696
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 696-704
Table I. Glass Transition Temperatures m t n
2 4 6
T,, "C -36 41 -45 ~
Table 11. Elastomer Moduli for m + n = 6 X modulus, N m - z 4
10'
6
1O6
8 10-20
105 104
Dorfman et al. do not even discuss cross-linkingmethods. Young discusses possible ways for incorporating sites for cross-linking in a linear triazine polymer. The methods that he discusses are considerablymore complex, requiring higher curing temperatures, and are not as specific as the cross-link reactions 4 and 5. Perfluoroalkyl ether synthesis has previously been limited to low molecular weight polymers, and elastomer synthesis was severly restricted. However, linear polymers with weight average molecular weights from 20000 to 28000 can be prepared following reactions 2 and 3 (Korus and Rosser, 1978; Rosser and Korus, 1980b). Size exclusion chromatography, viscometry, and infrared spectroscopy have been used to monitor reactions 2 and 3. Previous polymerization reactions of imidoylamidine and triazine derivatives gave products with molecular weights too low for good physical properties. These products were also sensitive to the reaction conditions and therefore were not easily reproduced (Young, 1972). The properties of the cured perfluoroalkyl ether triazine elastomers were affected by the length of the alkyl ether region of the polymer, m + n value, and by the degree of polymerization between crosslinks,3c. Increasing the alkyl ether portion of the elastomer gave more chain flexibility and a lower glass transition temperature (Table I). Increasing the degree of polymerization between cross-links reduced the elastomer modulus (Table 11).
Perfluoroalkyl ether triazine elastomers showed lower isothermal weight losses than poly(trifluoropropy1methane siloxane), a thermally stable polyester sealant, and perfluoroalkylether oxadiazole elastomers (Rosser and Korus, 1980a). The high-temperature oxidative stability of the perfluoroether triazine elastomers showed a very marked improvement over state-of-the-art thermally stable elastomers. Initial weight losses of perfluoroalkyl ether triazine elastomers in air at 300 " C were only about 2% of the weight losses experienced by poly(trifluoropropylmethane siloxane). After 6-12 h in air at 300 "C the triazine elastomers showed little change in physical properties while the siloxane elastomers are reduced to a char. Triazine polymer synthesis is not limited to the perfluoroalkyl ether triazine polymers described. Similar synthesis procedures have been used for several perfluorodinitrile monomers and ring-closing reagents other than trifluoroacetic anhydride (Rosser and Korus, 1980b). Conclusions The difficulties experienced in fluoroalkyltriazine elastomer synthesis can be overcome by a four-step reaction process involving chain extension, triazine ring closure, cross-linking, and elastomer curing. Molecular weight can be controlled in the initial polymer formation so that elastomer modulus can be determined. The final product elastomers exhibit a useful elastomeric range from approximately -45 " C to 300 " C with an oxidative stability superior to other broad range elastomers. Literature Cited Dorfman, E.: Emerson, W. E.; Carr, R. L. K.; Bean, C. T. Rubber Chem. Technol. 1966, 39, 1175. Korus, R. A.; Rosser, R. W. Anal. Chem. 1978, 50, 249. Rosser, R. W.; Korus, R. A. J. Polym. Sci. Polym. Lett. Ed. I980a, 18, 135. Rosser, R. W.; Korus, R. A. US. Patent 3242498, 1980b. Rosser, R . W.; Korus, R. A,; Shalhoub, I. M.; Kwong, H. J. Polym. Scl., Polym. Lett. Ed. 1979, 17, 635. Rosser, R. W.; Parker, J. A,; DePasquale, R. J.; Stump, E. C., Jr. ACS Symp. Ser. No. 6 1975, 185-198. Young, J. A. "Fluoropolymers"; In "High Polymer Series"; Wlley-Interscience: New York 1972; Vol. 25, Chapter 9.
Received for reuiew April 27, 1981 Accepted August 31, 1981
Analogues of Polyacetylene. Preparation and Properties Walter Deb, Peter Cukor,' Michael Rubner, and Harriet Jopson GTE Laboratories, Incorporated, Waltham, Massachusetts 02254
Several analogues of polyacetylene including poly(phenylacetylene),poly(propiolonitrile), poly(3-chloro-l-propyne), and poly(3,3,3-trifluoro-l-propyne) in which the conjugated backbone of polyacetylene is retained but where the hydrogen atoms are replaced by different pendant groups were prepared and their physical, thermal, and electrical properties were investigated. All of the polymers examined showed significant increases in conductivity after exposure to iodine vapor with the maximum conductivities observed ranging from 6 X to 2 X ohm-' cm-'. Although polyacetylene is a known electronic conductor, the preponderance of evidence indicated that poly(phenylacety1ene) conducts through a predominantly ionic mechanism. Similar behavior was also observed for poly(propiolonitrile), poly(3-chloro-l-propyne), and poly(3,3,3-trifluoro-l-propyne). The thermal properties of the various materials examined were also found to be similar with poly(propiolonitri1e) displaying the greatest thermal stability.
