Synthetic Chemistry Division,Defence Research and Development Establishment,Jhansi Road,Gwalior474002,India Received14October2003;accepted31December2003
DOI10.1002/app.20532
Published online in Wiley InterScience(www.interscience.wiley.com).
ABSTRACT:Five new poly(ether imides)have been prepared on reaction with oxydiphthalic anhydride(ODA)withfive differ-ent diamines:1,4-bis(p-aminophenoxy-2Ј-trifluoromethyl benzyl)benzene,4,4Ј-bis(p-aminophenoxy-2Ј-trifluoromethyl benzyl)benzene,1,3-bis(p-aminophenoxy-2Ј-trifluoro-methyl benzyl)benzene,2,6-bis(p-aminophenoxy-2Ј-triflu-oromethyl benzyl)pyridine,and2,5-bis(p-aminophenoxy-2Ј-trifluoromethyl benzyl)thiophene.Synthesized polymers showed good solubility in different organic solvents.The poly-imidefilms have low water absorption of0.3–0.7%,low dielec-tric constants of2.82–3.19at1MHz,and high optical transpar-ency at500nm(Ͼ73%).These polyimides showed very high thermal stability with decomposition temperatures(5%weight loss)up to531°C in air and good isothermal stability;only0.4% weight loss occurred at315°C after5h.Transparent thinfilms of these polyimides exhibited tensile strength up to147MPa,a modulus of elasticity up to2.51GPa and elongation at break up to30%depending upon the repeating unit structure.©2004 Wiley Periodicals,Inc.J Appl Polym Sci93:821–832,2004
Key words:fluoropolyimides;glass transition temperature; thermal properties;mechanical properties;dielectric con-stant;optical transparency
INTRODUCTION
Polyimides are an interesting class of polymers be-cause of their number of outstanding properties,such as excellent thermal and thermooxidative stability, solvent resistance,and mechanical and electrical prop-erties.1–8These materials were considered for use in numerous applications,which require robust organic materials including composites and precursors for high-performance aerospace materials as well as membranes for gas separation.Polyimides with low dielectric constant,low refractive index,low water absorption,and low coefficient of thermal expansion are receiving attention for interlayer dielectrics in elec-tronic devices such as integrated circuits.6,9,10
The main drawbacks of these classes of polymers are their insolubility and intractability,which cause difficul-ties in both synthesis and processing.Therefore,the pro-cessing of the polyimides is generally carried out via soluble poly(amic acid)precursors,which are cast onto glass plates and converted to thin polyimidefilms by a rigorous thermal treatment.However,this process has severe inherent limitations,including emission of vola-tile byproducts during curing and storage instability of the poly(amic acid)intermediate.11
To utilize the thermal stability of polyimides for fur-ther applications,and also to take advantage of other properties of these classes of polymers,it is desirable to synthesize soluble and/or melt-processible variations. Solubilizations of the polyimides were targeted by sev-eral means,such as introduction offlexible linkages, bulky substituents,and bulky units within the polymer backbone,non-coplanar,or alicyclic monomers.12The main concept behind all these approaches is the reduc-tion of several types of polymer chain–chain interac-tions,reduction of chain packing,and charge transfer electronic polarization interactions.Polyimides contain-ing hexafluoroisopropylidene(6F),pendent trifluorom-ethyl,or trifluoromethoxy groups are of special inter-est.13–29Incorporation of these groups serves to increase the free volume26of the polyimides,thereby improving various properties including solubilities,electrical insu-lating properties,without forfeiture of thermal stability. These groups also reduce water absorption,crystallinity, and color,while they increaseflame resistance,gas per-meability,and optical transparency.
In continuation of our research on semifluorinated poly(ether imides),12,30,31we report in this article on the successful synthesis offive novel poly(ether imi-des)and their detailed characterization including ther-mal,mechanical,and dielectric properties.
Experimental
General considerations
Carbon and hydrogen of the compounds were ana-lyzed by Prejel method and nitrogen was analyzed by KJeldhal method.1H-NMR(400MHz)and19F-NMR
Correspondence to:S.Banerjee(susanta_b20012001@ yahoo.com).
Contract grant sponsor:DRDO,New Delhi.
Journal of Applied Polymer Science,Vol.93,821–832(2004)©2004Wiley Periodicals,Inc.
