Macromolecules 1992, 25, 7392-7394
7392
Synthesis and Properties of Polyurethanes Containing Enaminonitrile Units in the Main Chain
Scheme I
Sang-TaeKim, Hyun-Syeok Moon, and Myoung-Seon Gong' Department of Chemistry, Dankook University, Cheonan 330-714, Chungnam, Korea Received April 22, 1992 Revised Manuscript Received September 3, 1992
Introduction It was reported that poly(enaminonitri1es) prepared by reacting p-bis( l-chloro-2,2-dicyanovinyl)benzene(3) with
Scheme 111
-2
I
3 -
diamines were thermally curable, stable polymers.'+ These polymeric precursors which cyclize to produce the thermally stable, rigid-rod polymer have been compared with polyimides as the thin films application without causing void and c~ntraction.~ Recently, it has been also reported that poly(enaryloxynitti1es)prepared from 3 and disodium salts of Bisphenol A showed excellent thermal stability after heat curing without evolution of small molecule^.^ Thus the synthesis of the polymers containing enaminonitrile units in the main chain has become an interesting consideration. A close analogy of chemical reactivity between the dicyanomethylidine group (=C(CN)z) and the carbonyl group has been pointed out by Wallenfels.8 l-(Chloro-2,2-dicyanovinyl)benzene (2) is in many ways similar to l-chloro-2,2-dicyanothene (1). It was conceivable that the incorporation of the phenyl group in 2 might make the carbon atom bearing chlorine less reactive toward nucleophilic substitution. One of the most remarkable reactions of 1 is its condensation with alcohol to give enalkoxynitrile, whereas 2 shows no reactivity to alcohol. Thus 2 condenses only with the amine group of amino alcohols to form alcohol derivatives containing an enaminonitrile group. In the present paper, we report details of a successful synthesis of a new class of thermal curable polyurethanes containing enaminonitrile units in the main chain. In addition, thermal properties of polyurethanes are investigated and presented.
Results and Discussion p-Bis(l-chloro-2,2-dicyanovinyl)benzene (3) can react with 2 mol of 2-(N-methylamino)ethanolto form the corresponding diol 4 containing an enaminonitrile group in high conversion as shown in Scheme I. Preparation of the model compound 5 was carried out before polymer synthesis to demonstrate the feasibility of the reaction for polymer formation and to obtain a model urethane compound containing the enaminonitrile functionality for use in polymer identification (Scheme 11). The polymerization proceeded by reacting 4 with various diisocyanates such as HDI, MDI, and TDI in an N-methyl2-pyrrolidinone (NMP) solution at 70 "C for 2 h in good yields (Scheme 111). 0024-9297/92/2225-7392$03.00/0
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The conditions adopted and the results of polymerization are summarized in Table I. When polymer 7 was compared with model compound 5, the spectral data of the polymer corresponded to those of the model compound. In the lH NMR spectra, the N-methyl and N-methylene protons in the 2-(N-methylamino)ethanol fragment appeared as a multiplet at 3.2 ppm, whereas 0-methylene protons are seen as a multiplet at 3.8 ppm in both 5 and 7. Polymer 7 was identified as a polyurethane by comparison of its N-H, C=O, and C-0 bands in the infrared spectra with that of 6. The proposed structures of polymers were also confirmed by satisfactory elemental analysis. When the solubility behavior of the polyurethanes was determined with powdered samples in excess solvent, all the polymers were soluble in polar aprotic solvents, such as DMF, DMSO, DMAc, and NMP, and partially soluble in 1,4-dioxane and acetonitrile. The polymers appeared to possess molecular weights of M,= 6500-7500 and& = 30 000-40 OOO. However, these are somewhat high molecular weights, judging from viscosity and GPC data. When films were cast by allowing the solvent to evaporate on a glass, clear and hard films were obtained. Polymer 8 shows interesting DSC traces (Figure 1). The small signal at 130 "C in the DSC curve of polymer 8 may be related to the glass transition temperature. Polymers 6-8 had similar DSC curves which exhibited a large exotherm at 272,302, and 293 OC,respectively, as shown in Table 11. This exothermic peak was completely absent when the samples were cooled and rescanned. After these polymers have been heated near the temperature of the exotherm, they are no longer soluble in the solvent for the untreated polymers. In addition, all three polymers displayed a rapid 0 1992 American Chemical Society
Macromolecules, Vol. 25, No. 26, 1992
Notes 7393
Table I Results of Polymerization of 4 with Diisocyanates diisocyanate solvent colop temp ( O C ) time (h) yield (%) Mnc MWC HDI NMP LB 70 2 93 0.52 6400 39000 MDI NMP LY 70 2 90 0.50 7600 43000 8 TDI NMP LY 70 2 88 0.65 6500 28000 Abbreviations: LY, light yellow; LB, light brown. * Viscosities of polymers were measured in NMP at a concentration of 1g/dL at 25 O C . c Values determined by GPC with DMF as a solvent (relative to polystyrene standards). polymer 6 7
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Figure 2. Infrared spectra of polyurethane derived from HDI after (a) 0 h and (b) 0.5 h at 300 OC under nitrogen. I
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Figure 1. (a) TGA and (b) DSC thermograms of the polymer obtained by tolylene 2P-diisocyanate and p-bis[l-[N-methylN-(hydroxyethyl)amino]-2,2-dicyanovinyllbenzene with a heating rate of 10 OC/min in N2. Table I1 Thermal Properties of Polyurethanes Containing Enaminonitrile Units 10% residual T, Tg exotherm wtloss wt at polymer (OC) (OC) (OC) ("CP 500 "C (%) 5 169 240 290 52 6 130 272 345 55 7 174 302 340 75 8 120 293 328 68 Weight loss is observed in TGA in nitrogen at a heating rate of 10 OC/min.