Introduction The conduction of electricity in doped polyacetylene is believed to be facilitated by the migration of holes or electrons, created by dopants, along the conjugated backbone of the polymer. An increasing amount of interest 0 196-4321/8 1I1220-0696$0 1.25/0
has consequently been shown in a number of analogues of polyacetylene in which the conjugated backbone of polyacetylene is retained, but where the hydrogen atoms are replaced by various pendant groups. Numerous analogues of this type have been synthesized over the years (Masuda 0 198 1 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 697
et al., 1966; Akopyan et al., 1975); however, with the exception of poly(phenylacety1ene) (Cukor et al., 1981) and poly(methylacety1ene) (Wnek et al., 1981),few studies have included detailed physical and electrical characterizations of the materials involved. The nature of the pendant group has nevertheless been shown to influence strongly the chemical, mechanical, and electrical properties of the resultant polymer. Analogues of polyacetylene often have enhanced solubilities, for example, and consequently are more processable than polyacetylene. One such material is poly(phenylacetylene), in which every other hydrogen atom of polyacetylene is replaced by a phenyl group. Poly(phenylacety1ene) has been synthesized by various workers with the most detailed physical and chemical characterizations having been carried out by Masuda et al. (1974) and by Simionescu et al. (1977),while Cukor and co-workers (Cukor et al., 1981; Cukor and Rubner, 1980) have conducted detailed examinations of both the thermal and electrical properties. Other analogues of polyacetylene that have been prepared, but whose properties have not been investigated in detail, include poly(propiolonitri1e) (MacNulty, 1966; Misono et al., 1966) and poly(3-chloro1-propyne) (Akopyan et al., 1975). This paper will describe the preparation and properties of a number of analogues of polyacetylene including polyacetylene itself (I), poly-
Preparative Procedures. Polyacetylene was prepared according to the method of Wnek et al. (1979). Poly(phenylacety1ene) was prepared by a variety of methods described earlier (Cukor et al., 1981). Propiolonitrile was prepared by the amidation and subsequent dehydration of ethyl propiolate using a procedure similar to that of Moureau and Bongrand (1920). Thus, a 500-mL reaction kettle equipped with a dry ice/acetone condenser, an addition funnel, and a magnetic stirring bar was cooled in a dry ice/acetone slush bath and charged with approximately 340 mL (240 g, 14 mol) of liquid ammonia. Ethyl propiolate (85 mL, 82 g, 0.84 mol) was then added dropwise over 25 min. The mixture was stirred at -84 "C for 40 h after which it was allowed to warm to room temperature while the excess ammonia was distilled off. The byproduct ethanol and residual ammonia were then removed with the aid of an aspirator. Recrystallization of the resultant solid residue from boiling benzene yielded 35 g (60%) of pale yellow crystals (mp 61-2 "C). Crystalline propiolamide (3.7 g, 0.05 mol) was then blended with 61 g of finely ground sand and charged into three 8-in. test tubes. Powdered phosphorus pentoxide (17 g, 0.12 mol) was then added to each tube and the mixture shaken to mix the contents. After the remaining open volume of each tube was filled with glass wool, the tubes were connected by way of a glass manifold to a 5-mL -kCH=CH-f; -kCH=Ct -fCH=F % I collection vessel. The entire apparatus was alternately I I evacuated and purged with argon a totalof four times. The collection flask was then cooled with a dry ice/acetone N slush bath while the tubes containing the reaction mixture were heated with an oil bath to 155-165 "C. Heating was maintained for 2 h. After the collection vessel was isolated from the reaction tubes and was flushed with argon, the product was distilled at atmospheric pressure to give 1.2 g (44%) propiolonitrile (mp 5 "C; bp 42.5 "C). I V CI Poly( propiolonitrile) was prepared by two methods. IV Method A. Propiolonitrile (1.0 g, 0.02 mol) was charged into a dry argon filled Schlenk tube. Triethylamine (0.20 (phenylacetylene) (II), poly(propiolonitri1e) (1111,poly(3g, 0.002 mol) was then syringed onto the interior wall of chloro-1-propyne) (IV), and the previously unreported the tube, seconds after which a jet black film could be seen poly(3,3,3-trifluoro-l-propyne)(V). forming on all exposed surfaces. After 30 min, residual monomer and catalyst were removed with the aid of a Experimental Section dynamic vacuum and the product was dried at mm Materials were obtained from the sources indicated and for 24 h (MacNulty, 1966). were purified as follows. Benzene (BJ), toluene (BJ), Method B. Propiolonitrile (1.0 g, 0.02 mol) was charged hexane (BJ),and heptane (BJ),were distilled from sodium into a 50-mL round-bottom flask containing 20 mL of metal or sodium/potassium alloy. Tetrahydrofuran (THF) toluene. A Ti(B~O)~AlEt~/toluene catalyst solution (1.0 (BJ) was distilled from lithium aluminum hydride. N,NmL) (prepared from 1.7 mL of T ~ ( B U Oand ) ~ 2.7 mL of Dimethylformamide (DMF) (F)was distilled from calcium A1Et3 in 20 mL of toluene according to the procedure of hydride. Ethyl propiolate (A), 3-chloro-l-propyne(procatalyst pargyl chloride (A)), and 1,1,2-trichloro-3,3,3-trifluoro-l- Wnek et al. (1979), or a Cr(a~ac)~/AlEt~/toluene solution (1.0 mL) (prepared from 1.4 g of C r ( a ~ a cand )~ propene (PB) were distilled under argon. Triethylamine 2.2 mL of A1Et3 in 20 mL of toluene according to the (A) was distilled from sodium metal. Titanium(1V) butprocedure of Misono et al. (1966)) was then added to the oxide (AV) was distilled at reduced pressure. Sea sand (F) rapidly stirred solution over 3 min. After a total of 2 h, was ground into a powder using a glass mortar and pestle, the reaction mixture was added to 300 mL of hexane. The and dried at 150 "C for 24 h. Chromium(II1) acetylresultant precipitate was washed repeatedly with fresh acetonate (chromium(II1) 2,4-pentanedionate (AV)) was mm for 24 h. hexane and dried at sublimed at reduced pressure. Naphthalene (F) was subPoly(3-Chloro-1-propyne)was prepared by two limed at 60 "C under argon. Sodium (AV) and potassium methods. (AV) metal were used in a freshly cut state. Ammonia (MI, Method A. 3-Chloro-1-propyne (8.0 g, 0.11 mol), palphosphorus pentoxide powder (F),triethylaluminum (E), ladium(I1) chloride (0.04 g, 0.003 mol), and DMF (30 mL) palladium(I1) chloride (F), zinc dust (F), zinc(I1) chloride were charged into a 50-mL round-bottom flask equipped (F), n-butyllithium (1.6 M in hexane) (A), and iodine (F) with an argon inlet and exit, a mechanical stirrer, a were used as received from freshly opened containers. thermometer, and a water-cooled condenser. The mixture (Key to suppliers: A, Aldrich Chemical Company; AV, Alfa was heated with stirring at a pot temperature of 100 "C Division-Ventron Corporation; BJ, Burdick and Jackson for 4 h after which the contents were poured into 200 mL Laboratories, Inc.; E, Ethyl Corporation; F, Fisher Scienof methanol. The resultant precipitated was washed retific Corporation; M, Matheson Corporation; PB, Pfaltz peatedly with fresh methanol and hexane and dried at and Bauer, Inc.)
