A composition comprising a polymer having a processing temperature of at least 200° and from about 0.1 wt % up to about 30 wt % of crosslinking agent said crosslinking agent comprising a compound of the formula ##STR1## wherein x is hydrogen and y is ##STR2## and x and y are substituents on adjacent carbon atoms of A or wherein x and y together form the imide ring system ##STR3## which is joined to A on adjacent carbons atoms, thereof, wherein A is an aromatic, heteroaromatic, alicyclic, or heterocyclic system or an open chain aliphatic moiety, where R is vinyl, allyl, methallyl or propargyl and wherein R' is hydrogen, C1 to C12 alkyl or R and mixtures thereof.
compounds per se and articles manufactured from the above-indicated polymer composition are also taught.
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1. A composition comprising an organic crosslinkable polymer having a melt processing temperature of at least 200° and from about 0.1 wt % up to about 30 wt % of crosslinking agent said crosslinking agent comprising a compound of the formula ##STR24## wherein x is hydrogen and y is ##STR25## and x and y are substituents on adjacent carbon atoms of A or wherein x and y together form the imide ring system ##STR26## which is joined to A on adjacent carbons atoms, thereof, wherein A is an aromatic, heteroaromatic, alicyclic, or heterocyclic system or an open chain aliphatic moiety, where R is vinyl, allyl, methallyl or propargyl and wherein R' is hydrogen, C1 to C12 alkyl or R, or a mixture of said compounds.
3. A composition in accordance with
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6. The composition of
7. The composition of
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9. The composition of
10. The composition of
11. The composition of
12. The composition of
13. A composition in accordance with
14. The composition of
15. The composition of
16. The composition of
17. A formed article comprising an electrical conductor having as an insulating coating thereover the product of the process of crosslinking the composition of
18. An article in accordance with
20. The article of
22. The article of
24. The article of
26. The product of
27. A composition according to
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A large number of high melting fluorocarbon polymers possess a combination of mechanical, dielectric and chemical properties which make them particularly useful as electrical insulation materials. In order to maximize utilization of these fluorocarbon polymers under high temperature or overload conditions, crosslinking of the fluorocarbon polymers is required. Crosslinking of high temperature resistant fluorocarbon polymers is particularly difficult since the polymers are normally processed at temperatures which are too high for most chemical crosslinking agents. As an alternative to chemical crosslinking, irradiation crosslinking of these polymers has been tried. However, to achieve a suitable level of crosslinking without degradation, it is necessary to add a crosslinking agent or coreactant to the fluorocarbon polymers, a so-called "prorad".
The prior art teaches the existence of a variety of prorads. See for example U.S. Pat. Nos. 3,970,770, 3,985,716, 3,911,192, 3,894,118, 3,840,619, 3,763,222 and 3,995,091.
However, all of these prior art crosslinking agents suffer from one or more shortcomings in comparison with the crosslinking agents of the present invention.
This invention relates to certain imide containing compounds which are novel compositions of matter. This invention also relates to polymeric compositions comprising high processing temperature polymers, especially fluorocarbon polymers, containing one or more imide containing crosslinking agents (prorads) including inter alia the aforesaid novel compositions of matter. This invention also relates to wire insulated with, and cable jacketed with, the aforesaid polymeric compositions in crosslinked form.
The prorads of the present invention are particularly useful for enhancing the crosslinking of fluorocarbon polymers which are processed, that is, extruded and/or molded at temperatures of 200° or greater, especially 250° or greater. Additionally, the crosslinking agents of the present invention improve the elevated temperature mechanical properties of the crosslinked polymers, especially elevated temperature elongation, abrasion and deformation resistance. Fluorocarbon polymers with which the crosslinking agents of the present invention may advantageously be utilized include homopolymers, copolymers and terpolymers such as ethylene-tetrafluoroethylene copolymers, ethylene-chlorotrifluoroethylene copolymers, polyvinylidene fluoride homopolymers, tetrafluoroethylenevinylidene fluoride copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride hexafluoropropylene copolymers, vinylidene fluoride hexafluoropropylene tetrafluoroethylene terpolymers and the like. Mixtures of any of the above enumerated polymers may also be advantageously crosslinked using the crosslinking agents of the present invention.
