14

Synthesis and Properties of Perfluorinated Polyimides

SHINJI ANDO, TOHRU MATSUURA, and SHIGEKUNI SASAKI

14.1. INTRODUCTION

14.1.1. Near-IR Light Used in Optical Telecommunication Systems

SIlIca-based smgle-mode optIcal fibers are used as the transmISSIOn medIUm m current optIcal telecommUnICatIOn systems 1 The transmISSIon lIght IS near-IR DegradatIOn of commUnIcatIon qualIty under transmISSIon IS mmImIzed by usmg a 1 3 ~m wavelength because the refractIve mdex dIspersIOn of these optIcal fibers IS zero at thIS wavelength, WhICh IS thus called the zero-dIspersIOn wavelength On the other hand, thIS optIcal fiber has a mmImum transmISSIOn loss at 1 55 ~m TechnIques have been developed to ShIft the zero-dIspersIOn wavelength of sIlIca­based optIcal fibers to 1 55 ~m Future telecommUnICatIOn subscnber systems WIll use both 1 3 and 1 55 ~m as commUnICatIOn wavelengths2 (e g, 1 3 ~m for commUnIcatIon servIce and 1 55 ~m for one-dIrectIOnal VIdeo servIce)

The refractIve mdex of the core of the optIcal fibers IS made slIghtly hIgher than that of the claddmg m order to confine the transmItted optIcal SIgnals A small amount of Ge02 IS doped mto the core of the commonly used SIlIca-based optIcal fibers m order to mcrease the refractIve mdex Smce dopmg mto the core IS undeSIrable from the pomt of VIew of decreasmg the transmISSIOn loss, fluonne IS doped mto the claddmg of optIcal fibers to achIeve very low transmISSIOn loss The

SHINJI ANDO, TOHRU MATSUURA, and SHIGEKUNI SASAKI SCIence and Core Technol­ogy Group, NIppon Telegraph and Telephone Corp, Musashmo-shl, Tokyo 180, Japan Present address of SHINJI ANDO, Department of Polymer ChemIstry, Tokyo InstJtute of Technology, Meguro-ku, Tokyo, 152, Japan

FluOIopohmers 2 Propertle" edIted by Hougham e f al Plenum Press, New York, 1999

277

278 Shinji Ando et aL

use of fluonne decreases the refractIve mdex of the medIUm and consIderably decreases water absorptIOn The mimmUffi loss of 0 154 dB/km at I 55 ~m obtamed from a fluonne-doped optIcal fiber IS close to the theoretIcal hmlt gIVen by RayleIgh scattenng and harmomc absorptIOn of oxygen-hydrogen (O-H) and sIhcon-oxygen (SI-O) bond stretchmg 3 The sharp absorptIOn peak appeanng at I 38 ~m IS due to the second harmomc of the O-H bond stretchmg vIbratIOn of the resIdual SI-OH groups 4 The optIcal commumcatIOn wavelengths, I 3 and I 55 ttm, are located m the valley between the absorptIOn peaks and are called wmdows ThIs explams the very low transmISSIOn loss at these wavelengths

14.1.2. Integrated Optics and Optical Interconnect Technology

WIth the advancement of optIcal telecommumcatIOn systems, "mtegrated optIcs" technologl and "optIcal mterconnect" technology6 are becommg more and more Important The major components of these two technologIes are photomc mtegrated CIrcUIts (PICs), optoelectromc mtegrated CIrcUIts (OEICs), and optoelectromc multIchiP modules (OE-MCMs) All the functIOnal deVIces, mcludmg optIcal and electromc components, are formed or attached to a smgle planar substrate OptIcal SIgnals are transmItted through optIcal wavegUIdes that mterconnect such components The pnnclple of optIcal transmISSIOn m wave­gUIdes IS the same as that m optIcal fibers To Implement these technologIes, both actIve optIcal devIces (such as hght sources, optIcal SWItches, and detectors) and paSSIve optIcal components (such as beam sphtters, beam combmers, star couplers, and optIcal multIplexers) are needed A WIde vanety of optical matenals has been studIed, e g, glasses, hthIUm mobate, III-V semIconductors, and polymers In partIcular, paSSIve optIcal components have been fabncated usmg glass optIcal wavegUIdes by IOn-exchange,7 or by flame hydrolYSIS depOSItIon and reactIve Ion etchmg (FHD and RIE) 8 In the case of sIhca-based glass wavegUIdes, all the wavegUIdes and the paSSIve optical components should be formed on the substrate before attachmg the actIve optIcal and electromc deVIces because very hIgh temperatures (up to 1300°C) are needed to consohdate sIhca when usmg FHD and RIE In addItIon, the mflexIblhty of glass wavegUIdes and the dIfficulty of processmg large (longer than 30 cm) waveguIdes make It dIfficult to achIeve PICs and OEICs As a result, there has been a strong demand for matenals for mterconnectmg wavegUIdes and paSSIve optical components that have hIgh processablhty, flexlblhty, and the posslblhty of fabncatmg wavegUIdes on the PICs, OEICs, or OE-MCMs after attachmg or formmg of optIcal and electromc components

Synthesis and PropertIes of Perfluorinated Polyimides 279

14.1.3. Polymeric Waveguide Materials for Integrated Optics

For the above reasons, polymers are expected to be used as waveguIde matenals for optIcal Interconnects and passive optIcal components on PICs, OEICs, and OE-MCMs 9 The current manufactImng process for ICs and MCMs Includes soldenng at 270°C and bnef processes at temperatures up to 400°C. WavegUIde polymenc matenals should therefore have hIgh thennal stabIlIty, Ie, a hIgh glass transItIOn temperature (Tg) and a hIgh polymer decomposItIOn temperature as well as hIgh transparency at the wavelengths of optIcal commUlllcatIOns (1 3 and 1 55 /lm)

ConventIonal polymenc matenals used In plastIc optIcal fibers and wave­gUIdes for short-dIstance optIcal datalInks, such as poly(methyl methacrylate) (PMMA), polystyrene (PS), or polycarbonates, do not have such thennal stabIlIty In addItIon, theIr optIcal loss at the wavelengths for optIcal commUlllcatIOns are much hIgher than at VIsIble wavelengths (0 4 ~ 08 /lm), because carbon­hydrogen (C-H) bonds hannomcally absorb near-IR radIatIon (0 8 ~ 1 7/lm) FIgure 14 1 shows the v1S1ble-near-IR absorptIOn spectrum of PMMA dIssolved In chlorofonn wIth a concentratIOn of 10wt% The Influence of C-H bonds of chlorofonn was neutralIzed by USIng the same amount of chlorofonn as a reference Two types ofC-H bonds In PMMA. those In the methyl and methylene groups, gIVe broad and strong absorptIOn peaks In the near-IR regIon Although 13 and 1 55/lm are located In the WIndows, absorptIOn OWIng to C-H bonds Increases the optIcal losses at these wavelengths