6
il
698
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981
mm for 24 h (Akopyan et al., 1975). Method B. A thick-walled glass polymerization tube was charged with DMF (15 mL), palladium(I1) chloride (0.03 g, 0.00016 mol), and 3-chloro-1-propyne (4.0 g, 0.05 mol). The mixture was degassed by carrying out a total of four freeze/thaw cycles after which the tube was sealed under vacuum. After 94 days, the tube was opened and the contents were poured into 100 mL of methanol. The resultant precipitate was washed repeatedly with fresh mm for 24 h. methanol and hexane and dried at 3,3,3-Trifluoro-l-propynewas prepared by a procedure similar to that of Finnegan and Norris (1963). Thus, a 500-mL round-bottom flask was equipped with a thermometer, mechanical stirrer, water-cooled condenser, and addition funnel. The outlet of the condenser was attached to a cold trap, which was in turn connected to a double manifold capable of operating as a vacuum line or as a dry argon supply. The entire apparatus was flame dried under an argon purge and was maintained under a positive pressure of argon throughout the course of the reaction. In a typical preparation, zinc dust (36.0 g, 0.550 mol), zinc(I1) chloride (3.40 g, 0.025 mol) and DMF (200 mL) were charged into the reaction vessel and heated to 100 "C. 1,1,2-Trichloro-3,3,3-trifluoro1-propene (50.0 g, 0.250 mol) was then added slowly to the reaction mixture over 50 min while maintaining the temperature at 100 "C. After the addition of the olefin had been completed, the mixture was cooled to 55 "C while a dry ice/acetone slurry was placed over the cold trap. Water (100 mL) was then added dropwise to the reaction mixture while it was stirred rapidly. The addition was complete in 40 min, during which time a quantity of clear liquid collected in the cold trap. After an additional 45 min stirring at 55-60 O C , the cold trap was isolated from the reaction apparatus and the liquid product was transferred to a previously evacuated stainless steel cylinder using standard trap-to-trap distillation techniques. A typical yield was 14.0 g (59%) of colorless volatile liquid (bp ca. -48 "C). Poly(3,3,3-Trifluoro-l-propyne)was prepared by two procedures. Method A. A thick-walled glass polymerization tube was charged with palladium(I1) chloride (0.020 g, 0.0001 mol) and DMF (10 mL) and degassed by carrying out a total of four freeze/thaw cycles. The tube was then cooled to -76 "C using a dry ice/acetone slush bath, and 3,3,3trifluoro-1-propyne (2.7 g, 0.03 mol) was transferred into it from a previously filled gas bulb of known volume using standard trap-to-trap distillation techniques. The tube was then sealed and allowed to come to room temperature. After 80 days, the tube was opened and the solid contents were washed repeatedly with methanol and heptane and mm for 48 h. dried at Method B. A 100-mL round-bottom flask was equipped with a thermometer, a dry ice/acetone cooled condenser, and a gas inlet. The entire apparatus was flame dried under argon purge and was maintained under a positive pressure of argon throughout the course of the reaction. In a typical procedure, the reaction flask was charged with heptane (40 mL) and degassed by cooling to -76 "C with a dry ice/acetone slurry and exposing to dynamic vacuum. 3,3,3-Trifluoro-l-propyne (17.6 g, 0.187 mol) was then transferred into the flask from a previously filled gas bulb of known volume, after which argon was introduced and the contents were allowed to warm to room temperature. Four 1.0-mL portions of n-butyllithium (1.6 mol/L in hexane) were then added over a 4-h period while an oil bath surrounding the reaction flask was raised to 110 "C. A vigorous reflux which commenced when the oil bath
temperature reached 45-50 O C continued throughout the course of the reaction. The reaction mixture was stirred for an additional 3 h, after which it was allowed to cool to room temperature and poured into 300 mL of methanol. The resultant precipitate was washed repeatedly with methanol and heptane and dried at mm for 48 h. Doping Procedures. Method A. Samples were exposed to iodine vapor at a pressure of 0.1 mm. The maximum uptake of iodine was determined by weighing the samples at periodic intervals until a constant weight was obtained. Method B. Samples were immersed in a sodium naphthalide solution (1.1g of sodium, 6.4 g of naphthalene according to a method described by Sorenson and Campbell (1968) in 50 mL of THF for 0.5 to 4 h after which they were washed repeatedly with fresh THF, then dried at lo4 mm for 8-24 h. Method C. Samples were exposed to sodium or sodium/potassium vapor by suspending them over molten sodium or a sodium/potassium alloy maintained at 170-180 "C. The sample chamber was maintained a t 110-120 "C and mm. Measurements. Infrared spectra were recorded on a Perkin-Elmer 299B infrared spectrophotometer and a Nicolet 3600E Fourier Transform infrared spectrophotometer. The solid state IR spectroscopy was not run with the exclusion of air and moisture. Therefore, the broad absorption peaks around 3400 cm-' were traced to the presence of moisture in the KBr pellet. Also, the carbonyl absorption around 1700 cm-' was probably due to oxidation of the polymers during handling. These extraneous features are absent in the spectra of the more vigorously handled liquid samples. X-ray diffraction patterns were recorded on a Phillips vertical diffractometer with a solid-state scintillation detector. Proton magnetic resonance spectra were recorded on a Varian EM390 nuclear magnetic resonance spectrometer. Scanning electron micrographs were obtained using a Jeolco U3 instrument. Diffuse reflectance measurements were made on a Cary 17D visible-ultraviolet spectrophotometer. Thermal analyses were carried out on a DuPont 990 differential scanning calorimeter and a DuPont 950 thermogravimetric analyzer. DC conductivities were measured on compressed pellets or films using standard four-point probe techniques.