The crosslinking agents of the present invention are suitably present in the polymer in an amount ranging from 0.1 to 30 weight percent,
Among suitable prior art prorads useful in such mixtures may be mentioned triallylcyanurate (Compound B, Table I), triallylisocyanurate (Compound D, Table I), i.e., 1,3,5-tri-(2-propenyl)-s-triazine-2,4,6(1H, 3H, 5H)-trione, triallyl trimellitate (Compound E, Table I), triallyl trimesate (Compound F, Table I), tetraallyl pyromellitate, diallyl-4,4'l -oxydibenzoate (Compound G, Table I), diallyl-4,4'-sulfonyldibenzoate (Compound A, Table I) and 2-propenyl 2,3-dihydro-3-[4-(2-propenoxycarbonyl) phenyl]-1,2,3-trimethyl-1H-indene-5 -carboxylate.
Suitable mixtures include mixtures of triallylisocyanurate with N,N'-di-(2-propenyl)-bicyclo[2.2.2.]oct-7-ene-2,3,5,6-tetracarboxylic-2,3: 5,6-diimide (Compound II, R=alkyl); N,N'-di-(2-propenyl)-1,2,4,5-benzenetetracarboxylic-2,3:5,6-diimide, or 2-propenyl 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)-isoindole-5-carboxylate (Compound III, R=allyl).
This invention is further illustrated by examples which serve to illustrate specific details, aspects and embodiments of the invention. All parts are by weight unless otherwise indicated. All temperatures throughout the specification and claims are in degrees centigrade. All tests unless otherwise indicated were carried out at 23°. The term melting point or crystalline melting point is defined as that temperature at which the last traces of crystallinity as measured by differential scanning calorimetry is observed. The polymer processing temperature as that term is used herein is defined as a temperature above the crystalline melting point of any polymeric component at which temperature the polymer melt has a viscosity of not more than 2×106 poise. The majority of polymeric components useful in the practice of the present invention, however, have melt viscosities of less than 105 poise at the processing temperature. The term wire can connote either bared conductor or jacketed conductor as is apparent from the context.
Certain of the tests utilized are first described.
To determine the relative level of crosslinking in these polymeric resins, a modulus test conducted at 320° was used because conventional methods to determine crosslinking levels by gel analysis require the polymer to be soluble. In the case of ethylene tetrafluoroethylene copolymers, there are no known solvents below 200°. This modulus test measures the stress required to elongate a resin by 100% at a temperature of 320°. High values obtained from this test indicate increasing resistance to elastic deformation or development of a significant amount of a three-dimensional network. The 320° temperature was chosen as it is intermediate between the decomposition temperature (∼350°) and the crystalline melting point (∼280°) for ethylene tetrafluoroethylene copolymers. The modulus measurement expressed as the M100 value can be calcuated by: ##EQU1## Should the sample rupture prior to 100% elongation, the M100 is calculated using the equation: ##EQU2##
A sample of the wire is placed between an anvil and a 90° included angle wedge shaped weighted knife blade having a 5 mil flat at the knife edge. The anvil is hung by means of a stirrup from the load cell of an Instron tensile tester and the knife blade mounted on the movable bar of said tensile tester also by a stirrup so that the blade edge lies transversely over the wire specimen. The knife edge is advanced towards the wire conductor at a speed of 0.2 in per minute. Failure occurs when the knife edge contacts the conductor. The resulting electrical contact causes the tensile tester to stop advancing the blade. The peak reading from the load cell is taken to be the cut through resistance of the wire. This cut through test is not to be confused with a cut through test identified by Bowers et al., IEC Product R&D 1, 89 (1962). The latter test simulates an accelerated creep test in which the viscoelastic flow of a polymeric resin is altered by radiation crosslinking. Further information pertaining to enhancement of polymer creep resistance through crosslinking can be found in "Mechanical Properties of Polymers and Composites," by L. E. Nielsen, Vol. 1, p. 87, 1974.