004r--------------------.~----~~

~ c as

003

of 0.02 o ~ as

0.01

poly(methylmethacrylate) (dissolved In CHCI3)

1 3

0.6 0.8 1.0 1.2 1.4

wavelength (flm)

1.6

Figure 14.1. Vlslble-near-JR absorplion spectrum ofpoly(methylmethacrylate) (PMMA) dissolved In

chloroform The same amount of chloroform was used as a reference (reproduced by permiSSIOn of the Amencan Chemical SOCiety, from Ando et a1 28

)

280 Shmji Ando et aL

PolYlmldes and epoxy resms have been mvestlgated as optical waveguide matenals because they have excellent thermal, chemical, and mechamcal stabl­hty 10-14 The first attempt to use polYlmlde for optical wavegUIdes was made by Furuya et al lO They fabncated a laser-waveguIde mtegratlOn by usmg a spm­coated polYImide for the core layer of the wavegUIde Franke and Crowl I discussed the mftuence of the cunng process of soluble polYlmldes and obtamed an optIcal loss of less than 03 dB/cm at 0633 /lm ThiS loss IS a measure of the change m the mtenslty of the hght SIgnal accordmg to the followmg expressIOn dB = -10 loge! / !o) In thiS case, the loss per centimeter IS approXimately 7% SullIvanl2 descnbed polYlmlde wavegUIdes fabncated by reactive etchmg HIgh­denSIty router, splItter, and combmer bUIldmg-block components have been developed m polYlmlde channel multimode wavegUides On the other hand, Hagerhorst-Trewhella et al 13 reported solvent or wet-etchmg reSIst processes usmg UV-curable epoxies and polYImides WIth 0 3 dB / cm loss at 1 3 /lm Ablated mIrrors usmg eXCImer lasers have been demonstrated for out-of-plane mput/output mterconnectlOns Reuter et al 14 have reported that optimally cured partially ftuonnated polYImides can be used to achIeve optical losses below o 1 dB/cm at vlSlble wavelengths (at 063 /lm), and that these losses are stable at temperamres up to 200°C and below 0 5 dB/cm up to 300°C

14.1.4. Optical Transparency of Fluorinated Polyimides at Near-IR Wavelengths

The authors IS-

17 demonstrated that smgle-mode embedded waveguIdes can be fabncated WIth ftuonnated polYlmldes (see thiS volume, Chapter 15) To fabncate these smgle-mode wavegUides, there must be precise control of the shape and SIze of the core and of the refractive mdexes of the core and the claddmg The polYlmldes used are copolymers syntheSized from pyromellItic dlanhydnde (PMDA) and 2,2-bIS(3,4-dicarboxyphenyl)hexaftuoropropane dIanhy­dnde (6FDA) as dlanhydndes and 2,2'-bIs(tnftuoromethyl)-4,4'-dlammoblphenyl (TFDB) as a dlamme 18 The syntheSIS, propertIes, and optical applIcatIOns of these partIally ftuonnated polYlmldes are descnbed m Chapter 15 These wavegUides have optical losses ofless than 0 3 dB/cm at 1 3/lm 16 The mcrease m optical loss was less than 5% after heatmg at 380°C for 1 h and at 85°C WIth relative hUlmdlty of 85% for over 200 h 17 These matenals also show hIgh transparency at VISIble wavelengths as well as low dielectnc constants, low refractive mdexes, and low water absorption In these propertIes, the matenals are supenor to those of conventIOnal nonftuonnated polYImldes and epOXIes used for the waveguIdes descnbed above 19 N onftuonnated polYlmldes have hIgh water absorptIOn of about 1 3-29 wt%,20 whIch causes sIgmficant optical loss at 1 3 and 1 55/lm Water molecules have strong absorptIOn peaks m the near-IR regIOn 21

SynthesIs and PropertIes of Perlluonnated Polyimldes 281

However, fluonnated polYImIdes also have some absorptIOn peaks m the near-IR regIOn owmg to C-H bonds m theIr phenyl groups FIgure 142 shows a schematIc representatIOn of the fundamental stretchmg bands and theIr harmomc absorptIOn wavelengths for the carbon-hydrogen (C-H), carbon--deutenum (C-D), and carbon-fluonne (C-F) bonds The wavelengths were measured for benzene, hexadeuterobenzene, and hexafluorobenzene WIth a near-IR spectro­photometer For SImplICIty, the absorptIOns from the combmatIons of the hannolllcs and the defonnatIOn vIbratIOn are not shown, and the absorptIOns that are due to the fourth and fifth hannomcs of the stretchmg vIbratIOn are neglIgIbly small The harmomcs of C-D and C - F bonds are dIsplaced to longer wavelengths than the C-H bond because the wavelengths for the fundamental stretchmg vIbratIOns of C-D and C-F bonds are about 1 4 and 2 8 tImes longer than that of the C-H bond

Smce the absorptIOn band strength decreases about one order of magmtude WIth each mcrease m the order of hannomcs (1 e, the vIbratIOnal quantum number),21 the losses at vISIble and near-IR wavelengths can be appreCIably reduced by substItutmg deutenum or fluonne for hydrogen atoms Kamo et aZ 22

,23

have produced low-loss optIcal fibers at vlSlble wavelengths from deuterated

2 JlCH

1.0 2.0 1.3 1.55

J/CH

2 JlCD

3.0

wavelength (/lm)

J/CD

4.0

H~:C H" H

H

DQeD D D

D

~F F F

F

5.0

Figure 14.2. Schematic representatIOn of fundamental stretchmg bands and their hal1llomc absorptIOn wavelengths for C-H, C-D, and C-F bonds observed for benzene, hexadeuterobenzene, and hexafiuorobenzene, respectively (reproduced by pel1llISS10n of the Amencan Chemical SOCiety, from Ando et al 2s)

282 ShIn]) Ando et aL

PMMAs and fluorodeuterated PSs Imamura et al 24 fabncated low-loss wave­guIdes of less than 0 I dB / cm at I 3 11m by usmg deuterated and fluorodeuterated PMMAs ThIS substItutIOn has a sIglllficant effect m reducmg the optIcal loss at vIsIble wavelengths and 1 3 11m However, the strength of the absorptIOn due to the harmolllcs of C-D bond stretchmg appeanng between I 4 and 1 6 11m IS not neglIgIble at I 55 11m An automatIc fiber lIne-testmg system usmg a I 65 11m wavelength as an IdentIficatIOn sIgnal IS also bemg developed 25 As can be seen m FIgures 14 1 and 14 2, the transparency of conventIOnal polymers havmg a C - H bond at 1 65 11m IS extremely low because the second harmolllcs of C-H bond stretchmg IS located at the same wavelength Such polymers cannot be used m the optIcal components for the future telecommulllcatIOn systems even If they are partIally deuterated or fluonnated

