Melt-processible aromatic polyamides

Abstract: Melt-processible aromatic polyamides are obtained by reacting certain N,N′-isophthaloyl bis(lactam) compounds with certain aromatic diamines.

Description: Background of the Invention Aramids are generally high temperature polymers. The commercial aramids, poly(m-phenylene isophthalamide) and poly(p-phenylene terephthalamide) are thermally stable polymers which on heating decompose before they melt. Hence, they are processed from solutions containing a minor proportion of polymer and, in the case of the meta aramid, large amounts of salt, such as CaCl₂. They may be prepared by the acid chloride route which consists of reacting, for example, isophthaloyl chloride or terephthaloyl chloride, with an aromatic diamine, such as m -phenylene diamine in the presence of a solvent. In the manufacture of poly( m -phenylene isophthalamide, the HCl generated in the reaction is neutralized with a base such as Ca(OH)₂. The poly( m -phenylene isophthalamide) solution is then dry spun. JP-A-70 19714 discloses polyamides made by polymerizing bislactams (e.g. from isophthaloyl chloride and caprolactam) with aromatic diamines (e.g. 1-methyl-2,4-phenylene diamine). The products are described as having melting points. The acid chloride route is used for the synthesis of aramids because the normal melt condensation of aromatic diamines with aromatic dibasic acids does not occur or results in low molecular weight, infusible materials. The acid chloride route, on the other hand, has its own drawbacks such as (1) the chloride-related corrosion of equipment, and (2) the need to remove solvent and salts from fiber. Further, the polymers made by the acid-chloride route are usually non-meltable and thus are not melt-processible. A worthwhile objective has been to prepare a salt-free aramid or aramid copolymer by a melt process. Such polymers and copolymers have the high glass transition temperature, T g , and good thermal stability of aramids and, at the same time, have the advantages of low cost melt-processibility to give products free of salt for superior electrical properties. Because of their high , thermal stability, and good electrical properties, aramid fibers are used to prepare a variety of thermally resistant products, such as fire blocking fabrics and papers for electrical insulation in motors. Summary of the Invention This invention provides a melt-processible polyamide consisting of the following repeat units: wherein n is 4 or 5; X is from 0.03 to 0.50 wherein X and 1-X represent mole fractions of these units, preferably 0.03 to 0.30; and Ar is at least one divalent aromatic radical consisting of 1,3-phenylene, 1-methyl-2,4-phenylene, 1-ethyl-2,4-phenylene, 3,4'-oxydiphenylene, 1,3-bis(3-phenyleneoxy)benzene, and 1,4-bis-(4-phenyleneoxy)-2-phenyl benzene, or a mixture of said radicals said polyamide having an inherent viscosity of at least 0.7 measured at 25°C as a solution of 0.5 g of polymer in 100 ml of a 4 wt% lithium chloride solution in dimethyl acetamide. Also included in the invention are melt-processible compositions of such polyamides plasticized with a lactam of the group of caprolactam, valerolactam and 3-methylvalerolactam. The process of the invention for preparing the polyamides comprises reacting in substantially equimolar proportions and at a temperature of from 180°C to 280°C, aromatic diamine of the group of meta-phenylene diamine, 1-methyl-2,4-phenylene diamine, 1-ethyl-2,4-phenylene-diamine, 3,4'-diaminodiphenyl-ether, 1,3-bis(3-amino-phenoxy)benzene, or 1,4-bis(4-aminophenoxy)-2-phenyl-benzene, or mixtures thereof with an N,N'-isophthaloyl bis(lactam) selected from N,N'-isophthaloyl bis(caprolactam), N,N'-isophthaloyl bis(valerolactam) and N,N'-isophthaloyl bis(3-methyl-valerolactam), in which the bis(lactam) has a carboxyl content of less than 30 µeq. (microequivalents) of carboxyl groups per g. Melt-processed fibers and films of the resulting polymer are part of this invention as well as the novel precursors, N,N'-isophthaloyl bis(valerolactam) and bis(3-methyl-valerolactam). Detailed Description of the Invention This invention relates to a new class of polyamides and to their preparation by the reaction of certain N,N'-isophthaloyl bis(lactam) monomers with certain aromatic diamines as depicted below for the bis(caprolactam) or bis(valerolactam): wherein n, X and Ar are as defined above. The preferred polymer of the invention is the copolymer consisting of the following units and in which the bis(valerolactam) is employed: where X is as above. The bis(lactam)monomers used are N,N'-isophthaloyl bis(valerolactam) (IBV) (n=4), N,N'-isophthaloyl bis(3-methylvalerolactam) (IB3MV) and N,N'-isophthaloyl bis(caprolactam) (IBC)(n=5). The aromatic diamines employed are m-phenylene diamine (MPD), 