J. MATER. CHEM., 1994, 4( 1), 105-1 11 Organo-soluble Segmented Rigid-rod Polyimide Films Part 5.t-Effect of Orientation Fred E. Arnold Jr., Dexing Shen, Frank W. Harris and Stephen 2. D. Cheng* Institute and Department of Polymer Science, The University of Akron, Akron, Ohio, 44325-3909, USA A series of semi-rigid aromatic polyimides have been synthesized via a one-step polymerization in which the poly(amic acid) precursors were not isolated. The polyimides were synthesized from 3,3’,4,4’-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and 2,2’-bis(trifluoromethyl)-4,4’-diaminobiphenyl(PFMB) in refluxing rn-cresol. Uniaxially oriented films were utilized in order to investigate the chain orientation in the ordered state. Wide-angle X-ray diffraction (WAXD) patterns showed an increase in the crystal orientation and the crystallinity for oriented CPI(1OO/O) films with increasing draw ratio.Dichroic ratios obtained under polarized Fourier transform infrared spec- troscopy (FTIR) represented overall orientation factors attributed to both ordered and non-ordered regions, and they were a function of the incident angle and draw ratio. This indicates that the conformational arrangement and chain packing changed during deformation. The orientation along the molecular chain axis and the lateral orientation of the imide planes became increasingly enhanced with increasing draw ratio, an indication of planar alignment of the imide planes as well as uniaxial orientation of the molecular axis.The surface morphology of unoriented and uniaxially oriented films was also studied via transmission electron microscopy (TEM). The lateral crystal dimension of the ordered regions observed from TEM corresponded well to the apparent crystallite sizes of the (310) crystalline plane in BPDA-PFMB crystals obtained from WAXD experiments. For many years it has been recognized that ‘in-plane orien- tation’ of wholly aromatic polyimides exists in thin films, namely the crystallographic c-axis preferentially aligns itself parallel to the surface of the film. The majority of work carried out thus far concerns poly( 4,4‘-oxydiphenylene- pyromellitimide) synthesized from pyromellitic dianhydride (PMDA) and 4,4’-oxydianiline (ODA),’,2 which is commer- cially available under the trade name of Kapton produced by Du Pont.and widely used in electronic packaging applications. In recent years this kind of structural anisotropy has been observed in other aromatic polyimide films such as a polyimide synthesized from 3,3’,4,4’-biphenyltetracarboxylicdianhydride (BPDA) and p-phenylene diamine (PDA).3 In the first two publications of this series we reported a detailed study of the structure formation and macroscopic properties of the polyimide film synthesized from 3,3’,4,4’-biphenyltetracarboxylicdianhydride (BPDA) and 2’2’-bis(trifluoromethyl)-4,4’-diaminobiphenyl (PFMB) in refluxing rn-~resol.~.~ BPDA-PFMB thin films with a thickness of 10-30 pm were found to exhibit an in-plane orientation of the crystallographic c-axis, which preferentially orients itself parallel to the surface of the film.This was determined through ~ t Part 4:F. E. Arnold et al., J. Mater. Chem., 1993, 3, 353. B PD A-P FM B both transmission and reflection modes of WAXD experi- ment~.~The in-plane orientation of the crystals can also be characterized by finding a correspondence between a highly oriented fibre pattern scanned along both the equatorial and the meridianal directions and the pattern obtained from unoriented films using these two geometrical modes. It has been speculated that this structural anisotropy is the result of the rigidity and linearity present in aromatic polyimides. Part 3 in this series was concerned with the effect of forming copolymers by the incorporation of pyromellitic dianhydride (PMDA) into the BPDA-PFMB system.The focus was on the effect of varying the molar percentage of PMDA-PFMB on the thermal and dynamic mechanical properties of BPDA-PFMB-based copolyimides. Chain rigidity and lin- earity were two crucial parameters which determined the thermal mechanical and dynamic mechanical properties of the copolymers studied.6 Part 4 in this