14.1.5. The Effect of Perftuorination on Optical Transparency

For the reductIOn of optIcal loss at near-IR wavelengths, perfiuonnatIOn IS, m pnnclple, supenor to perdeuteratIon Table 14 1 shows the molecular structure and the propertIes of three kmds of eXlstmg perfiuoropolymers, Teflon-AF (DuPont), Cytop (Asahl Glass Co ), and poly(tetrafluoroethylene) (PTFE) A semI crystallIne polymer, PTFE cannot be used for lIght-transmlttmg applIcatIOns As expected from the perfiuonnated molecular structure and the amorphous nature, Cytop has been reported to have no absorptIOn peaks between 1 0 and 2 5 11m 26 However, ItS low Tg may not be SUItable for waveguIde applIcatIOns for mtegrated optIcs On the other hand, the Tg and the refractIve mdex of Teflon-AF can be controlled by changmg the copolymer ratIO decreasmg the tetrafluoroethylene content mcreases the Tg over 300°C In addItIon, ItS low dlelectnc constant and hIgh chemIcal

Table 14 1 Molecular Structure and Properties of Amorphous and Semlcrystallme Perfiuoropolymers

Perfluoropolymer Teflon AF Cytop PTFE

o~o o~o o?5<o ", o 0

Morphology Amorphous Amorphous SeIll1crystalhne Fluonne content (wt%j 67 I, 650 679 760 Glass transition temperature ee) 160, 240a 108 Meltmg pomt (0C) 327 Dlelectnc constant I 89-1 93 21-22 21 Refractive mdex 129-131 135 138 Optical transmittance (%) (VISible regIOn) >95 95 Opaque

a Glass tranSItIon temperature of no TFE content IS hIgher than 300°C

SynthesIs and PropertIes of Perftuorinated Polyimides 283

stabilIty IS preferable because optlcal waveguides are also used as msulatmg layers for electrolllc ClrcUlts m OEICs and OE-MCMs

14.2. CHARACTERIZATION AND SYNTHESIS OF MATERIALS FOR PERFLUORINATED POLYIMIDES27

,28

14.2.1. Reactivity Estimation of Pertluorinated Diamines

By perfiuonnatron of polYlmldes, we expected to achieve not only low optical losses at 1 3 and 1 55 /lm but also high thermal, chemical, and mechalllcal stabilIty, low water absorptIOn, and low dJelectnc constants Perfiuonnated polYlmldes can be synthesized from perfiuonnated dlanhydndes and dJammes Figure 14 3 lIsts a dlanhydnde and dlammes that can be used for the synthesIs of perfiuonnated polYlmldes Tetrafluoro-p-phenylenedJamme (4FPPD), tetrafluoro­m-phenylenedJamme (4FMPD), and 4,4' -dlammooctafluoroblphenyl (8FBZ) are commerCially aVaIlable BIS(2,3,5 ,6-tetrafluoro-4-ammophenyl)ether (8FODA) and bls(2,3,5,6-tetrafluoro-4-ammophenyl)sulfide (8FSDA) were prepared as descnbed m the lIterature 2930 1,4-Bls(tnfluoromethyl)-2,3,5,6-benzenetetracar­boxylIc dlanhydnde (P6FDA) was the only prevIOusly known perfiuonnated dlanhydnde that was synthesized m our laboratory 31

Fluonne IS highly electronegatIve, which means that substItutmg It for hydrogen conSiderably decreases the acylatIOn reactIvity of the dlamme monomers and mcreases the reactIvity of the dJanhydnde monomers Dme-Hart and Wnght32

synthesized a polYlmlde denved from PMDA and 8FBZ, but they could not obtam polymers with a high enough molecular weight for film formatIon

To generate high-molecular-weight perfiuonnated polYlmldes, It IS first necessary to determme how fluonne affects the reactivity of the monomers In particular, the effect of substItutmg hydrogen with fluonne on dlamme reactlVlty IS Important because kmetIc studies of the acylatIon of conventIOnal monomers have revealed that acylatIOn rate constants can differ by a factor of 100 among different dJanhydndes, and by a factor of 105 among dIfferent dIammes 33

To estImate the acylatIOn reactivity of the perfiuormated dIammes, poly(amlc aCld)s were prepared from the five dJammes lIsted m Figure 143 and 6FDA dlanhydnde at room temperature EqUlmolar amounts of dlanhydnde and dJamme were added to N,N-dlmethylacetamlde (DMAc) to a concentratIOn of 15 wt% and stIrred at room temperature for 6 days under llltrogen Table 142 shows the end­group content of the poly(amlc aCld)s determmed from 19F_NMR 4FMPD shows the' lowest end-group content, Ie, the highest reaCtIVity, and 4FPPD shows the next highest However, acylatrons were not complete for any of the dlammes, and end-group contents were high even after 6 days of reactIOn at room temperature

284 Shinji Ando et aL

o~=O=~ t,' / I C\ p C ,# C II CF II o 3 0

t= F

"'Ni tN~ F F

4FPPD

P6FDA

F

H2N~NH2

FVF F

4FMPD

t= F F. F

"~i K t N

"' F F F F

8FBZ

t= F F. F

"'Ni tsi tN~ F. F F. F

"~i toi tN"' F F F F F F F F

8FSDA 8FODA

FIgure 14.3. Structures of a dlanhydnde and dUllmnes that can be used for perfluonnated polYlmlde synthesIs (reproduced by penmSSlOn of the Amencan ChemIcal SocIety, from Ando et al"8

)

When 8FBZ dIamme, the least reactIve one, was reacted wIth 6FDA, no NMR sIgnal of the correspondmg poly(amic aCld) was detected

We reported the relatIOnshIps between the NMR chemIcal ShIftS and the rate constants of acylatIOn (k) as well as such electromc-property-related parameters as IOmzatlOn potentIal (IP), electromc affimty (EA), and molecular orbItal energy for a senes of aromatIc dIammes and aromatIc dianhydndes 34 The usefulness of

Table 14 2 End-Group Contents of POly(AmIC ACId)s SynthesIzed from Perfiuonnated Dlammes and 6FDA

Dlanhydnde

DIalmne

4FPPD 4FMPD 8FODA 8FSDA 8FBZ

End-group content (%)