1-methyl-2,4-phenylene diamine, 1-ethyl-2,4-phenylene diamine, 3,4'-diaminodiphenyl ether (3,4'-DDE), 1,3-bis-(3-aminophenoxy)benzene or 1,4-bis(4-aminophenoxy)-2-phenylbenzene. These diamines may be used individually or as mixtures. Amounts of other aromatic diamines, such as p-phenylenediamine (PPD) and 4,4'-diaminodiphenyl ether may replace a minor portion of the aforementioned diamines providing they do not adversely affect the desired properties of the resulting polyamides. It has been found that certain of the lactams form a heterogeneous product unsuitable for melt-processing when reacted with certain of the diamines. This is evidenced, for example, by the presence of a precipitate as discussed in EXAMPLE 7 below. Such products can generally be avoided by judicious selection of the reacting components. In EXAMPLE 7, heterogeneity was eliminated by use of a (bis)lactam having fewer carboxyl groups. Use of mixtures of the aromatic diamines has also been found to overcome the problem, as has switching to the use of the bis(caprolactam) rather than the other bis(lactam)monomers. The resulting polymers are plasticized by the in situ generated lactams, which may be extracted from the polymers, if desired. Both the plasticized polymers and the polymers from which the lactam has been extracted are melt-processible into fibers, films, and shaped forms. By "melt-processible" is meant that the polyamides can be melt-spun into fibers, melt-pressed into films or melt-extruded into shaped forms without undue degradation. Preparation of IBC, IBV and IB3MV IBC was prepared by the following procedure: A 2-liter,, three-neck flask was fitted with a mechanical stirrer, reflux condenser, and a dropping funnel. The apparatus was thoroughly dried under N₂. To the flask were charged 113 g (1.0 mol) of caprolactam, 101 g (1.0 mol) of triethylamine, and 500 ml of toluene. The mixture was stirred and cooled in ice. A solution of 101.5 g (0.5 mol) of isophthaloyl chloride in 150 ml of toluene was added dropwise over a period of about 40 min. and after the addition was complete, the reaction mixture was stirred at room temperature for 30 min. and then filtered. The white solid was air dried, washed by stirring in 200 ml of water to remove Et₃NH⁺Cl⁻ and then filtered and washed twice on the filter paper using 1000 ml of distilled water each time. The solid was dried overnight in a vacuum oven at 80°C; yield 154 g (86.5%). Its melting point was 139-140°C. IBV was prepared by the following procedure: A 3-liter, three-neck flask was fitted with a mechanical stirrer, reflux condenser, and a dropping funnel. The apparatus was thoroughly dried under nitrogen. To the flask were charged 149 g (1.5 mols) of valerolactam (2-piperidone), 152 g (1.5 mols) of triethylamine, and 750 ml of toluene. The mixture was stirred. A solution of 152 g (0.75 mol) of isophthaloyl chloride in 250 ml of toluene was added dropwise over a period of about 30 min. After the addition was complete, during which the reaction became quite hot, the reaction mixture was stirred for several hours until it became cool. Then it was allowed to stand overnight without further stirring. The slurry was vacuum filtered, the filter cake was washed with a small amount of toluene (sufficient to wet the entire cake), and then it was aspirated dry. The reaction flask was rinsed with a liter of water into the filter cake to dissolve the triethylamine hydrochloride). The contents of the filter were gently agitated and the aqueous phase was filtered off. The cake was washed with small batches of water totalling 4 liters, and then was again aspirated dry. The cake was then placed in a glass tray and dried overnight in a vacuum oven at 80°C. The product, which weighed 211 g (85.8%) after drying, was N,N'-isophthaloyl bis(valerolactam), which had a melting point of 163-164°C. IB3MV was prepared by the following procedure: A one-liter, three-neck flask was fitted with a mechanical stirrer, reflux condenser, and a dropping funnel. The apparatus was thoroughly dried under nitrogen. To the flask were charged 56.5g (0.5 mol) of 3-methylvalerolactam (3-methyl-2-piperidone), 50.5 g (0.5 mol) of triethylamine, and 250 ml of dry toluene. The mixture was cooled in an ice bath and stirred. A solution of 50.75g (0.25 mol) of isophthaloyl chloride in 100 ml of toluene was added dropwise over a period of about 15 min. The mixture, which had a yellow appearance with only a small amount of solid visible, was stirred at room temperature for three hours. Little or no increase in the amount of solid present was noted. The solution was then filtered. The solid on the filter paper was soluble in water (presumably triethylamine hydrochloride) and was discarded. The yellow filtrate was distilled. A pasty yellow solid was left behind. It was