Jan., 19511 HASLAM AND CLASPER 33 Some Further Observations on the Analysis of Nylon Type Polymers BY J. HASLAM AND M. CLASPER Methods have been devised for the analysis of mixtures of hexamethylene diamine dihydrochloride and 6-amino caproic acid hydrochloride that may be obtained on the application to certain types of nylon polymer of the methods of hydrolysis previously reported by the authors. The method for the determination of the 5-amino caproic acid hydrochloride is based on titration with standard alkali, phenolphthalein being used as indicator; the method of determination of hexamethylene diamine dihydrochloride depends on the passage of a solution of the mixed hydrochlorides through a column of Amberlite IRA 400 resin and titration of the hexamethylene diamine passing through the column with standard alkali, methyl orange being used as indicator.Samples of polymer produced ( a ) by the interaction of hexamethylene diisocyanate and 1 : 4-butanediol and ( b ) from w-amino undecanoic acid have been submitted to hydrolysis by hydrochloric acid solution and the hydrolytic products examined along the lines laid down for nylon type polymers in the previous paper. As a result of our work on the examination of nylon and related polymers,l it seemed to us that methods for the examination of mixtures of hexamethylene diamine dihydrochloride and 5-amino caproic acid hydrochloride would be extremely useful. THE RESOLUTION OF MIXTURES OF HEXAMETHYLENE DIAMINE DIHYDROCHLORIDE W'e have been able to show that 5-amino caproic acid hydrochloride may be readily determined in mixtures of 5-amino caproic acid hydrochloride and hexamethylene diamine dihydrochloride by titration of the aqueous solution of the hydrochlorides with 0-1 N sodium hydroxide solution, phenolphthalein being used as indicator.Known weights of the two hydrochlorides were dissolved in 20ml of water and the solution was titrated with 0.1 N sodium hydroxide, phenolphthalein being used as indicator. One millilitre of 0.1 N sodium hydroxide is equal to 0.01675 g of 5-amino caproic acid hydrochloride. The results are shown in Table I. AND &AMINO CAPROIC ACID HYDROCHLORIDE TABLE I RECOVERY OF &AMINO CAPROIC ACID HYDROCHCORIDE FROM SYNTHETIC MIXTURES WITH HEXAMETHYLENE DJAMINE DIHYDROCHLORIDE Composition of mixture A I -l Hexamethylene diamine 5-Amino caproic dih ydrochloride, acid hydrochloride, g g nil 0.5014 0.1512 0.3494 0.2512 0.2496 0-3496 0- 1489 0.5021 nil 5-Amino caproic acid hydrochloride recovered, g 0-4989 0.3469 0.2479 0.1503 0.0017 Further, a method has been devised for the determination of hexamethylene diamine dihydrochloride in mixtures of hexamethylene diamine dihydrochloride and 5-amino caproic acid hydrochloride.The method is based on the passage of an aqueous solution of the hydrochlorides through a column of Amberlite IRA 400 ion-exchange resin. We are indebted to Dr. K. W. Pepper of the Chemical Research Laboratory, Teddington, for the suggestion that this resin might prove to be useful for our purpose. The hexamethylene diamine passing through the column is finally titrated with 0.1 N hydrochloric acid solution, methyl orange being used as indicator.34 [Vol.76 ION-EXCHANGE METHOD- The method is as follows: 10 g of Amberlite IRA 400 dried at 100" C are mixed into a slurry with water and transferred to an ion-exchange column, Fig. 1. The excess of water is then run off until the resin in the column is just covered with water. At all times care must be taken to ensure that the liquid in the column is not drained beneath the head of the ion-exchange resin: the passage of air into the resin impairs the absorption capacity. The Amberlite IRA 400 resin is activated by passing about 800 ml of N sodium hydroxide through the column at a rate of about 2 to 3 ml per minute. The apparatus and the resin are then washed with water until 50 ml of effluent give a titration of less than 0.1 ml of 0.1 N hydrochloric acid, methyl orange being used as indicator.Normally, about 250 ml of wash water are sufficient. The ion-exchange column. is now ready for use; it must be used immediately after the water washing has been completed. About 0.5 g of the mixed hydrochlorides is, weighed, dissolved in 50 ml of water and the solution transferred to the separating funnel, A. This solution is allowed to pass through the column at a rate of 2 to 3 ml per minute. The