series discussed the relationship between the structural anisotropy and the resulting anisotropic properties in the unoriented copolyim- ide films.7 In this paper we focus on the anisotropic structure of the BPDA-PFMB-based copolyimides in the oriented state as opposed to unoriented films. The chemical structures can be expressed by PMDA-PFMB J.MATER. CHEM., 1994, VOL. 4 and are designated as (BPDA-PFMB),-( PMDA-PFMB),. It can be further simplified to CPI(X/Y), where X and Y represent the molar percentages of the comonomers ranging from 0 to 100. CPI(lOO/O) represents the homopolyimide BPDA-PFMB, while CPI( 50/50) represents a statistically alternating copolyimide of BPDA-PFMB and PMDA-PFMB. This family of copolyimides is soluble in hot phenolic solvents and was prepared by a one-step polymeriz- ation in which the poly(amic acid) precursors were not At high temperatures above 140 "C, the copolyimides show a homogeneous solution state up to a concentration of 12% (m/m). Upon cooling, the copolyimide solutions undergo a sol-gel transition to form a gel-like state as well as an ordered structure.The transition temperatures and kinetics depend upon the concentration, molecular weight and the chain rigidity of the polyimides.'O.ll Aromatic polyimide films are of great interest because they possess excellent electrical and mechanical properties together with high thermal, thermo-oxidative and dimensional stabilit- ies. High-modulus aromatic polyimide fibres have also been spun from the isotropic state by a dry-jet wet-spinning pro- c~ss.'~,'~In order to understand the localized order existing in unoriented films it is advantageous to study oriented samples (films and fibres). WAXD and polarized infrared spectroscopy (FTIR) were employed to determine the effect of orientation on unoriented and oriented samples and to investigate the change in the three-dimensional crystalline order as the molar percentage of PMDA-PFMB was increased.The resulting morphology for both oriented and unoriented films was also studied by TEM. Experimental Materials The copolyimides were synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and 2,2'-bis( trifluoromethy1)-4,4'- diaminobiphenyl (PFMB). The diamine monomer synthesis was first reported by Rogers et for polyamide synthesis. A macro-monomer was first synthesized from 1mol of BPDA and 2 mol of PFMB to form soluble blocks within the m-cresol. For CPI( 50/50)another mole of PMDA was added to the polymerizing solution, and statistically one obtains an alternating copolyimide of BPDA-PFMB and PMDA-PFMB.Owing to the difference in the chemical reactivities of the two dianhydrides they must be added separately to avoid phase separation, which can be observed optically and through dynamic mechanical experiment^.'^ Detailed polymerization procedures are discussed in other publication^.^.^ The intrinsic viscosities of CPI(100/0), CPI(85/15), CPI(70/30) and CPI(50/50) are 4.5, 3.5, 3.5 and 3.0 dl g-', respectively.6 Film Preparation CPI(X/Y) films were prepared by spreading a 2% (m/m) rn-cresol solution on a glass plate and drying at 150°C for 5 h and 250°C for an additional 2 h under reduced pressure in a vacuum oven. In this manner, films were prepared with thicknesses of 10-30 pm.Precise control of the solution concentration and the thickness of the casting dope on the glass plate was necessary to control the final thickness. Oriented films of CPI(lOO/O) were prepared to study the orientation of the chain molecules with respect to the draw direction. The films were drawn under tension at ca. 400-450°C up to 500% extension. Oriented CPI(X/Y) films were prepared in a similar manner. Wide-angle X-ray diffraction WAXD experiments were conducted using a Rigaku X-ray generator with a 12 kW rotating anode. The point focused beam was monochromatized by a graphite crystal sensitive to Cu-Ka radiation. In order to study the orientation in the films, a Siemens 2-dimensional area detector was used for the oriented CPI(X/Y) films.Crystal orientations in oriented CPT(X/Y) films were meas- ured based on the Hermans equation: 2f, =3(C0S2 bc)-1 (1) where fc is the orientation factor along