4 Synthesis of Fluorinated Polyimides

Shigekuni Sasaki and Shiro Nishi Nippon Telegraph and Telephone CorporatIOn, Musashmo-shl, Toltyo, Japan

I. INTRODUCTION

PolYlmlde matenals have been extensively used m the aerospace and electromcs fields because they are thermally stable, mechamcally strong, and electncally msulatmg [1-3] These fields al~o need transparent polYlmlde matenals to cover solar cells and polYlmldes that have low permittivity to decrease the delay time of electncal CircUits Optoelectromcs needs polyuTIlde matenals with transparency at wavelengths longer than those of the VISIble light regIOn and a controllable refractive mdex One of the most effective ways to satisfy these needs IS to m­troduce fluonne mto polYlmlde matenals [4,5] FlUOrinated polymers, such as poly(tetra­fluoroethylene), have attractive features such as low water uptake, water and/or Oil repellence. low permittivity, low refractive mdex, resistance to wear and abraSIOn, and both thermal and chemical stability The fluonne atom mducmg these properties IS the second smallest atom, and ItS 2s and 2d electrons are close to the nucleus Its electnc polarity IS therefore ~mall, and It IS the most electronegative of all the elements ThiS high electronegatlVIty results m strong bonds between carbon and fluonne atoms, glvmg fluorocarbon matenals high thermal and chemical stability The low polarIty of fluorme gives fluorocarbons a low refractive mdex and low dlelectnc constant, and the low coheSive energy and surface free energy due to the low polarIty result m a low uptake of water, water and Oil repellence, and resistance to wear and abraSion The mtroductlOn of fluorme atoms mto polYlmldes IS therefore expected to produce polYlmldes With many attractive features However, there IS also a danger that the resultant polYlmldes may have some undeSirable properties such as low adheSIOn strength, low mecham­cal strength, or a high coeffiCient of thermal expanslOn(CTE) The goal of fluonnated polYlmlde research IS to obtam the advantages of mtroducmg fluonne atoms Without sacnficmg the many advantages of polYlmldes

In 1972 Cntchley et al reported on the synthesl~ and properties of polYlmlde~ bonded With perfluoroalkylene mOieties [6,7] They syntheSized fluonnated polYlmldes m two ways by solutIOn polymenzatIOn and by melt polymenzatIOn. Figure I shows the syntheSIS scheme for one of the perfluoroalkylene-Imked polYlmldes Melt polymerIzatIOn, which IS carned out by fuSIOn of dlamme and dlanhydnde, has the advantage of ~hortenmg the syntheSIS path, but It

71

72

SolutIOn Polymerlz.tuon

Melt PolymerizatIOn

TemperalUre 240 "e

+

Solvent DMAc Temperdlure RT

Sasaki and Nishi

Figure 1 SynthesIs scheme for Cntchley's fluonnated polYlmlde. (From Ref 6)

IS restncted to a narrow range of fusible dlammes and dlanhydndes Solution polymenzatlOn, on the other hand, can synthesize the whole range of polYlmldes

In the 1980s, polYlmldes prepared from 2,2-blS(3,4-dlcarboxyphenyl) hexafluoropropane dlanhydnde (6FDA) were reported by other researchers [5,8-11] The 6FDA polyimldes, which can be synthesized through conventional solution polymenzatlOn (Fig. 2), have good trans­parency [9], and have lower dielectric constants than those prepared from other nonfluorinated dianhydrides [11].

Many researchers have recently been mvestIgatmg the next generation of fluonnated polyimides for electrorucs and optoelectronics apphcatlons For electronics, there are two trends m the development of fluonnated polYlmldes. One IS to make the dielectnc constant as low as possIble, and the other IS to mtroduce fluorine atoms whIle mamtaining many of the ad­vantages of polYlmldes. Fluorinated polyimides have recently attracted attention for optoelec­trorucs because optical polymers require thermal stability as well as transparency, and fluori­nated polYImides have the possIbIhty to fulfill these requirements

This chapter reVIews recent developments m fluormated polYImides for electrorucs and optoelectronics WIth particular emphasis on theIr synthesis.