To a stirred slurry of 49.6 parts of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic-2,3:5,6-dianhydride in 200 parts of glacial acetic acid was added dropwise with cooling (ice bath) 26.2 parts of allylamine over a period of 5-10 min. The reaction mixture was gradually heated and held at reflux for 30 min, resulting in a clear amber solution. Upon cooling, a crystalline material precipitated, was collected by filtration and was recrystallized from toluene to give 58.5 parts (90%) of colorless crystals: mp 202°-3°. Thinlayer chromatography indicated one compound (SiO2 /CHCl3 as eluent). Nuclear magnetic resonance and infrared spectral analysis confirmed the formation of the desired diimide N,N'-di(2-propenyl)-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic- 2,3:5,6-diimide (Compound II, R=allyl): nmr: δ(CDCl3) ppm, 2.9-3.2 (multiplet, 4H, --CH--CH--C═O), 3.6-3.9 (multiplet, 2H, --CH--CH-- C═O), 4.05 (doublet, 4H, --CH2 --CH═CH2). 4.9-6.0 (multiplet, 6H, --CH2 --CH═CH2), 6.15 (triplet, 2H, --CH--CH═CH--CH--); ir: (KBr)cm-1, 3130 (w) and 3020 (m) [unsat. CH], 1770 (s) and 1705 (vs) [imide--C═O].
A sample of N,N'-di-(2-propenyl)-1,2,4,6-benzenetetracarboxylic-1,2:4,5-diimide (Compound I, R=ally) was prepared by a reaction analogous to that of Example I from 1,2,4,5-benzenetetracarboxylic-1,2:4,5-dianhydride and allylamine (93% yield): colorless crystals, mp 222.5°-223.5°. The material was shown to be one compound by thinlayer chromatography. Its identity was established by nuclear magnetic resonance and infrared spectral analysis: nmr: δ(CDCL3) ppm, 4.35 (doublet, 4H, --N--CH2 --CH═CH2), 5.0-6.3 (multiplet, 6H, --CH2 --CH═CH2), 8.25 (singlet, 2H, aromatic hydrogen); ir:(KBr) cm-1, 3120 (m, aromatic H), 2950 (w, aliphatic H), 1765 (s) and 1710 (vs) [imide--C═O].
A sample of 2-propenyl 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)isoindole-5-carboxylate (Compound III, R-allyl) was prepared in a three-step sequence: 1,2,4-benzenetricarboxylic anhydride (57.6 parts) was treated in the same manner as in Example I with excess allylamine (37.7 part) to give 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)isoindole-5-carboxylic acid(47.4 parts); colorless crystals, mp 155°-7°. A sample of 27.3 parts of this material was refluxed in 50 parts of thionyl chloride which contained approximately 0.5 parts of dimethylformamide. After a reaction time of 1 hour excess thionyl chloride was removed by distillation to give a crystalline residue of 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)-isoindole-5-carboxylic acid chloride. An aliquot of 5.0 parts of this material was dissolved in 10 parts of pyridine and 1.3 parts of allyl alcohol (excess) was added dropwise with stirring at room temperature. The resulting mixture was briefly heated to reflux, then cooled to room temperature followed by dilution with water to give a crystalline precipitate. Recrystallization first from aqueous acetic acid and then from methanol produced 3.6 parts of colorless crystals: mp 65°-6°. Thinlayer chromatography (SiO2 /CHCl3 as eluent) indicated one single component. Nuclear magnetic resonance and infrared spectral analysis confirmed the identity of the desired 2-propenyl 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)isoindole-5-carboxylate; nmr: δ(CDCl3) ppm. 4.30 (doublet, 2H, N--CH2 --CH═CH2), 4.90 (doublet, 2H, O--CH2 --CH═CH2), 5.0-6.5 (multiplet, 6H, --CH2 --CH═CH2), 7.85 (doublet, 1 H, aromatic hydrogen), 8.1-8.4 (multiplet, 2H aromatic hydrogen); ir (KBr) cm-1, 3120 (w, aromatic H), 2950 (w, aliphatic H), 1770 (m) 1718 (vs) [imide and ester --C═O], 1280 (s, aromatic ester--C--O).