42 15 75 91

>99

SynthesIs and PropertIes of Perlluorinated Polyimides 285

NMR chemical shifts for estImatmg the reactiVIty of polYlmide monomers was first reported by Okude et aZ 35 We revealed that the 15N chemIcal shifts of the ammo group of dmmmes (bN ) depend monotonIcally on the loganthm of k (log k) and on IP For the syntheSIS ofperfluonnated polYImides, we attempted to estimate the reactivity of the five perfluonnated dlammes from I5N_ and IH-NMR chemIcal ShIftS of the ammo groups (bN and OH) and calculated IPs (IPeal) FIgure 144 plots bN agamst bH, with upfield dIsplacement of chemIcal shifts (bN and bH are decreased) mdicatmg the hIgher reactIvIty for acylatIOn The IP cal values calculated usmg MNDO-PM3 semlempmcal molecular orbItal theory36 are also mcorporated m the figure From the bN , bH , and IP cal values of the diammes, 4FPPD IS suggested to have the hIghest reactivity among the five, and 4FMPD IS the next However, thiS does not comclde With the end-group contents of poly(amlc aCId)s denved from the expenments descnbed above As shown m FIgure 145, the acylatIOn starts WIth a nucleophIhc substItutIOn m WhICh diamme donates an electron to the dIanhydnde 33 ThIS reactIOn IS called "first acylatIon" and It affords a monoacyl denvatIve (MAD) Poly(amic aCId)s are generated by the

60

-C")

:I: Z 50 E o --E Q.

.9: 40 z

c,o

30

F F F F

F F F F H:!N-Q-S-Q-NH2

%( F F F F HIJ ~ J ~ J NH2 ......... 8FSDA

F 8FBZ ...• IP"al=956 F 921 ... /

H~ANH2 . H .....• FFFF

: F .... / H1={0X NH2 4FMPD ./

.' F F 906 ~ .. , 8FODA

.·<iFPPD F F 937 ./ 877 K

j:. ~V-NH2 high F F

reactlvity I

4.0 5.0 6.0 7.0

bH (ppm from TMS) FIgure 14.4. 15N_ and lH-NMR chemIcal shIfts and calculated lOUlzatlOn potentIals (eV) of perfluonnated dJammes

286 Shinji Ando et aL

1 st. Acylation

~\ f? e o 0 H II II I c_ .-c ~

0' R '0 + H,N -R'-NH, 'c...... ........c' -- c_ ...... c-N-R'-NH,

0' R ' ...... , II II o 0

Dlanhydnde

2nd. Acylation e

o ~ ~ ~_ ...... c-N-R'-NH,

0' R + 'c...... 'C-OH

" " o 0

MAD

Dlarnlne

o 0 II It c_ ___c

0' R '0 'c......... "c" " II o 0

If C-OH o 8 Monoacyl Derivative

(MAD)

o 0 H tH 0 0 H t \ /I I I II II I 'c ~C-N-R'-NH, N -c C-N -R' 1- , , /"

o R -- R 'c...... , ...... , "C-OH HO-C C-OH o II " " 000

Poly (arnlc aCid)

Figure 14.5. Two-step acylatIOn reactIOns that generate poly(amlc aCid) from dlamme and tetra­carboxylic aCid dlanhydnde (reproduced by permissIOn of the Amencan Chemical SOCiety, from Ando et al 28

)

succeedmg "second acylatIOn," m whIch MAD reacts wIth dianhydnde, dIamme, or MAD Therefore, the reactIvIty of MADs rather than that of dIammes should be exammed for synthesIzmg high-moiecuiar-weight poly(amic aCId)s

The five perfluormated dIammes were reacted wIth eqmmolar amounts of phthahc anhydnde m tetrahydrofuran to estImate theIr MAD reactIvIty The molecular structures, 8N, and 8H of the diammes and the MADs are shown m FIgure 14 6 The dIamme of 8FBZ IS not shown because no MAD could be obtamed The 8N of 4FPPD was dIsplaced downfield by 125 ppm m reactmg to MAD that corresponds to a more than 103 decrease of acylatIOn rate constant On the other hand, the dIsplacements of 8N and 8H for the other diammes are much smaller ThIS means that the reactIvIty of the reSIdual ammo group IS httle affected by the first acylatIOn, unless two ammo groups are located at the para-posItIon m the same benzene nng As a result, 4FMPD-MAD shows the hIghest reactiVIty comcldmg WIth the result of the end-group content of poly(amic aCId)s DespIte the fact that the 8N and 8H of 4FPPD-MAD are close to those of 8FODA-MAD, the end-group content of the poly(amic aCId) denved from 4FPPD and 6FDA was lower than m the case of 8FODA and 6FDA There may be some dIfference m the stenc effects dunng the generatIOn of poly(amic aCld)s between one- and two­benzene nng diammes

Synthesis and Properties of Perfluonnated PolYImides 287

F. F

H~i ~~ -F F

ON = 35 4 OH = 4.85

FIgure 14.6. 15N_ and IH-NMR chemIcal ShIftS of perfluonnated dlammes and theIr chemical ShIft changes caused by the first acylahon (reproduced by perrmSSlOn of the Amencan ChemIcal SocIety, from Ando et a1 28

)

DespIte the dIfficulty noted above, Hougham et a1 37,38 succeeded m

prepanng contmuous films from 4FPPD and 8FBZ as diammes and 6FDA as a dianhydnde usmg skIllful methods They showed that two stages of polymenza­tIon are necessary to obtam hIgh-molecular-weIght polYImides from the perfluonnated dIammes a solutIOn polycondensatIOn at temperarures between 130 and 150°C followed by a hlgh-temperarure solId state cham extenSIOn of up to 350°C FTIR spectra were measured for sequentIally cured and cooled films of 6FDA/8FBZ, and they concluded that the cham extenSIOn begms at temperarures between 200 and 300°C, however, optimal mechamcal propertIes were not realIzed wIth cure temperarures below 350°C Usmg 13C-NMR, we have observed

288 ShlDJI Ando et al.

a sImIlar phenomenon for a partIally fluonnated 6FDA(fFDB polYlmide dIssolved m dlmethylsulfoxlde-d6 (DMSO-d6) 39 Hougham et aZ 37 reported that mcreased fluonne m the polYlmide backbone leads to a sIglllficant mcrease m the ~-transitIon temperatures, and they suggested that a strong ~-transitIOn helps m polymenzatIOn m the solId