(100MHz)spectra were recorded on a Bruker ARX 400instrument (Switzerland)[reference,0ppm with TMS (1H-and)or CFCl 3(19F-NMR)].IR spectra of the polymer films were recorded with a Bruker IFS 55spectrophotometer instrument.DSC measurements were made on a TA Instruments DSC-2920instru-ment,at a heating/cooling rate of 20°C/min under nitrogen.Glass transition temperature (T g )was taken at the middle of the step transition in the second heating run.Thermogravimetry was measured on a TA Instruments thermogravimetric analyzer (model TGA-2950).A heating rate of 10°C/min was used for determination of the decomposition temperature (T d )at 5%weight loss under synthetic air.Isothermal gravimetric was performed at 315°C for 5h in air on a TA-2950instrument.Dynamic mechanical thermal analysis was performed on a Netzsch DMA-242in-strument (Germany)in the tension mode on thin film samples with a heating rate of 5°C/min (1and 10Hz).Mechanical properties of the thin polymer films were performed at room temperature on a Miniature Mate-rials Tester (Rheometric Science)under strain rate of 5%/min.Dielectric constant of the poly(ether imide)films (20m)was measured by the parallel plate capacitor method with a YHP 4278capacitance meter at 1kHz at a temperature 30°C.Dry specimens were made by keeping the samples at 140°C for 4h under high vacuum.Water absorption of the films was mea-sured by a Mettler microbalance of sensitivity of 10Ϫ6g after immersing the films into double-distilled water for 72h at 30°C.UV–Vis spectra of the polymer films were recorded with a Speccord Version 2.1E,Analytik Jena AE instrument (Germany).
Starting materials
All reagents were purchased from Aldrich,Fluka,Chempure,or Fluorochem Chemical Co.and used as received unless otherwise noted.Oxydiphthalic anhy-dride (ODA;99.99%,Fluka,Switzerland)was heated at 180°C prior to use.N ,N -dimethylformamide (DMF;E.Merck,India)was purified by stirring with NaOH and distilled twice from P 2O 5under reduced pressure.Detailed syntheses of the diamine monomers are re-ported in previous articles.12,30,31Polymerization
An equimolar amount of diamine and dianhydride monomer was reacted under constant flow of nitro-gen.A representative polymerization procedure is as follows.
In a 50-mL round-bottomed flask equipped with a nitrogen inlet,a stir bar and Dean–Stark trap fitted with a condenser was charged with 0.6g (1.0335mmol)of 1,3-bis [3Ј-trifluoromethyl-4Ј(4Љ-amino ben-zoxy)benzyl]benzene and 10mL of DMF.The solu-tion was stirred until the diamine dissolved com-pletely;0.32g (1.0335mmol)(ODA)was slowly added to this solution.The resulting highly viscous solution was stirred slowly and continuously for 3h at room temperature under nitrogen.The poly(amic acid)so-lution was cast onto clean and dry glass plates by a doctor blade;the films were dried in an oven at 80°C for 6h,at 150,200,250,and 300°C for 1h at each temperature,and 350°C for 15min.Polyimide films were removed by immersing the glass plates in boiling
water.
Polyimide 1a.A nal .calc.for (C 54H 28F 6O 7N 2)n (930.81g mol Ϫ1)n :C,69.73%;H, 3.03%;N, 3.01%.Found:C,68.53%;H,2.83%;N,2.98%;IR (KBr)(cm Ϫ1):3492(—N Ͻstretch);3074,3050(aromatic C—H stretching);1786and 1737(asymmetric and symmetric —CO—stretch);1619(C A C ring stretching band);1508,(band due to C—F absorption);1375(asymmetric C—O—C stretch);
1143,1050(symmetric C—O—C stretch);722(aromatic C—H band out-of-plane).1H-NMR (CDCl 3):␦(ppm)7.96(d,J ϭ8Hz,2H,H9);7.(s,2H,H1);7.(m,10H,H2,and H4);7.50(s,2H,H7);7.40(m,6H,H6,and H8);7.15(m,6H,H3,and H5).19F-NMR (CDCl 3):␦(ppm)Ϫ62.14(CF 3
).
