1438
I n d . Eng. Chem. Res. 1989, 28, 1438-1441
Epoxy-Modified Diallylbisphenol A and Bis(maleimidopheny1)methane Thermoset Compositions: Composition and Dynamic Mechanical Thermal Analysis Mohinder S. Chattha,* Ray A. Dickie, and Keith R. Carduner Research Staff, Ford Motor Company, Dearborn, Michigan 48128
Epoxy-modified bis(ma1eimide) high-temperature polymers suitable for high-performance adhesive, coating, and composite applications are described. Addition of epoxies to bis(ma1eimide) and diallylbisphenol A compositions provides low viscosity melts that produce, upon further heating, thermally stable cross-linked networks. When the epoxy is reacted separately with diallylbisphenol A, linear oligomers are obtained. These oligomers easily blend with bis(maleimidopheny1)methane t o provide thermoset powders. The powders produce homogeneous melts upon heating a t about 150 "C. Upon further heating above 200 "C, a highly cross-linked network is produced. Thermal gravimetric analyses (10 "C/min) of these compositions show that they do not undergo any thermal degradation in air up to 375 "C. The glass transition temperatures (T,) of the fully cured compositions are above 250 "C. The powder compositions exhibit more defined homogeneous structures and higher Tg'sthan the fully cured in situ epoxy-modified systems. For a polymer to be successful as a structural matrix, it must exhibit a favorable combination of processability, performance charcteristics, and price. High-temperature polymers for composite, adhesive, and coating applications must exhibit adaptability to conventional processing techniques at low temperature and pressure and must exhibit desirable mechanical properties as well as cost effectiveness. Polyimides offer desirable high-temperature mechanical properties; however, the severe processing conditions required have limited their use. In addition, many polyimide compositions are based upon condensation chemistry, which tends to result in the formation of voids in cured comositions, be they adhesives, coatings, or composites. Bis(maleimides), on the other hand, provide void-free cross-linked compositions. The materials have elevated temperature performance better than that of epoxies but not as good as that of polyimides. We have recently described the dynamic mechanical thermal analysis (DMTA) of bis(ma1eimide) and diallylbisphenol A compositions (Chattha and Dickie, 1989) that offer high-temperature properties desirable for adhesives and composites (Carduner and Chattha, 1987; Chaudhari et al., 1985; King et. al., 1984; Zahir and Renner, 1978). In this study, we describe the effects of including epoxy resins in these compositions as an integral part of the network. When the epoxies are added directly to the bis(maleimide) and diallylbisphenol A compositions, easily processable low viscosity melts are obtained. When the epoxies are prereacted with diallylbisphenol A and the resulting products compounded with bismaleimide, thermoset powder compositions are obtained.
Experimental Section Materials. Bis(maleimidopheny1)methane (1) was obtained from Ciba-Geigy Corporation. It is a commercial grade, yellow powder containing greater than 85 % theoretical maleimide double-bond content. Diallylbisphenol A (2) is also a Ciba-Geigy Corp. product. It is a commercial-grade, amber viscous liquid at room temperature, and its hydroxyl content is typically greater than 0.62 equiv/100 g. It was distilled under reduced pressure (bp 195-197 "C/0.05 mm), before use. The epoxy resins employed in this investigation were bisphenol A diglycidyl ether (Epon 828, Shell Chem. Co.) and epoxy resin Araldite XU252, which is a novalac-type multifunctional epoxy resin obtained from Ciba-Geigy Corp.