14.2.2. Reactivity and Structural Problems of an Existing Perftuorinated Dianhydride

Because of the hIgh electronegatIvity of fluonne, the mtroductIOn of fluonne or fluonnated groups mto dlanhydndes should mcrease the reactIvIty FIgure 14 7 shows structural formulas of conventIonal and fluonnated dlanhydndes arranged m order of calculated electron affilllty (EAcaD usmg the MNDO-PM3 method and 13C-NMR chemIcal ShIft of carbonyl carbons (oc) 40 The fluonnated dlanhydndes m whIch trlfluoromethyl (-CF3) groups are dIrectly bonded to benzene nngs (P6FDA and P3FDA) are located nghtmost wIth the largest EAcaJ values and the smallest oc, suggestmg conSIderable mcrease m reactIvIty m the acylatIOn reactIOn 34 The EAcaJ of 6FDA, m contrast, IS located between the unfluonnated PMDA and BPDA, and ItS OC IS larger than PMDA ThIS fact mdlcates that the reactlVlty enhancement caused by the mtroductIOn of a hexafluorOIsopropylIdene [-C(CF3h-] group IS not as hIgh as that of a dIrectly bonded -CF3 group ThIS IS because the electron-drawmg effect of fluonnes IS blocked by the quaternary carbon P6FDA IS therefore expected to compensate for the low reactIvIty of perfiuormated dlammes However, the end-group content of the poly(amlc aCId) synthesIzed from 4FMPD and P6FDA was 36%, whIch IS hIgher than that of poly(amlc aCId) prepared from 4FMPD and 6FDA ThIs reason IS not clear, however a certam portIOn of anhydnde nngs mIght be open before the synthesIs because thIS dIanhydnde IS very senSItIve to atmosphenc mOIsture and mOIsture m the polymenzatIon medIUm, although dIanhydndes were sublImated under reduced pressure and all the synthesIs procedures were carned out under llltrogen

The resultant perfiuonnated polYlmide [P6FDA/4FMPD (1)] was cracked and bnttle and dId not form a contmuous film In the case of the other four

~=¢r=CFa ~ /C ~ C,

N I N \ A /

C &r C II II F o CFa 0

F

(1)

F F

P6FDAl4FMPD

Synthesis and PropertIes of Perftuorinated Polyimides

>

P3FDA

350 1577/1602

PMDA

\J):~ < I p C Ue

J ~

BTDA

314 1612

~\ ~ ~ p~c~c,

<\ . .J...J l,..l. p if ~\ o 246 0

1623

289

6FDA

~\ F3C(, P3 ~ > 6~C~Cb ~~ v-.- / 8 ~

268 1622/1620

ODPA o 0

> }Y)0i(Y~~ 'c~ v--..c' II \I o 238 0

1623

FIgure 14.7. Aromatic dianhydndes arranged ill order of calculated electron affimty (EAca1) and 13C_ NMR chermcal ShIft of carbonyl carbon (be) Larger EAcal and smaller be correspond to the strong electron-acceptmg property of a dianhydnde

dlammes, the polYlmldes prepared usmg P6FDA are coarse powder or films that have many cracks One reason for the noncontmuous film IS probably that the hIgh reactivIty of the perfiuonnated dmnhydnde could not compensate for the very low reactivIty of perfiuonnated dlammes However, the effect of the ngldlty of the polYlmlde cham cannot be neglected m the cases of P6FDA and one-benzene-nng dmmmes In thIS sltuatlOn, bond rotatlOn IS penmtted only at the ImIde lmkage (mtrogen-aromatic carbon bonds) However, thIS rotation IS restncted by stenc hmdrance between the fluonne atoms and carbonyl oxygens DespIte the bent structure at the meta-hnkage of 4FMPD, the mam cham of thIS polYlmlde should be very ngld As Hougham et al 37

38 have pomted out, a hIgh-temperature solId state cham extenslOn should take place for the formation of hIgh-molecular-weIght polYlmldes However, thIS process accompames conformatlOnal changes and molecular reonentatlOn of polYlmldes The cham extenslOn reactlOn should be senously Impeded by the ngld molecular structure ofP6FDA/4FMPD

14.2.3. Synthesis of a Novel Perftuorinated Dianhydride

The lack of flexlblhty of the polymer cham has to be Improved by mtroducmg lmkage groups mto the dlanhydnde component Accordmgly, contm­uous and flexIble films of perfiuonnated polYlmldes are expected to be obtamed by combmmg dlammes, whIch have hIgh reactivIties, WIth dlanhydndes, WhICh have flexIble molecular structures

A novel perfiuonnated dmnhydnde, I ,4-blS(3 ,4-dlcarboxymfluorophenoxy)­tetrafluorobenzene dmnhydnde (lOFEDA), was synthesIzed accordmg to Scheme

290 Shinji Ando et aL

1 It should be noted that thIS molecule has two ether lmkages that gIve fleXIbIlIty to the molecular structure In addItIon, the bulky -CF3 groups m P6FDA are replaced by fluonne atoms The be of lOFEDA (1575 ppm from TMS) was almost the same as that of P6FDA (157 6 ppm), so thIS dlanhydnde should have hIgher reactIvIty than unfluonnated and partIally fluonnated dlanhydndes

14.3. SYNTHESIS AND CHARACTERIZATION OF PERFLUORINATED POLYIMIDES

14.3.1. Synthesis of Perfluorinated Polyimide (10FEDA/4FMPD)

To prepare the poly(amIc aCId), eqmmolar amounts of lOFEDA and 4FMPD were added to DMAc to a concentratIOn of 15 wt% and stIrred at room

Scheme 1. SynthesIs of lOFEDA dlanhydnde

Synthesis and Properties of Perfluorinated PolYlmldes 291

temperature for 7 days under mtrogen The end-group content of the poly(amic aCId) estlmated from 19F_NMR was 6%, WhICh IS much less than that of P6FDA/4FMPD poly(amic aCId) (36%) ThIS IS posSIbly due to the consIderable mcrease m the flexIbIhty of the dianhydnde structure and the substltutIOn of -CF 3 groups for fluonnes The poly(amic aCId) denved from P6FDA IS thought to have more structural dIstortIOn than that from 10FEDA because the molecular confonnatIOn around the amIde group m the fonner IS more restncted than m the latter by the stenc hmdrance between the bulky -CF3 group and carbonyl oxygens

The solutIon of poly(amic aCId) was spm-coated onto a sIhcon wafer and heated first at 70°C for 2h, at 160°C for 1 h, at 250°C for 30mms, and finally at 350°C for 1 h (Scheme 2) The resultant perfluonnated polYImide [lOFEDA/4FMPD (2)] was a 95-).lm-thIck, strong, fleXIble film, pale yellow m color hke conventIonal unfluonnated polYImides The chemIcal fonnula of the lOFEDA/4FMPD polYImide was confinned by elemental analysIs The fully cured film was not soluble m polar orgamc solvents, such as acetone, DMAc (DMF), and N,N-dimethylfonnamide Thennal mechamcal analysIs (TMA) showed that the glass transitlon temperature was 309°C (FIgure 148), WhICh IS about 30°C hIgher than the soldenng temperature Thennal gravimetnc analysIs (TGA) showed the InItIal polymer decomposItIon temperature to be 407°C The dIelectrIC constant was 2 8 at 1 kHz

