DE2730248A1 - PROCESS FOR THE PRODUCTION OF A LINEAR POLYAMIDE FROM EPSILON-CAPROLACTAM AND NEW EPSILON-CAPROLACTAMPOLYMERES - Google Patents

Description

The melt polymerization of ε-caprolactam in the presence of water is well known and has been used on a large scale for many years. Such a polymerization is generally carried out at temperatures of about 180 to 300 ^° C. in the presence of about 0.05 to 10 mol of water per mol of lactam. As a rule, the polymerization takes place in a closed system under increased pressure until a larger proportion of the monomer has been converted into the polymer; the reactor is then opened and the water is allowed to distill off under atmospheric or reduced pressure. The polymerization mixture reaches an equilibrium at which it contains 10 to 12% by weight of material which can be extracted with methanol and which consists of unreacted caprolactam and oligomers of caprolactam. However, the presence of such monomers and oligomers is often undesirable when processing polycaprolactam in fibers, films or other molded articles. The polymerization of ε-caprolactam in the presence of amines is also known from US Pat. No. 3,555,114.

The subject of this invention is a process for the production of a linear polyamide from ε-caprolactam by heating a polyamide-forming cap ro Iac camo -

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Compound to a temperature of 180 to 300 ⁰ C in the presence of water and an amine. This process is characterized in that the reaction is carried out under elevated pressure in the presence of 0.6 to 5 mol%, based on the initially present compound, of a primary or secondary amine which boils at a temperature of at least 245 ° C. under atmospheric pressure , or a mixture thereof begins and that after a greater part of the polymerization has taken place, the system is depressurized and placed under an atmosphere of an inert gas or a vacuum for a time which is sufficient to reduce the proportions extractable with methanol to less than 5 wt% to reduce.

The reaction is preferably carried out under increased pressure until at least 75 % of the polymerization has occurred, with at least 85 % of the polymerization having taken place particularly preferably, which means that less than 15% by weight of the originally polymerizable material can be extracted with methanol.

The content of the polyamide extractable by methanol is determined as follows: 2 g of the polymer, which has been passed through an ASTM sieve No. 20 (sieve opening 0.84 mm), are extracted with boiling methanol for 90 minutes. The mixture is cooled and filtered. The filtrate is on a steam bath under a pressure of 10 mm Hg abs. 15 minutes after any visible liquid

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has disappeared. The previously weighed container is then dried for a further 10 minutes at 100 ^° C. in an air circulation oven. The container and residue are placed in a dryer and, after cooling to room temperature, weighed. Then the percentage of extractables is calculated.

Particularly suitable amines correspond to the formula

NH

in which R ₁ and R_ are each hydrogen, alkyl radicals, cycloalkyl radicals, hydroxyalkyl radicals, alkyl sulfide radicals, hydroxyalkyl sulfide radicals, amidoalkyl radicals, amidohydroxyalkyl radicals, aromatic radicals, ar-alkyl radicals, alkaryl radicals or carboxyalkylsulfide radicals, the various radicals being up to 18 carbon atoms. may contain. The amide can be a free amine or it can be in the form of an amine salt of an organic or inorganic acid. Preferably the amine is added before the polymerization is initiated, but it can also be added after a slight conversion of the lactam to the polymer has occurred.

The starting materials for the production of the ε-caprolactam polymer can only contain ε-caprolactam alone as a polymerizable component, but it is

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also possible to use the f-caprolactam in admixture with other materials that form linear polyamides, such as equimolar amounts of hexamethylenediamine and adipic acid or other well known polyamide-forming materials.

The invention also includes a new ε-caprolactam polymer, which is characterized by:

(1) a relatively high degree of heat resistance, so that the polymer shows an increase in έ-caprolactam content of no more than 50% when stored at 275 ° C in a nitrogen atmosphere for a period of 12 hours,

(2) a content of not more than 5% by weight of methanol extractable material in the condition by removing the polymer from the reactor without leaching or extraction,

(3) a content of less than 30 milliequivalents of carboxyl end groups per kg of the polymer,

(4) a relative viscosity of about 1.7 to 3 as determined using a 1 g solution of the polymer and 182.5 g of 96% strength sulfuric acid at a temperature of 25 ° C.

Preferably, the content of methanol-extractable material in these ε-caprolactam polymers in the state in which the polymer is removed from the reactor without leaching or extraction is less than 2 % by weight. Fibers made from these polymers show a high affinity for acidic dyes.