separating funnel and sides of the column are carefully washed down with water, the washings being allowed to pass through the column. When this washing has been completed the separating funnel is filled with water, which is allowed to pass through the column at a steady rate of 2 to 3 ml per minute.The first 150 ml of effluent are collected and titrated with 0.1 N hydrochloric acid, methyl orange being used as indicator, and each succeeding 50 ml of effluent are collected and similarly titrated until the titre is less than 0.1 ml of 0.1 N hydrochloric acid. The combined titres are then calculated tcl a percentage of hexamethylene diamine dihydrochloride in the mixture by means of the following factor- HASLAM AKD CLASPER: SOME FURTHER OBSERVATIONS ON THE 1 ml of 0.1 N hydrochloric acid = 0.009457 g of hexamethylene diamine dihydrochloride Application of the above method to five mixtures of hexamethylene diamine dihydro- chloride and &amino caproic acid hydrochloride gave the results shown in Table 11.The titres of the successive volumes of liquid passing through the columns are also shown. TABLE I1 RECOVERY OF HEXAMETHYLENE DIAMINE DIHYDROCHLORIDE FROM SYNTHETIC MIXTURES WITH &AMINO CAPROIC ACID HYDROCHLORIDE MIXTURES TAKEN- Col. ;1 Col. 2 Col. 3 Col. 4 Col. 5 Hexamethylene diamine dihydrochloride, g 0.5013 0.3510 0.2520 0-1502 nil 5-Amino caproic acid hydrochloride, g. .. nil 0.1480 0.2471 0.3490 0.4997 TITRE, ML OF 0.1 N HYDROCHLORIC ACID- Effluent, ml: 150 .. .. .. .. . . 51.86 35.70 25.52 15.12 0.23 50 . . .. .. .. . . 0.29 0.28 0.18 0.08 0.06 50 . . .. .. .. . . 0.23 0-18 0.10 50 . . .. .. .. . . 0.06 0.08 0.06 Tptal titre, ml . . .. I . . . 52.44 36.24 25.86 15.20 0.29 Hexamethylene diamine added, g 0,5013 0.3510 0.2520 0.1502 nil dihydrochloride { found, g 0.4958 0.3427 0.2445 0.1437 0.0027 Although the results for the recovery of hexamethylene diamine dihydrochloride are slightly low, we have found that the above method when used in conjunction with the direct titration method for the determination of 5-amino caproic acid hydrochloride, p.33, is extremely valuable in the examination of the hydrolysis products of interpolymers of nylon 66, 610 and 6. NOTES ON THE ION-EXCHANGE METHOD- (i) The volume of sodium hydroxide solution used to generate the active base from the Amberlite IRA 400 is extremely large, but in our experience the use of smaller volumes of sodium hydroxide solution or faster rate of passage of the sodium hydroxide solution through the column is accompanied by a reduction in efficiency.(ii) Other proprietary resins have been tried in place of Amberlite IRA 400, but without success. When De-Acidite F was used, the removal of excess alkali by washing with water after the initial activation was much more difficult than when Amberlite IRA 400 was used. When an aqueous solution of hexamethylene diamine dihydrochloride was passed through anJan., 19511 ANALYSIS OF NYLON TYPE POLYMERS 35 activated Amberlite IRA 400 column, the recovery of hexamethylene diamine in the effluent was almost theoretical. When the corresponding experiment was carried out with De-Acidite F, although the recovery of hexamethylene diamine in the effluent was reasonably in agree- ment with theory, it was extremely difficult to reach finality in the process. When experiments were carried out by passage of aqueous solutions of 5-amino caproic acid hydrochloride through activated columns of Amberlite IRA400, the proportion of base in the effluent titratable to methyl orange indicator was negligible.With the De-Acidite F, however, successive volumes of effluent gave distinct positive titrations to methyl orange indicator. These titrations were of the order of 1.5 ml of 0.1 N hydrochloric acid per 50 ml of effluent. EXAMINATION OF POLYMER PRODUCED BY THE INTERACTION OF HEXAMETHYLENE The polymer produced by the interaction of hexamethylene diisocyanate and 1 : 4- butanediol appears to be known to the trade as Igamide “U” or Perlon.2 The sample melted at 179” C and had a nitrogen content (macro-Kjeldahl) of 10.58 per cent.The infra-red spectrum was as shown in Fig. 2a. DIiSOCYANATE AND 1 : 4-BUTANEDIOL Fig. 2. Infra-red spectra of polymers (a) produced by the interaction of hexamethylene diisocyanate and 1 : 4-butanediol, and ( b ) produced from w-amino undecanoic acid Considerable attention has been paid to the identification