DE1620925C - Process for the production of poly amide molded bodies - Google Patents

Description

The invention relates to a method of manufacture of polyamide moldings by polymerizing anhydrous lactams with more than 6 ring members or mixtures thereof at 100 to 270 ° C. by means of alkaline catalysts in the presence of a cocatalyst.

It is known that the polymerization of anhydrous lactams initiated by the addition of alkali metals is accelerated can be when diacylimides, esters of organic and inorganic acids, carboxylic acid halides and anhydrides, carboxylic acid cyanamides, isocyanates, isothiocyanates, ureas, monocarbodiimides, Thioureas, urethanes, guanidines, sulfenic acid derivatives, N-halolactams, carbamic acid esters, organic carbonates, perhalogenated ketones, lactimethers or substituted triazines are added (see, for example, U.S. Patents 3,015,652, 3,018,273 and 3,028,369, as well as the British Patent specification 863 859, the Austrian patent specification 218 744 and the German Auslegeschrift 1 067 591). With such additives, the polymerization can also be carried out at temperatures which are lower are than the melting point of the polyamide concerned, so that a solid product is obtained which has assumed the shape of the reaction vessel.

Known catalysts for lactam polymerization are, for. B. alkali lactams and substances with Lactams form such lactam-metal compounds, e.g. B. alkali metal alkyls, alkali metals, alkali hydrides, Alkali hydroxides, alkali carbonates and Grignard compounds such as alkyl magnesium bromide.

The concentration of these catalysts is 0.1 to 1.5 mole percent. However, higher concentrations are also available from 1.5 to 5 mol percent possible.

The molded or cast parts produced directly from the monomers consist of linear structures Polyamides and have the known disadvantages, such as stress corrosion cracking, in use Notched impact strength (especially when dry) and great swellability in certain organic Solvents. They are in the usual solvents, such. B. in concentrated sulfuric acid, soluble.

It is also known from the laid-out documents of the Belgian patent 647 513, in polymerization of lactams by means of alkaline. Catalysts to use polyisocyanates as cocatalysts, polyamides with high notched impact strengths are obtained.

The aim of the invention is a process for the polymerization of lactams using alkaline catalysts, which avoids the known disadvantages and the production of void-free polyamides with a cross-linked structure and particularly good properties also allowed when the monomers are polymerized in molds directly to form large moldings of the desired dimensions. This The aim is achieved by the method according to the invention.

The process according to the invention is characterized in that the cocatalyst is an aromatic Polycarbodiimide of the formula

N = C = N-

in which R is an alkyl group having 1 to 4 carbon atoms and η is a number above 2, is used.

The polymerization temperature can be in the temperature range of 100 to 270 ^° C. known for the anionic polymerization of lactams. A temperature of 140 to 160 ° C. is preferably used.

The concentration of the cocatalyst can vary within wide limits. Usually amounts to it is 0.2 to 5.0 percent by weight, preferably 0.3 to 1.5 percent by weight (based on the Lactam).

Not only the known lactams, e.g. B. caprolactam, oenantblactam, Caprylic lactam, methylcaprolactam and laurolactam, but also, for the production of mixed polyamides, Mixtures of two or more of the abovementioned lactams can be used.

The polymerization mixture can contain light and heat stabilizers, matting agents, inert plasticizers, soluble dyes and color pigments, finely divided metals, glass and asbestos fibers; or fillers are added. , Y:

The process according to the invention can be carried out in a simple manner by mixing the cocatalyst and the catalyst with the lactam and heating this mixture to the polymerization temperature In

be performed. However, the cocatalyst is preferably added while dissolving in the molten material Lactam at polymerization temperature after the addition of the catalyst. The polymerization time is, depending on the cocatalyst concentration, a maximum of 1 to 2 hours. This creates a Polyamide molding that takes on the dimensions of the casting mold. A small shrinkage makes this easier Remove. The polymerization itself is preferably carried out with the exclusion of moisture and atmospheric oxygen. If the surface of the polyamide molding is mechanically reworked, then these are Protective measures superfluous.

The polyamides obtained represent very high quality plastics that are insoluble in concentrated sulfuric acid are and have an extremely high notched impact strength, and are as a result of their cross-linked Structure particularly resistant to mechanical, thermal and chemical stress. Even with very large dimensions, they are free of voids and stress, since the inventive Use of a polycarbodiimide as a cocatalyst in the polymerization of lactams by means of alkaline catalysts this polymerisation does not proceed as quickly and so local overheating be avoided. Such slower polymerization is also permitted in the monomer casting process more convenient filling of several forms in

know time intervals. As comparative tests have shown, these advantageous phenomena occur when using polyisocyanates as cocatalyst ^ n does not occur in the polymerization of lactams by means of alkaline catalysts. Here sets immediately rapid polymerization; the entire heat of polymerization is released in a few minutes, while in the process according to the invention the heat of polymerization over a longer period Period is given.

The monomer content corresponds to the normal temperature equilibrium and is 0.3 to 6 percent by weight.

Since the low shrinkage allows the production of dimensionally correct parts, this process can be used for Manufacture of wheels, rollers, tubes, profile parts, rods or slide rails are used will.

If the polymerization takes place above the melting point instead, the process can also be carried out continuously in a known manner.

The following examples serve to illustrate the invention.

example 1

To 10 kg of caprolactam at 150 ⁰ C 0.42 mole percent Äthylmagnesiumbromid added (as 40% solution in diethyl ether). After the solvent has evaporated, 1.15 percent by weight of poly (o, o-dimethyl) -ρ-phenylenecarbodiimide is added. In a heating cabinet at 150 ^° C., the polymerization begins after 40 minutes. After 2 hours the polymer has assumed the shape of the mold. The polycaprolactam obtained is insoluble in concentrated sulfuric acid.