A number of dlammes and dianhydndes are mentlOned. For easier comprehension, we have listed theIr chemIcal structures and abbreVIations. Tables 1-4 show fluorinated dlanhy-

--

Synthesis of Fluorinated Polyimides

+ H.N-R- NH.

R 1,1'-ODA, 2 4'-ODA, 1,4'-ODA 4,4'-ODA 1,4(4)-APB,I,1(4)-APB 1,4(1)-APB,I,1(1)-APB

PolymeriZatiOn ~olvent DMAc Temperature R T

tH 0 0 H I I II F3C, /CF3 II I N-C~C~C-N-R

HO-C~ ~C-OH II II o 0 n

6FDA Poly(anllc aCId)

Imldization + Temperature 300°C

6FDA PolYllmde

Figure 2 SynthesIs scheme for 6FDA polYlmlde (From Ref 9)

73

dndes, nonfluorinated dianhydndes, fluonnated diamines, and nonfluonnated diamines, respec­tively.

II. FLUORINATED POLYIMIDES FOR ELECTRONICS

When a polYlmlde IS used as an InsulatIng matenal, the speed of sIgnal transmIsSiOn In the electrical circuit Increases as the dlelectnc constant of the polyimide decreases, because the delay time of an electncal ClrcUlt IS proportlOnal to the square root of the dIelectric constant of the InsulatIng matenal. A low dielectrIc constant is the most attractIve property of polYlmlde materials for electronics apphcatlOns Introducing fluonne atoms into polyimides IS one of the most efficIent ways to obtain this In thIS case, it IS Important to achIeve the low dielectnc constant while maintaining many of the advantages of polyimldes such as high thermal stabil­Ity and mechamcal strength.

In thIS sectlOn we descnbe novel fluonnated polYlmldes denved from new fluorinated dlamIneS or dlanhydndes invented after the 6FDA polYlmldes.

For easy comprehenslOn, the charactenstlcs of the fluonnated polYlffiides In each subsectlOn are shown In similarly formatted tables that show the monomers used, ImldlzatlOn conditions, poly(amlc acid) (PAA) VIscosity, molecular weIght, film formatlOn, and dIelectric constant.

74 Sasaki and Nishi

Table 1 Chemical Structures of Fluonnated DIanhydndes

Chemical structure Abbreviation

~CF~ o ~ 0 CF3

6FDA

F3C, /CF3 C

)§(o)§( 6FCDA

~ /CF3 3FCDA C

)§( )§( 0

CF3

X9( P6FDA

CF3

CF3

)Q( P3FDA

~ JF3@ CF3 C C/ PXPXDA

)9()9()§(

~~o:« lOFEDA OFF 0

F F F F

Synthesis of Fluorinated Polyimides 75

Table 2 Chemical Structures of Nonfluonnated Dmnhydndes

Chemical structure Abbreviation

)§r@( BPDA

:©l~)§( C BTDA

)§( PMDA

"--' 0

)§Jl§( ODPA

0

-)Q>-~-<Q( DSDA

~ 0 II

)§JClQ(lQ( IDPA

-)Q>-Y~ o ?I 0 SIDA

'-" CH3

)§(-@-S-@-0l§( BDSDA

)g(-@-0l§( HQDEA

76

Table 3 ChemIcal Structures of Fluonnated Diammes

ChemIcal structure

'©:C. OCH2(CF2)3F

'©:C. OCH2(CF2)eF

'©:C. OCH2(CF2)7F

'©:C. OCH2(CF2)10H

~ ..-cF3 H2 -C-CF2-CF2-CF3

'CF3

~ CF(CF3)2 O ......... C=C./

F3C'/ ......... CF(CF3)2

~ F F

W F F F F

CF3

A

F F

~o-@-~~o~ -~ CF3 ~

F F

Sasaki and Nishi

AbbreviatIon

7FMDA

13FMDA

15FMDA

20FMDA

RtbMPD

PFDA

TFPDA

OFB

35-DABTF

124-0BABTF

4FBDAF

Synthesis of Fluorinated Polyimides 77

Table 3 Contmued

ChemIcal structure AbbrevIatIOn

DTDE

DTHE

-@-NH[- Rf-~HN-@-Rf = -CFCF3(OCF2CFCF3)m-O(CF2)SO-(CFCF3CF2)n-CFCF3- where (m+n) = 3