of the products of hydrolysis of this type of polymer, and the following experiments were carried out. Experiment 1-The sample, 5 g, was hydrolysed with 200 ml of 50 per cent. v/v hydro- chloric acid for 60 hours. The hydrolysis product had the characteristic odour of a chlorinated hydrocarbon. A Dean and Stark apparatus was then fitted to the flask and the solution was boiled for 2 hours. At the end of this time a small amount of immiscible liquid was collected at the bottom of the graduated side arm.This part of the apparatus was dis- connected when cool, and the upper liquid in the graduated arm was removed by a suction pipette. The recovered liquid remaining in the Dean and Stark apparatus was washed36 HASLAM AND CLASPER: SOME FURTHER OBSERVATIONS ON THE [Vol. 76 successively with about 2 ml of water until the wash1 water was neutral to litmus; five washings were required. The washed liquid was transferred to a 2-ml centrifuge tube, a small amount of sodium sulphate (anhydrous) was added and the whole allowed to stand overnight. The dried liquid had a boiling-point of 154.5" C, a refractive index of 1.4556 and a chlorine content of 55.25 per cent. These figures were consistent with the material being 1 :4-dichlorobutane, characteristic figures for which are : boiling-point, 155.0" C, refractive index at 20" C, 1.4566, and chlorine eontent, 55-84 per cent.Experiment 2-In a second experiment 15 g of the sample were hydrolysed with 600 ml of 50 per cent. v/v hydrochloric acid in the apparatus shown in Fig. 3. As the hydrolysis proceeded, a layer of immiscible liquid began to accumulate in the side arm. The liquid in this side arm was run off from time to time arid separated in a separating funnel. The E 0 u1 T Sintered Glass i / i 1 n Fig. 1. Ion-exchange column Fig. 3. First apparatus for hydrolysis upper layer was reserved and the lower layer returned to the hydrolysis flask. After about 24 hours, approximately 26ml of upper layer had been obtained, and this liquid was dried overnight with anhydrous potassium carbonate.The dry liquid was then distilled in a small side-arm distillation flask. Three fractions were collected of the following approximate boiling ranges and amounts- Boiling range, Volume, " c ml Fraction 1 . . .. .. 63 to 65 0.6 Fraction 2 . . .. .. 65 to 70 1.3 Fraction 3 . . .. . . Above 70 (boiled 0.6 mainly at 160" C)Jan., 19511 ANALYSIS OF NYLON TYPE POLYMERS 37 A micro-analytical examination of these fractions gave the following carbon, hydrogen and chlorine figures- Carbon, Hydrogen, Chlorine, % % Fraction 1 . . .. .. 64.0 9-3 1.4 Fraction 2 . . .. .. 65.4 9-8 0.3 Fraction 3 . . .. .. 49.8 7-2 24.4 0' /O The figures for carbon, hydrogen and chlorine contents of the fractions pointed strongly to the presence of a large proportion of tetrahydrofuran in fraction 2 and a rather smaller proportion in fraction 1.Tetrahydrofuran was known to oxidise with nitric acid to give succinic acid, and fractions 1 and 2 were therefore oxidised with nitric acid, authentic tetra- hydrofuran being oxidised similarly as a control, in the following manner. Half a millilitre of water and 0.2 ml of the fraction were taken in a test tube and cooled in ice-cold water. The cold liquor was added to 2 ml of ice-cold concentrated nitric acid and the mixture left standing overnight in a beaker of ice and allowed to come slowly to room temperature. The nitric acid solution was evaporated to dryness on the water-bath in a tared evaporating basin and the residue moistened once or twice with water previous to re-evaporation. After drying at 100" C for 1 hour, a white crystalline residue was obtained which had the following properties- Fraction 1 Fraction 2 Tetrahydrofuran Melting-point, O C .. . . 182 to 187 185 to 188 185 to 187 Equivalent weight . . .. 