822BANERJEE,MADHRA,KUTE
Polyimide 1b.A nal .calc.for (C 48H 24F 6O 7N 2)n (854.72g mol Ϫ1)n :C,67.45%;H, 2.83%;N, 3.27%.Found:C,66.83%;H,2.63%;N,3.11%;IR (KBr)(cm Ϫ1):3493(—N Ͻstretch);3072,3048(aromatic C—H stretching);1782and 1732(asymmetric and symmetric —CO—stretch);1612(C A C ring stretching band);1506(band due to C—F absorption);1372(asymmetric C—O—C stretch);
1140,1048(symmetric C—O—C stretch);720(aromatic C—H band out-of-plane).1H-NMR (CDCl 3):␦(ppm)7.92(d,J ϭ8Hz,2H,H9);7.84(s,2H,H1);7.(d,J ϭ8Hz,2H,H2);7.58(s,4H,H4);7.47(s,2H,H7);7.36(m,6H,H7and H6);7.09(m,6H,H3,and H5).19F-NMR (CDCl 3):␦(ppm)Ϫ62.11(CF 3
).
Polyimide 1c.A nal .calc.for (C 48H 24F 6O 7N 2)n (854.71g mol Ϫ1)n :C,67.45%;H,2.83%;N,3.27%.Found:C,66.76%;H,2.73%;N,3.19%;IR (KBr)(cm Ϫ1):3492(—N Ͻstretch);3068,3047(aromatic C—H stretching);1780and 1729(asymmetric and symmetric —CO—stretch);1614(C A C ring stretching band);1511(band due to C—F absorption);1371(asymmetric C—O—C stretch);
1141,1051(symmetric C—O—C stretch);719(aro-matic C—H band out-of-plane).1H-NMR (CDCl 3):␦(ppm)7.92(d,J ϭ8Hz,2H,H11);7.85(s,2H,H1);7.66(m,3H,H2,H6);7.47,(m,5H,H4,H5and H9);7.37(m,6H,H8and H10);7.09(m,6H,H3and H7).19F-NMR (CDCl 3):␦(ppm)Ϫ62.07(CF 3
).
Polyimide 1d.A nal .calc.for (C 47H 23F 6O 7N 3)n (855.70g mol Ϫ1)n :C,65.97%;H,2.70%;N,4.91%.Found:C,65.13%;H,2.52%;N,4.78%;IR (KBr)(cm Ϫ1):3491(—N Ͻstretch);3071,3047(aromatic C—H stretching);1779and 1729(asymmetric and symmetric —CO—stretch);1618(C A C ring stretching band);1506(band due to C—F absorption);1372(asymmetric C—O—C stretch);
1139,1046(symmetric C—O—C stretch);718(aro-matic C—H band out-of-plane).1H-NMR (CDCl 3):␦(ppm)8.39(s,2H,H1);8.2(d,J ϭ8Hz,2H,H2);7.94(d,J ϭ8Hz,2H,H10);7.82(m,1H,H4);7.66(d,J ϭ8Hz,2H,H5);7.50(s,2H,H8);7.40(m,6H,H7,and H9);7.13(m,6H,H3,and H6).19F-NMR (CDCl 3):␦(ppm)Ϫ62.20(CF 3
).
Polyimide 1e.A nal .calc.for (C 46H 22F 6O 7N 2S)n (860.74g mol Ϫ1)n :C,.18%;H,2.57%;N,3.25%.Found:C,63.84%;H,2.48%;N,3.09%;IR (KBr)(cm Ϫ1):3495(—N Ͻstretch);3070,3044(aromatic C—H stretching);1779and 1727(asymmetric and symmetric —CO—stretch);1619(C A C ring stretching band);1508(band due to C—F absorption);1375(asymmetric C—O—C stretch);
1143,1050(symmetric C—O—C stretch);722(aro-matic C—H band out-of-plane).1H-NMR (CDCl 3):␦(ppm)7.93(d,J ϭ8Hz,2H,H9);7.82(s,2H,H1);7.63(d,J ϭ8Hz,2H,H2);7.47(s,2H,H7);7.38(m,6H,H5,and H8);7.21(s,2H,H4);7.10(d,J ϭ8Hz,4H,H6);6.99(d,J ϭ8Hz,2H,H3).19F-NMR (CDCl 3):␦(ppm)Ϫ62.04(CF 3).
POLYIMIDE 6CHARACTERIZATION 823
RESULTS AND DISCUSSION
The diamino monomers were reacted with ODPA to give the corresponding poly(ether imides),as shown in Figure 1.