A sample of 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)isoindole-5-carboxylic acid chloride (5 parts), whose preparation was described in Example III, was dissolved in 10 ml of pyridine, and 2.2 parts of diallylamine was added dropwise with stirring while cooling to maintain a reaction temperature of approximately 10°-15°. The resulting reaction mixture was heated briefly to reflux, and then cooled and poured into water. An oil separated which was taken up in ether and washed sequentially with aqueous hydrochloric acid, aqueous potassium carbonate, and water. The ethereal solution was then freed of colored impurities by treatment with charcoal and alumina, followed by evaporation to dryness to give 5.5 parts of a colorless oil. The material consisted of one compound as shown by thinlayer chromatography (SiO2 /CHCl3 as eluent). Nuclear magnetic resonance and infrared spectral analysis confirmed the identity of the desired 2,3-dihydro-1,3-dioxo-1H-2-(2-propenyl)isoindole-5-(N,N-di-2-propenyl)carb oxamide (Compound V, R═allyl) ; nmr: δ(CDCl3) ppm, 3.7-4.3 (multiplet, 4H, --N,N-amide--CH2 --CH═CH2), 4.30 (doublet, 2H, N-imide-CH2 --CH═CH2), 5.0-6.3 (multiplet, 6H, N,N,N-imide amide--CH2 --CH═CH2), 7.7-8.0 (multiplet, 2-3H, aromatic hydrogen); ir:(neat) cm-1, 1630-1640 (s) [secondary amide--C═O], 1710 (s) and 1770 (m) [imide--C═O].
A sample of ethenyl 2,3-dihydro-1,3-dioxo-1H-(2-propenyl)isoindole-5-carboxylate (Compound III, for N-R, R═allyl, for O-R, R═vinyl) was prepared in two steps: 4-carboethenoxy-1,2-benzenedicarboxylic anhydride was synthesized according to the procedure given in Organic Syntheses, Coll. Vol. IV, p. 977, from vinyl acetate and 1,2,4-benzenetricarboxylic anhydride by effecting a mercuric acetate catalyzed ester interchange. A pale yellow crystalline material was obtained: mp 123°-127°;nmr:δ(CDCL3) ppm, 4.85 (quartet, 1H) and 5.20 (quartet, 1 H)[--CH═CH2 ], 7.48 (quartet, 1 H, --CH═CH2), 7.9-8.7 (multiplet, 3 H, aromatic hydrogen): ir; (Nujol) cm-1, 1645 (w) [CHR═CH2 stretch], 1730 (s) [ester --C═O], 1775 (s) and 1845 (m) [anhydride --C═O]. The above compound (21.8 parts) was dissolved in 175 parts of glacial acetic acid, and 5.7 parts of allylamine was added dropwise with stirring at room temperature. The reaction exotherm was controlled by cooling with water. After completing amine addition the reaction solution was concentrated to a volume of 125 parts by distillation of acetic acid. The resultant concentrate was allowed to cool to room temperature. A crystalline, colorless precipitate formed which was collected by filtration. Recrystallization from heptane produced 13.1 parts of colorless needles (mp 91.5°-93.0°). Thinlayer chromatography indicated one compound and a trace of non-moving impurity. A sample of 6.2 parts of this material was further purified by treatment with charcoal and alumina in chloroform solution. This process, after solvent removal, produced 6.0 parts of colorless crystals which consisted of one compound as shown by thinlayer chromatography (SiO2 /CHCl3 as eluent). Nuclear magnetic resonance and infrared spectral analysis confirmed the identity of the desired ethenyl 2,3-dihydro-1,3-dioxo-1 H-(2-propenyl)isoindole-5-carboxylate; nmr: δ(CDCl3) ppm, 4.30 (doublet, 2H, --N--imide--CH2 --CH═CH2), 4.6-5.1 (multiplet, 2H, --O--CH═CH2), 5.2-6.2 (multiplet, 3H, --N--imide--CH2 --CH═CH2), 7.38 (quartet, 1 H, --O--CH═CH2), 7.85 (doublet, 1 H, aromatic H) 8.1-8.5 (multiplet 2H, aromatic H); ir:(Nujol) cm-1, 1645 (m) [CHR═CH2 stretch], 1720 (s) [vinyl ester --C═O], 1735 (s) and 1770 (m) [imide --C═O].