59.2 59.5 59.6 The figures for succinic acid are- Melting-point, 185" C Equivalent weight, 59.05 As a result of the above experiment we concluded that the hydrolysis of this type of polymer with 50 per cent. v/v hydrochloric acid under the above conditions produced an appreciable proportion of tetrahydrofuran. At the same time we concluded from Experiment 1 that when the action of hydrochloric acid was prolonged, 1 :4-dichlorobutane could also be isolated from the hydrolysis products. Experiment 3-A further 1 g of the sample was hydrolysed for 60 hours with 50 per cent.v/v hydrochloric acid, and the aqueous solution was filtered and the filtrate was taken to dryness on a water-bath. The residue was then purified by dissolving in alcohol, boiling with animal charcoal, filtering and re-precipitating by adding acetone to the cold alcohol solution. This procedure was repeated three times and the precipitate finally obtained was dried under vacuum. The material so obtained melted at 252" C, and micro-analytical examination gave the following ultimate analyses: carbon, 38.15 per cent. ; hydrogen, 9.5 per cent. ; nitrogen, 14-6 per cent.; chlorine, 37.60 per cent. Corresponding figures for hexamethylene diamine dihydrochloride are as follows : melting- point, 253" C; carbon, 38-10 per cent.; hydrogen, 9.6 per cent.; nitrogen, 14.81 per cent.; chlorine, 37.49 per cent.We now sought to use the information we had obtained as a result of the three experiments to develop a test which could be applied in a simple way to samples suspected to be of this type of polymer. Such a test is described below as applied to 1 g of a sample. One gram of the polymer was hydrolysed by boiling with 20ml of 50 per cent. v/v hydrochloric acid in the apparatus shown in Fig. 4. There was little visible change in the appearance of the dispersion during the first 24 hours of boiling. It was necessary to shake the flask and contents from time to time so that the whole of the sample was removed from the sides of the flask and subjected to hydrolysis.After 24 hours the particles in suspension appeared to become much finer and this process continued. After about 48 hours the mixture appeared to clear to a certain extent and the hydrolysis was then continued for a further period of 12 hours, that is, a total of 60 hours. At the end of this period the solution was a pale brownish colour and contained a small amount of material in suspension. After hydrolysis for about one hour the liquid in the condenser and siphon began to assume an oily appearance, and after three hours a distinct layer of oily liquid was visible at point A, Fig. 4, above the aqueous layer in the siphon. At this stage, i.e., on the appearance of an oily upper layer in the siphon, the liquid in this tube, including the aqueous layer,38 HASLAM AND CLASPER: SOME FURTHER OBSERVATIONS ON THE [Vol.76 was withdrawn by means of a capillary pipette. After hydrolysis for a further 3 hours a second oily upper layer was formed in the siphon and this also was withdrawn and added to the original distillate. The combined distillates were cooled in ice-cold water and added to 2 ml of ice-cold concentrated nitric acid contained in a test tube. The test tube was then n 85 mrn. I - 7 rnm. I 160 mm. -A - - - Fig. 4. Second apparatus for hydrolysis Fig. 5. Modified apparatus for hydrolysis All dimensions in millimetres placed in a beaker containing iced water and the whole left overnight. As the ice melted there was a gradual increase of temperature until. room temperature was reached and also a gradual increase in colour of the solution from colourless to yellowish-green. On the following morning the nitric acid solution was evaporated to dryness on the water-bath and the test was completed as described under Experiment 2, p.37. The white crystalline residue so obtained weighed 0.0763 g, had a melting-point of 185" to 187" C and an equivalent weight of 59.4: as determined by semi-micro titration in alcoholic solution with 0.02 N sodium hydroxide and phenolphthalein indicator. The pale brownish coloured hydrochloric acid solution from the hydrolysis was filtered through a tared sintered glass crucible No. 1, G:3, and the residue well washed with water prior to drying at 100" C. The hydrochloric acid filtrate was evaporated to dryness in a tared evaporating basin and dried t o constant weight at 100" C.This residue weighed 0.7258 g and had a melting-point of 248" to 254" C and a chlorine content of 36.6 per cent. We have shown that the principle of the above test can he applied to as little as 0.5g of sample by use of the modified apparatus shown in Fig. 5. The dry residue weighed 0.0170 g.Jan., 19511 ANALYSIS OF NYLON TYPE POLYMERS 39 EXAMINATION OF POLYMER PRODUCED FROM w-AMINO UNDECANOIC ACID Within recent months we have been called upon to examine several samples of a nylon- type material that has been proved to consist of the so-called polymer "R".3 This polymer has also