Results and Discussion Polyacetylene. Polyacetylene samples with varying microstructures were prepared using a variety of experimental procedures (Deits et al., 1981a). The conductivity of those materials after doping with iodine was found to be related to the morphology, crystallinity, and configuration of the polymer chains, the closest relationship being with the crystallinity as evidenced by X-ray diffraction. Highly crystalline and semicrystallinesamples were found to be highly conducting (conductivities ranging from 50 to 500 ohm-' cm-') with the most crystalline samples showing the highest conductivity. Other semicrystalline materials, on the other hand, were found to contain an appreciable amorphous fraction whose presence was indicated by appearance of a broad peak in the various X-ray diffraction patterns at 26 = 16" and which coincided with greatly decreased levels of conductivity (-5 X lo4 ohm-' cm-'). All of the materials prepared were insoluble, doped to high levels ((CH)10,15to (CH)10.25)and each exhibited a distinct semiconductor to insulator transition. The doping process itself was essentially irreversible, as in the case of each polymer only minimal amounts of iodine could be removed through solvent extraction, dynamic vacuum, or electrolysis. Detailed accounts of the thermal, mi-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 800
crostructural and electrical properties are described ehewhere (Deits et al., 1981b). Poly(phenylacety1ene). Poly(phenylacety1ene) was prepared in the amorphous (cis and trans) and crystalline (cis) states. Amorphous material was prepared by the methods reported in a series of papers by Masuda and co-workers (Masuda et al., 1979). The procedures involved utilized a catalyst solution in benzene for the polymerization of phenylacetylene monomer. Using a MoCl, catalyst at temperatures below 40 O C , for example, yielded the cis isomer almost exclusively, while a trans-rich polymer was obtained from a WCl, catalyst solution. The cis amorphous material was also separated into high and low molecular weight portions by fractional precipitation, ushg benzene as a solvent and methanol as a nonsolvent. The predominantly cis material was an orange powder, while the trans-rich polymer had a reddish brown color. Both the cis and trans amorphous polymer were readily soluble in nonpolar solvents. Crystalline cis-poly(phenylacety1ene), on the other hand, was prepared by the method of Kern (19691, which involved polymerizing phenylacetylene in benzene solution with the aid of a Fe(a~ac)~/Al(Bu)~ catalyst mixture. The polymer thus obtained was an orange powder which was insoluble in common organic solvents; heating to about 120-130 OC, however, converted it to the soluble, amorphous trans isomer. This transformation was evidenced by changes in the IR spectra and its mechanism is thought to involve bond breaking and rearrangement (Simionescu et al., 1980). Although there were qualitative differences in the electrical properties of the various forms prepared, no quantitative difference emerged. In the course of the characterization of the polymer, it was noted that the polymer underwent chain scission without loss of weight upon heating above 130 O C (Cukor and Rubner, 1980). The significance of this strong molecular weight dependence on thermal history is realized when one considers the inconclusive and often contradictory results obtained by earlier workers in studies concerned with the electrical properties of polyphenylacetylene (Holob, 1975). As with polyacetylene, the conductivity of poly(phenylacetylene) also increased drastically upon iodination. The conductivity of the parent polymer was about ohm-' cm-', while the maximum conductivity on iodination was near lod5ohm-' cm-'. This occurred at the maximum doping level of 100 mol % iodine uptake where mole percent is defined as gram-atoms of I per gram-atom of repeat units of the polymer expresed as a percentage. The dependence of conductivity on iodine concentration could be expressed by the equation u = ,6 exp(yc(1 - c ) - y/4) where u is dc conductivity and c is mole fraction of iodine expressed as I and y is an experimentally determined constant related to slope of the log uRT vs. c(1- c) curve. No semiconductor to metal transition was observed and the level of maximum conductivity was considerably below that of doped polyacetylene. Iodine was shown to be present as 13-and Is-. It was observed that the activation energy of conductance decreased as dopant concentration increased. The doping process itself was also shown to be reversible; i.e., it was possible to quantitatively remove the dopant from the polymer using either solvent extraction or dynamic vacuum techniques. Furthermore, electrolysis of iodinated poly(phenylacety1ene) led to a polarization of the electrodes and the deposition of an iodine-containing film on the positive electrode. This occurred after relatively small amounts of current had passed through the
m
3000
2000
1m
1200
800
WAVENUMBER (cm-1)
Figure 1. Infrared spectra of (a) propiolonitrile and (b)poly(propiolonitrile).
system. On the other hand, polyacetylene, a known electronic condudor, passed large amounts of current without any polarization (Chiang et al., 1978). On the basis of the preponderance of evidence, we have developed the hypotheais that poly(phenyiacety1ene)becomes an ionic conductor upon iodine doping (Cukor et al., 1981). This conclusion is substantiated by calculations involving the Nemst-Einstein equation in which calculated maximum conductivities are essentially identical with measured ones. The model of conductance arrived at suggests that a thermally activated charge transfer takes place between the iodine and the polymer, forming negatively charged iodine species. This charge-transfer process becomes easier at higher iodine concentrations. The iodine ions migrate and carry the electric current through the polymer with the extent of conductivity being determined by the number of charge carriers rather than by their mobility. This model explains the behavior of many iodinated polymers that differ considerably from polyacetylene. Synthetic procedures, as well as detailed evaluations of the thermal and electrical properties of poly(phenylacetylene),are described in some of our earlier publications (Cukor et al., 1981; Cukor and Rubner, 1980). Poly(propiolodtri1e). In addition to polyacetylene and poly(phenylacetylene), amorphous poly(propio1onitrile), where every other hydrogen atom of polyacetylene has been replaced by a nitrile group, has also been prepared. The preparation of the monomer (propiolonitrile) was straightforward starting with ethyl propiolate which, when reacted with liquid ammonia, gave propiolamide in nearly 40% yield. Pale yellow crystals of propiolamide were isolated by recrystallization from boiling benzene. A major byproduct of this reaction was a yellow oil whose IR spectrum indicated that it was a co-oligomer of ethyl propiolate and propiolamide. Propiolonitrile can be readily polymerized upon exposure to base. The organic base triethylamine was utilized to form a very black powdery polymer in high yield. The polymerization reaction could be carried out either in the liquid or in the gas state. When triethylamine was introduced into a vessel containing gaseous propiolonitrile, for example, initiation took place in the gas phase and the poly(propiolonitri1e)was deposited as a film on the walls of the reaction vessel. This technique was utilized to coat strips of Teflon and glass with a layer of polymer approximately 0.025 mm thick. The Teflon strips coated in this manner could be bent OF cut without cracking the polymer coating. The infrared spectrum of both the monomer and polymer (Figure l) matched those described in the literature (MacNulty, 1966) with major absorption bands at 3320 cm-' (H-C E stretching), 2270 cm-* (C= N stretching), 2070 cm-' (C C stretching), and 1320,
700
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, I981 -5 I
/ 20
z 51
0
10
20
30
50
40
60
70
80
HOURS
Figure 2. Iodine uptake of poly(propio1onitrile) prepared with (a) as a function of T ~ ( B U O ) ~ / A(b) ~ EEt3N, ~ , and (c) Cr(a~ac)~/AlEt$ time.