The syntheses of polyimides were carried out via poly(amic acid)intermediate.Initially,diamines were dissolved in a measured amount of dry DMF and the dianhydride monomer was added to it slowly.In all cases,the reaction mixture became highly viscous within 10–15min;the reactions were continued for 3h.The inherent viscosities and molar masses of the poly(ether imides)shown in Table I indicated forma-tion of high molar masses.The poly(amic acid)solu-
tions were cast on clean glass plates and the film was heated through various stages up to 350°C to remove solvent and water formed by the imidization.Trans-parent,pale-yellowish films were obtained in all cases.All polyimides films were tough.
Polymer solubility
The solubilities of the resulting poly(ether imides)by thermal imidization were investigated in different or-ganic solvents.The solubility behavior of these poly-mers in different solvents is presented in Table II.These polymers exhibited very good solubility behav-ior in common organic solvents such as CHCl 3,CH 2Cl 2,DMF,N ,N -dimethyl acetamide (DMAc),and N -methyl-2-pyrrolidinone.Insolubility of these poly-mers in DMSO,while their solubility in amide sol-vents,such as NMP,DMF,DMAc,at room tempera-ture (although these types of dipolar aprotic solvents have similar properties)indicates that polarity alone is not the only parameter sufficient for selecting a poly-mer solvent.In comparison to the previously reported semifluorinated poly(ether imides),26,27these poly-mers exhibited dramatic improvement in solubility.This is possibly due to additional ether linkage in dianhydride
moiety.
Figure 1Reaction scheme and structures of the poly(ether imides).
TABLE I
Physical Properties of the Poly(Ether Imides)
Polymer inh M n PDI Light trasmission at 500nm (%)
1a 1.1265,700 2.91731b 1.0342,320 2.65711c 0.8536,280 1.85691d 1.2255,850 3.12651e
0.82
-
-
70
inh ,0.5weight %solution of pol(ether imide)films in DMF at 30°C.
824BANERJEE,MADHRA,KUTE
The formation of poly(ether imides)was confirmed by FTIR spectroscopy.FTIR spectra of the polyimide films prepared by thermal imidization method show the absorption bands at about1780cmϪ1(C A O asym-metric stretching),1730cmϪ1(C A O symmetric stretching),1378cmϪ1(C—N stretching),721cmϪ1 (C A O bending)corresponding to the characteristic of imide bands.25–26No absorption band existed at3400–2900cmϪ1corresponding to amide(—NH—)and acid (—OH)stretching1720cmϪ1corresponding to C A O cmϪ1stretching of carboxylic acid,1660correspond-ing to C A O cmϪ1amide stretching of the polyim-ides.30,311H-NMR spectra of the polymers did not show any amide or acid protons,indicating full imi-dization.The representative1H-NMR spectrum of poly(ether imide)1e is shown in Figure2.There is very good matching of integrated peak areas for dif-ferent chemically different protons in all polymers. The analytical details of the polymers are provided in Experimental.UV–Vis spectroscopic studies of the polymers revealed that polymers have very good op-tical transparency at500nm.
Glass transition temperature versus polymer structure
The poly(ether imides)exhibited no crystallization or melting transition in DSC measurements.These poly-mers show glass transaction temperature,which indi-cates amorphous or glassy morphology.DSC curves of the polymers are shown in Figure3.The
glass
Figure21H-NMR spectrum of poly(ether imide),1e.
TABLE II
Solubility of the Polyimides
Polymer NMP DMF DMAc DMSO THF CHCl3CH2Cl2Acetone 1aϩϩϩϪϪϩϩϪ1bϩϩϩϪϩϩϩϪ1cϩϩϩϪϩϩϩϪ1dϩϩϩϪϩϩϩϪ1eϩϩϩϪϪϩϩϪϩ,Soluble;Ϫ,insoluble at reflux.
POLYIMIDE6CHARACTERIZATION825
Figure 3DSC plots of the poly(ether imides).