Test specimens that were mechanically worked from the block had, according to DIN 53 453, a non-measurable, high notched impact strength (> 500 cm · kg / cm ² ).

Production of the cocatalyst

The poly - (o, o - dimethyl) - ρ - phenylenecarbodiimide can be prepared as follows: 100 parts by weight of 2,6-dimethylbenzene-1,4-diisocyanate are stirred for 3 hours at 200 ° C. with 2 parts by weight of lead naphthenate, with strong CO ₂ development occurs. The residue obtained is insoluble in the usual solvents and can be used directly as a cocatalyst.

Example 2

10 kg of caprolactam are polymerized with the aid of 0.4 percent by weight cocatalyst from Example 1. At an oven temperature of 150 ⁰ C a polyamide block is obtained from the dimension of the mold after 2 hrs of polymerization. The relative viscosity cannot be measured because the polyamide is insoluble in concentrated sulfuric acid. The notched impact strength according to DIN 53 453 cannot be measured either (> 500 cm kp / cm ² ).

B e i s ρ i e 1 3

A mixture of 16 kg of caprolactam and 4 kg of laurolactam is heated to 145 ° C. in a ring shape made of sheet aluminum in a heating cabinet. 0.5 mol percent of the sodium salt of caprolactam and then 0.8 percent by weight of poly (0,0 '- diisopropyl) - ρ - phenylene carbodiimide are added to this lactam melt. The mixed polyamide obtained is insoluble in concentrated sulfuric acid and has a notched impact strength of over 500 cm kp / cm ² . A product with the same properties can also be obtained by using poly- (o, o'-dipropyl) -p-phenylenecarbodiimide) as cocatalyst

- sator.

, Production of the cocatalyst

100 parts by weight of 2,6-diisopropylbenzene-l, 4-diisocyanate are stirred at 200 ⁰ C with 2 parts of lead naphthenate 3 hours ,, wherein eine'starke C (^ evolution occurs. The residue obtained is insoluble in the usual solvents and is used directly as a cocatalyst.

Unexpected technical advantages of the method according to the invention over the known methods can be seen from the following comparison tests:

Comparative experiment 1

0.2 mol percent of the sodium salt of caprolactam and 0.4 mol percent of diisopropylcarbodiimide (Ber. 74.1285 [1941]) are added at a polymerization temperature of 175.degree. C. to 1 mol of melted caprolactam. The linear polyamide obtained has a viscosity number (η) of 1.88.

If 0.4 mol percent dicyclohexylcarbodiimide (Ber. 74, 1285 [1941]) is used as the cocatalyst, a polyamide with a viscosity number (η) of 2.0 is obtained.

The polyamide moldings obtained according to this example have, in the dry state, a notched impact strength (according to DIN 53 453) of 3 to 4 cm kp / cm ² .

When using monomeric carbodiimides, the measured solution viscosity is the one obtained Polyamide as a function of the concentration of carbodiimide used; i.e. for larger quantities a lower degree of polymerization is achieved.

45 Comparative experiment 2

2.26 kg (20 moles) of caprolactam were melted under nitrogen in a glass flask and heated to 15O ⁰ C. Then the catalyst is added (9 g NaH dispersion in paraffin oil [50:50]).

Sodium caprolactam is formed into caprolactam with the elimination of hydrogen. Then takes place the addition of the cocatalyst, with a polyisocyanate in one experiment and a polyisocyanate in another experiment a polycarbodiimide is used.

55 Experiment 2 a

60 7.2 g polyisocyanate (0.055 mol) with a molecular weight of 132 (based on one unit)

This polyisocyanate has the formula

NCO

Experiment 2 b

8.0 g polycarbodiimide (0.055 mole)

with a molecular weight of 145

(based on a unit).

This polycarbodiimide has the formula

CH,

N = C = N-

CH,

The polymerizable mixtures were poured into a 5-1 beaker and immediately placed in a heating cabinet (temperature: 155 ° C.). A thermocouple was placed in the middle of each of the two mixtures. The temperature profile provided information about the rate of polymerization and the heat of polymerization and crystallization released. When the polyisocyanate was used as cocatalyst, the entire heat of polymerization and crystallization was released in about 7.5 minutes, with about 210 ^° C. being reached. With the polycarbodiimide, the same temperature was only reached after about 90 minutes; the temperature-time curve showed a 'continuous course.

The following results were obtained:

When using polycarbodiimide, polymerization and heat treatment run side by side, so that the large polyamide parts obtained in this way are more free from tension. For example, it is known that extrudates made from PA granulate can only be made somewhat stress-free ^{by long-term tempering at 130 to 170 ° C.}

The blocks obtained after the experiments described above were on after cooling Room temperature parted. The block polymerized with polyisocyanate had a large number fei η distributed voids, while the polymer obtained with polycarbodiimide was flawless.

Claims (2)

'Patent claims: 1. A process for the production of polyamide moldings by polymerization of anhydrous lactams with more than 6 ring members or their mixtures at 100 to 270 ⁰ C by means of alkaline catalysts in the presence of a cocatalyst, characterized in that the cocatalyst is an aromatic polycarbodiimide of the formula N = C = N- Start of polymerization ... Solidification of the mass End of the polymerization ..... With polyisocyanut Min. 2.5 ■
7 to 8 With polycarbodiimide Min. about 20
45
90 In in which R is an alkyl group having 1 to 4 carbon atoms and η is a number above 2, is used. 2. The method according to claim 1, characterized in that 0.3 to 1.5 percent by weight Cocatalyst, based on the lactam to be polymerized, can be used.