TFATFDADP

F. F

-@-o*o-@- BAT

F F

BAD

F F F F

BDAF

-TFDB

TFMOB

OCF2CF2H

~ TFEOB

(contmued)

78 Sasaki and Nishi

Table 3 Contmued

Chemical structure Abbreviation

DFPOB

3FdIamme

3,3'-6F

4,4'-6F

4FMPDA

*-0* 8FODA

F F F F

8FSDA

A. Fluorinated Polyimides with a Pendant Fluorinated Group

Ichmo et al [12] synthesIzed novel fluonnated polYImides contammg a fluonnated alkoxy side cham m order to achIeve a low dielectnc constant They first synthesIzed four novel fluon­nated alkoxy diammes. FIgure 3 shows theIr synthesIS routes Fluonnated dImtro-compounds, WhICh were synthesIzed by the ethenficatIOn of fluonnated alcohols and 2,4-dImtrofluoro­benzene m Et3N/N,N-dimethylacetamide (DMAc) at room temperature for 2 h, were reduced wIth SnCI2/HCI to obtam the four fluonnated alkoxy dIammes

FIgure 4 shows the synthesIs scheme for these polYlmides PAA synthesIs was carned out m N-methyl-2-pyrohdone (NMP) at 25°C PAA solutIOn was cast onto a glass plate and then heated at lOO°C for 1 h, 200°C for 1 h, and 350°C for 1 h to obtam poly ImIde film Table 5 shows the charactenstIcs of these fluonnated polYImides The mherent VIscosIties of these

Table 4 ChemIcal Structures of Nonfluonnated Dlammes

ChemIcal structure AbbrevIatIon

-@-o-@-4,4'-ODA

@-O-@ 3,3'-ODA

@-o-@-

3,4'-ODA

@-o-@-2,4'-ODA

-- -@-o-@-o-@-1,4(4)-APB

-@-O-©-O-@-1,3(4)-APB

l§r0-@-o-©-1,4(3)-APB

-©-o-©-0lQJ-1,3(3)-APB

l§r

MPD

-@- PDA

--~ DMDB

H3C

-@-@-@- DPTP

H~' DAD

H3C CH3

~ 1,5-DAN

80

NO''C(0' + I~

#F

NO'~O' I~ # OCH,(CF,)nX

SnC'fHC'

Sasaki and Nishi

Figure 3 SynthesIs route for fluonnated alkoxy dlammes X = F, n = 3 7FMDA, X = F, n = 6 13FMDA, X = F, n = 7 15FMDA, X = R, n = 10 20 FMDA (From Ref 12)

poly(amlc aCId)s are relatIvely low and tend to decrease WIth mcreasmg length of the fluon­nated alkoxy group There are two causes for thIS behavIor One is a reductIOn m nucleophilIc reactIvity of fluonnated diammes by the strong electron-attractmg force of a fluonnated alkoxy group, and the other IS stenc hmdrance of the reactIOn of the adjacent ammo group in the fluonnated diammes by the bulkmess of the fluonnated alkoxy group.

The dielectnc constant of the polYImides at 1 kHz decreased wIth mcreasmg fluonne content as shown m Figure 5 The lowest dielectnc constant measured was 2 6. The PolYImIde WIth the hIghest fluonne content exhIbIted low water absorptIon, so the stabIlIty of ItS dielec­tnc constant was good After agmg at 25°C m a relatIve humIdity of 70% for 5 days, the mcrease m dielectnc constant was only 0 1 But the polYImide WIth thIS dielectnc constant had relatIvely poor thermal StabIlIty ItS glass transItion temperature was 189°C and the polymer decomposItIOn temperature gIVmg 10% weIght loss was 455°C ThIS shows that the introductIon of a long fluorinated alkoxy group mto PolYImIdes lowers the dielectnc constant, but also lowers the thermal propertIes

Auman et al. [13] have reported the synthesIs of polYImides wIth a pendant bis(tnfluoro­methyl)heptafluoropentyl group They synthesIzed a novel fluoroalkylated diamme (RtbMPD) that had good reactivIty and thennal stabIlIty as well as a hIgh fluonne content FIgure 6 shows the synthesIs scheme for the amme.