I
2
Sample Preparation. Sample A (Reaction Product of 1, 2, and Epon 828). Bis(ma1eimide) 1 (11.5 g), diallylbisphenol A (2,8.75 g), and Epon 828 (5 g) were placed in a beaker and stirred to obtain a paste. The beaker was placed in an oil bath at 150 "C, and the mixture was stirred to obtain a homogeneous melt. Equal amounts of the melt were poured into two aluminum pans, heated at 150 "C for 1 h, and then heated at 250 "C for 4 h. Sample B. This was prepared as sample A by employing only 3 g of the epoxy resin. Sample C (Reaction Product of Bis(ma1eimide) 1 with Oligomer Resulting from 2 and Epon 828). Epon 828 (4.7 g) and diallylbisphenol A (8.7 g) were mixed in a beaker and heated at 140 "C for 20 h. The infrared spectrum of the reaction mixture showed that the epoxy functionality of Epon 828 had essentially disappeared. Part of the product (250 mg) was drawn for NMR studies, and the remaining was allowed to cool to room temperature to obtain a solid material. Bis(maleimide) 1 (10 g) was added to the above product, and the mixture was maintained at 150 "C with stirring. In about half an hour, a homogeneous solution was formed. The melt was poured into a shallow pan, allowed to cool, and then ground to a powder. Half of this powder was placed in an aluminum pan and was heated in a vacuum oven at 150 "C; vacuum was applied to obtain bubble-free melt. It was heated at 150 "C for 1 h and then at 250 "C for 4 h. Sample D. Epon 828 (4.7 g) and diallybisphenol A (8.7 g) were reacted as described under sample C. Bis(ma1eimide) 1 (8 g) was then added to the reaction product, and the preparation was carried out as described under sample
c.
0888-5885189f 2628-1438$01.50/0 0 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 1439 DSC
236.8" C
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Figure 1. High-resolution 13C NMR spectrum acquired at 75.4 MHz using broad-band decoupling of the reaction product of 2 and Epon 828. Numbered resonances correspond to the reaction product shown in the text.
Sample E (Reaction Product of 1 with Oligomer Resulting from the Reaction of 2 with Araldite XU 252). Diallylbisphenol A (2,8.7 g) and epoxy resin Araldite XU 252 (4.3 g) were mixed in a beaker and placed in an oven at 140 "C for 16 h. The resulting solid product was reacted with 10.2 g of bis(maleimide) 1 as described under sample C. Thermal Characterization. Thermal decomposition of the polymers was studied with a Du Pont thermal gravimetric analyzer (TGA); the initial softening points were determined with a Du Pont 943 thermal mechanical analyzer (TMA) employing the penetration mode with a heating rate of 10 "C/min. The cure temperature and the heat of reaction were determined with a Du Pont 910 differential scanning calorimeter (DSC) at the heating rate of 5 "C/min under argon. The tensile storage modulus, E', and loss tangent, tan 6, were determined with a Polymer Laboratories dynamic mechanical thermal analyzer (DMTA) in the dual-cantilever beam mode. The sample was subjected to small oscillating deformation a t 0.1, 1.0, and 10 Hz while the temperature was increased from 50 to 450 "C at 1 "C/min. NMR Spectroscopy. High-resolution I3C spectra were acquired with a Bruker MSL 300 spectrometer at a resonance frequency of 75.4 MHz under conditions of broadband 'H decoupling. The acquisition employed a 30-deg read pulse and a 1-s recycle delay (Shoolery, 1977). Following acquisition, the time domain data were processed using standard Fourier transformation and phasing (Fukushima and Roeder, 1981). Spectra and referenced to TMS a t 0 ppm. Samples were prepared by 50/50 mixing of reaction products with deuterated chloroform. Results and Discussion Distillation of diallyl compound 2 at N 200 "C left only a small amount of liquid in the distillation flash. This indicates that the allyl groups are thermally stable and do not polymerize upon heating up to 200 "C. When 2 is heated with Epon 828, the phenol groups of 2 react with the epoxide groups of Epon 828 to produce allyl-bearing oligomers. The oligomers can be easily ground to powders that upon heating produce low viscosity melts. The formation of the oligomer was confirmed by I3C solution NMR of the reaction mixture of 2 and Epon 828. A representative spectrum is illustrated in Figure 1. The reaction of the epoxy groups was confirmed by the appearance of only residual intensities for the two carbons as-
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Figure 2. Differential scanning calorimetry of the starting reaction mixture of composition A at the heating rate of 5 OC/min.