E E 20 e E

M '0

c o 10 :; CI C o

'G)

o~~~----~--~----~--~----~--------~ o 100 200

temperature ('C)

300 400

Figure 14.8. Thermal mechamcal analYSIS (TMA) curve of lOFEDAj4FMPD film cured at 350 c C (reproduced by permIssIon of the Arnencan ChemIcal SOCIety, from Ando et a1 28

)

292 Shinji Ando et aL

~ In DMAc under N 2

@')=(@OH H

HOO~O~-§ o~~-~~~ C¥F F F FVCOOH FVF g F ®' ® F F

@" '" ~ ®

OFvFF (~O II II

N~c=¢r~ 0 ~ J O¢=~ C> C ""FF FF ""C " (j) ® II F OFF 0

(5)

(2)

10FEDA/4FMPD

F

®

F @

Scheme 2. SynthesIs of IOFEDAj4FMPD polYlllude

14.3.2. Imidization Process Estimated from NMR and IR Spectra

DespIte the InsolubIlity of fully cured perfluonnated polYImIde, the lOFEDA/4FMPD films cured below 200°C are soluble In polar orgamc solvents The same phenomena have been observed for partially ftuonnated polYImides 40 FIgure 149 shows the 19F_NMR spectra of lOFEDA/4FMPD prepared at the final cunng temperatures of 70, 120, 150, and 200°C They were dIssolved to a concentratIon of 5 wt% In DMSO-d6 The Signals In the spectra were aSSIgned by USIng substltuent effects determIned from model compounds 41 It IS noteworthy that the SIgnals aSSIgned to the end groups of poly(amic aCId) and/or polYImide are observed In all the NMR spectra The termInal structures wIth amInO groups of poly(amic aCId) and polYImide are shown In FIgure 14 10 The symbols of the peaks In FIgure 149 correspond to the ftuonnes In Scheme 1 and FIgure 14 10 The end-group contents determIned from the IntenSIty ratios of SIgnal c (aSSIgned

Synthesis and Properties of Perfluonnated Polyimides 293

70·C @'

®"

@"@)' @'

@,

120·C

150·C

@ (])

200·C @

@

@ CD

@ ® @

-120 -125 -130 -135 -140 -145 -150 -155 -160 -165

19F Chemical Shift (ppm from CFCI3)

Figure 14.9. 19F_NMR spectra of IOFEDA/4FMPD cured III nttrogen to 70, 120, 150, and 200°C dissolved III dlmethylsulfoxlde-~ (the numbermg of peaks corresponds to the fluonnes III Scheme 2 and Figure 14 10

294 ShinJi Ando et at.

to the end-group) to sIgnal 3 (assIgned to the mner part of the polymer cham) are 8%, 15%, 9%, and 6% for lOFEDA/4FMPD cured at 70, 120, 150, and 200°C, respectIvely ThIS mdIcates that the degree ofpolymenzatIOn of the 120°C sample IS smaller than that of PAA, suggestmg that a depolymenzatIOn reactIOn occurs at amIde groups of PAA at around 120°C. However, thIS low-molecular-weIght polymer IS gradually converted mto a hIgher-molecular-weIght polYImIde by subsequent cunng at hIgher temperatures (150'" 200°C) because the end-group content decreases wIth mcreasmg cunng temperature As Hougham et a1 37

,38 and the authors39 have confirmed for partIally fluonnated polYImIdes, condensatIOn of the umeacted end groups of perfluonnated polYImIdes took place m the subsequent hIgh-temperature cunng between 200 and 350°C The dIfference m solubIlIty between the polYImIdes cured at 200 and 350°C can be explamed by thIS cham extensIOn reactIOn and by mcreased aggregatIOn of the polyImIde molecules WIth cunng above Tg

The NMR spectra m FIgure 14 9 mdIcate that the ImIdIzatIOn reactIOn began at 70°C and was completed at 150°C for lOFEDA/4FMPD A I3C-NMR exammatIOn of 6FDAjTFDB polYImIde (3), m contrast, showed that the ImIdIza­tIon became sIgmficant at 120°C and was complete at 200°C 39 The ImIdlZatIOn reactIOn of lOFEDA/4FMPD occurred at lower temperatures than 6FDAjTFDB ThIS can be explamed by the hIgher electron-acceptmg propertIes and more fleXIble structure of 10FEDA compared to 6FDA

The IR spectra of 6FDAjTFDB and lOFEDA/4FMPD cured at three final cunng temperatures are shown m FIgure 14 11 These spectra also confirm the NMR results The absorptIOn peaks speCIfic to ImIde groups (1800 and 1750 cm -1) are clearly seen m the 120°C sample of lOFEDA/4FMPD, and the spectrum IS very SImIlar to that of the fully cured polYImIde at 350°C On the other hand, the absorptIOn peaks speCIfic to the ImIde groups (1790 and 1740 cm - 1) can be observed for the 120°C sample of 6FDAjTFDB, however, the spectrum IS much more SImIlar to that of the 70°C sample m whIch most of the polymers have not been converted to polYImIdes

o H @' F II I F

-O~C-N~NH2

FVCOOH,:VF F ((f)' F (5)'

0' Figure 14.10. Amme-tenmnal structure of IOFEDA/4FMPD polYlmlde

SynthesIs and PropertIes of Perfluonnated Po\yimides 295

(3)

6FDAfTFDB

14.4. OPTICAL, PHYSICAL, AND ELECTRICAL PROPERTIES OF PERFLUORINATED POLYIMIDES

14.4.1. Optical Transparency at Near-IR and Visible Wavelengths

The near-IR absorptIOn spectrum of lOFEDA/4FMPD film cured at 350°C IS shown m FIgure 14 12 together wIth that of parttally ftuonnated polYlmlde (6FDAjTFDB) The film thIcknesses were about 25 J..lm The perfiuonnated polYlmlde has no substanttal absorptIOn peak over the wavelengths for opttcal commumcatton except for a very small absorptIOn peak at 1 5 J..lm that may be due to the fourth harmomc of the C=O stretchmg VIbratIOn of ImIde groups Parttally ftuonnated polYlmlde, on the other hand, has an absorptton peak due to the thIrd harmomc of the stretchmg vlbratton of the C-H bond (11 J..lm), a peak due to the combmatIOn of the second harmomc of stretchmg VIbratIOn and deformatIOn VIbratIOn ofthe C-H bond (l 4 J..lm), and a peak due to the second harmomc of the stretchmg VIbratIOn of the C-H bond (165 !lm) AbsorptIOn peaks were assIgned accordmg to the peaks observed m PMMA 21-23