TABLE III
Thermal Properties of the Poly(Ether
Imides)
Polymer Ar T g (°C)
T d (°C)
Weight loss in air (315°C/5h)
DSC DMA (tan ␦)5%Weight loss 10%Weight loss
1a
254
258
531
563
0.4
1b 2422465195530.5
1c 2112225175480.6
1d 2412505145590.7
1e 234239486526 1.4
826BANERJEE,MADHRA,KUTE
transition values are summarized in Table III.The polymers 1a and 1b exhibited higher T g values than other polymers,which is due to the presence of rigid quadriphenyl and terphenyl unit in the backbone.31
It is interesting at this stage to compare the glass transition temperatures of the polymers shown in Ta-ble III.The polyimides containing 4,4Ј-diphenyl biphe-nyl (quadriphenyl)unit in the polymer backbone exhibited highest glass transition temperatures in comparison to the analogous polyimides containing 1,4-diphenyl benzene,1,3-diphenyl benzene,2,6-di-phenyl pyridine,and 2,5-diphenyl thiophene moieties.The following order on glass transition temperature is obtained:quadriphenyl Ͼ1,4-diphenyl benzene Ͼ2,6-diphenyl pyridine Ͼ2,5-diphenyl thiophene Ն1,3-diphenyl benzene.This order could be explained on considering three factors:rigidity,catenation angle of the different groups (Fig.4),and polarity.A macro-molecule exhibits more extended geometry (i.e.,higher catenation angle providing by the different building blocks is expected to have higher glass tran-sition temperature).Similarly,if the polymer molecule is built up of rigid units,it is expected to have higher glass transition temperature.The highest glass transi-tion temperature of the polymer 1a is due to its most rigid backbone structure compared to others.The cat-enation angle between 4,4Ј-diphenyl biphenyl and 1,4-diphenyl benzene is the same;however,the polymers containing 4,4Ј-diphenyl biphenyl units exhibiting higher T g is due to the rigidity of this unit.The poly-imides containing 1,5-diphenyl benzene is expected to have lower glass transition temperature compared to the above two,as it has less extended geometry (cat-enation angle 120°)and the same result is obtained.It will be more interesting to take a close look at the glass transition temperatures of the polyimides containing 1,6-phenyl pyridine and 1,5-phenyl thiophene units and their comparison to the polyimides containing 1,5-diphenyl benzene.Although the catenation angle of 1,6-diphenyl pyridine unit is 28°lower than 1,5-diphenyl thiophene unit (catenation angle for 1,6-di-phenyl pyridine unit is 120°and for thiophene is 148°),32the T g ’s of the pyridine-containing polymer is higher.The high T g of polymer-containing pyridine moiety may be due to the polarity of the pyridine ring.Thiophene has a more extended geometry than
pyri-
Figure 4Catenation angles of the different substituted arylene
groups.
Figure 5TGA plots of the poly(ether imides).
dine;at the same time pyridine has four times more polarity than thiophene (pyridine ϭ7.4ϫ10Ϫ30Cm;thiopene ϭ1.83ϫ10Ϫ30Cm),33which is the probable reason for higher T g for pyridine ring containing poly-mer.
The T g values of these polymers are higher than com-mercial poly(ether imide),Ultem 1000(T g ,217°C),based on bisphenol-A(diphthalic anhydride)(BPADA)and (m -phenylene diamine)(MPD)34and comparable to BTDA–ODA (T g ,279°C)35based polyimide.However,the T g values of these polymers are lower than Kapton films derived from PMDA–ODA (T g ,390°C).7Thermal stability
The thermal properties of the poly(ether imides)were evaluated by TGA.The TGA curve for the polymer is shown in Figure 5.The thermal properties of the poly-mers are summarized in Table III.The 5%weight loss temperature in the air of these polymers is in the range of 486–531°C.In general,all these polymers showed very good high thermal stability in air as expected for polyimides except 1e .Low thermooxidative stability of polymer 1e in comparison to others is due to the presence of oxidizable thiophene ring in the polymer
backbone.This is in agreement of our previous find-ings with polymers containing thiophene moiety.It could be possible that at high temperature thiophene moiety gets oxidized to thiophene oxide and loses its aromaticity with a consequence of low thermal stabil-ity.This hypothesis was proved when the thermal stability of these polymers was investigated under nitrogen atmosphere;a comparable result was ob-tained in all cases.As 5%weight loss temperature does not provide much information about the suitabil-ity of a material for long-term applications at high temperatures,the isothermal stabilities of the poly-(ether imides)were investigated at 315°C for 5h.The polymers exhibited very good isothermal stability with a loss of as minimum as 0.4wt %in the case of 1a .DMA measurements
The dynamic mechanical behaviors of the polymer films are shown in Figure 6.The T g ’s taken from the tan ␦peaks at 10Hz are given in Table III.These values are comparable with the calorimetric T g values.The polymers retained very good mechanical proper-ties up to T g ’s as can be observed from the storage modulus plots of the polymers.