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The invention is explained in more detail in the following examples. All information about parts and percentages are weights, unless otherwise stated.

example 1

A mixture of the following ingredients was placed in a 45 ml Parr bomb: 23.75 g (0.21 mol) L- caprolactam, 1.25 g (0.0084 mol) 6-amino-4-thiahexanoic acid (6- Amino-4-thiacaproic acid) and 0.28 g (0.0156 mol) water. The bomb was closed and kept in the temperature range from 250 to 265 ^° C. for a period of 6 hours. At the end of the period of 6 hours, the bomb was vented to the atmosphere and maintained in the range of 250 to 26O ⁰ C for a further period of 6 hours. At the end of this period, the bomb and its contents were cooled and a solid polyamide plug was then removed from the bomb. The polymer was ground to a fine powder in the presence of dry ice. Then the polymer was heated, dried and weighed. 24.9 g of a slightly gray powder were obtained, which corresponds to a yield of 99.9%. The melting point was in a Fisher-Jones - determined apparatus at 210 ° to 215 ° C and the differential thermal analysis showed a melting point 209-218 ⁰ C on. The presence of caprolactam was not found in any of these determinations.

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Comparative experiment 1

The procedure of Example 1 was repeated except that the bomb was loaded with 24.87 grams (0.22 moles) of caprolactam, 0.13 grams (0.00084 moles) (0.4 mole percent) of 6-amino-4 -thiahexanoic acid and 0.45 g (0.025 mol) of water was charged. A solid polymer was obtained in 97% yield, which formed an almost white powder. An examination of the melting behavior in the Fisher-Jones apparatus indicated partial melting at 60 ^° C. and complete melting in the range from 180 to 200 ^° C. The differential thermal analysis indicated melting points at 59 to 65 ° C and 186 to 196 ° C. It can be seen that this product contained unpolymerized caprolactam.

Comparative experiment 2

The procedure of Example 1 was repeated using 25 g (0.22 mol) of caprolactam and 0.45 g (0.025 mol) of water. The polymer obtained showed in examining in a Fisher-Jones - apparatus that it completely melted partially at about 60 ⁰ C and at 200 to 215 ° C. It therefore contained unpolymerized caprolactam.

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Example 2

The procedure of Example 1 was repeated using 24.64 g (0.218 mol) of caprolactam, 0.36 g (0.00242 mol, 1.1 mol%) 6-amino-4-thiahexanoic acid and 0.41 g (0.227 mol) water were used. There was 25.1 g of the polymer obtained as a gray powder. A melting range of 212 to 222 ° C was determined in the Fisher-Jones apparatus, from which it can be seen that no unreacted caprolactam was present.

Example 3

The procedure of Example 2 was repeated except that a larger Parr bomb was used and each raw material was used in an amount 8.5 times that of Example 2. At the end of the period For 6 hours the reactor was placed under a vacuum varying between about 30 to 50 mm Hg. It a gray polymer powder was obtained in a yield of 97.3%, the melting range of which was 220 to 235 ° C, determined in a Fisher-Jones apparatus. This melting range indicates that there is no unreacted Caprolactam was present.

Part of the product was subjected to thermogravimetric analysis. The sample showed a weight loss of 4% up to a temperature of 21O ⁰ C. Upon further heating occurred no additional weight loss

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until decomposition of the polymer at a temperature above 400 ^° C. occurred. Samples of the polymers from Comparative Experiments 2 and 1 lost 38 and 32% by weight, respectively, on heating to 210 ^° C. This weight loss indicates the presence of caprolactam and its oligomers.

Example 4

The procedure of Example 3 was repeated except that instead of applying a vacuum a nitrogen flow was maintained in the vessel. The product was a thermogravimetric Subjected to analysis and showed a weight loss of 0.4% on heating to a temperature of about 210 ° C.

Example 5

A large number of amines have been used for the polymerization of ε-caprolactam. For this purpose, the procedure of Example 1 was repeated and in each case 24.86 g (0.220 mol) of caprolactam, 0.36 g (0.0198 mol) of water and 0.0022 mol (1 mol%) of the corresponding amine were used. In each case, the yields of the polymer, the melting points in the Fisher-Jones apparatus and the isothermal weight loss after 4 hours at 210 ^° C. at atmospheric pressure were determined. The results are shown in Table I below. Polymers that are weight

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Showing losses of less than 5% are considered to be products that did not contain caprolactam. Polymers with Weight losses of more than 10% by weight clearly indicate the presence of caprolactam. The last three trials are comparative trials.