FIgure 14 13 shows the UV-vlslble absorptIon spectra of perfiuonnated (lOFEDA/4FMPD), parttally ftuonnated (6FDAjTFDB), and unftuonnated [PMDA/ODA (4)] polYlmldes The cut-off wavelengths (absorptIOn edge, AD) of the absorptIOn caused by electromc tranSItIOn for lOFEDA/4FMPD (around 400 nm) IS located between those of 6FDAjTFDB and PMDA/ODA ThIS causes the yellowIsh color of 10FEDA/4FMPD The coloratIOn of poly 1m Ides IS closely related to the extent of the charge transfer (CT) between altematmg electron-donor (dlamme) and electron-acceptor (dtanhydnde) mOIettes 42 Kotov et aZ 43 dIscussed the quantttatIve color changes m the polYlmldes denved from pyromelhtlc dtanhydnde from theIr ADS values m the optIcal absorptIOn spectra They found that the AD IS mversely correlated WIth the IOmzatIOn potentIal of dlammes and they attnbuted thIS mamly to the CT mteractIOn Reuter and Feger et aZ 44

-46 clanfied that the optIcal losses m polYlmldes are caused by absorptIOn that IS due to the CT complexes and by scattenng owmg to ordenng of the polYlmlde chams The behavIOr of the optIcal losses at 830 nm could not be predIcted from that at 633 nm because the CT complexes absorptIOn does not

296

CD (,) r:: ~ ... o III .c

<C

6FDAlTFDB

PolYlmide

tt

350·C

Poly-I (amlc l acid)

10FEDAlTFDB Poly- I Imldel

t Poly-I (amlc l acid)

Shmji Ando et al.

2000 1800 1600 1400 2000 1800 1600 1400

Wavenumber (cm-1) Wavenumber (cm-1)

Figure 14.11. IR spectra of 6FDA(TFDB and IOFEDA/4FMPD cured III mtrogen to 70, 120, and 350'C

affect the losses at 830 nm They suggested that the cham ordenng, WhICh IS the mam cause of the optIcal losses at 830 nm, can be hmdered stencally by the mtroductIOn of bulky sIde groups such as -CF3 or -C(CF3h- The authors40

have recently dIscussed the relatIOnshIps between the color mtensitIes of poly­ImIde films and the electronIc propertIes of aromatIc diammes and aromatIc dianhydndes The arrangement of the diamme mOIetIes m the order of color mtensity of the polYImides shows fairly good agreement WIth the order of the electron-donatmg propertIes of the diammes estImated from 15N-NMR chemIcal ShIftS (ON) On the other hand, the arrangement of the dianhydnde mOIetIes m order of the color mtensity of the polYImides agrees WIth the order of the electron-

Synthesis and Properties of Perfluonnated PolYImides 297

2VCH

0006 2vc.t8CH G)

6FDAfTFDB (.) c 0.004 ~ CO .0 10FEDAl4FMPD ~

0 I/) 0.002 .tl <C

0 1.31lm 1.55Ilm1.65f.lm

t t 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

Wavelength (~m)

Figure 14.12. Vlslble-near-IR absorption spectra of IOFEDA/4FMPD and 6FDAfTFDB polYlmlde films

acceptmg propertIes of the dianhydndes estlmated from the expenmental and calculated electron affimtles From thIS pomt of VIew, the coloratlOn of perfluon­nated polYImides IS mterestmg because the polYImides are synthesIzed from the combmatlOn of the dianhydndes, havmg high-electron-acceptmg propertIes, and the diammes, havmg low-electron-donatmg propertIes Although It IS dIfficult to predIct the color mtensity of perfluonnated polYImides from the combmatlOns of dianhydndes and diammes, the Ao and yellowIsh color of lOFEDA/4FMPD mdicate that the extent of the CT mteractlOn of perfluonnated polYImide IS stronger than that of partially fluonnated 6FDA/TFDB (no color) but slIghtly weaker than that of unfluonnated PMDA/ODA (pale yellow)

(4)

PMDAlODA

298

100

- 80 ~ 0 -8 60 c as = 'E 40 en c as l-

t- 20

0 300 400 500

10FEDAl4FMPD PMDAlODA

600 700 Wavelength (nm)

ShinJi Ando et aL

800

Figure 14.13. UV -vIsIble transmIssIOn spectra of partIally fluonnated (6FDA/fFDB), perfiuonnated (IOFEDA/4FMPD), and unfluonnated polYImlde (PMDA/ODA) films

14.4.2. Mechanical Properties

Table 143 lIsts the strength and flexIbIlIty ofperfluonnated polyimide films synthesIzed from the two dianhydndes and five diammes Polymenzmg 10FEDA wIth 8FODA or 8FSDA produced contmuous, flexIble films, but the films are slIghtly bnttle compared wIth IOFEDA/4FMPD As descnbed above, P6FDA dId not gIve any contmuous films Table 144 lIsts the mechamcal properties of IOFEDA/4FMPD, 6FDA/TFDB, and PMDA/ODA 47 All the films were prepared m our laboratory by spm-coatmg of poly(amic aCId) on sIlIcon substrates and cured at the hIghest temperature of 350°C under mtrogen IOFEDA/4FMPD films have suffiCIent toughness for optical wavegUide applIcatlOns, and theIr mechamcal properties are SImilar to those of 6FDA/TFDB, relatively hIgher tensile stress, hIgher elastIc modulus, and lower elongatlOn at break compared to PMDA/ODA

14.4.3. Thermal, Electrical, and Optical Properties

Table 14 5 lIsts the thermal, electncal, and optIcal propertIes of perfluonnated polYlmldes, along WIth those of partially fluonnated and unfluonnated polYlmldes Because of the fleXIble structure of the 10FEDA component, the polymer decomposItion temperatures and Tg values of perfluonnated polYlmldes are slIghtly lower than those of conventlOnal polYlmldes ThIS comcides WIth the results of Hougham et al ,37 who reported that an mcrease m fluonne content m

Synthesis and Properties of Perfluormated POl)'lmldes 299

Table 14 3 Strength and Flexibility of Perfluonnated PolYlmlde Films

Dlamme Dlanhydnde

10FEDA P6FDA

4FPPD No film 4FMPD Strong and flexible Bnttle and cracked 8FODA flexible No film 8FSDA Flexible No film 8FBZ No film No film