As previously indicated, the compounds of the present invention possess a combination of properties which make them uniquely superior to prior art prorads. This and the following examples illustrate some of these advantages such as higher homopolymerization temperatures and lower volatility without comprising prorad response to ionizing radiation or compatibility with polymeric resins.
The temperature at which a variety of reported prior art fluorocarbon prorads, and also compounds according to the present invention commence thermally induced homopolymerization, was evaluated by differential scanning calorimetry. In all cases, the compounds were tested in a nitrogen atmosphere at a heating rate of 20°/minute from 50° to 400°. Results are reported in Table I.
Polymerization at 250° or below drastically reduces the usefulness of the prorad since exposure to temperatures above 250° is required to process many of the most useful fluorocarbon polymers. As is apparent from Table I, only three of the prior art compounds, viz., Compounds F, G and H had polymerization initiation temperatures above 250°. These results indicate that most prior art compounds, e.g., Compounds A-E, undergo significant homopolymerization during processing. This causes a significant reduction of crosslinking enhancement and leads to incorporation of undesirable prorad-homopolymer into the fluorocarbon host polymer.
| TABLE I |
| __________________________________________________________________________ |
| Homopolymerization Temperatures of Selected Prorads |
| Compound |
| Structure Polymerization |
| __________________________________________________________________________ |
| Temp.,° |
| ##STR13## 210 |
| B |
| ##STR14## 220 |
| C |
| ##STR15## 230 |
| D |
| ##STR16## 250 |
| E |
| ##STR17## 250 |
| F |
| ##STR18## 260 |
| G |
| ##STR19## 260 |
| H |
| ##STR20## 280 |
| I |
| ##STR21## 360 |
| II |
| ##STR22## 330 |
| III |
| ##STR23## 260 |
| __________________________________________________________________________ |
The effectiveness of a prorad is dependent on its concentration in the host polymer during irradiation. Prorads of high volatility are expected to be lost, at least in part, during melt processing due to evaporation. To illustrate this point a variety of known prorads and several of the compounds of the instant invention were compared on the basis of volatility using thermogravimetric analysis at a heating rate of 20°/minute under a nitrogen atmosphere. The results are shown in Table II. Examination of these data reveals that the prior art compounds A, C, G, and H have volatility comparable to compounds of the instant invention, while all other prior art compounds manifest excessive volatility at 250°. However, these results are far from conclusive since prorad loss can result from homopolymerization and evaporation. Table III takes this factor into account by analyzing weight loss below the homopolymerization temperature. As is apparent from the data, the prorads of the present invention again show excellent results. However, under these experimental conditions which measure merely evaporative loss, only two of the known prorads, i.e. compounds A and H, demonstrate the comparably low volatility of the prorads of the instant invention, while the other prior art prorads show a significantly greater relative weight loss, by a factor of three or more, under identical conditions.
| TABLE II |
| ______________________________________ |
| Volatility of Selected Porads by Thermal Gravimetric Analysis1 |
| Weight % loss at |
| Compound 200° 250° |
| 300° |
| ______________________________________ |
| A 0 1 4 |
| B 15 91 100 |
| C 2 5 12 |
| D 22 95 100 |
| E 3 14 54 |
| F 2 7 37 |
| G 1 5 24 |
| H 0 2 7 |
| I 0 4 23 |
| II 0 1 6 |
| ______________________________________ |
| 1 Heating rate of 200°/minute, N2 atmosphere |
| TABLE III |
| ______________________________________ |
| Volatility of Selected Prorads by Isothermal Weight Loss1 |
| Weight % loss after exposure time (min) |
| Compound 5 10 20 30 |
| ______________________________________ |
| A 0.0 0.0 0.1 0.2 |
| B 4.3 12.2 27.2 41.3 |
| C 1.7 2.8 3.8 4.4 |
| D 11.3 27.2 56.7 87.0 |
| E 1.2 3.1 6.9 10.9 |
| F 0.8 1.6 2.8 4.2 |
| G 1.0 1.6 3.3 3.5 |
| H 0.1 0.3 0.7 1.1 |
| I 0.1 0.6 0.9 1.1 |
| II 0.0 0.0 0.0 0.0 |
| ______________________________________ |
| 1 Temperature = 175°, N2 atmosphere |
Examination of the simultaneous effect of volatility and homopolymerization can be made by processing a standard formulation containing various prorads and comparing the resultant extrudates. The processability of prior art prorads is compared with prorads of the instant invention using a 3/4 inch Brabender extruder, to produce a thin wall (10 mil) Tefzel (duPont, ethylenetetrafluoroethylene copolymer) insulation on 20 AWG tin plated copper conductor. The results are given in Table IV.