1305 and 680-645 cm-' (H-C = deformation overtones) and at 3450 (H-C stretching), 3050-2960 cm-' (aliphatic C-H stretching from Et,N end groups), 2290 (C N stretching), and 1620 and 1480 cm-' (C = N and C E C conjugated structures), respectively. Poly(propio1onitrile) was also prepared using both a mixture of chromium(II1) acetylacetonate and triethylaluminum in toluene, a homogeneous ZieglerNatta type catalyst commonly used for preparing polymers from acetylene derivates, and a mixture of titanium tetra-n-butoxide and triethylaluminum in toluene (the "Shirakawa catalyst") (Ito et al., 1974), an effective catalyst for the preparation of unsubstituted polyacetylene. Both preparations yielded a small amount of dark brown material with an infrared spectrum identical with that obtained from the triethylamine catalyzed mixture. The electrical conductivities of the three preparations were also similar I: ohm-' cm-'). All of the preparations yielded material that was found to be insoluble in common organic solvents. Meaningful CHN analysis of poly(propiolonitri1e) is difficult to obtain due to the tendency for spontaneous combustion. Similar difficulties were reported by MacNulty (1966). These problems preclude the estimation of molecular weight by end group analysis. Poly(propiolonitri1e)showed no significant weight gain or increase in conductivity after exposure to sodium vapor at 110-120 "C for 5 days, or after immersion in an ether/sodium naphthalide solution for 2 h. Upon exposure to iodine vapors, however, the triethylamine and the chromium acetylacetonate/triethylaluminum catalyzed materials picked up 52 and 49 mol ?% iodine, respectively, after 260 h, while the material prepared with the titanium tetra-n-butoxide-triethylaluminum catalyst picked up 68 mol 5% iodine after only 43 h. The iodine uptake of the various materials as a function of time is illustrated in Figure 2. The conductivity of all of the materials increased rapidly with an increase in iodine content; however, the distinct semiconductor to metal transition present in the case of polyacetylene is clearly absent in this case, as can be seen in Figure 3. The maximum conductivities of all of the poly(propiolonitri1e) samples prepared were nearly the same, ranging between 9 X and 1 X lo-' ohm-' cm-' for the anionically initiated material. Upon exposure to dynamic vacuum, the iodine doped polymers rapidly lost weight, eventually leveling off after approximately 12 h (Figure 4). The Ziegler-Natta catalyzed polymers had a 30-32 mol % iodine level remaining. Despite the difference in residual iodine content, however, the conductivity of the titanium tetra-n-butoxideltriethylaluminum prepared material dropped back down to the level of the undoped material ohm-' cm-'1, while the triethylamine prepared polymer retained a conductivity of 3 X lo4 ohm-' cm-'. Both solvent extraction and electrolysis also resulted in a rapid loss of iodine with an accompanying decrease in conductivity. f
-11
20
0
60
40
80
IODINE CONTENT (MOLE %)
Figure 3. Conductivity of poly(propio1onitrile) prepared with (a) Et3N and (b) Ti(BuO),/A1Et3as a function of iodine content.
-
0
10
30
20
40
50
HOURS
Figure 4. Iodine content of poly(propiolonitri1e) prepared with (a) Ti(BuO),/A1Et3,(b) Cr(aca~)~/AlEt~, and (c) Et3N as a function of time exposed to dynamic vacuum.
I 0
1
I
I
I
J
100
200
300
400
500
TEMPERATURE ( " C )
Figure 5. Differential thermogram (DTA) of polypropiolonitrile prepared with EbN.
The infrared spectra of the iodinated materials showed an increase in the absorption intensity of the band at 1620 cm-l, indicating that an interaction with the unsaturated portions of the molecules had taken place. After exposure to dynamic vacuum, however, the infrared absorption cit 1620 cm-' was of lower intensity than that of the fully iodinated material, although it was still more intense than that of the native noniodinated polymer. This is consistent with the notion that the polymer iodine interactions are at least partially reversible upon exposure to dynamic vacuum.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 701 r
"
"
"
"
"
"
"
1
8
'O0O 8o
200
400
600
800
1000
1200
TEMPERATURE ('C)
(b)
'
Figure 6. Gravimetric thermogram (TGA) of polypropiolonitrile prepared with Et3N.
Differential thermal analysis (DTA) of Et3N initiated polypropiolonitrile (Figure 5 ) showed three distinct exotherms centered at 140,215, and 255 OC (heating rate 10 OC/min), the latter two of which appeared to correspond with steps observed in the thermogravimetric analysis (TGA) (Figure 6) at 225 "C (heating rate 20 OC/min). Furthermore, an examination of the infrared spectrum of a sample of poly(propiolonitri1e) annealed in nitrogen at 135 OC for 10 min shows a significant increase in the intensity of the absorption at 1620 cm-'with a proportionate decrease in the intensity of the absorption at 1450 cm-'. Samples annealed at 210 and 255 OC showed similar behavior with the respective increase and decrease in absorption intensities more pronounced at the higher temperatures. "his behavior is indicative of thermally induced chain transformations such as isomerization, cycIization, cross-linking, and degradation. Thus,the DTA exotherm occurring at 140 "C can be attributed to a cis-trans isomerization similar to that observed in polyacetylene and poly(phenylacety1ene) at 145 and 130 OC, respectively. The assignment of this thermal event to an isomerization is speculative in the respect that it is based on analogy. It is however, supported by the TGA data which showed little weight loss below about 175 OC. It is not unreasonable to expect a significant amount of cyclization involving the pendant nitrile groups to occur on heating (eq 11, as is
I 4000
I
1
3000
I
1
2000
1
I
1
1600
I
I
1200
I
800
WAVENUMBER (cm-')
Figure 7. Infrared spectra of (a) 3-chloro-1-propyneand (b) poly(3-chloro-1-propyne).