change in the IR spectra within 30 min at 300 "C. The urethane N-H stretching band at 3300-3400cm-l and the nitrile band near 2200 cm-l decreased as illustrated in Figure 2. At the same time, a broad, strong band at 17001580cm-l attributable to the C=C or C=N double bonds appeared. Besides the phenomena mentioned above, a slight loss of weight in their TGA curves up to the exotherm temperature also indicated that the structure of the polymer had changed. It might have happened that the rearrangement or cross-linking occurred during the heat treatment a t the temperature of exotherm. We cannot confirm at this time whether the curing occurred via intermolecular or intramolecular reactions of the polymer chain. It was found that the films of these polymers retained flexibility even after heating at 300 "C. The TGA curves of these polyurethanes are shown in Figure 1, and thermal data are listed in Table 11. The polymers retained 70-8076 of their mass at 400 "C and 55-70% at 500 "C. Upon comparison with poly(enaminonitrile~),~-3 the polyurethane containing enaminonitrile groups showed lessthermal stability despite similar DSC curves and curing
properties, which may probably be attributable to the presence of aliphatic hydrocarbon units in the chain.
Experimental Section p-Bis(l-chloro-2,2-dicyanovinyl)benzenewas synthesized by the modified method previously reported by Moore et al.3 Hexamethylene diisocyanate (HDI), 4,4'-methylenebis(pheny1isocyanate) (MDI), and tolylene 2,4-diisocyanate (TDI) were purified by the traditional purification method. The IR spectra were obtained with a Perkin-Elmer Model 1310spectrophotometer, and lH NMR spectra were recorded on a Varian 60-Am spectrometer. Elemental analysis data were obtained with a Yanaco MT-3, CHN analyzer. Thermal analyses were performed with a Du Pont ZOO0 thermal analyzer. Preparation of p-Bis[ 1-[N-methyl-N-(hydroxyethy1)amino]-2,2-dicyanovinyl]benzene(4). A total of 2.0 g (6.6 mmol) of 3 in 30 mL of methylene chloride was added slowly to 2.0 g (26.6 mmol) of 2-(N-methylamino)ethanolin 10 mL of methylene chloride, and the mixture was maintained at 40 OC with stirring for 20 min. The yellow solid was filtered and washed with 0.1 N NaOH and water. Recrystallization of the solid from acetonitrile gave 2.4 g (yield 80%)of 4. Mp: 237.6 OC. lH NMR (60 MHz, DMSO-&, ppm): 7.7 ( 8 , 4 H, phenyl), 4.3 (m, 2 H, 2 OH), 3.0-3.7 (m, 14 H, ~ C H ~ N C H ~ C HIR Z )(KBr, . cm-l): 3500 (OH), 2990 (CH), 2250 (CEN), 1600 (C=C), 1210-1110 (CO) cm-l. Anal. Calcd: C, 63.8; H, 5.3; N, 22.3. Found C, 64.1; H, 5.2; N, 22.2. Reaction of 4 with Phenyl Isocyanate for the Model Reaction. A solution of 1.0 g (2.6 mmol) of 4 in 10 mL of N-methyl-2-pyrrolidinone (NMP)was added slowly to a mixture of 1.9 ,uLof triethylamine and 0.63 g (5.3 mmol) of phenyl isocyanate in 5 mL of NMP under nitrogen. The temperature was raised to 70 OC and maintained for 2 h. The pale yellow solution was allowed to cool and was poured into a large amount of water to precipitate the