stirred in 200 ml of ethanol for 30 minute and filtered, leaving white solid on the filter paper. The white solid was washed twice with 50-ml quantities of ethanol and then dried in a vacuum oven at 80°C for three hours. The product, which weighed 49g after drying, was subjected to a proton-NMR determination, the results of which were consistent with identifying the product as N,N'-isophthaloyl bis-(3-methylvalerolactam); m.p. 123°C. The crude products obtained by the foregoing procedures may contain varying amounts of carboxyl groups. The carboxyl groups are believed to derive from isophthalic acid or the isophthaloyl monolactam and may influence the final polymer composition. The content of carboxyl groups can be reduced by washing the crude product with aqueous base, e.g., dilute aqueous sodium carbonate solution, or by washing them with methanol or ethanol. A bis(lactam) containing virtually no carboxyls can be produced by recrystallizing from a suitable solvent, e.g., tetrahydrofuran or acetone for IBC, and acetonitrile/methanol or methyl ethyl ketone for IBV. In the examples that follow, the N,N'-isophthaloyl bis (lactam) compounds with the indicated carboxyl levels were obtained by treating the crude lactam compound in this manner. The carboxyl levels can be determined readily by titration procedures well-known in the art. Polymerization of N,N'-Isophthaloyl Bis(lactam) Compounds with Diamines The isophthaloyl bis(lactam) compounds are polymerized with aromatic diamines as shown above. The polymerization is carried out at temperatures above 180°C, preferably between 220°C and 280°C. It has been found that removal of some lactam by application of vacuum during a portion of the polymerization will enable the production of higher molecular weight polymers than otherwise. The polymers were then ground and washed in boiling methanol and dried in a vacuum oven at about 100°C prior to making the nuclear magnetic resonance, NMR, and Tg measurements. Polymers of fiber forming molecular weight, inherent viscosity of at least 0.7, are prepared. Measurements were made as described below. The polymers may contain amounts of the lactam formed in situ from the bis(lactam) starting material. Presence of the lactam plasticizes the polymer and renders it more amenable to melt-processing. If desired, however, substantially all of the in situ produced lactam may be removed by extraction procedures. Test Methods Carboxyl Determination of Isophthaloyl Bis-Lactams. The carboxyl level in isophthaloyl bis-lactams is determined by the titration method described by G. B. Taylor and J. E. Waltz in Anal. Chem. , 19 , 448 (1948). Determination of Polymer Composition. Determinations of the composition of the copolymers of this invention are made by determining the proton-NMR spectra of samples of the copolymers in deuterated dimethyl sulfoxide (DMSO-d₆). A copolymer sample to be tested is first ground into particles, if it is not already in finely divided form, and then thoroughly washed in boiling methanol to remove any material soluble in methanol, such as free lactam compounds. The sample should be washed at least twice in boiling methanol, each time for at least 30 minutes, using at least about 8 ml of methanol per g of sample. After the sample is washed, it is dried in a vacuum oven at 100°C for at least 3 hours. The proton-NMR spectrum of the sample in a DMSO-d₆ solution is then recorded, using a Nicolet NT-300 spectrometer or the equivalent. The relative molar amounts of aliphatic and aromatic portions in the copolymer are then determined by integrating the areas under the -NH-proton absorption curves for the portions of the curves which are characteristic, respectively, for the aliphatic and the aromatic amide -NH-protons, and comparing them in turn with the total area of -NH-proton absorption. The areas to be integrated usually appear, expressed in chemical shifts in parts per million (ppm), at portions of the curve corresponding to: Aromatic amide -NH- protons = 10.67 to 10.30 ppm (area "A") Aliphatic amide -NH- protons = 10.06 to 9.82 ppm (area "B") Aliphatic amides are defined as those amide groups in which either the nitrogen atom or the carbonyl group, or both, are attached to an aliphatic carbon atom. Aromatic amides are defined as those amide groups in which both the nitrogen atom and the carbonyl group are attached to aromatic carbon atoms. The following approximate formulas are used to calculate the amount of the aliphatic component in the copolymer, e.g. -(C=O)-(CH₂)₅-NH- for the component derived from caprolactam, in wt.