FIgure 7 shows the synthesIs scheme for the polYImides wIth a pendant bls(tnfluoro­methyl)heptafluoropentyl group. Table 6 shows the charactenstIcs of the fluonnated polYImides.

--

Synthesis of Fluorinated Polyimides

6FDA BPDA BTDA

+

NMP

x = F n = 1 7FMDA X = F n = 6 11FMDA X = F, n = 7 1 ~FMDA X=H,n= 10 20FMDA

n

n

81

Figure 4 SynthesIs scheme for fluormated polYlmldes wIth fluonnated alkoxy sIde cham (From Ref 12 )

The RfbMPD was reacted wIth several fluonnated and nonfluonnated dianhydndes to form poly(amic aCId)s m the conventional way Then the poly(amic aCId)s were converted mto the polYlmldes by thermal or chemIcal ImldlzatlOn TheIr charactenstics are shown m Table 6 These polYlmldes had a relatIvely hIgh molecular weIght and low dlelectnc constant In par­ticular 6FCDA/RfbMPD had a hIgh glass transItIon temperature, at 34rC, as well as a very low dlelectnc constant, 2 3 at 1 MHz The CTE, however, was hIgh for polYlmlde, probably a result of the bulky pendant fluorocarbon cham The polYlmldes wIth a pendant bIs(tn­fluoromethyl)heptafluoropentyl group are mterestmg because they have both a low dlelectnc constant and hIgh glass transItion temperature

Yusa et al [14] have reported the synthesIs of polYlmldes wIth a perfluorononenyloxy group FIgure 8 shows the synthesIs scheme for the fluonnated polYlmldes Table 7 shows theIr charactenstics A new monomer, 1,3-dlammo-S-(perfluorononenyloxy)benzene (PFDA) was reacted wIth dianhydndes m the conventlOnal way to form P AAs and converted these mto polYlmldes by heatmg at 2S0-300°C The Inherent VIscosIties of the PAAs were relatively low,

Table 5 Charactenstlcs of Fluonnated PolYlmldes

Monomers Imldlzation conditions Dlanhydnde Dlamme Solvent, temperature(°C)/tlme (h)

6FDA MPD NMP, 100/1, 250/1, 350/1 6FDA 7FMDA NMP, 100/1, 250/1, 350/1 6FDA 13FMDA NMP, 100/1,250/1,350/1 6FDA 15FMDA NMP, 100/1, 250/1, 350/1

6FDA 20FMDA NMP, 100/1,250/1,350/1

BPDA MPD NMP, 100/1, 250/1, 350/1 BPDA 7FMDA NMP, 100/1, 250/1, 350/1 BPDA 13FMDA NMP, 100/1, 250/1, 350/1 BPDA 15FMDA NMP, 100/1,250/1, 350/1

BPDA 20FMDA NMP, 100/1, 250/1, 350/1 BTDA MPD NMP, 100/1,250/1,350/1 BTDA 7FMDA NMP, 100/1, 250/1, 350/1 BTDA 13FMDA NMP, 100/1, 250/1, 350/1 BTDA 15FMDA NMP, 100/1, 250/1, 350/1 BTDA 20FMDA NMP, 100/1,250/1, 350/1

"Inherent VIscosIties were measured With 0 5 wt% NMP solulion at 30°C bMeasuremenlS were made at 23°C, 50% RH, and 1 kHz Source Ref 12

P AA vIscosity' Molecular Film (Tj[dl/g)) weight formatIOn

070 Yes 038 Yes 031 Yes 033 Yes 029 Yes 093 Yes 047 Yes 032 Yes 034 Yes 025 Yes 072 Yes 041 Yes 030 Yes 030 Yes 028 Yes

Dlelectnc constantb

30 29 27 26 26 35 32 30 30 30 35 33 30 29 29

Q) I\)

en I» f/) I» 25: I» ~ Q.

Z fir ::T

Synthesis of Fluorinated Polyimides

40~----·-----------------,

o 6FDA {':, BPDA o BTDA

20L-__ ~ __ ~ __ ~ __ -L __ ~~

o 10 20 30 40 50

Fluorine content (wt%)

83

Figure 5 RelatIOnship between dlelectnc constant at 1 kHz and the fluonne content of fluormated polYlmldes and the reference nonfluormated polYlmldes (From Ref 12)

o 17 dl/g, because of the low reactlVlty of PFDA due to Its strong electron-withdrawing char­actenstIc The dlelectnc constant of 6FDA/PFDA was low, 2 5 at 10 kHz.