product. The precipitate was filtered and recrystallized in hot methanol to give 1.38 g (yield 85%)of the model compound 5. Mp: 169 OC. lH NMR (60 MHz, DMSO-d6,ppm): 6.8-7.5 (m, 14 H, aromatic H's) 4.2 (m, 2 H, 2NW, 3.8 (m, 4 H, 2CHzO), 3.2 (m, 10 H, 2N(CH3)CHz). IR (KBr,cm-l): 3400 (NH),3000 (CH), 2200 (C=N), 1710 (C=O), 1600 (C=C), 1100-1300 (CO) cm-l. Anal. Calcd C, 66.5; H, 4.9; N, 18.2. Found: C, 66.2; H, 4.8; N, 17.9. Polymerization of 4 with Hexamethylene Diisocyanate (HDI). A solution of 1.0 g (2.6 mmol) of 4 in 10 mL of NMP was added to a three-necked flask equipped with a dropping funnel and a nitrogen inlet. After 3.7 p L (0.01 mmol) of triethylamine
7394 Notes
Macromolecules, Vol. 25,No. 26, 1992
CH&H20), 2.4 (8, 3 H, PhCH3). IR (KBr, cm-): 3400 (NH), was injected, a mixture of 0.44 (2.6 mmol) of HDI in 5 mL of 2920-2800 (CH), 2250 (C=N), 1720 (C=O),1610 (C=C), 1300freshly distilled NMP was added to the reaction flask with 1100 (CO) cm-1. Anal. Calcd for (CmH~Ns04)~: C, 63.3; H, 4.8; vigorous stirring. The temperature was raised to 70 OC and N, 20.4. Found: C, 63.8; H, 4.8; N, 20.1. maintained for 2 h. The pale yellow solution was allowed to cool and was poured into a large amount of water to precipitate the polymer. The precipitate was filtered and dried in vacuo (0.1 References and Notes Torr) at 60 "C for 12 h. Moore, J. A.; Robello, D. R. Polym. Prepr. (Am. Chem. SOC., Similar procedures were employed for the polymerization of Diu.Polym. Chem.) 1986, 27 (2), 127. 4 with 4,4'-methylenebis(phenylisocyanate) and tolylene 2,4Moore, J. A.; Robello, D. R. Macromolecules 1986,19, 2667. diisocyanate. Moore, J. A.; Robello, D. R. Macromolecules 1989,22, 1084. 6. Yield: 93%. 'H NMR (60 MHz, DMSO-&, ppm): 7.5 (8, Moore, J. A.; Mehta, P. G. Macromolecules 1988,21, 2644. 4 H, phenyl), 4.9 (m, 2 H, 2 NH), 2.3-4.0 (m, 18 H, 2N(CH& Moore, J. A.; Mehta, P. G. Polym. Mater. Sci. Eng. 1990,63, CH2CH2and 2NHCH2), 1.2 (m, 8 H, NCHK2Z2CH2CH2CHz351. CH2N). IR (KBr, cm-l): 3500 (NH),2250 (C=N), 1710 (C=O), Kim, S. T.; Lee, J. 0.;Gong, M. S. Polymer (Korea) 1991,15, 1610 (C==C), 1210 (CO) cm-l. Anal. Calcd for (C28H3204),,: C, 95. 61.7; H, 5.9; N, 20.6. Found C, 61.5; H, 6.0; N, 20.6. Kim, S. T.; Moon, H. S.; Gong, M. S. Makromol. Chem.,Rapid Commun. 1991,12, 591. 7. Yield: 90%. 'H NMR (60 MHz, DMSO-de, ppm): 7.0-7.7 Wallenfels, K.; Friedrich, K.; Rieser, J. Angew. Chem., Znt. (m, 12 H, aromatic H's), 4.8 (m, 2 H, 2NH), 3.2-3.9 (m, 14 H, Ed. Engl. 1976, 15, 261. ~N(CH~)CHZCH~O), 4.5 (m 2 H, PhCH2Ph). IR (KBr, cm-l): 3350 (NH), 3000-2800 (CH), 2250 (C=N), 1750 (C=O), 1610 (C=C), 1300-1200 (CO) cm-I. Anal. Calcd for ( C ~ S H ~ N ~ O ~ ) , , : Registry No. 3,103134-51-6; 4,144513-91-7; 5,144513-90-6; 6 (copolymer), 144513-97-3; 7 (copolymer), 144513-98-4; 8 (coC, 67.1; H, 4.8; N, 17.9. Found: C, 66.9; H, 4.8; N, 17.8. polymer), 144513-99-5;CHaH(CHz)20H, 109-83-1;PhNCO, 1038. Yield: 88%. 'H NMR (60 MHz, DMSO-&, ppm): 7.2 (m, 71-9. 7 H, aromatic H's), 4.6 (m, 2 H, 2NH), 3.2 (m, 14 H, 2N(CH3)-