TABLE IV
Mechanical and Dielectric Properties of the Poly(Ether
Imides)
Polymer Ar
Tensile break
(MPa)
Modulus (GPa)Elongation at break (%)
Dielectric constant (1MHz)Water absorption
(%)
1a
147
2.18
30
2.82
0.4
1b 129 2.5122 2.880.4
1c 118 1.745 2.920.6
1d 131 1.586 3.240.9
1e 116 2.2315 3.190.8
The mechanical properties of thin polyimidefilms cast from DMF are shown in Table IV.In general,the mechanical properties of the polyimidefilms are ex-cellent and exhibited very high tensile strength and modules.The polyimides containing most rigid quad-riphenyl unit exhibited highest tensile strength up to 147MPa and Young modulus up to2.18GPa.These polymers also exhibited very high elongation at break up to30%(Fig.7).Our previous experience with the poly(aryl ethers)containing quadriphenyl moieties ex-hibited higher tensile strength and higher elongation at break in comparison to the similar poly(aryl
ethers) Figure6DMA plots of the poly(ether imides).containing terphenyl moieties.28,29It is also observed from the Table IV that the polymers having more extended geometry results in more elongation at break than the polymers having less extended geometry. Polyimides containing1,3-phenyl(1c)and2,6-pyri-dine moieties(1d)exhibited very low elongation at break in comparison to the polymers containing1,4-phenyl,1,4-biphenyl moieties.Surprisingly,the poly-mer with2,5-thiophene moiety(1e)showed somewhat more elongation at break than1c and1d.
These values are comparable to those of many other commercially available polyimides(Ultem1000:ten-sile strength,105MPa;tensile modulus,3.0GPa;elon-gation at break,60%;Ultem6000:tensile strength,
103 Figure6.(Continued from the previous page)MPa;elongation at break,30%;Avimid N:tensile strength,110MPa;tensile modulus,4.13GPa;elonga-tion at break,6%).7
Dielectric properties
The dielectric constant of the polymerfilms was de-termined from capacitance values by using a capaci-tance meter1MHz at30°C under wet conditions (relative humidity,45%).The dielectric constant val-ues are presented in Table IV.The dielectric constant values for1a,1b,and1c are compared with the theo-retical dielectric constants values,calculated from the group increments given in Van Kravelen’s book on properties of polymers.36Water-adsorption values of these polymers are as low as0.4wt%in the case of1a characteristics of semifluorinated poly(ether imides). The dielectric constant values of thesefilms are lower than Kapton H(⑀ϭ3.5at1kHz),Upilex R(⑀ϭ3.5at 1kHz),Upilex S(⑀ϭ3.5at1kHz),and Ultem1000(⑀ϭ3.15at1kHz)type of polyimide materials and comparable to those of many semifluorinated poly-(ether imides)(6FDA–MPD:⑀ϭ3.0;6FDA–7FMDA:⑀ϭ2.9;6FDA–13FMDA:⑀ϭ2.7).8,35
CONCLUSION
Five new poly(ether imides)were prepared on reac-tion of oxydiphathalic anhydride with different triflu-oromethyl-substituted diamines.The polymers were well characterized for their thermal,mechanical,and dielectric properties.The synthesized polymers exhib-ited very good solubility in different organic solvents. The resulting poly(ether imides)are amorphous,ex-hibiting outstanding thermal stability in air such as many other thermally stable polyimides without sub-stituents.These polymers have high mechanical strength and high modulus.Poly(ether imides)based on these materials were shown to have valuable prop-erties for electronic applications,such as low moisture absorption,low dielectric constant,and high optical transparency.These polymers mayfind use in plastics,fiber,and membrane for separation applications.
S.B.thanks K.Sekhar,Director,and Dr.D.K.Jaiswal,Asso-ciate Director,DRDE,Gwalior,for providing necessary fa-cilities and for useful discussion.M.K.M.thanks DRDO, New Delhi forfinancial support in the form of a research fellowship.
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