% or in mol%: where A and B are defined above, FW a = Formula weight of aromatic amide repeat unit, e.g. for -HN-C₆H₄-O-C₆H₄-NH-(C=O)-C₆H₄-(C=O) , FW a = 330, and FW b = Formula weight of aliphatic repeat unit, e.g. for -(C=O)-(CH₂)₅-NH- , FW b = 113. Determination of Glass Transition Temperature. The glass transition temperature, T g , of a copolymer is determined by subjecting a sample of the copolymer to a Differential Scanning Calorimeter (DSC) Test in the manner described in U.S. 4,501,886 to J. P. O'Brien, col. 4, lines 10 - 25, except that a Du Pont 2100 Thermal Analyzer was used and the transition in the range of about 180° - 250° C is taken as the T g of the sample of copolymer. Inherent Viscosity. The inherent viscosity of a polymer which is soluble in a suitable solvent is conventionally used as a measure of the degree of polymerization of the polymer and is defined as measured by determining the flow times of a solution of the polymer at a concentration C in the solvent at a temperature of 25° C, where t is the flow time of the solution and t₀ is the flow time of the solvent alone. With the copolymers of the invention, the inherent viscosity values were determined using a solution of 4 wt.% lithium chloride (LiCl) in dimethylacetamide (DMAc) as the solvent, in which the copolymer sample was dissolved at a concentration of about 0.5 g of the copolymer per 100 ml of the solvent. The following examples are illustrative of this invention and are not intended as limiting: EXAMPLE 1 In this example IBC was reacted with 3,4'-DDE. Caprolactam was liberated during the polymerization reaction, and some was distilled from the mixture while the reaction was in progress. The copolymer which formed was plasticized by the remaining caprolactam and was melt spun into fibers. The polymer was prepared in a glass tube reactor fitted with a distillation condenser. The following amounts of ingredients were charged into the reactor: 17 80g (0.05 mol) IBC containing 7.3 micro-equivalents (µeq.) of carboxyl per g., and 10.00 g (0.05 mol) 3,4'-DDE. The reaction mixture was thoroughly purged using a N₂/vacuum cycle and then under a reduced pressure of 27 mm of Hg (3.6 kPa) was heated in a Wood's metal bath at 250°C. The mixture melted and after a few minutes caprolactam started to distill. After 5.5 g (50% of theoretical) of caprolactam was collected, nitrogen was introduced at atmospheric pressure and the reaction mixture was maintained at 250°C under nitrogen for 6 hours. The result was a clear light yellow plug of plasticized copolymer, in solution with residual caprolactam. The reaction tube was allowed to cool to room temperature and the plug of plasticized copolymer was isolated by breaking the tube. About 3g of the plug was ground into particles and washed twice in 200 ml of boiling methanol, each time for 1.5 hours to extract caprolactam and other methanol-soluble materials, the washed copolymer was dried in a vacuum oven at 110°C for 3 hours. The inherent viscosity was 1.31. Its Tg (by DSC) was 211.9°C. The composition of the plasticized polymer was established by proton-NMR spectrum as follows: Copolymer: Aramid repeat units = 72.5 wt.% (79.5 mol % of copolymer) repeat units=6.4 wt.% (20.5 mol % of copolymer) Free Caprolactam = 21.1 wt.% Another portion of the plasticized polymer was pressed into a plug at 125°C/5000 psi/5 min. (125°C/34475 kPa/5 min), and was spun at 290°C using a five-hole spinneret. The spun yarn denier was 97, its tenacity (T) was 0.66 gpd, and its elongation (E) was 170.0%. EXAMPLE 2 In this example, IBC was reacted with 3,4'-DDE in an autoclave equipped with a stirrer. The liberated caprolactam was not distilled off while the reaction was in progress. The resulting polymer was shaped into a film. The polymer was prepared as follows: 2848g (8.0 mol) of 106 containing 16 µeq. of carboxyl per g. and 1600 g (8.0 mol) of 3,4'-DDE were charged into the autoclave. The autoclave was thoroughly purged with N₂, closed, and then heated. After 1 hr., the temperature had reached 170°C and the agitator was started at 20 rpm. In another hour, the temperature reached 250°C and the pressure inside the autoclave was 80 psi (552 kPa). At this point, the agitator speed was reduced to 6 rpm, the temperature was held at 250°C., and the autoclave pressure reduced to atmospheric over a period of 1.5 hr. After 30 min., agitation was stopped and the copolymer allowed to pool at bottom of the autoclave for about 15 minutes. It was then extruded as a ribbon under N₂ end quenched in a bath of water. About 20 g. of the solidified copolymer in solution with residual caprolactam was ground and extracted twice in 300 ml of boiling methanol, each time for 3 hrs. The extracted polymer was dried in a vacuum oven at 100°C for 24 hours. Its inherent viscosity was measured to be 0.86. Its proton-NMR spectrum showed 13.6% (34.2 mol %) of -C-(CH₂)₅-NH- repeat units in the copolymer chain, i.e. X was 0.34. The remainder of the plasticized copolymer 3.86 kg (8.5 lbs.) was cut into particles of