the draw direction, and #c represents the angle between the centre of diffraction of this plane and the c-axis of the crystal unit cell. The numerical values of the mean-square cosines in this equation can be determined from the fully corrected intensity distri- bution reflected from the (003) crystalline plane, Ic(bc,a), averaged over the entire surface of the orientation sphere: Polarized Fourier Transform Infrared Spectroscopy Polarized FTIR were carried out on a Mattson galaxy model 5200 FTIR. Polarization experiments were performed using a Harrick Ge polarizer coupled to a variable Brewster angle holder.Uniaxially oriented films [CPT (Xi Y I] were mounted onto the Brewster holder. Film thicknesses were in the range 5-10 pm. Two principal vibrational bands were studied, the 1778 cm-' and 738 cm-'. The transition moment vectors of the carbonyl symmetric and asymmetric stretching (1778 cm-') mode and in-plane and out-of-plane bending (738 cm-l) mode are shown in Fig. 1.16 The intensity of the absorption is proportional to the dot product of the electric- field vector (E)and the transition moment vector (M)accord-ing to: IKE.M=E~cos 0 (3) The intensity is thus maximized when the two vectors are perfectly aligned (6 =0). The stretching (1778 cm- ') mode possesses a transition moment vector lying along the imide plane and thus parallel to the chain direction (in-plane).The bending mode of the carbonyl unit (738 cm-') possesses a transition moment vector that is perpendicular to the imide plane (out-of-plane). l7 For the FTIR experiments, both vertically and horizontally (b ) 0 +out of plane 0 -into plane Fig. 1 Two vibrational modes for in-plane and out-of-plane vibrations of imide rings. (a) 1778 cm-' absorption band; (b)738 cm-' absorp-tion band. J. MATER. CHEM., 1994, VOL. 4 polarized infrared radiation was used. The orientation in uniaxially oriented CPI(X/Y) films can be measured from the dichroic ratio of these two bands discussed previously in order to obtain the relative orientation with respect to the draw direction: (4) The dichroic ratio (R)is defined as the ratio of absorbance of radiation polarized parallel to the draw direction (All)to the absorbance of the that polarized perpendicular to the draw direction ( L41).For a film with random orientation R =1. It is often more convenient to determine the ratio of the optical densities (II,and IJ rather than the absolute absorbance. Dichroic ratios will be calculated as a function of both the draw ratio as well as the angle of incidence relative to the plane of the film. The experimental set-up is shown in Fig. 2. Eqn. (4) was used to calculate the dichroic ratios of the 738 cm-' band, while the dichroic ratios of the 1778 cm-' band were calculated in an inverse manner. Transmission Electron Microscopy TEM was used to study the surface morphology of unoriented and oriented films.The morphological studies were conducted in a JEOL 1200 EX11 transmission electron microscope. A single replica technique was employed.18 The oriented samples were coated with Au-Pt (40-60, 30" oblique to the sample surface) and carbon (90' to the sample surface) uia vacuum deposition. The film was then soaked in methylene chloride-- trifluoroacetic acid (CH,Cl,-TFA) to dissolve the polyimide and the replicas were recovered for analysis. The unoriented samples were subjected to a potassium permanganate etching prior to the vacuum deposition." Results and Discussion Orientation in the Films As shown in Fig.3, the WAXD fibre patterns for CPIs clearly indicate that the copolyimides do not possess three-dimensional order since no quadrant diffraction spots can be seen. The addition of PMDA-PFMB thus disrupts the three- dimensional order which exists in CPI( 100/0), and leads to a two-dimensional mesophase order. WAXD fibre patterns for oriented CPI( 100/0) films with different draw ratios reveal that the overall crystallinity is increased by observing the further development of the diffraction spots located in the quadrant regions.', The crystal orientation has to be investi- gated since the macroscopic properties depend on both the overall orientation and the ~rystallinity.'