stretching), 1650 and 1585 cm-' (C=C stretching doublet), 1470 cm-' (CH2 deformation), 1025 cm-' (out of plane 4 - H stretching), and 885 and 865 cm-' (C-Cl stretching doublet) consistent with the expected structure. It should also be noted that the acetylene C=C stretching band of the monomer at 2130 cm-' is absent in the spectrum of the product. A high yield of material identical in appearance and infrared spectrum was also obtained by sealing propargyl chloride in a glass polymerization tube with a mixture of PdC12in DMF' for 94 days at rmm temperature. This material was also found to be insoluble in common organic solvents. When exposed to iodine vapor poly(3-chloro-1-propyne) increased rapidly in weight, eventually becoming a soft, almwt pastelike material that could be easily pressed into shiny pellets. The dc conductivity of the iodinated material was found to be approximately 2 X ohm-' cm-l, four orders of magnitude higher than that of the native polymer (a = lo-' ohm-' cm-'). Poly(3,3,3-trifluoro-1-propyne). The preparation of poly(3,3,3-trifluoro-l-propyne)(V) utilized 3,3,3-trifluoro-1-propyne (VI) as a starting material, which was in turn obtained through the dehalogenation of 1,1,2-trichloro-3,3,3-trifluoro-l-propene(VII) with zinc dust as shown in eq 2. Although a number of solvents including ZnCll
I
I
I
I
(1)
observed during the formation of "black orlon" (MacNulty, 1966). This cyclization consequently would lead to the formation of a significant amount of thermally stable ash. This is, in fact, what was observed in the TGA analysis where nearly 50% of the material remained after heating to 1100 "C. Poly(3-chloro-1-propyne). Poly(3-chloro-1-propyne) (IV) was produced in nearly quantitative yield from 3chloro-1-propyne monomer when refluxed with PdClz,in DMF at 110 "C for 4 h. The polymer, a dark black solid, was found to be insoluble in nearly all organic solvents; however, a small fraction of the material could be solubilized upon prolonged extraction with methylene chloride. The infrared absorption spectrum of the material (Figure 7) shows broad peaks centered at 3420 cm-' (=C-H stretching) and 2970 cm-' (-C-H stretching), as well as narrower'and more well defined peaks at 2780 cm-' (-C-H
CF3CC1=CC12 + 2Zn (VII) (CF3C=C)2Zn or CF3CrCZnC1
HpO
CF3C=CH (2)
VI N,N-dimethylacetamide and N-methyl-2-pyrrolidoneare suitable for the preparation of VI, DMF was found to give the cleanest product in the highest yield. It should also be noted that upon addition of water, gaseous products are evolved rapidly; hence, care must be taken so as to prevent unnecessary frothing of the reaction mixture as well as appreciable loss of product and subsequent lowering of yield. Thus, using the procedure described, VI was isolated as a colorless, volatile liquid (bp ca. -48 "C)and stored in a clean, dry stainless steel cylinder. The infrared spectrum of VI (Figure 8) revealed the expected C-H stretching band at 3330 cm-', a C=C stretching band at 2155 cm-l, and strong C-F stretching bands at 1260,1255, 1245, and 1180 cm-'. 3,3,3-Trifluoro-l-propyne was subsequently reacted with a PdClZ/DMFcatalyst/solvent mixture for 5 h at 60 "C to produce a viscous brown oil that was found to be soluble in most organic solvents. The infrared spectrum of the
-
702 Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 3000
4000
2000
I 4000
,
, 3600
,
,
3200
,
,
2800
I
,
I
2400
I
,
I
1
2000
800
1200
1600
'
I
I
"
I
1600
'
/
1
1
1200
,
1
I
BOO
WAVENUMBER (em-') l
Figure 8. Infrared spectra of (a) 3,3,3-trifluoro-l-propyne and (b) poly(3,3,3-trifluoro-I-propyne).
product was characteristic of the expected polymer structure (V) with a weak vinyl C-H stretch at 2965 cm-', a weak C S stretch from 1600 to 1700 cm-', and broad C-F stretching absorbances from 1000 to 1400 cm-I with strong maxima at 1150 and 1260 cm-'. A weak absorbance at 800 cm-', characteristic of amorphous perfluorinated hydrocarbon polymers, was also observed. It should also be noted that the strong c--=C stretch at 2155 cm-' present in the spectrum of the monomeric starting material was absent in the spectrum of the product. The polyene structure was also confirmed by NMR as only a single sharp resonance at 6 5.25 was observed, consistent with the presence of numerous equivalent vinyl protons. The broad solubility of the material coupled with its low inherent viscosity (0.08 dL/g; 0.5% in DMF) were indications that the product was of low molecular weight, however. Although the PdC12/DMF catalyst system produced a low molecular weight viscous brown oil when reacted with VI for 5 h at 60 "C, a high yield of insoluble light brown powder was produced when it was sealed in a polymerization tube with VI for nearly 80 days at room temperatwe. The infrared spectrum of the product (Figure 8)was similar to that of the material isolated from the first procedure; however, additional absorptions at 1375 and 905 em-' were also present. On the other hand, the use of n-butyllithium as an initiator in hexane yieIded an insoluble brown powder with an infrared spectrum essentially identical with that of the soluble oil produced with the PdC12/DMF catalyst. The reaction with n-butyllithium, although slow at -76 "C, was rapid at elevated temperatures (50-60 "C), yielding over 16% product in less than 4 h. The results of the elemental analysis for the PdC12 catalyzed polymer were C, 30.25;H, 0.94; N,0.37; F, 62.6 (neutron activation); for the n-butyllithium initiated polymer, the values were C, 34.34;H, 1.4;N,0.12;F, 61.1;the theoretical values are C, 38.32;H, 1.07;F, 60.6. All of the poly(3,3,3-trifluoro-l-propyne) samples prepared were highly insulating, having conductivities less than ohm-' cm-l. When exposed to iodine vapor for 96 h, however, the n-butyllithium initiated material picked up 98 mol % iodine, calculated as [I]/[repeat unit of polymer] X 100,and reached a maximum conductivity of 9.5 X 10" ohm-' cm-' without going through a distinct insulator to semiconductor transition. Although this represented an increase in conductivity of over five orders of magnitude, it appeared that this was more the result
I
200
,
I
400
,
I
/
600
TEMPERATURE I C 1
Figure 9. Differential thermograms (DTA's) of poly(3,3,3-trifluoro-l-propyne): (a) n-butyllithium initiated material run in nitrogen; (b) n-butyllithium initiated material run in air; and (c) PdC12/DMF catalyzed material run in nitrogen.