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TABLE I.

ο cc 00 OC GO

AMTN Kp ^ ¹ ' POLYMER
YIELD Sp (2) ISOTHER
MIXER
WEIGHT
LOSS 6-amino-4-thiahexanoic acid > 300 ° C 97.3% 220-235 ° C 3.4% Methylenedianiline > 300 ° C
(2650/10 mm Hg) 99.7 % 220-235 ° C 4.0% Aminoethyl octyl
sulfide 318 ⁰ C
(126.5 ° C / 0.3 mm Hg) 100.0 % 220-235 ⁰ C. 4.3 % Diphenylamine 302 ° C 99.1 % 225-235 ⁰ C. 3.1% 2-aminoethyl-2'-hydroxy
ethyl sulfide 285 ° C
(128 ° C / 2.3 mm Hg) 99.9 % 225-235 ° C 3.3% Diethanolamine 269 ° C 96.1% 220-235 ⁰ C. 3.8 % Diisopropanolamine 248 ⁰ C 99.8% 218-238 ⁰ C. 4.8% Bisaminoethyl sulfide 238 ⁰ C 99.5% 217-23O ⁰ C 7.5 % Ethanolamine 174 ° C 98.0% 218-226 ⁰ C.
(small amount
at 60OC) 13.8 % no
(Comparison) »» W 96.0% 218-22O ⁰ C
(small amount
at 60OC) 13.9 %

(1) = bp - boiling point of the amine

(2) = Sp - melting point

u> ι

OC

Example 6

The procedure of Example 5 was repeated using different amines at a level of 1 mol% became. The obtained polymer was analyzed by gas chromatography to determine the proportion of the remaining Determine caprolactams. In most cases, the proportion of methanol extractable was also determined Components determined. The remaining polymer was weighed and the percentage of the original Sample was reported as a non-extractable polymer. The results are in the table II summarized.

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TABLE II

AMIN Kp v * / Sp **> % CAPRO-
LACTAM CH3OH
EXTRACT
BAR NOT EXTRA
AVAILABLE HERE
POLYMERES no 220-228 ⁰ C 8.8 % 15.5 7. 84.5% Diisopropylamine 33 ° C 214-23O ⁰ C 4.4 7o 10.5 % 89.5 7o Ethanol amine 175 ° C 218-235 ° C 4.2 7o 6.5% 93.5 7. aniline 188 ° C 218-235 ° C 4.7 7o 10.0 7o 90.0 7o Bisaminoethyl sulfide 238 ⁰ C 220-235 ⁰ C. 2.3 7o S 0 7 95.0 7o σ
<ο Diisopropanolamine 248 ⁰ C 225-235 ⁰ C. 2.0 7o 3.5 7. 96.5 7o OO
00 Diethanolamine 269 ° C 220-235 ⁰ C. 0 - 1.5% 0 - 1.5% 98.5-100 7o CO
O 2-aminoethyl-2'-hydroxy
ethyl sulfide 285 ⁰ C 225-235 ⁰ C. 1.0 7o ... (O Diphenylamine 302 ⁰ C ... (3) 1.5 7o (O Amino ethyloctyl sulfide 318 ⁰ C 220-235 ⁰ C. 0.6 7o 6-amino-4-thiahexane
acid 300 ° C 220-235 ⁰ C. 0 - 1% 0 - 1% 99.0 - 100 7o Taurine
(H NCH ₂ CH ₂ SO ₃ H) 30O ⁰ C ... 1.25 7o 1.5 7o 98.5 7o

(1) »bp - boiling point of the amine

(2) ^β Sp - melting point

(3) = not determined

OJ

ho OO

In Table II, the first five trials are comparative trials and the other experiments are in accordance with the invention. The ones for diethanolamine and 6-amino-4-thiahexanoic acid The test results given correspond to several tests.