approximately 1.6 mm end extracted with 38 liters of methanol by essentially the same procedure as above. The extracted polymer was then dried in a vacuum oven at 100°C for 24 hours. It was then extruded into clear films ranging in thickness from 0.7 to 9 mils (17.8 to 229 µm). One film (∼ 5.5 mil (140 µm) thickness) was biaxially oriented 2x in each direction at 200°C, to a thickness of about 1.37 mil (34.8 µm). Its tensile properties are described in the following table: Ten 13.8 Kpsi (95.2 MPa) Elong., 26.3% Mod., 614 Kpsi (4237 MPa) EXAMPLE 3 This example demonstrates the use as a thermoplastic molding resin, a similar polymer to that of Example 2 prepared from the same ingredients in an analogous manner. The IBC contained 7.3 µeq. of carboxyl per g. Some of the caprolactam liberated was distilled from the mixture while the reaction was in progress, similar to Example 1. The remaining caprolactam was extracted from the polymer before compression molding. The polymer inherent viscosity was 1.01. Its proton-NMR spectrum showed 8.6% (21.6 mol %) of repeat units in the polymer chain, i.e. X was 0.22. Its Tg (by DSC) = 207.9°C. The extracted polymer was compression molded at 305°C/1380 psi (9517 kPa)/15 min into 15.2 cm X 15.2 cm plates having a thickness of 3.175 mm. Their static tensile properties are given in the Table below. Strength 12.4 Kpsi (85.5 MPa) Young's Modulus 560 Kpsi (3861 MPa) Poisson's Ratio 0.3 Shear Modulus 215 Kpsi (1482 MPa) EXAMPLE 4 In this example, IBV was reacted with 3,4'-DDE with liberation of valerolactam to form a copolymer plasticized by some of the valerolactam. The copolymer was extracted with methanol to remove the free lactam and the methanol-extracted copolymer was melt spun into strong fibers which could be drawn to increase their strength and modulus. A quantity of 3,4'-DDE was reacted with IBV in such a manner that the valerolactam liberated during the reaction was not distilled from the mixture while the reaction was in progress. Into a glass tube reactor, fitted with a mechanical glass stirrer, was placed 6.56 g (0.02 mol) of IBV containing 14.9 µeq of carboxyl per g and 4.00 g (0.02 mol) of 3,4'-DDE. The reaction mixture was thoroughly purged, using a nitrogen/vacuum cycle; then, while under nitrogen, it was heated in a Wood's metal bath at 250°C. As soon as the mixture melted, the stirring was started. The reaction mixture became quite viscous over a period of 90 minutes. The reaction mixture was cooled to room temperature. The product was a clear plug of plasticized copolymer (3,4'-DDE-I/5) in solution with residual valerolactam. The plug was ground into particles and the particulate copolymer was washed three times in boiling methanol, using 200-ml quantities of methanol and boiling for 2 hours each time to extract valerolactam and any other methanol-soluble materials. The washed product was then dried in a vacuum oven at 100°C for 3 hrs. This product was white and had an inherent viscosity of 0.70. Its proton-NMR spectrum showed 4.9 wt. % (14.66 mol %) of repeat units in the copolymer chain, i.e. X = 0.15. Its glass transition temperature, Tg, was determined by a DSC Test to be 225°C. Another polymerization was carried out, using substantially the same procedure, except that some of the valerolactam generated during the polymerization was distilled out under vacuum. Into a glass tube reactor, fitted with a stainless steel helical stirrer and a distillation condenser, was placed a mixture of 60.0 g (0.3 mol) of 3,4'-DDE and 98.4g (0.3 mol) of IBV containing 28.6 µeq of carboxyl per g. To this mixture was added 0.0197g of phenylphosphinic acid as an anti-oxidant. The system was purged thoroughly using a nitrogen/vacuum cycle and then put under a vacuum of 70 mm of mercury (93 m bar). It was then heated in a Wood's metal bath at 250°C. The mixture melted and valerolactam began to distill from the mixture. After 20.4 g of valerolactam (34.3% of the theoretical amount of 59.4g of valerolactam in the total mixture) was collected in the receiver, the reaction mixture was placed under nitrogen and the mixture was stirred for 90 minutes. It was then cooled to room temperature. The result was a clear plug of 3,4'-DDE-I/5 copolymer in solution with residual valerolactam. The plug was isolated by breaking the tube. The plug was ground into particles and the particulate copolymer was washed three times in boiling methanol, using 800-ml quantities of methanol and boiling for 2 hours each time to extract valerolactam and any other methanol-soluble materials. The washed product was then dried in a vacuum oven at 100°C for 12 hours. This product had an inherent viscosity of 0.71. Its proton-NMR spectrum showed 4.4 - 5.3 wt. % of repeat units, in the copolymer chain. Its glass transition temperature, Tg, was determined by