldering) is often required. In the aircraft industry there also is a great demand for polymers having a high Tg.

A drawback to high Tg polymers is that they can be melt processed only with difficulty or not at all. This is caused on the one hand by the difference between decomposition temperature and processing temperature being too small and on the other by the commonly used processing equipment as a rule not being operable at temperatures above 400°C. If the diamines according to the invention are polycondensed with aliphatic difunctional acid derivatives or mixtures of aliphatic and aromatic difunctional acid derivatives, polymers having a Tg up to about 280°C are obtained. Thus, the invention also provides polymers that may be melt processed by conventional techniques, such as moulding, injection moulding, and extrusion, even though a lower Tg will have to be accepted then.

The invention also permits preparing copolymers in which the diamines according to the invention are replaced in part with other diamines of an aliphatic or aromatic structure or in which mixtures of diacids or diacid chlorides- are employed.

Alternatively, the diamines according to the invention may be polymerized with cyclic anhydrides of tetracarboxylic acids, such as pyromellitic acid and benzophenone tetracarboxylic acid. Such a process generates a polyamic acid from which a polyimide may be formed by ring closure. Of course, this may also be achieved using tricarboxylic anhydrides. The process of casting a polyamic acid film which is subsequently cured with i ide forming is known to the man skilled in the art. The polyamic acids formed by using diamines according to the invention are amorphous and may consequently be processed from a solution into products, such as films, by conversion into polyimides.

The diamines according to the invention are also suited to be used for preparing polyimides by reaction with a dicarboxylic acid derivative in which a preformed imide structure is present. Such imide monomers and polyimides prepared therewith are described in Vysokomol soyed. A18:No. 12, 2681-2686 (1976).

This preparative process is particularly advantageous in that it prevents voids and cracks in the polymer surface.

By reaction steps known in themselves the diamines according to the invention may be prepared from t-butyl isophthalic acid (t-BulPA) ot t-isobutyl isophthalic acid chloride (t-BulPA-Cl) and o-, m-, or p- nitroaniline. The resulting dinitro compound may be reduced to the diamine in a known manner. Especially in the preparation of polyamides of a relatively high Tg preference is given to diamine prepared from t-BulPA or t-BulPA-Cl and para-nitroaniline. This compound will be referred to hereinafter as p-tBulPA-diamine. In analogous fashion reference is made to meta- and ortho-tBulPA-diamine.

The preparation of the polyamides according to the invention may be carried out in a manner analogous to the one described for the known polyamides in Kirk-Othmer, Encyclopaedia of Chemical Technology, 3rd ed. Vol. 3, pp. 229-237 (1978).

In the preparation on a laboratory scale use may be made of a method described by Ya azaki et al . in J. Pol. Sci . 13 (1975) pp. 1373-1380. For preparation on an industrial scale preference is generally given to interfacial polymerization or polymerization from the solution. The invention will be further described in, but not limited by the following examples.

Examples

Example 1

Preparation of t-BulPA-diamine

a) Preparation of m-dinitro compound

from diacid chloride + m-nitroaniline

Weighed into a 6-1 round bottomed flask fitted with a thermometer, a stirrer, a heating device, a dropping funnel, a reflux condenser, and a bubble gauge in an N2 atmosphere are:

790 g of m-nitroaniline (5,72 moles)

41 of N-methyl pyrrol i done (NMP) dried on molecular sieves 3A.

Obtained, with stirring, is a clear, dark-brown solution, to which

726 g of molten (45°C) t-BulPA-Cl (2,80 moles) are slowly added dropwise. The contents of the flask are kept at < 20°C by cooling.

After the whole has been added (3 hours), stirring is continued for a further hour, whereupon the reaction mixture is left to stand for 16 hours.

Next, the clear dark-brown solution is precipitated in 20 1 of water, with stirring, and then filtered off. The resulting pale yellow solid is agitated with 20 1 of fresh washing water and filtered off again.