sociated with the epoxy group at 49.5 and 43.8 ppm. Most of the resonances in this spectrum may be associated with the carbons of the reactants that are not involved directly in the oligomerization reaction. These have been assigned previously (Carduner and Chattha, 1988). The new carbon resonances labeled by numbers (Figure 1)correspond to the numbered carbons in the following reaction formula and are consistent with the oligomerization mechanism due to the reaction of the epoxide moieties with the phenolic groups: ,CH2CH=CH, &OH
'-'
+- CHzCHCH2-0
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When bis(ma1eimide) 1, diallyl compound 2, and Epon 828 are heated together (samples A and B), phenol 2 reacts with both 1 and 3 below 160 "C as seen from DSC (Figure 2) of the starting reaction mixture (sample A). The shape of the lower temperature exotherm shows that there is probably more than one reaction. The reaction at higher temperature (237 "C) is due to the cross-linking of maleimide and allyl unsaturations (Carduner and Chattha, 1987; Chattha and Dickie, 1989; Chaudhari et al., 1985; King et al., 1984). In the preparation of samples C-E, the epoxy groups are completely consumed by their reaction with the phenolic groups during prolonged heating a t 150 "C. The cross-linking in the compositions takes place through maleimide and allylic double-bond polymerization. The thermal mechanical analyses (TMA) did not indicate any distinct softening point up to 300 "C for any of these materials (Chattha and Dickie, 1989). In thermal gravimetric analysis, all of the cured compositions start to decompose in air around 400 "C. Thermal decomposition of composition A is shown in Figure 3. There is no loss of weight up to about 400 "C in air. Since these compositions showed only small and indistinct transitions in TMA, dynamic mechanical measurements were undertaken to obtain a more definitive investigation of the glass-transition behavior. Tensile storage modulus ( E ' ) and loss tangent (tan 6) data are presented in Figures 4-7 for samples A-E, respectively. The two ir? situ reacted materials (samples A and B) show a broad, gradual transition spanning a temperature range of at least
1440 Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 TGA
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Temperature, ("C) Figure 6. Dynamic mechanical thermal analysis, tensile storage modules, of compositions C (-), D (---), and E (--I.
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Figure 5. Dynamic mechanical thermal analysis, loss tangent, of compositions A (-) and B (- - -1.
100 "C. The breadth and shallowness of the transition is clearly responsible for the absence of a distinct transition in TMA experiments on these materials. The maximum in the loss tangent occurs at about 195 "C for sample A and at about 210 "C for sample B; the breadth of the transition is such, however, that the difference has no great significance. The drop in modulus accompanying the transition is less than 1order of magnitude. The breadth of the transition suggests a substantially heterogeneous structure. The shallowness of the drop in the modulus indicates that this structure is a tightly cross-linked one. At temperatures in excess of about 320 "C, there is an
abrupt drop in the modulus and increase in the loss tangent. From visual observations of the specimens, these changes appear to correspond to the onset of thermal degradation. The prereacted materials (samples C-E) display somewhat more distinct, but still relatively broad, transitions. The loss tangent maxima of samples C-E are centered at 260, 280, and 285 "C respectively. The drop in modulus corresponding to the glass transition is again rather shallow and decreases in magnitude in the order C > D > E. A detailed interpretation in terms of cross-link density is risky at best for these highly cross-linked materials, but the combination of increased transition temperature and smaller modulus drop do suggest that samples D and E are somewhat more highly cross-linked than in sample C. The onset of thermal degradation for these materials is observed at temperatures in excess of 350 "C, about 30 "C higher than was the case for the in situ reacted materials. A comparison of the in situ and prereacted products indicates that the in situ reaction produces materials of substantially more heterogeneous structure, lower glasstransition temperature, and probably lower thermal stability. Comparison of the properties of samples C, D, and E suggests that further optimization of the material properties can be achieved by adjustments in bidmaleimide) concentration and the molecular structure of the epoxy resin used. Conclusions Epoxy resins can be coreacted with bis(ma1eimide) and diallylbisphenol A thermoset compositions to produce high Tgpolymeric networks. The epoxy resin can either be
Ind. Eng. Chem. Res. 1989, 28, 1441-1446
added directlv to obtain low-visocitv melts or it may be prereacted with diallylbisphenol A and the resuiting product and then blended with bidmaleimide) to obtain thermoset powders. The fully cured powder compositions display higher Tg's than the networks obtained from the in situ reaction of the epoxy resins. All of the compositions are thermally stable in air up to 375 "C. The results demonstrate that relatively inexpensive and readily available epoxies can be employed to obtain easily processable bis(ma1eimide) and diallylbisphenol A high-temperature polymeric compositions. Acknowledgment The authors thank D. M. Muschott and L. M. Skewes for their technical assistance during the course of this work. Registry No. (1)(2)(Epon 828) (copolymer), 65720-88-9; (1)(2)(Araldite) (copolymer), 122093-48-5.