a DSC Test to be 224.1°C. About 40 g of the copolymer prepared and methanol extracted as described in the previous paragraph was pressed into a plug at 289°C for 5 minutes. The plug was melt spun at 325°C, using a five-hole spinneret, into a 165 dtex (150 denier), 5-filament yarn. Its tenacity as-spun was 2.45 g/dtex (2.7 gpd), its elongation was 90%, and its modulus was 30 g/dtex (33 gpd). Upon drawing 1.3X at 200°C, its tenacity was 2.9 g/dtex (3.2 gpd), its elongation was 72% and its modulus was 37.3 g/dtex (41 gpd). EXAMPLE 5 In this example, IB3MV was reacted with 3,4'-DDE with liberation of 3-methylvalerolactam to form a copolymer plasticized by some of the 3-methylvalerolactam. The plasticized copolymer was extracted to remove the monomer. Into a glass tube reactor, fitted with a mechanical glass stirrer, was placed 7.12g (0.02 mol) of IB3MV containing 3.0 µeq of carboxyl per g and 4.00g (0.02 mol) of 3,4'-DDE. The reaction mixture was thoroughly purged, using a nitrogen/vacuum cycle; then, while under nitrogen, it was heated in a Wood's metal bath at 250°C. The mixture melted within about 5 minutes to a light yellowish turbid liquid. Stirring was started. During the first 30 minutes, the mixture turned clear and amber in color. Within one hour it had become thick. After 3 hours, the polymer was pulled out while hot. The product, which was clear and filmy, was a plasticized copolymer (3,4'-DDE-I/3MV) in solution with residual 3-methylvalerolactam. It was ground into particles and the particulate copolymer was washed three times in boiling methanol, using 100-ml quantities of methanol and boiling for 2 hours each time to extract 3-methyl valerolactam and any other methanol-soluble materials. The washed product was then dried in a vacuum oven at 100°C for 3 hours. The product had an inherent viscosity of 0.70. Its proton-NMR spectrum showed 1.9 wt. % (5.35 mol %) of repeat units in the copolymer chain, i.e. X = 0.05. Its glass transition temperature, Tg, was determined by a DSC Test to be 200.8°C. EXAMPLE 6 In this example, a mixture of 3,4'-DDE (50 mol%) and MPD (50 mol%) is reacted with IBC to form a copolymer. Into a glass tube reactor, which was not fitted with a stirrer, was placed 7.12g (0.02 mol) of IBC containing 8 µeq of carboxyl per g and a mixture of 1.08 g (0.01 mol) of m-phenylenediamine (MPD) and 2.00 g (0.01 mol) of 3,4'-DDE. The reaction mixture was thoroughly purged, using a nitrogen/vacuum cycle; then, while under nitrogen, it was heated in a Wood's metal bath at 250°C. As soon as the mixture melted, the mixture was manually shaken to mix the ingredients. The mixture was then left under nitrogen for 6 hours. The reaction mixture remained clear during this time. The mixture was then cooled to room temperature. The product was a plasticized copolymer where Ar is (3,4'-DDE/MPD-I/6) in solution with residual caprolactam. The plasticized copolymer was ground into particles and the particulate copolymer was washed twice in boiling methanol, using 200-ml quantities of methanol and boiling for three hours each time to extract caprolactam and any other methanol-soluble materials. The washed product was then dried in a vacuum oven at 100°C for 3 hours. The product had an inherent viscosity of 0.73. Its proton-NMR spectrum showed 16.6 wt.% (33.3 mol %) of repeat units in the copolymer chain, i.e. X = 0.33. Its glass transition temperature, Tg, was determined by a DSC Test to be 203.5°C. EXAMPLE 7 Into a glass tube reactor, which was fitted with a mechanical glass stirrer, was placed 7.12g (0.02 mol) of an IBC reagent containing 21.3 µeq of carboxyl per g and 2.16 g (0.02 mol) of MPD. The mixture was thoroughly purged, using a nitrogen/vacuum cycle; then, while under nitrogen, it was heated in a Wood's metal bath at 250°C. The mixture melted and in a few minutes began to thicken. Over a period of 90 minutes it became quite thick. The mixture remained clear and light amber in color throughout the reaction. No precipitate was observed in the molten mixture. The polymerization was stopped by cooling it to room temperature. The product was a plasticized copolymer (MPD-I/6) in solution with residual caprolactam. A plug of the plasticized copolymer was melt spun from a five-hole spinneret to form filaments. A plug of the plasticized copolymer was ground into particles. The plasticized particulate copolymer was washed twice in boiling methanol, using 100-ml quantities of methanol and boiling for 30 minutes each time to extract caprolactam and any other methanol-soluble materials. The washed particulate product was then dried in a vacuum oven at 100°C for 3 hours. The product had an inherent viscosity of 0.78. Its proton-NMR spectrum showed 22.8 wt. % (38.4 mol %) of repeat units in the copolymer chain, i.e., X = 0.38. Its glass transition