This washing procedure is repeated a further 3 times, whereupon

the resulting product is dried for 8 hours at 65°C in a vacuum of

12 mmHg, and subsequently for 16 hours at 65°C in a vacuum of 0,2 m Hg, until a constant weight is obatined. Obtained are 1236 g of a pale yellow solid.

Yield: 95,5%.

Melting range: 239,6°-241,5°C.

The corresponding p-dinitro compound is prepared in analogous fashion. Obtained is a pale yellow solid having a melting point of 302°C (determined by DSC). The yield is 97,3%.

Preparation of m-diamino compound

Catalytic reduction of the dinitro compound of la to the corresponding diamino compound.

Introduced into a 2-1 steel high-pressure autoclave fitted with a stirring device are:

300 g of dinitro compound (0,65 moles)

+ 30 g of 50% Raney nickel suspension

+ 1 1 of dried NMP.

After having been evacuated 3 times, followed by flushing with N-?, the autoclave is brought under an H2 atmosphere at an atmospheric pressure of 40-45. The reaction takes place at 80°-90°C. Upon its completion there remains a brownish black solution. The catalyst remainders are filtered off over infusorial earth and at reduced pressure. The remaining NMP solution is precipitated in 12 1 of water, with stirring. The finely divided pale beige precipitate formed is filtered off. Next, the precipitate is again agitated with water and filtered off 3 times. Finally, the solid is dried until the weight is constant, viz. for 16 hours/60°C/12 mmHg, followed by 8 hours/70°C/0,5 mmHg and finally 8 hours/110°C/0,5mmHg.

Obtained is a fine pale beige solid.

Weight: 250,1 g.

The yield is 95,7%.

The melting range is 228,2°-230,l°C.

Inidentical fashion the corresponding p-diamino compound is prepared, resulting also in a high yield. Obtained is a lilac solid having a melting point of 297°C, determined by DSC.

Example 2

Preparation by the Yamazaki method of a polyamide from a diacid and a diamine.

Weighed into a 500-ml three-necked flask fitted with a contact thermometer, a reflux condenser with bubble gauge, a stirrer, a heating device, and an N2 apparatus are:

24,85 g of meta-t-BulPA-diamine (0,06 moles)

13,85 g of 1-10 dόcanedicarboxylic acid (0,06 moles)

120 ml of dry NMP

90 ml of pyridine

8,4 g of lithium chloride

48 g of triphenyl phosphite (excess) (0,15 moles)

After it has been flushed with N2. the flask with its contents is heated to 80°-85°C.

After 10 minutes a lightly coloured precipitate is formed in the solution, which up to then has been a clear brownish black. Also, the viscosity of the flask's contents increases.

After a reaction time of 2 hours there remains a viscous beigish brown mass. The reaction being continued at 90°C for another hour does not cause a further increase in viscosity. After being cooled, the contents of the flask are precipitated in 3 1 of methanol , with stirring, and then filtered off. Subsequently, the whole is agitated and filtered off a further three times. The resulting beigish grey polymer precipitate is then dried for 7 hours/65°C/15 mmHg, followed by 2 hours/120°C/0,3 mmHg and then finally 5 hours/150°C/0,3 mmHG, until a constant weight is obtained.

Obtained are 32,5 g of beigish grey polymer.

The yield is: 90,6%.

The relative viscosity is 1,85.

Example 3

Preparation of a polyamide from a diamine and a diacid chloride.

Procedure:

Charged i nto a 500-ml three-necked fl ask fi tted wi th a sti rrer, a powder meteri ng funnel , a thermometer, and a refl ux condenser wi th bubbl e gauge and cool i ng devi ce are :

24, 15 g of meta-t-bul PA-di ami ne (0 , 06 mol es)

300 ml of dry NMP .