of iodine adsorption rather than the formation of a charge-transfer complex. When exposed to dynamic vacuum, the iodinated material quickly lost weight, dropping from 98 mol % to 26 mol % in less than 5 h. The conductivity during this stage dropped rapidly, reaching the level of the noniodinated material within 10 h. Similar results were obtained through the use of solvent extraction techniques. It should also be noted that the color of the bulk of the polymer did not change during the doping process; however, the surface of the polymer did change from brown to purple (the characteristic color of adsorbed iodine) at the higher dopant levels. This was in contrast to poly(phenylacetylene),which changes from red to black upon exposure to iodine vapor. In contrast to the n-butyllithium initiated material, the PdC12/DMF catalyzed polymer only picked up 16 mol 70 iodine and showed no significant change in conductivity. Although poly(3,3,3-trifluoro-l-propyne) interacts only weakly with iodine, a p-type dopant, the strong electron withdrawing CF, pendant groups on the polymer chain should enhance the ability of the polymer to form an ntype semiconductor. For this reason, n-butyllithium initiated material was exposed to a 0.08 M solution of sodium naphthalene, an n-type semiconductor dopant, for 72 h. Within 1 h the color of the solution changed from greenish-black to clear, indicative of the destruction of the sodium naphthalide charge-transfer complex. Although it seems reasonable that the polymer had indeed formed a new charge-transfer complex with the sodium cation, and despite the fact that the polymer was found to have picked up 57 mol % sodium, no significant change in conductivity was observed. An extensive thermal investigation was also performed on the polymer. DTA and TGA curves (Figures 9 and 10, respectively) were generated for each material in both air and nitrogen. The n-butyllithium initiated polymer showed no weight loss at temperatures below 240 "C in either air or nitrogen. A t temperatures above 240 "C, however, there was a rapid weight loss which could be associated with intense exothermic activity in the DSC curve. In the case of the DSC run in nitrogen, the exotherm started near 150 "C and continued until almost 450
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 703
20
ln
40
9 c
-
i
-
1
-
4 3
60-
3
1
80
I
c,
0
P 4
rl
2
-
looo
'
I
200
1
8
400
'
'
I
600
E
"1
800
1000
1200
TEMPERATURE ( " C )
Figure 10. Gravimetric thermograms (TGA's) of poly(3,3,3-trifluoro-1-propyne): (a) n-butyllithium initiated material run in nitrogen; (b) n-butyllithium initiated material run in air; and (c) PdC12/DMF catalyzed material run in nitrogen.
"C with three discernible peaks occurring within this range. This behavior is similar to that observed with polyacetylene, which also exhibits three broad major exothermic peaks corresponding to cis/trans isomerization, hydrogen migration accompanied by cross-linking, and thermal decomposition. The DSC run in air, on the other hand, had two small exothermic peaks, one at 175 "C and one at 350 "C, followed by a very large exotherm at 460 "C. The latter exotherm corresponded to a second major weight loss at the same temperature in the TGA curve run in air. The TGA run in nitrogen, however, had only one continuous weight loss starting at 240 "C and continuing up to 900 "C. In contrast, PdC12/DMF catalyzed material started to lose weight at 200 "C in nitrogen, corresponding to an exothermic peak in the DSC curve at 200 "C and reaching a maximum at 250 "C. The thermograms of this material closely resemble the profiles obtained for poly(phenylacetylene). Summary A number of analogues of polyacetylene in which the conjugated backbone of polyacetylene is retained, but where the hydrogen atoms are replaced by various pendant groups, have been prepared and characterized. These include polyacetylene, poly(phenylacetylene), poly(propiolonitrile), poly(3-chloro-l-propyne),and poly(3,3,3trifluoro-1-propyne). The electrical properties of the various analogues of polyacetylene are summarized in Table I. Although the four substituted analogues of polyacetylene were similar in many respects, all differed markedly from the unsubstituted polymer. Polyacetylene, for example, reaches high levels of conductivity upon doping with iodine, while the substituted analogues only reach semiconducting levels. In addition, the marked semiconductor to metal transition that can be observed with polyacetylene is absent in the analogues. The nature of the polymer iodine charge-transfer complex also seems to differ as the formation of the complex is an essentially irreversible process in the case of polyacetylene, while the majority of the incorporated iodine can be removed from the doped analogues by solvent extraction, dynamic vacuum, or electrolysis. The thermal properties of all the materials are similar in many respects with cis-trans isomerization and/or cross-linking possible in all cases. However, polyacetylene seems to be less susceptible to significant weight loss due to thermal treatment than are the analogues. Because of the similarities the four substituted analogues of polyacetylene exhibit, and in light
0 rl
2
u
c, I
3 rl
2
E
P
-3
42 I
3 r(
1
E
P 4
Y
3 3
n 2
c
P
!i
Y
0 5
P a 0
.t:
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 704-708
704
of the convincing evidence for the presence of ionic conductivity in poly(phenylacety1ene) presented in our earlier work (Cukor et al., 1981), it is reasonable to postulate a similar conductance mechanism for the other substituted materials. This is in contrast to the demonstrated electronic conductivity present in polyacetylene (Chiang et al., 1978). The reasons for this difference are not readily apparent at this time; however, the possibility of steric hindrance to the doping and/or conduction mechanisms due to the relatively large pendant groups present in the analogues is not unreasonable. This possibility is substantiated by work done by Wnek et al. and Deits and co-workers who demonstrated similar low conductivities for the polyacetylene analogues poly(methylacety1ene) (Wnek et al., 1981) and acetylene/methylacetylene copolymers, and acetylene/phenylacetylene (Deits et al., 1981c) copolymers, respectively. However, relatively high conductivities (lo-' ohm-' cm-') were reported for the sterically hindered iodine doped poly( 1,6-heptadiyne) (Gibson et al., 1980). While generally inferior to polyacetylene in their electrical properties, the analogues and copolymers demonstrate that the substitution of organic moieties for at least some of the hydrogen atoms in polyacetylene does lead to an increase in the solubility or swellability of many of these polymers. Poly(pheny1acetylene), for example, is completely soluble in a number of nonpolar solvents in its amorphous form, while other analogues such as poly(3,3,3-trifluoro-l-propyne)are soluble in many common solvents in their low molecular weight form. This can be envisioned as leading to a number of advantages in processing, for example, or in the ability to incorporate stabilizers or additives into the polymers.