Table 144 Mechamcal Properties of Perfluonnated (lOFEDA/4FMPD), Partially Fluonnated (6FDA(fFDB), and Unfiuonnated (PMDA/ODA) PolYlmlde FIlmsa

PolYlmlde Fma! cure Tensile 5% Tensile ElongatIOn Elastlc temperature (" C) strength stress at break modulus

(kgf/mm2) (kgf/mm2) (%) (kgf/mm2)

IOFEDA/4FMPD 350 132 103 9 248 6FDAjTFDB 350 125 114 9 303 PMDA/ODA 350 105 65 40 232

a All samples were prepared under the same condlllOns

the polYImide backbone led to only slIght overall decrease m Tg but had lIttle effect on dynamIc thermal or thermo oXIdatIve stabIlIty The thermal stabIlIty of these films IS nonetheless hIgh enough to wIthstand the manufactunng process for IC's and multIchip modules In addItIon, the dIrect mtroductIOn of fluonnes mto the aromatIc nngs does not cause a sIgmficant mcrease m fluonne content

The adheSIveness of the perfluormated polYImides IS thus eqUivalent to that of partially fluonnated polYImides used for smgle-mode wavegUide fabncatIOns TheIr dielectnc constants (c) at 1 kHz and average refractive mdexes are as low as those of the partIally fluonnated polYImides ThIS IS pnmanly because the fluonne content of perfluonnated polYImides IS comparable to that of partially fluonnated polYImides Hougham et aZ 38

,48,49 mvesbgated the fluonnatIOn effect on dIelectnc constants and refractIve mdexes for a senes of polYImides They aSSIgned the observed decrease m relatIve permIttIVIty and refractIve mdex caused by fluonne substItutIOn to effects of local electromc polanzatIOn and fractIonal free volume The free-volume contnbutIOn was found to range from 25% for the polYImides wIth planer diammes to 94% for the polYImides wIth -CH3 and very bulky -CF3 groups 49 Takmg mto account theIr elUCIdatIOn, one finds that the similanty of dielectnc constants and refractIve mdexes of perfluonnated polYImides to partIally fluonnated polYImides WIth TFDB dIamme IS not straIghtforward because the

300 ShmjI Ando et aL

Table 145 Thermal, Electncal, and OptIcal PropertIes of Perfluonnated, PartIally Fluonnated, and Unfiuonnated PolYImides

Fluonne Decomp Glass Dlelectnc Average In-planejout-of-content temperature transll10n constant refractive plane

(%) (UC) temperature (E) mdex birefringence ( C) (II) (~n-L)

IOFEDAj4FMPD 366 501 309 28 1562 0004 IOFEDAj8FODA 384 485 300 26 1552 0004 10FEDAjSFSDA 377 488 278 26 1560 0006

10FEDAjTFDB 351 543 312 28 1569 0009 6FDAjTFDB 313 553 327 28 1548 0006 PMDAjTFDB 227 613 >400 32 1608 0136

PMDAjODA 0 608 >400 35 1714 0088

former has a planer dlamme structure and no -CF3 group whIle the latter has at least two -CF 3 groups

It IS worth notmg that the m-plane/out-of-plane blrefnngence (L1nJJ* of perfiuonnated polYlmldes IS lower than the partIally fluonnated polylmldes WIth TFDB dlamme The low blrefnngence IS convement for deslgnmg wavegmde structures m OEICs and m OE-MCM mterconnectlOns and for reducmg polanza­tlOn dependence of the optlcal wavegmde Clrcmts Reuter et aZ 14 reported that a very low L1n-L of 0 0034 at 633nm was obtamed by mtroducmg two -C(CF3h­groups and a meta-phenylene lmkage mto the polYlmlde mam cham The authors so reported that the conformatlOnal energy map calculated for decafluoro­dlphenylether (C6FS-O-C6FS) usmg the MMP2 method IS more SImIlar to the energy dlstnbutlOn of 2,2-dlphenylhexafluoropropane (C6Hs-C(CF3h-C6Hs) than that of diphenylether (C6HS-O-C6HS) Although the perfiuonnated phenyl nngs can rotate around the ether lmkage, decafluorodiphenylether shows a much smaller low-energy reglOn than diphenylether, and Its optlmum geometry, 1 e , a twISt conformatlon, IS the same as that of 2,2-diphenylhexafluoropropane Hence the low birefnngence of perfiuonnated polYImides synthesIzed m thIS study ongmates from the stenc effect between perfiuonnated aromatIc nngs and from a number of bent structures such as ether, thlOether, and meta-phenylene lmkages

These charactenstIcs show that perfiuonnated polYImides are promlSlng matenals for wavegmdes m mtegrated optics and optIcal mterconnect technology The thermal, mechamcal, and optIcal propertIes of perfiuonnated polYImides can be controlled by copolymenzatlOn m the same manner as partially fluonnated polYlmldes 19

*In-planejout-of-plane birefringence (~n-L) IS defined m thiS volume Ch 15

Synthesis and PropertIes of Perfluorinated PolYlmldes 301

14.5. CONCLUDING REMARKS

Novel polymenc matenals, lOFEDA/4FMPD, lOFEDA/8FODA, and lOFEDA/8FSDA perfiuonnated polYlmldes, were synthesIzed These matenals can wIthstand soldenng (270°C) and are hIghly transparent at the wavelengths of optical commumcatlOns (10-1 7 J.lm) To generate hIgh-molecular-weIght perfiuonnated poly(amlc aCld)s, the reactivIties of five dlammes and theIr monoacyl denvatlVes were estimated from the end-group contents of the correspondmg poly(amlc aCId), 15N_ and IH-NMR chemIcal ShIftS, and calculated lOmzatlOn potentmls A new perfiuonnated dmnhydnde, 10FEDA, that has two ether lmkages was syntheSIzed m order to proVIde flexlblhty to the polymer cham The perfiuonnated polYlmldes prepared from lOFEDA dmnhydnde gave fleXIble films wIth Tg values over 270°C and hIgh optical transparency over the entire optical commumcatlOn wavelength range wIth suffiCIent mechamcal strength In addItion, theIr dlelectnc constants and refractive mdexes are as low as those of conventlOnal fluonnated polYlmldes, and theIr m-plane/out-of-plane blrefungence IS low These charactenstIcs mdlcate that perfiuonnated polYlmldes are promlSlng matenals for optical commumcatIon apphcatlOns

14.6. REFERENCES

Y Suematsu and K Iga, IntroductIOn to Optical Fiber CommUniCatIOns, 10hn Wiley and Sons, New York (1982), 208 pp

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