Example 7

The procedure of Example 4 was repeated with the exception that some polymerizations without amine and two polymerizations with 1 mol% diethanolamine were carried out. The polymer obtained was examined for its content of ε-caprolactam and the proportion of constituents which could be extracted with methanol. The carboxyl end groups (CEG) and the amine end groups (AEG) were determined according to the method by W. Sweeny and J. Zimmerman, Encyclopedia of Polymer Science and Technology, 10, 542-543 (1969) Interscience. The relative viscosity (RV) was determined in 967 _o sulfuric acid. For this purpose, the viscosity of the acid and a solution of 1 g of the polymer in 182.5 g of the sulfuric acid was determined ^{at 25 ° C.} Relative viscosity is the viscosity of the acid plus polymer divided by the viscosity of the acid. The molecular weight (MW) was calculated according to the following equation:
[log MW = 0.301 log (11,300 RV - 23,000) + 3.27 δ]

The results are shown in Table III ^forth · 709883/0799

TABLE III

% CAPRO- % CH ₃ OH CEG LACTAM EXTRACTABLE AEG

RV

MG

none 8.0% 11.5%

Diethanolamine 1.1% 1.9% diethanolamine 1.9% 1.9%

40 - 60 2, 3-2.8 20000
29000 119 3, 9 36000 114 2, 7th 28000

The values given for the polymerization without amine correspond to several tests.

Example 8

The procedure of Example 4 was repeated with the exception that 1 mol% amine was used and that a nitrogen purge was carried out for a period of 6 hours at a reaction temperature ^{in the range from 275 to 280 ° C.} The results are summarized in Table IV.

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TABLE IV

Diethanolamine
Diethanolamine
Diethanolamine
Diethanolamine
comparison

REACTION- % CAPRO- % CH-OH RV TIME h LACTAM EXTRACTABLE

6 6 5 5 6

0.9 1.3 0.4 0.3 4.0

MG

2.8 29000 2.9 29000 2.7 28000 3.4 34000 2.8 29000

-J GJ CD K)

Example 9

This example contains information about tests according to the invention and about comparative tests.

For purposes of comparison, a commercially available poly-ε-caprolactam was examined for its ε-caprolactam content, the proportion of non-extractables and of those that could be extracted by methanol. A first sample, Sample A, was found to contain zero caprolactam and zero extractables. After two hours of heating at 250 ⁰ C, a portion of the sample A contained 1.5% <£ caprolactam and about 4.5% by methanol extractables. A sample of a polymer according to the invention (sample B), which had been prepared using 0.9% diethanolamine, contained 1 % ε-caprolactam and 1 % methanol extractables before heating. After heating a portion of the sample B for two hours at 250 ⁰ C, the content of £ -caprolactam had risen to about 1.5%, and extractables by methanol ingredients to 1.5%.

Another sample of a commercially available poly-C-caprolactam, Sample C, contained 0.06 % ε-caprolactam and 0.65 % methanol extractables. A portion of Sample C was heated 12 hours 250 ⁰ C. After heating, Sample C contained 1.9% £. -Caprolactam and 2.5 % methanol extractables.

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Another sample, Sample D, was prepared according to the invention by heating 339 g £ -caprolactam, 4.9 g water, 3.2 g of diethanolamine, and 12 hours in a Parr - bomb was heated to 250 ⁰ C. After 12 hours, the steam was released and the vessel was purged with nitrogen for a period of 10 hours, while the temperature was maintained at 250 ⁰ C. The polymer was cooled to room temperature. It contained 1.3% caprolactam and 1.5% methanol extractable components.

After heating a portion of the sample D at 250 ⁰ C for 12 hours, the sample 2.3 "L £ -caprolactam contained, the content while the total extractable by methanol shares at about 2% by weight was.

Parts of Samples C and D were compared by heating them to 275 ° C for 12 hours. Sample C at the end of this reference period contained 4.2 % ε-caprolactam and had 4% extractables and 95 "L non-extractables. Sample D after a similar heat treatment contained 1.9% ε -Caprolactam, 97.3% non-extractable material and 2.5% components extractable by methanol. It follows that the polymer according to the invention clearly has a greater heat resistance than the commercially available samples A and C. The ·

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This also applies when the polymer according to the invention has a larger proportion of extractable constituents contains before heat treatment.

Example 10

This example contains a further comparison between caprolactam polymers according to the invention and known caprolactam polymers.