~"~ Hermans orien- tation factors were calculated for CPI(lOO/O) based on eqn.(1) and (2) from WAXD results which is an indication of the crystal orientation. It is clear that with increasing draw ratio, the crystal orientation increases drastically. Fig. 4 shows the orientation factors as a function of the draw ratio. At low draw ratios the crystallites are less aligned. As the draw ratio \I IU film Fig. 2 Experimental set-up (top view) for polarized FTIR experiments at different angles between the incident beam and film surface increases one observes a drastic increase in orientation with a plateau being reached at a draw ratio of ca. 5. Dichroic ratios were measured for different draw ratios of CPI( 100/0) films. Fig. 5 illustrates the spectra for CPI( 100/0) films drawn to 500%. The 1778 cm-' absorption band is very prominent when the electric-field vector of the polarized IR beam is parallel to the draw direction.This is not surprising since the transition moment vector is oriented parallel to the imide planes (in-plane). If one investigates the 738 cm-' absorption band when the electric-field vector is parallel to the draw direction, the intensity is close to zero. This indicates a planar alignment of the imide planes which is more or less parallel to the surface of the film. On the other hand. when the electric-field vector is oriented perpendicular to the draw direction, one observes a drastic decrease in the intensity of the 1778cm-' band and an increase in the 738cm-' band. The decrease in the 1778 cm-' band is expected owing to the orientation of the transition moment vector (parallel to the imide plane) while an increase of the 738 cm-' band reflects the imide planes are not perfectly parallel to the film surface, and instead, they are tilted relative to the film surface.The tilting of the transition moment vector is, however, always perpendicular to the draw direction. Fig. 6 shows the variation of the dichroic ratios as a function of the draw ratio for CPI( 100/0)films. The dichroic ratios for the 738cm-' band were calculated using eqn. (4) while the dichroic ratios for the 1778 cm-' band were calculated in an inverse manner in order to compare the degree of order on the same scale, and in this case R=l represents random orientation, while R =0 represents perfect alignment of the transmission moment vectors.It is evident that upon increas- ing the draw ratio the alignment of the chain molecules is drastically enhanced. The in-plane alignment of the imide planes is also improved as the draw ratio is increased. It is clear that the value of dichroic ratio of the 738 cm-' band is small compared to that of the 1778 cm-' band at the same draw ratio. Moreover, the variance (the rate of change) in the dichroic ratios of the 738 cm-' band is larger than those of the 1778 cm-I band. Note that the magnitude change of the dichroic ratios is a measure of the alignment of the imide planes along two perpendicular directions. As the draw ratio increases the change of dichroic ratio of the 738 cm-I band is an indication that the planar alignment is increased owing to a reduction of the tilting of the imide planes.On the other hand, the variance of the 1778 cm-' absorption band reflects the enhanced alignment of the molecular axis relative to the draw direction. This variance is, furthermore, expected to be smaller than that of the 738 cm-' band since for the 738 cm-' band the inplane orientation of the molecular chain axis originally existed in the unoriented films. This experimental observation manifests that with increasing draw ratio, the alignment of the imide planes parallel to the film surface is relatively easier than the alignment of those along the molecu- lar chain axis. This can be understood by the fact that the tilting of the imide planes is only associated with the torsional angle change of the covalent bonds and the change of conju-gational length in CPI, while the change of alignment of the imide planes along the molecular chain direction has to involve a larger scale molecular motion related to the chain conformational change.The former largely belongs to an intramolecular, non-cooperative