Makmg polylmldes with a pendant fluonnated group IS a useful way to obtam polyimldes with a high fluonne content By choosmg a fluonnated group, one can obtam fluonnated polYlmldes with a high molecular weight, and such polYlmldes have both a low dlelectnc constant and a high glass transition temperature However, they have the disadvantage of havmg a high CTE because of the bulkmess of the pendant group.

B. Fluorinated Polyimides Prepared from Bis(trifluoromethyl)diaminobiphenyl

2,2' -bls(tnfluoromethyl)-4,4' -dlammoblphenyl (TFDB) IS mterestmg as a monomer of fluori­nated polyimldes TFDB, whose synthesIs route IS shown m Figure 9, was synthesized by Makl and Inukat m 1972 [15]

Matsuura et al. [16] synthesized fluonnated polYlmldes from TFDB and 6FDA or pyro­melhtlc dlanhydnde or PMDA m the conventIOnal way (Fig 10). Table 8 shows the charac­tenstIcs of the fluormated polYlmldes from TFDB They had high mtnnslc viscosities 6FDAI TFDB had excellent properties such as low dlelectnc constant (2 8 at MHz) and high trans­parency, and PMDA/TFDB had a low CTE (-05 x 10-5 °C-I) 6FDA/TFDB IS discussed as an optical matenal m Sec. III B

6FDA/TFDB has another charactenstIc. It IS soluble m common polar orgamc solvents, such as acetone or tetrahydrofuran. Matsuura et al. used IH nuclear magnetic resonance (NMR) to charactenze the ImldlzatIon process and found that the ImldlzatIOn reaction began at just over 70°C and was completed by about 200°C

Ando et al [17] obtamed more detailed infonnatIOn about the molecular structure of 6FDAI TFDB poly(amlc acid)s and polYlmldes dunng ImldizatIOn under various conditions by mea­sunng l3C NMR Figure 11 shows l3C NMR proton-decoupled spectra of 6FDA/TFDB samples cured at vanous temperatures Small peaks ongmating from polYlmlde are seen m the 70°C sample because the ImldlZatIOn reactIOn begins at just over 70°C. Significant changes are caused

84

II ~Iow adliltlOn PBrl I CHCll 2 leflux,2 h

NO'yO' CH2Br

KFI DMAc RT II days

H2• 60 pSlg I RT

Pd IC, EtOH, 4 h

RtbMPD

Figure 6 SynthesIs scheme for RfbMPD (From Ref 13)

Sasaki and Nishi

by ImidizatIOn at 120°C. The chemIcal ShIftS of the two signals resonated at right (shown by arrows) are the same as those of TFDB. ThIS means that depolymenzation of the poly(amic aCId) main cham occurred at 120°C. Figure 12 shows the VISCOSIty coefficIents of 15 wt% DMAc solutions of 6FDA/TFDB cured under the same condItIOns as the samples for NMR measurements. The low VISCOSIty of the 120°C sample IS consIstent with the depolymenza­tIon at the poly(amic aCId) amId group and decrease of molecular weIght identIfied m the NMR analysIs ViSCOSIty mcreases monotorucally WIth cunng temperatures from 120°C to 300°C. ThIS shows that the polycondensatlOn reactIOn proceeds and the molecular weight of PolYlffiIde mcreases even after ImidizatIOn IS completed (at 200°C)

Synthesis of Fluorinated Polyimides

PMDA 6FDA BPDA 6FCDA B1DA 1FCDA

+ I~ NH2~H2

~C(CF'),CF2CF2CF3 RfbMPD

NMP

n

I. thermal imidization

2 chemical or Imimzation

n

85

Figure 7 SyntheSIS scheme for fluonnated polYlmldes with a pendant bls(tnfluoromethyl)heptafluoro­pentyl group (From Ref 13)