For comparison purposes, Example 1 of US Pat. No. 3,555 was repeated twice using 1 mole percent and 8 mole percent diethanolamine, respectively. Two polymerizations according to the process of this invention were carried out under similar temperature conditions, the polymerization system being kept under pressure for 11 hours and then being purged with nitrogen for 11 hours (nitrogen purge). In the second attempt, the pressure was maintained for 11 hours and then purging was carried out at a vacuum of 50 mm Hg for about 11 hours (vacuum purging). In all samples, the polymer yield, the softening point by Fisher-Jones, the residual content of £ -caprolactam by gas chromatography and the isothermal weight loss was determined by heating for 4 hours at 210 ⁰ C at atmospheric pressure. The melt viscosity was determined at 233 ° C. by a method by PA Small, J. Polymer Science, 28, 233, (1959). It is assumed that the isothermal weight loss corresponds to the total loss of the ε-caprolactam originally present and the oligomers. When a range is given, it indicates

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that several attempts have been made. In the results summarized in Table V, the mole * Weight calculated according to the following equation:

log MW - 0.301 log ι + 3.2782 where η is the melt viscosity at 233 ° C.

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TABLE V

U.S. Patent 3,555 invention

OO 00 CJ

example

Nitrogen purging vacuum purging

Weight%
Diethanoiamine 0.9 % 6.9% Mole%
Diethanolamine 1.0 % 8.0% Polymer yield
Sp 99.4%
215-225 ° C 98.8 %
208-220 ⁰ C. remaining
Caprolactam 5.2% 2.9 % Isothermal *
Weight loss 7.3-7.7 % 6.8-7.1 % η 223OC 1870 ps. 620-730 ps. MG 15800 11400-12000

* - total value for caprolactam and oligomers \ β viscosity at 233 ⁰ C Poise MG - molecular weight 0.9 %
1.0%

96.5%
227-24O ⁰ C

0-1.0%

0-1.0 %
4480 ps
20400

0.9% 1.0%

96.1 % 220-235 ° C

0%

0 %

1780 hp 15500

κ>

CJ O K)

Comparative experiment 3

25 g of a commercial poly-i-caprolactam were mixed with 25 g of diethanolamine and heated 17 hours at 200 ⁰ C. The initial ε-caprolactam content of the polymer was 0.6% and was not changed by this treatment. The methanol extractable content was initially 0.65 % and was 7.5 % after heating. The initial content of oligomers was 0.6% and, after the heat treatment, 7.4 %.

A second sample of a poly-i-caprolactam, which initially 8.8% £ -caprolactam, 6.8% and 84.5% oligomers not containing extractables, was treated with monoethanolamine and heated for 15 hours 25O ⁰ C. As a result, the content of ε-caprolactam was reduced to 1.8% and of oligomers to 5.2%, while the content of non-extractable components rose to 90%. A second serving of this material was treated with diet hanoi and heated for 15 hours. This reaction mixture was sampled and heated for an additional 15 hours. The ε-caprolactam content was 2.3 and 4.7%, the oligomers 7.7 and 7.8% and the non-extractable components 93 and 87.5%. In each of these treatments, 1 mol% ethanolamine or diethanolamine was used.

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Example 11

Using the apparatus of Example 1, a variety of polymerizations were carried out. In one series of experiments (a), the starting materials were heated for 12 hours 25O ⁰ C under pressure and it joined heating for 10 hours at 275 ° C under nitrogen purge. In a second series of experiments, (b), the starting materials were heated for 6 hours at 25O ⁰ C and then heated under a nitrogen purge for 6 hours at 25O ⁰ C. The results are given in Table VI below.

TABLE VI yield Capro
lactam Polymer Methanol
extractable sample 84.7 7o 1, J / o 98.5 7o 1.5 7o (a) 0.9 70
Diethanolamine 90.0 7o 1.1 7o 98.3 7o 1.9 7o (b) 0.9 %
Diethanolamine 84.8 7o 0.8% 94.5 7o 5.8 7o (a) Comparison 92.9 7o 4.0% 93.0 tons 6.9 7o (a) Comparison 86.7 7o 6.0 7o 88.5 7o 11.5 7 " (b) comparison

As can be seen from these values, those made using 0.9 mole percent diethanolamine have Polymers not only have a low content of residual ε-caprolactam, but also a content of Fractions extractable by methanol of less than 2% by weight. 7 0 9883/0799

