Miscibiuty in Blends of Polybenzimidazole and Fluorine Containing Polyimides
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MISCIBIUTY INBLENDS OF POLYBENZIMIDAZOLE AND FLUORINE CONTAINING POLYIMIDES Hiroaki Yamaoka*, Norman E. Aubrey, William J. MacKnight** and Frank E. Karasz** *Mitsubishi Monsanto Chemical Company, Yokkaichi Research & Development Dept. 1 Toho-Cho Yokkaichi-City, Mie, JAPAN ..Polymer Science & Engineering Dept., University of Massachusetts, Amherst, MA 01003 ABSTRACT Blends of polybenzimidazole (PBI) with either of two fluorine-containing polyimides were prepared by casting from solution and by precipitation. Dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) were used to study miscibility in the two blend systems. The blends of PBI with the first polyimide, the polysulfonimide PI-1, consisted of a single phase when the blends contained less than 30 wt% PI-1; above 50 wt% PI-1, phase separation occurred even at room temperature. The PBI blends containing the second polyimide, PI-2, were immiscible. INTRODUCTION Miscible polymer blends consisting of high performance polymers, aromatic polybenzimidazoles and polyimides, have been studied for several years [1-4]. Miscibility in these blend systems was confirmed by the presence of single, compositiondependent Tg's lying between those of the constitutent polymers, by well-defined composition-dependent tan 8 peaks associated with the glass transition and by the formation of clear films. In this contribution, the phase behavior in blends of polybenzimidazole (PBI) with two fluorine containing polyimides, PI-1 and PI-2, is presented. EXPERIMENTAL Materials and blend preparation Poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole (PBI) (Hoechst-Celanese) was used as the representative polybenzimidazole. The fluorine containing polyimides, PI-1 and PI-2, with the structures shown below were prepared by NASA-Langley.
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II
0
CF3
.[ cI ,
0
II •A _..cII1
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PI-1
Mat. Res. Soc. Symp. Proc. Vol. 171. ©1990 Materials Research Society
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198
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P1-2 Elemental analyses of PI-I and PI-2 were performed by the University of Massachusetts Analytical Laboratories. Mw and Mn were obtained by size exclusion chromatography (SEC) using dimethylformamide as solvent at 60°C. Four columns of pore sizes 106, 105, 104 and 500 A were used and were calibrated with poly(methyl methacrylate) standards. The results of elemental analysis and SEC are listed in Table I. Table I Elemental Analysis and SEC results for PI-I and PI-2 Elemental Anaylses
Mw
Mn
Mw/MKln Tg (°C)
PI-1
Caic. C: 56.71% H: 2.13 N: 4.27 F: 17.37 S: 4.87 Found C: 54.88 H: 2.57 N: 4.08 F; 17.50 S: 4.96 PI-2 Calc. C: 61.18 H: 2.30 N: 4.61 F: 18.75 Found C: 61.22 H: 2.55 N: 4.65 F: 19.07
17.2 3.1 x 105 x 105 67.0 x 105
36.8 x 105
5.5
276
1.82
232
Blends were prepared by mixing 3% (w/v) solutions of PBI and polyimides in N,Ndimethylacetamide (DMAc) in the desired proportions. The polyimides dissolved readily in DMAc under ambient conditions but even in a pressure vessel at 225 0C, PBI left an insoluble residue which was removed by filtration. Films
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