motion, while the latter to an intermolecular cooperative motion. From the dichroic ratios (Fig. 6) for oriented CPI( 100/0) films a plateau region is not observed at higher draw ratios, and linear relationships for both 1778cm-' and 738cm-' absorption bands as a function of the draw ratio are evident. However, from Fig. 4, WAXD experiments illustrate a plateau which is reached at a draw ratio of five.Note that WAXD J. MATER. CHEM., 1994, VOL. 4 Fig. 3 WAXD fibre patterns for uniaxially oriented CPT copolyimides with compositions of (a)CPI( 100/0), (h)CPI(85/15), Ic) CPI(70/30) and (d)CPl(50/50) 1.oo-0.92.-f0-5 0.84.-I0-.-5 0.76:; 0/c. (I)cCal.-Z 0.68.-/ Fig. 4 Crystal orientation factor changes with different draw ratios for CPI( 100/0) films experiments provide only the degree of crystal orientation, and FTIR analysis is a representation of the overall orien- tation, which is attributed to the orientation of both crystalline and non-crystalline regions. So at high draw ratios the overall orientation is improved mainly by the alignment of the chain molecules in the non-crystalline regions.In order to study detailed chain conformation and packing changes during the deformation of the films, a systematic investigation on the intensities of the two vibrational absorp- tion bands (1778 cm-' and 738 cm-') at different incident angles under a polarized IR beam was conducted. Note that I!!!! !!I!/ I ] ' " ' ! !';I 1900 1640 1380 1120 860 600 wavenumberkm-' Fig. 5 Polarized FTIR spectra of CPI(lOO/O) films at a draw ratio of five along the directions (a) parallel and (h) perpendicular to the elongation when the R values were calculated for the 1778 cm-' band, the electric-field vector was parallel to the draw direction, while for those of the 738 cm-l band, the electric-field vector was perpendicular to the draw direction.The experimental set-up is shown in Fig. 2. Fig. 7 and 8 show the dichroic ratios J. MATER. CHEM., 1994, VOL. 4 magnitude and the variance (the rate of change) of the0.701 738 cm-' band is relatively high. This indicates that at low incident angles the transition moment vector of this absorption band is tilted with respect to the incident beam, and there is a larger component of the vector parallel to the vibrational direction of the incident beam. This component contributes R much to the absorbance of the polarized IR beam at low 0.28 incident angles. With increasing incident angle, the R values of the 738 cm-' band drastically decrease, revealing that this component contribution to the absorbance decreases hecause the tilting angle between the transition moment vector and incident beam becomes smaller.One can thus conclude that 0.141+-LLL0.001 2 3 4 5 6 in the highly oriented CPI( 100/0) films the imide planes are nearly parallel to the film surface. draw ratio Furthermore, for both absorption bands, the R values Fig. 6 Dichroic ratio changes with the draw ratio for CPI( 100/0) decrease with increasing draw ratio. This is an indication that films for (0)1778 and (0)738 cm-I with increasing draw ratio, both orientations of the molecular chain axis along the draw direction (observed from the change of 1778cm-') and lateral orientation of the imide planes (observed from the change of 738 cm-') are enhanced. This kind of chain conformation and packing leads to a conceivable physical picture of uniaxial planar orientation. Fig.9 and 10 show the changes of the R values as a function 0.66 0 of the incident angle for the 1778 and 738 cm-' bands for both CPI(70/30) and CPI(50/50)films at a draw ratio of two. R 0 Greater sensitivity of the R values to the incident angle in the 738 cm-' band for CPI(70/30) films and CPI(50/50) films was observed compared to those of the 1778 cm-' band. Furthermore, if one looks at the three CPI films at the same 0.421 draw ratio of two, the absolute R values for both the Fig. 7 Relationship between dichroic ratio at 1778 cm-' absorption and incident angle for CPI(100/0) films with different draw ratios: 0,2x; 0,3x; A,4x; A,5x .oo 0.e 1.o 0.42 0 0 00 0 0 0 0.6 0 0 F20 36 52 68 84 100R 4 0 A 0 incident angle/degrees 0 0 Fig.9 Relationship between dichroic ratio at (0) 1778 and f. 0 (0)738 cm-' and incident angle for CPI(70/30) films at a draw ratio 4.0 0 of 2 0.2 4 A 0.90O.Ot! ............. .........10 27 44. 