1441
Literature Cited Carduner, K. R.; Chattha, M. S. Cross-linked Polymers: Chemistry, Properties, and Applications;Dickie, R. A., Bauer, R. S., Labana, S. S., Eds.; (America1 Chemical Society: Washington, DC, 1988); pp 379-394. Carduner, K. R.; Chattha, M. S. Polym. Mat. Sci. Eng. 1987,56,660. Chattha, M. S.; Dickie, R. A. J . Appl. Polym. Sci. 1989, in press. Chaudhari, M. A.; Galvin, T. J.; King, J. J. Proceedings of the 30th National SAMPE Conference, 1985; pp 735-746. Fukushima, E. N.; Roeder, S. B. W. Experimental Pulse N M R ; Addison-Wesley: Ontario, 1981. King, J. J.; Chaudhari, M. A.; Zahir, S. A. Proceedings of the 29th National SAMPE Conference, 1984; pp 392-408. Shoolery, J. N. Prog. N M R Spectrosc. 1977, 11, 79. Zahir, S. A.; Renner, A. US.Patent No. a4,100,140, to Ciba-Geigy Corporation, July 11, 1978.
Received for review January 30, 1989 Accepted June 15, 1989
COMMUNICATIONS
A Simple Expression for the Nonrandomness Parameter crii in the NRTL Equation for Completely Miscible Systems
+
The substitution aij = 1 / ( 2 GijGji)is proposed for modifying the original three-parameter NRTL equation to make it a true two-parameter model for completely miscible systems. The performance of the proposed expression is compared with the value of aij set according t o the rules of Renon and Prausnitz, in correlating VLE data of binary systems, as well as in predicting binary systems from infinite-dilution activity coefficients and ternary systems from binary data. Very good results are obtained, a t least as good as when aij is set according t o the Renon rules, for both correlation and prediction of VLE data. The expression proposed in this paper is applicable only to the vapor-liquid equilibria of systems t h a t are completely miscible in the liquid phase. Combination of the two-liquid theory of Scott (1956)and the local composition idea suggested by Wilson and expressing the local composition in terms of mole fractions rather than volume fractions lead to the NRTL (nonrandom two-liquid) equation derived by Renon and Prausnitz (1968). The expression for the excess Gibbs energy of the liquid mixture is c
the i-j interaction. The parameter aij = aji is related to the nonrandomness in the liquid mixture; when aij is zero, the mixture is completely random and the NRTL equation is reduced to the two-suffix Margules equation. For a binary system, the activity coefficients are given by
c
and the liquid-phase activity coefficients are given by L
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The significance of gij is similar to that of hij in Wilson's equation, namely, an energy parameter characteristic of
The NRTL equation provides a good representation of binary vapor-liquid equilibrium (VLE) experimental data, and it is readily generalized for multicomponent mixtures with only binary parameters. It is superior to the Wilson equation in that it can represent liquid-liquid equilibrium (LLE). Also, it is simpler in form than the UNIQUAC (Abrams and Prausnitz, 1975) equation but has the main disadvantage of involving three adjustable parameters (G,, Gji,and aij = aji)for each pair of components. From both practical and theoretical standpoints, it is desirable to minimize the number of parameters needed to describe as wide a variety of systems as possible.
0888-5885/89/2628-1441$01.50/0 0 1989 American Chemical Society