Example 12

In a 2 liter Parr bomb, 271.2 g (2.40 mol) of ε-caprolactam were polymerized with 3.9 g (0.22 mol) of water and various amounts of diethanolamine. The starting materials were weighed and placed in the bomb. The bomb was then purged with nitrogen for 10 minutes with stirring. The reactor was then closed while maintaining the nitrogen atmosphere, ^{heated to 250 °} C. and kept at this temperature for 6 hours with stirring. The reactor was then depressurized and purged with nitrogen for a period of 6 hours at 25O ⁰ C. At the end of this period, the bomb and its contents were cooled and the polymer tested for residual ^ -caprolactam, water extractables, and water non-extractables. The water extractables were determined generally in the same manner as the methanol extractables. A polymer passed through an ASTM No. 20 sieve (0.84 mm sieve opening) was extracted in boiling water at atmospheric pressure for 90 minutes. The values obtained with the water extraction agree with those obtained with the extraction with methanol. The results are shown in Table VII.

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TABLE VII Mon 1% , Diethanoi-
amine / capro
lactam Sp % Capro
lactam % extractable
(H ₂ O) % not-
extractable I. Gew7o diet
nolamine 1.2 1/85 225-24O ⁰ C 1.7 3.0 97.0 Oo
I. 1.1 * 1.0 1/100 227-24O ⁰ C 0-1.0 0-1.0 99.0-100 0.9 0.74 1/135 225-24O ⁰ C 1.2 2.5 97.5 0.7 0.54 1/185 220-240 ⁰ C. 4.5 6.0 94.0 0.5 0.32 1/310 220-232 ⁰ C. 4.4 9.5 90.5 0.3 0.16 1/629 220-227 ⁰ C 4.8 13.5 86.5 709883, 0.15 * Would result in lower levels of caprolactam and extractables
have resulted when the pressure stage has been longer than 6 hours Components
were. / 0799

If a pressure cycle of 6 hours and a flush cycle of 6 hours at 250 ° C are used, is the molar ratio of diethanolamine to c-caprolactam preferably between 1:75 and 1: 150, in particular between 1:75 and 1: 135.

Example 13

A 45 ml Parr bomb was charged with 11.3 g of 61-caprolactam, 0.1 g of diethanolamine, 7.2 g of adipic acid and 6.2 g of a 90% strength by weight solution of hexamethylenediamine in water. The bomb was flushed with nitrogen in order to remove the remaining oxygen and was then kept at 250 ^° C. for a period of 12 hours. The bomb was then released and its contents transferred to another vessel which was equipped with facilities for continuous nitrogen purging. ^{The reaction mixture was heated to 250 °} C. for 12 hours with continuous flushing with nitrogen. The product obtained weighed 17.74 g. The analysis for caprolactam showed a content of 1.1% and the polymer contained 1.5 % of materials which were extracted by water at 100 ^° C. in the course of 1.5 hours. The granulate was previously passed through an ASTM No. 20 sieve (mesh opening 0.84 mm). The polymer's 3.91 relative viscosity indicated a molecular weight of 38,000.

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Example 14

A 2 liter Parr bomb equipped with a stirrer and a line for nitrogen purging was mixed with 339 g of ε-caprolactam, 4.9 g of water and 6.9 g of the adduct of one mole of isopropanolamine with one mole £ -Caprolactam loaded. This product contained 80 to 90 % of N-2-hydroxypropyl-6-aminohexanamide of the formula:

CH ₃ 0

The reactor was closed and heated to 250 ° C. for 12 hours. It was then vented and a nitrogen flow was passed through the reactor for a period of 10 hours, while the temperature was maintained at 250 ⁰ C. After cooling, the analysis of the polymer obtained showed a content of 0.25% free ε-caprolactam, 1.0% proportions which can be extracted by methanol and a relative viscosity of 3.51, corresponding to a molecular weight of 35,400.

Example 15

The procedure of Example 14 was repeated except that 12.4 grams of N-2-hydroxypropyl-6-aminohexanamide was used. The resulting polymer contained 0.40 wt% free £ -caprolactam, 1.5 X extractable by methanol fractions and had a

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relative viscosity of 2.48, corresponding to a molecular weight of 24,700.