61. 78 95 incident angle/degrees Fig. 8 Relationship between dichroic ratio at 738 cm- 'absorption and incident angle for CPI( 100/0) films with different draw ratios: 0,2x; 0,3x; A,4x; A,5x R 0 (R)of CPI( 100/0) films as a function of both the draw ratio and the incident angle. With increasing incident angle the values of dichroic ratios decrease, and it seems that this is a 0.24 0 general trend for every draw ratio. Since the transition moment vector for the 1778cm-' band is parallel to the imide planes, and thus to the molecular chain axis, the change of R with respect to the incident angles is not as prominent as in the case of the 738cm-' band.This change obtained from the Fig. 10 Relationship between dichroic ratio at (0) 1778 and 1778cm-I band ranges between 0.1 and 0.14 at each draw (0)738 cm-l and incident angle for CPI(50/50) films at a draw ratio ratio. On the other hand, at low incident angles both the of 2 1778 cm-I and 738 cm-' absorption bands decrease with increasing PMDA-PFMB composition. At an incident angle of 30" the R value of CPI(lOO/O) films was 0.64 for the 1778 cm-I band, and it decreased to 0.49 for CPI(50/50) films; that of CPI( 100/0) was 0.82 for the 738 cm-' band, and decreased to 0.53 for CPI( 50/50)films.Again, the decrease of the R value in the 738 cm-' band based on the composition is more drastic compared to that of the 1778 cm-' band. On the other hand, the incident angle changing from 20 to 90" leads to a 0.4 decrease for the 738 cm-' band, and less than 0.15 for the 1778 cm-' band for all the three cases. These experimental observations may be explained by confor-mational and chain packing changes during the deformation. In particular, these changes indicate that with increasing PMDA-PFMB composition, the chain rigidity and linearity increase. As a result, both orientations along the molecular chain axis and lateral orientation of the imide planes are enhanced.Therefore, the microscopic structure in orientated CPI thin films is conceivably closer to a uniaxial planar orientation with increasing PMDA-PFMB composition. Surface Morphology Fig. 11 and 12 represent surface morphologies of unoriented and oriented CPI(lOO/O) thin films at different draw ratios (two and four) obtained by TEM. For unoriented films, the etching method is necessary in order to observe the ordered texture. Fig. 11 shows that in the unoriented polyimide film some ordered regions exist, which are fibril shaped with a lateral size of ca. 5 nm. The fibril direction in this figure is randomly distributed. If one assumes that the chain direction is parallel to the fibril direction which is true based on the electron diffraction in very thin films," this TEM observation reveals a random distribution of the c-axis of the ordered crystal regions in the film plane, which is recognized as 'in- plane orientation'.With increasing draw ratio, as shown in Fig. 12(a) and (b), the fibril type of texture becomes clearer and more oriented along the draw direction. It is interesting that the lateral size of the fibril region seems to decrease with increasing draw ratio, and corresponds well with the apparent crystallite size of the (310) crystalline plane observed from WAXD experiments using the Sherrer equation.12 Note that the (310) crystalline plane is one of the (hkO) planes in a monoclinic crystal lattice of the CPI( 100/0)crystals, and it is perpendicular to the c-axis [(OOl) crystalline plane].For example, a draw ratio of two leads to a lateral size of the fibril texture of ca. 4.5 nm (upper limit), and at a draw ratio of five, this lateral size decreases to ca. 3.5 nm (lower limit). Fig. 11 TEM surface morphology of unoriented CPI(100/0) film after etching J. MATER. CHEM., 1994, VOL. 4 Fig. 12 TEM surface morphology of CPI(100/0)film at a draw ratio of (a) 2 and (b)4 Furthermore, the fibril textures start clustering along the lateral direction. Fig. 13 includes the results obtained both from WAXD (points) and from TEM (vertical bars) obser- vations. A similar surface morphological observation with fibril texture can also be found in other CPI films at a draw ratio of two. These morphological observations indicate that under deformation the CPI films undergo a transition from an in-plane orientation to a uniaxial planar orientation of the chain molecules with a formation of the ordered regions which 4.4 .