As is apparent from this Table, only the prorads of the instant invention provide a commercially viable product. Prior art prorads each demonstrate a degree after processing product discoloration, porosity, gelation, and surface imperfections. Each of these drawbacks magnifies the difficulty of extruding the thin wall wire insulation required of a high performance product.
| TABLE IV |
| ______________________________________ |
| Processing Comparison of |
| Several Prorads in a Standard Formulation |
| Extrusion Temp. Profile |
| Extruded Insulation Properties |
| Com- Zone Zone Zone Surface In- |
| pound 1 2 3 Head Color Appearance |
| tegrity |
| ______________________________________ |
| B 265 310 330 330 tan v. rough foamed |
| D 265 310 330 330 tan v. rough foamed |
| F 245 295 330 340 tan rough foamed |
| G 265 310 335 345 off lumps good |
| white |
| H 240 300 340 370 off lumps good |
| white |
| I 240 300 340 380 white excellent |
| good |
| II 240 300 340 370 white excellent |
| good |
| III 265 300 340 370 white good good |
| ______________________________________ |
| 4.0 Wt. % prorad concentration in Tefzel fluoropolymer for all samples at |
| start of processing. |
Each of the previous examples delineates parameters which influence the performance of a prorad containing polymer composition when subjected to thermal processing and subsequent ionizing radiation in order to effect crosslinking. The ultimate choice of a prorad is dictated by a combined consideration of processing behavior and end product performance. The significant overall advantages accruing from the use of prorads of the instant invention over those of the prior art was demonstrated by conducting appropriate test extrusions and product evaluations. Identical polymer formulations containing none or 5% of a prior art prorad or 5% of a prorad of the instant invention, were compared as a wire product after extrusion from a 3/4 inch Brabender extruder to produce a thin wall (10 mil) insulation on 20 AWG tin plated copper conductor, followed by irradiation to 12 Mrads and annealing at 150° for 1 hour. These wire insulations were than subjected to identical analyses for comparison. The results are provided in Table V. Examination of these data clearly shows the advantages of the prorads of the instant invention, as demonstrated by superior processing behavior and significantly improved wire insulation properties. Comparison of the cut through resistance at room temperature and at elevated temperature shows an improvement greater than 50% over the best of the prior art prorad containing wire compositions.
| TABLE V |
| __________________________________________________________________________ |
| Processing and Performance Evaluation of Prorad Formulations |
| Crosslinking |
| Ultimate |
| Cut Through |
| Density |
| Elongation |
| Resistance |
| Compound |
| Tp1 |
| Volatility2 |
| Appearance M100, psi |
| % 25° |
| 150° |
| __________________________________________________________________________ |
| None N/A |
| N/A Smooth, clear |
| melts 160 24 3.9 |
| D 250 |
| 50 Badly foamed |
| E 250 |
| 11 Badly foamed |
| Extrudate integrity was inadequate |
| F 260 |
| 4 Foamed for testing |
| Uneven, contained |
| H 280 |
| 1 gel particles |
| 97 102 29 4.1 |
| I 360 |
| 1 Smooth, yellow |
| 590 100 50 6.5 |
| II 330 |
| 0 Smooth, white |
| 220 130 42 6.3 |
| __________________________________________________________________________ |
| 1 Polymerization temperature, |
| 2 Volatility at 175° after 30 minutes, % weight loss. |
Jansons, Viktors, Gotcher, Alan J., Germeraad, Paul B.
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