temperature, Tg, was determined by a DSC Test to be 200.6°C. A quantity of the washed particulate product was placed on an aluminum foil coated with polytetrafluoroethylene and pressed for 5 minutes at a temperature of 330°C and a pressure of 13.8 MPa (2000 psi). A clear, pliable film was formed which could readily be separated from the foil. The reaction was repeated, except that the IBC reagent contained 35.8 meq of carboxyl per g. Again, no precipitate was observed in the molten mixture. However, the washed particulate product had an inherent viscosity of only 0.49. When an attempt was made to press a film from the particulate product following the procedure described in the preceding paragraph, it was observed that the particles stuck to the foil and no film was formed. The reaction was repeated twice more, except that the IBC reagents contained 91.2 and 399.4 µeq of carboxyl per g, respectively. In each of these reactions, a white precipitate was observed in the molten mixtures. The washed particulate product had inherent viscosities of only 0.28 in each of these cases. When an attempt was made to press a film from the particulate product following the previously described procedure, it was observed that the particles stuck to the foil and no film was formed. It will be noted that N,N'-isophthaloyl bis (valerolactam) and N,N'-isophthaloyl bis(3-methyl-valerolactam) provide an unexpected advantage over N,N'-isophthaloyl bis(caprolactam) in preparing the polymers of the present invention. Both valerolactam and 3-methylvalerolactam are liberated more readily from IBV and IB3MV than caprolactam is from IBC during the melt polymerization reaction, thereby resulting in a lower level of aliphatic content in the polymer and less diminution of properties provided by the aromatic nature of the polymer while still sufficient to permit melt-processibility. The liberated lactam can be distilled off and recovered for reuse. The level of aliphatic content is shown in the examples by the X values. EXAMPLE 8 In this example IBC was reacted with a mixture of 3,4'-DDE and PPD in a glass tube reactor without removing caprolactam liberated in the reaction until the polymerization was completed. The following amounts of ingredients were charged into the reactor: 7.12 g (0.02 mol) of IBC containing 48.9 µeq of carboxyl per g, 2.00 g (0.01 mol) of 3,4'-DDE, and 1.08 g (0.01 mol) of PPD. The mixture was thoroughly purged using several N₂/vacuum cycles. The reactants were heated in a Wood's metal bath at 250°C. The mixture melted into a clear, light yellow liquid. Stirring of the reactants was begun as soon as the mixture melted. In about 15 minutes the reaction mixture got quite thick and began to ball around the stirrer. The reaction was stopped after 1 hr. While molten the reaction product, 3,4'-DDE/PPD (50/50)-I/6 copolymer, could be pulled into films. A quantity of the product was ground into particles and the particulate copolymer was washed twice in boiling methanol to extract the free caprolactam, using 200-ml quantities of methanol and boiling for 30 min. each time. The resulting product had an inherent viscosity of 0.77. EXAMPLE 9 In this example a 60/40 mol. percent mixture of MPD and 2,4-diaminotoluene was reacted with IBC to form a copolymer. Into a glass tube, which was not fitted with a stirrer, was placed 8.0 g (0.022 mol) of IBC containing less than 10 µeq of carboxyl per g and 1.46 g (0.014 mol) of MPD and 1.10 g (0.009 mol) of 2,4-diaminotoluene. The reaction mixture was purged with nitrogen, and the tube was sealed with a polytetrafluoroethylene lined screw cap. The tube was heated at 225°C for approximately 23 hours. As soon as the mixture melted, the tube was manually shaken to mix the ingredients. A copolymer plug was formed upon cooling. After extraction of free lactam, the copolymer had an inherent viscosity of 0.79. Its Tg was determined to be 231°C (by DSC). The isolated polymer was spun into fiber using a press spinning apparatus at 308°C and 36.5 MPa (5300 psi). Physical properties of the fiber were determined to be: tenacity, 2.1 g/dtex(2.3 gpd), elongation at break, 24%, and modulus, 51 g/dtex (56 gpd). EXAMPLE 10 In this example IBV with a low carboxyl content was reacted with 3,4'-DDE to give a copolymer with Very low aliphatic content. After removal of excess lactam, strong fibers were prepared. Into a large glass polymer tube was placed 40.05 g (0.2 mol) of 3,4'-DDE and 65.81 g (0.2004 mol, 1.002 equiv.) of IBV with 1.3 µeq carboxyl per g. The tube was sealed with a vacuum distillation apparatus and a down-pumping stainless steel helical stirrer. The reactor was purged thoroughly by cycling between vacuum and nitrogen, and put under a vacuum of 70 mm of mercury (93 m bar). The tube was immersed in a Wood's metal bath set at 250° C