After flushing with 2, the diamine is dissolved with stirring, whereupon 12,18 g of isophthalic acid dichloride (0,06 moles) are slowly added to the remaining dark brown solution at < 20°C. After the whole amount has been added, there is obtained a clear brown viscous solution, which is stirred for a further 3 hours. Upon completion the polymer solution is precipitated in a mixture of 4 1 of water and 1 1 of methanol , with stirring, filtered off, and washed with methanol several times. Finally, the precipitate is dried for 8 hours/80°C/15 mmHg, followed by 8 hours/155°C/0,4 mmHg, until a constant weight is obtained.

Obtained are 31,4 g of very pale beige polymer.

The yield is: 98,3%.

The relative viscosity is 1,54.

Data on other polymers prepared in conformity with the specifications of Examples 2 and 3 is to be found in Table 1.

Abbreviations used in this Table are:

TGA: thermogravimetric analysis

DSC: differential scanning calorimetry.

The relative viscosity was determined as follows:

An 0,50% solution of the appropriate polymer in dimethyl acetamide (DMA) with 5% of lithium chloride is prepared and filtered.

The efflux times of both the solvent and the solution are measured under the same conditions in an Ubbelohde viscometer at 25,0°C.

efflux time of polymer solution irel- efflux time of solvent

Both in the aforesaid case and in the table η _τe ] was measured each time in an 0,50% solution.

Example 4

Preparation of polyamidimides using a polyamic acid prepared from p-t-BulPA-diamine and 3,3' ,4,4'-benzophenone.

Into a 1-1 three-necked flask fitted with a stirrer, a thermometer, a heating device, a distillation cooler, and an N2 apparatus are introduced:

15,0 g of dianhydride (0,466 moles)

18,7 g of p-t-BulPA-diamine (0,466 moles)

500 ml of dry NMP.

After they have been flushed with N2, the contents of the flask are kept at 65°C for 90 minutes, with stirring, to prepare the intermediary polyamic acid. Next, heating is continued slowly to a temperature of 175°C, at which cyclisation occurs, with water being split off which is distilled off immediately. After 90 minutes, the contents of the flask, which are dark in colour, are cooled and precipitated in a 60/40 mixture of water and methanol.

The yellowish brown precipitate is after-washed with methanol several times and finally dried for 8 hours/80°C/13 mmHg, followed by 8 hours/150°C/0,3 mmHg, until a constant weight is obtained.

Obtained are 29,6 g of yellow polymer.

The yield is: 90,9%. The relative viscosity is 1,27.

Example 5

Polyimide based on imido diacid chlorides and t-BulPA-diamine

Acid chlorides in which an imide structure is already present may be prepared as described by Bruma and Neamtu in Revue Roumaine de Chimie, 26_ 87 (1981). Using diamines according to the invention this method

permits the preparation of polyimides as described hereinafter for para-t-BulPA-diamine.

Into a 500-ml three-necked flask fitted with a stirrer, a thermometer, a cooler, a bubble gauge, and a nitrogen apparatus are introduced:

14,27 g of para-t-BulPA-diamine (0,0355 moles)

250 ml of dry NMP.

After the flask's contents have been dissolved, the dark brown solution formed is cooled to 2°C prior to 12,35 g of diacid chloride

(0,0355 moles) being added slowly. There is such a high increase in viscosity that an additional 200 ml of NMP have to be added during the reaction to enable stirring of the contents of the flask to be continued. After 1 hour of continued stirring the polymer solution is precipitated in 5 1 of methanol, with stirring, and filtered off.

The resulting dark yellow polymer is washed several times and finally dried for 8 hours/60°C/12 mmHg, followed by 8 hours/100°C/12 mmHg and finally 8 hours/150 ^c C/0,2 mmHg, until a constant weight is obtained.

Thus are obtained 25,18 g of yellow polymer.

The yield is 105% because the high viscous polymer contains encapsulated solvent.

The relative viscosity is 3,26.

For data on other polyimides prepared in conformity with the specifications of Examples 4 and 5 see Table 2.

TABLE 2 ι Pol yam I lmLdeS