Literature Cited Akopyan, L. A.; Grigoryan, S. G.; Zhan Rochyan, 0. A.; Matsoyan, S. 8. Vysokomol. Soyedin. 1975, A77, 2517 (translated in Polym. Sci. USSR 1975, 17, 2896). Cukor, P.; Rubner, M. F. J . Polym. Sci. Polym. Phys. Ed. 1960, 18, 909. Cukor, P.; Krugier, J. I.; Rubner, M. F. Mekromol. Chem. 1981. 182, 165. Chang, C. K.; Druy, M. A.; Gau, S. C.; Heeger, A. J.; Louis, E. J.; MacMarmid, A. G . , Park, Y. W.; Shirakawa, H. J. Am. Chem. SOC.1978, 100,
1013. Deits, W. J.; Cukor, P.; Rubner, M. F.; Jopson, H. J. Electron. Meter. 196la 10, 683. Deits, W. J.; Cukor, P.; Rubner, M. F. I n "Conducting Polymers"; Seymour, R., Ed.; Plenum Press: New York, 198lb. Deits. W. J.; Cukor, P.; Rubner, M. F.; Jopson, H. Synth. Met. 196lc, in press. Finnegan, W. G.; Nwris, W. P. J. Org. Chem. 1963,2 8 , 1139. Gibson, M. W.; Bailey, F. C.; Pochan, J. M.; Epstein, A. J.; Rommeiman, H. Org. Coating Pfast. Chem. 1960. 42, 603. Hoiob. 0. M. "Electron Spin Resonance and Electrical Conductivity in Polyphenylacetylene and its Charge Transfer Complex with Iodine"; Xerox University Microfilms: Ann Arbor, MI. 1975. Ito, T.; Shirakawa, M.; Ikeda, S. J. Polym. Sci. Polym. Chem. 1974, 12,
11. Ito, T.; Shirakawa, M.; Ikeda, S. J. Polym. Sci. Polym. Chem. 1975, 73,
1943.
Kern, J. J. Polym. Sci. Part A- 7 1969, 7 , 612. MacNuity, 6. J. Polymer 1966, 7 , 6. Masuda, T.; Masegawa. K.; Higashimura, T. Macromolecules 1974. 7 , 720. Misono, A.; Noguchi, M.; Noda, S. J. Polym. Sci. Pokm. Len. 196& 4 , 985. Moreau, C.; Bongrand, J. C. Ann. Chim. 1920, 14. 47. Simionescu, C. I.; Percec, V.; Dumitresu, S. J. Polym. Sci. Polym. Chem. Ed. 1977, 15, 2497. Simionescu, C. I.; Percec, V. J. Polym. Scl. Polym. Chem. Ed. 1960, 78,
147.
Sorenson, W.; Campbell, T. In "Preparative Methods of Polymer Chemistry". 2nd ed.;Interscience Publishers: New York, 1968. Wnek, G. E.; Chien. J. C. W.; Karass, F. E.; huy, M. A.; Park, Y. W.; MacDlarmid, A. G.; Heeger, A. J. J. Polym. Sci. Polym. Len. 1979, 17, 779. Wnek, G. E.; Capistran, J.; Chien, J. C. W.; Dickinson, L. C.; Gable, R.; Gooding, R.; Gourley, K.; Karasz, F. E.; Ullya, C. P.; Yao, K. D. "Conducting Polymers"; Seymour R., Ed.; Plenum Press: New York,
1981.
Received for review April 15, 1981 Accepted August 10,1981
Gluabifity of Copolymer Resins Having Higher Replacement of Phenol by Agricultural Residue Extracts Chla M. Chen School of Forest Resources, The University of Georgia, Athens, Georgia 30602
The newly developed copolymer resins with more than 50 wt % of the standard phenol replaced by the sodium hydroxide extracts of peanut hulls and pecan nut pith were evaluated by gluing southern pine plywood and three-layer oriented strand boards. By evaluation of southern pine plywood gluelines, the copolymer resins retain their fast curing characteristics even though 60 % by weight of the standard phenol was replaced by the extracts. In bonding the oriented strand boards, three copolymer resins with 60%, 80%, and 100% by weight of their standard phenol replaced by the peanut hull extracts were evaluated. The copolymer resin with 60 wt % of phenol replacement exhibited superior bonding qualities compared with the commercial resins. The resins with 80% and 100% by weight of phenol replacement had possibly pre-cured during the redrying process after the strands were coated with resins due to the excessive moisture content in the mat.
Introduction As the author reported in previous papers (Chen, 1981b,c),a family of fast curing copolymer resins made of bark and agricultural residue extracb has been developed for gluing exterior grade structural plywood, particleboards, oriented or nonoriented flakeboards,and composite panels. The copolymer resins with 40 wt % of standard phenol replaced by the extracts of natural residues provided satisfactory bond qualities in plywood, particleboards, flakeboards, and composite panels at approximately two-
third of the cure time required by the commercial control phenol-formaldehyde resins. The majority of the reports and patents by previous investigators indicated that the substitution of standard phenol with bark and other residue products was limited to less than 50% of the phenol. The use of more than 50% natural products to replace the standard phenol resulted in resins requiring a substantial increase of cure time (Herrick and Bock, 1958; McLean and Gardner, 1952; Stephan, 1954).
0196-4321/81/1220-0704$01.25/00 1981 American Chemical Society