$ 3.8 cd c v)x 3.2 c m 2.0t : : : ! : ; 1 ! : : ' ! ! ! : : 1 ,L,1 3 5 ~ 7 ~ 9 draw ratio Fig.13 Apparent crystallite size of (310) crystalline plane observed from WAXD and crystal size perpendicular to the draw direction observed from TEM J. MATEK. CHEM., 1994. VOL. 4 is either crystalline [for CPT(100/0)] or mesophase type in nature (for other CPT copolyimides). Conclusions Oriented CPI films have been studied through WAXD and FTIR experiments to investigate the orientation effect on chain conformational and packing changes.As the draw ratio increases, both the orientation along the molecular chain axis (and therefore, the draw direction) and the lateral orientation of the imide planes with respect to the film surface are enhanced. Furthermore, with increasing PMDA-PFMB com-position. the imide planes also become increasingly parallel to the film surface in oriented films. The surface morphology investigation indicates that the ordered regions in both unori- ented and oriented films are fibril in nature. The fibril direction becomes increasingly parallel to the draw direction of the films. In oriented CPT( 100/0)films the lateral size of the fibril texture decreases with increasing draw ratio, which corre- sponds well to the apparent crystallite size change of the (310) crystalline plane observed from WAXD experiments.This work was supported by SZDC’s Presidential Young Investigator Award from the National Science Foundation (DMR-9157738) and the industrial matching funding from Hercules Inc. Support was also provided by the National Center of Science and Technology for Advanced Liquid Crystalline Optical Materials (ALCOM) from the National Science Foundation (DMR-8920147) at Kent State University, The University of Akron and Case Western Reserve University. References 1 H. Lee, D. Stoffey and K. Neville, New Linear Polymers. McGraw-Hill, New York, 1967, pp. 183 and 224. 2 C. E. Scroog, J. Polym. Sci., Macromol. Rec.. 1976,11,161 3 D. Y.Yoon, W. Parrish, L. E. Depero and M. Ree, ,Vuterial Science of High Temperuture Polymers for Microelectronic s, MRS Symposium Proceedings, Pittsburgh, PA, 1991, vol. 227. 4 S. Z. D. Cheng, F. E. Arnold Jr., A. Zhang. S. L. C. FIsu and F. W. Harris, Macromolecules, 1991,24, 5856. 5 F. E. Arnold Jr., S. Z. D. Cheng, S. L. C. Hsu, C. J. Lee and F. W. Harris, Polymer, 1992,33, 5179. 6 F. E. Arnold Jr., D. Shen, C. J. Lee, F. W. Harris, S. Z. D. Cheng and H. W. Stark-weather Jr., J. Muter. Chem., 1993,3, 185. 7 F. E. Arnold Jr., D. Shen, C. J. Lee, F. W. Harris, S. Z. D. Cheng and S.-F. Lau, J. Mater. Chem., 1993, 3, 353. 8 F. W. Harris and S. L.-C. Hsu, High Perform. Polym., 1980, 1, 1. 9 F. W. Harris, in Polyimides, ed. D. Wilson, H. D. Stenzenberger and P. M. Hergenrather, Chapman and Hall, New York, 1990, pp. 1-37. 10 S. Z. D. Cheng, S. K. Lee, J. S. Barley, S. L. C. Hsu and F. W. Harris, Macromolecules, 1991, 24, 1883. 11 S. K. Lee, S. Z. D. Cheng, C. J. Lee, F. W. Harris, T. kyu and C. Yong, Polym. Znt., 1993,30,215. 12 S. Z. D. Cheng, Z. Wu, M. Eashoo, S. L. C. Hsu and F. W Harris, Polymer, 1991,32, 1803. 13 M. Eashoo, D.-X. Shen, Z.-Q. Wu, C. J. Lee, F. W. Harris and S. Z. D. Cheng, Polymer, 1993,34, 3209. 14 H. G. Rogers, R. A. Gaudiana, W. C. Hollinsed, J. S. Manello, C. Mcgowan and R. Sahatjian, Macromolecules, 1985, 18, 1058. 15 F. E. Arnold Jr., Ph.D Dissertation, University of Akron Akron, Ohio, 44325-3909, 1993. 16 R. W. Snyder and C. W. Shen, Appl. Spectrosc., 1988,42, i03. 17 J. L. Koenig, Spectroscopy of Polymers, American C hemical Society, Washington D.C., 1992. 18 R. H. Olley, D. C. Bassett and D. J. Blundell, Polymtr, 1986, 27,344. 19 S. Z. D. Cheng, J.-Y. Park, C. J. Lee and F. W. Harris Polym. Prep., ACS, Dic. Polym. Chem., 1993,34(1), 774. Paper 3/04449A; Received 26th July, 1993