Example 16

A 45 ml Parr bomb was charged with 24.86 g £ -caprolactam, 0.36 g water and 0.0007 moles of each of the following amines: diethanolamine, bis (4-aminophenyl) methane, diisopropanolamine, 6- Amino-4-thiahexanoic acid, 2-aminoethyl-2'-hydroxyethyl sulfide, hydroxyethyl octyl sulfide, diphenylamine and N-2-hydroxypropyl-6-aminohexanamide. The bomb was flushed with nitrogen in order to remove the remaining oxygen and was kept at a temperature of 250 ^° C. for a period of 12 hours. The bomb was then depressurized and its contents transferred to another vessel which was equipped with means for continuously passing nitrogen through it. The reaction mixture was ^{heated to 250 °} C. for 12 hours under a continuous stream of nitrogen. The product obtained had a methanol extractable content of 2%, a relative viscosity of 1.92, corresponding to a molecular weight of 17,700, determined using the following equation:

log MW x = 0.031 (log 2.990 RV - 4080) + 3.2782

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In all of the foregoing examples of the invention, the number of amine end groups in the polyamide was at least twice as large as the number of carboxyl end groups. The carboxyl end groups were at a level of less than 30 milliequivalents per kg of polymer.

In a similar way, caprolactam can be converted into a polymer polymerize with other amines with a low content of free caprolactam. Examples are Benzylphenylaniline, ortho-, meta- or para-benzyltoluidine, Dicyclohexylamine,!, L'-diphenylethylamine, 2,2'-diphenylethylamine, Di-n-octylamine, di-2-octylamine, 3-hydroxydiphenylamine, 4-hydroxydiphenylamine, di-2-tolylamine, Di-3-tolylamine, di-4-tolylamine, ethyl-2-tolylamine, Ethyl-2-tolyl-2-hydroxyamine, l-naphthyl-4-tolylamine, and 2-naphthyl-2-tolylamine.

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Claims (10)

Patent claims: 1 / Process for the preparation of a linear polyamide from £ caprolactam by heating a polyamide-forming caprolactam at a temperature from 180 to 300 ⁰ C in the presence of water and an amine, characterized in that the reaction under elevated pressure in the presence of 0.6 to 5 mol%, based on the initially present compound, of a primary or secondary amine which boils under atmospheric pressure at a temperature of at least 245 ° C, or a Mixing of these begins and that, after a greater part of the polymerization has taken place, the system is depressurized and placed under an atmosphere of an inert gas or a vacuum for a time which is sufficient to reduce the proportions that can be extracted with methanol to less than 5 _r ~ . ₄ 709883/0799% by weight. ORIGINAL / NSPECTED 2. The method according to claim 1, characterized in that the amine is diethanolamine. 3. The method according to claim 1, characterized in that the amine is bis (4-aminophenyl) methane. 4. The method according to claim 1, characterized in that the amine is diisopropanolamine. 5. The method according to claim 1, characterized in that the amine is 6-amino-4-thiahexanoic acid. 6. The method according to claim 1, characterized in that the amine is a hydroxyalkyl sulfide amine. 7. The method according to claim 6, characterized, that the amine is 2-aminoethyl-2'-hydroxyethyl sulfide. 8. The method according to claim 1, characterized in that the amine is the adduct of one mole of isopropanolamine with one mole of 6-caprolactam. 709883/0 7 9. The method according to claim 1, characterized in that the amine is a mixture of 2 or more of the compounds diethanoiamine, bis (4-aminophenyl) methane, Diisopropanolamine, 6-amino-4-thiahexanoic acid, 2-aminoethyl-2 * -hydroxyethyl sulfide, hydroxyethyl octyl sulfide, Is diphenylamine and N-2-hydroxypropyl-6-aminohexanamide. 10. A 6-caprolactam polymer, marked by (a) a relatively high degree of heat resistance, so that the polymer can be stored at 275 ° C in a nitrogen atmosphere for a period of 12 hours an increase in the ε-caprolactam content of not more than 50% shows (b) a content of not more than 5% by weight of methanol extractable material in the condition; by removing the polymer from the reactor without leaching or extraction, (c) a salary of less than 30 million equivalents Carboxyl end groups per kg of polymer, (d) a relative viscosity of about 1.7 to 3, determined using a solution of 1 g of the polymer and 182.5 g of 96% sulfuric acid at a temperature of 25 ^° C., this polymer showing little tendency to evaporate caprolactam when it is spun into a fiber and the number of amine end groups of the polymer is at least twice as high as the number of carboxyl end groups. 709883/0799