and stirring was started at low speed. A quantity of 16 mL (17 g, 43 %) valerolactam was vacuum distilled from the initial melt. The copolymer was stirred for 1.5 hours until the stirrer halted as it became very viscous. The copolymer was then held for 2.5 hours at the same temperature and pressure. The stirrer was slowly removed at the end of the run, so that the copolymer could drain into a plug. The reactor was removed from the bath, cooled to room temperature,and immersed in dry ice to shatter the tube to collect the plug. After extraction of free lactam the copolymer, 3,4'-DDE-I/5, had an inherent viscosity of 1.26 and a T g of 236.37°C. Its proton NMR spectrum showed that the copolymer was free of valerolactam and contained 2.35 wt % (7.41 mol %) of -C(=O)-(CH₂)₄-NH- repeat units in the copolymer chain, i.e. X was 0.074. A small plug (5-10 g) of the lactam-free copolymer was melt spun at 335°C ,using a one-hole spinneret. The as-spun monofilament of 41.4 dtex (37.6 denier) had a tenacity of 3.01 g/dtex (3.31 gpd), its elongation was 127 %, and its modulus was 27.3 g/dtex (30.0 gpd). Upon drawing 1.7X at 200°C, the 22.0 dtex (20.0 denier) monofilament had a tenacity of 3.8 g/dtex (4.18 gpd), its elongation was 11.4 %, and its modulus was 61.9 g/dtex (68.1 gpd). Upon drawing 2.5X at 220°C the 15.1 dtex (13.6) denier monofilament had a tenacity of 4.23 g/dtex (4.65 gpd), its elongation was 22.5 %, and its modulus was 52.0 g/dtex (57.2 gpd). Another sample of the copolymer was prepared using the same general procedure, except that a few grams of the plasticized copolymer from which the valerolactam had not been extracted was press spun at 290°C through a .23 mm (9 mil) orifice to give a plasticized 29.0 dtex (26.4 denier) monofilament. The plasticized copolymer which was spun contained approximately 35 wt. % valerolactam. At maximum load the monofilament had a tenacity of 0.45 g/dtex (0.5 gpd) and 2.88 % elongation. Its tenacity and elongation at break were 0.29 g/dtex (0.317 gpd) and 45.1 %. Its modulus was 16.5 g/dtex (18.1 gpd). When the valerolactam was extracted from a portion of this polymer, it had an inherent viscosity of 0.96, a T g of 233.8°C, and contained 2.43 wt % (7.66 mol %) of -C(=O)-(CH₂)₄-NH- repeat units in the copolymer chain, i.e. X was 0.08.

Claims: A melt-processible polyamide consisting of the following repeat units: wherein n is 4 or 5; X is from 0.03 to 0.50, wherein X and 1-X represent the mole fraction of these units; and Ar is at least one divalent aromatic radical consisting of 1,3-phenylene, 1-methyl-2,4-phenylene, 1-ethyl-2,4-phenylene, 3,4'-oxydiphenylene, 1,3-bis(3-phenyleneoxy)benzene, or 1,4-bis(4-phenyleneoxy)-2-phenylbenzene, or a mixture of said radicals, said polyamide having an inherent viscosity of at least 0.7 measured at 25°C as a solution of 0.5 g of polymer in 100 ml of a 4 wt. % lithium chloride solution in dimethylacetamide. A polyamide according to claim 1 wherein X is from 0.03 to 0.30. A polymer according to either of claims 1 and 2 consisting of the repeat units: A polymer according to either of claims 1, and 2 consisting of the repeat units: A polymer of claim 4 wherein Ar is 3,4'-oxydiphenylene. A polymer according to either of claims 1, and 2 consisting of the repeat units: A polymer of claim 6 wherein Ar represents both 1,3-phenylene and 1-methyl-2,4-phenylene radicals. A polymer of claim 6 wherein Ar represents 3,4'-oxydiphenylene. A polymer of claim 6 wherein Ar represents 3,4'-oxydiphenylene and minor amounts of 1,4-phenylene radicals. A melt-processible composition consisting of a polyamide of any one of claims 1 to 9 plasticized with a lactam of the group of caprolactam, valerolactam and 3-methylvalerolactam. A fiber or film of the polymer of any one of claims 1 to 9. A process for preparing polyamides according to claim 1 comprising reacting in substantially equimolar proportions, and at a temperature of from 180°C to 280°C, aromatic diamine of the group of meta-phenylene diamine, 1-methyl-2,4-phenylene diamine, 1-ethyl-2,4-phenylene diamine, 3,4'-diaminodiphenylether, 1,3-bis(3-aminophenoxy)benzene, or 1,4-bis(4-aminophenoxy)-2-phenylbenzene, or mixtures thereof with an N,N'-isophthaloyl bis(lactam) selected from N,N'-isophthaloyl bis(caprolactam), N,N'-isophthaloyl bis(valerolactam) and N,N'-isophthaloyl bis(3-methylvalerolactam), in which the bis-lactam has a carboxyl content of less than 30 µeq. (microequivalents) of carboxyl groups per g., said reaction being continued until a polyamide having an inherent viscosity of at least 0.7 is produced. N,N'-Isophthaloyl bis(valerolactam). N,N'-Isophthaloyl bis(3-methylvalerolactam).

Inventors: SINGH GURDIAL, SINGH, GURDIAL
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1989
Main classification: C08G69
IPC codes: C08G69, C08L77