been described as type 11 nylon, i.e., the polymer made from w-amino undecanoic acid by the removal of the elements of water. The infra-red spectrum of the polymer is shown in Fig.2b. We have found that this polymer is attacked by 50 per cent. v/v hydrochloric acid, and when 0.5 g of an authentic sample of the polymer was boiled under reflux for 40 hours with 20ml of 50 per cent. v/v hydrochloric acid and the solution subsequently cooled, a crystalline deposit was formed. The hydrolysis product possessed a characteristic odour. The hydrolysis product was transferred with the aid of about 20 ml of water to the apparatus for continuous ether extraction1 and the solution extracted with ether for approximately 6 hours. The ether extract was evaporated to dryness and the residue dried at 100" C and weighed. The solution of the hydrochlorides was evaporated to dryness, dried to constant weight at 100" C and weighed. The melting-point and chlorine content of the residual hydrochlorides were determined, and the equivalent weight was calculated from the results of the titration of the hydrochlorides with standard alkali, phenolphthalein being used as indicator.determined, as well as the melting-point. In addition, carbon, hydrogen and nitrogen in From this examination the results shown in Table I11 TABLE I11 EXAMINATION OF 0 . 5 ~ SAMPLE OF POLYMER w-AMINO UNDECANOIC ACID Polymev- Nitrogen, 7.01 % : carbon, 70.957; ; hydrogen, 11.76% Melting-point, 185" to 186" C Hydrolysis products of polymer- Ether extract of hydrolysed product . . .. . . products . . .. ,. .. . . . . . . Residue after evaporation of ether extracted hydrolysis , Base hydvochlovide- the original polymer were also were obtained.PRODUCED FROM 1 2 4.1 yo 5.7 yo 125.20/:, 122.5% Melting-point of base hydrochloride . . . . . . 145" to 147" C 146" C Chlorine in base hydrochloride . . . . . . . . 14.5276 14.65 Yo Equivalent weight of base hydrochloride (calculated from phenolphthalein titre) . . .. .. . . 245.8 242.0 OBSERVATIONS ON THE DATA IN TABLE III- (i) The nitrogen, carbon and hydrogen figures are not in strict agreement with those we should expect to obtain for the pure polymer obtained from w-amino undecanoic acid by removal of one molecule of water. The theoretical figures for this pure polymer would be: nitrogen, 7.64 per cent. ; carbon, 72.06 per cent. ; hydrogen, 11.54 per cent. (ii) The melting-point of the sample examined was 185" to 186" C. We have encountered samples of this polymer of rather lower melting-point, i.e., about 180" C.(iii) The proportion of ether extract and hence of residual base hydrochloride do not agree. Infra-red examination has indicated that this ether extract consists essentially of the base hydrochloride, i.e., the hydrochloride of m-amino undecanoic acid. This hydro- chloride is slightly soluble in ether and the varying results are due to the fact that the through- put of ether is not the same in the duplicate extractions. (iv) There is a certain amount of evidence to support the view that the hydrolysis product of this polymer does not consist completely of the hydrochloride of w-amino undecanoic acid. In our experience there is present in the hydrolysis a rather flocculent material that is to a certain extent insoluble in water and which is almost certainly present as an impurity in the base hydrochloride. This would account for the fact that the figures obtained are not in strict agreement with theory. The theoretical figures for the chlorine content of w-amino undecanoic acid hydrochloride and its equivalent weight are : chlorine content, 14-91 per cent. ; equivalent weight, 237.8.40 RILEY: THE DETERMINATION OF ACETYL VALUES FOR USE I N [Vol. 76 We are indebted to Mr. H. Willis for the infra-red spectra of the two polymers and to Mr. N. Payne for his assistance in the design of the apparatus used in the examination of polymers produced by the interaction of hexamethylene diisocyanate and 1 : 4-butanediol. REFERENCES 1. Clasper, M., and Haslam, J., Analyst, 1949, 74, 224. 2. First Review of German Science, 1939-46, “Preparative Organic Chemistry, Part 111,” Office of the Military Goverment for Germany, Field Information Agencies, Technical ; British, French, 1J.S.; p. 310. Salk and Rayon, December, 1948. 3. IMPERIAL CHEMICAL INDUSTRIES LIMITED PLASTICS DIVISION BLACK FAN ROAD WELWYN GARDEN CITY, HERTS. July. 1950