Hams et al. [18-20] have mvestIgated ngld soluble fluonnated polYlmldes from TFDB and vanous dIanhydndes, PMDA, (BTDA), ODPA, DSDA, 6FDA, and BPDA usmg a one­step procedure Figure 13 shows the synthesIs scheme for the fluonnated PolYlffildes, and Table 9 shows their charactenstlcs The polymenzatiOn was carned out m refluxmg m-cresol con­tammg lsoqumohne Under these conditions the mtermedIate poly(amlc aCld)s spontaneously cychzed to the correspondmg polYlmldes Except for PMDA/TFDB, all the polYlmldes were soluble m m-cresol. Their Inherent VIscosIties were from 1 0 to 4.9 dl/g

c. Fluorinated Polyimides Prepared from Perfluoro Aromatic Diamines

Hougham and Tesoro [21] have reported the syntheSIS and properties of polYlmldes from perfluoro aromatic dlammes The alffi of their study was to obtam po1Ylmides With a high glass tranSitiOn temperature and low dlelectnc constant for use as an msulator

Table 6 Charactenstlcs of Fluonnated PolYlmldes

Monomers Imldlzatlon conditIOns Dlanhydnde Dlamme Solvent, temperature(°C)/tlme(h)

PMDA RtbMPD NMP, 135/05, 200/0 5, 350/1 PMDA RtbMPD NMP, 135/05, 200/0 5, 350/1 BPDA RtbMPD NMP, 135/05, 200/0 5, 350/1 BTDA RtbMPD NMP, 135/05, 200/0 5, 350/1 6FDA RtbMPD NMP, 135/05, 200/0 5, 350/1 6FDA RtbMPD NMP/acetlc anhydnde/pyndme (chemical) 6FCDA RtbMPD NMP/acetIc anhydnde/pyndme (chemical) 3FCDA RtbMPD NMP/acetIc anhydnde/pyndme (chemical)

'Number-average molecular weights by GPC of PAA In DMAc/LIBr/H3POiTHF at 35°C bNumber-average molecular weights by GPC of polYlmlde In DMAc at 135°C "Measurements were made at 0% RH and 1 MHz Source Ref 13

P AA VISCOSity (T][dl/g])

Molecular Film weight formatIOn

50,800' Yes 92,100' Cracked 56,000' Cracked 31,500' Yes 82,700' Yes 47,500' Yes 53,2oob Yes

122,000' Yes

Dlelectnc constantC

32

27 23 25

co Q)

CJ) III til III ~ III ::::J Q,

Z 0" ::::J'"

-

Synthesis of Fluorinated Polyimides 87

+

6FDA BTDA

DMAc

thermallmldlzatlOn

Figure 8 SynthesIS scheme for fluonnated poly 1m Ides wIth a pendant perfluorononenyloxy group (From Ref 14)

The perfluoro aromatlc dlammes they used were I,4-tetrafluorophenylene dlamme (TFPDA) and 4,4' -octafluorobenzldme (OFB) In all the polYlmldes obtamed usmg the per­fluoro aromatlc dlammes, only low-molecular-welght ohgomers (Table 10) were obtamed after the solutlon stage of the reactlon because of the low reactlvlty of these dlammes By optlmlz­mg the synthesls condltions, It lS posslble to form fdms Good films of 6FDA/TFPDA were made from the product of the 130°C and 150°C reactlOns, but the product of 22°C reactlOn dld not form a ftIm 6FDA/OFB gave almost the same results The anhydnde structure is an lmportant factor m formmg good film Nelther TFPDA/BTDA nor TFPDA/PMDA formed films ImldlzatlOn condltlons are also an lmportant factor m formmg good film They followed the cham extenslOn reactlOn by FTIR on sequentlally cured and cooled films of 6FDA/OFB

Table 7 CharactenstIcs of Fluormated PolYlmldes

Monomers ImldlzatlOn condItIons Dlanhydnde Dlamme Solvent, temperature( °C)/tIme(h)

6FDA PFDA DMAc,250-300/-BTDA PFDA DMAc,250-300/-6FDA 4,4'-ODA DMAc,250-300/-BTDA 4,4'-ODA DMAc,250-300/-

'Inherent VIscosIties were measured wIth 0 1 g/dl DMAc solution at 30°C bMeasurements were made at 10 kHz Source Ref 14

P AA VISCOSity" Molecular Film (YJ[dllg]) weight formatIon

o 17 Yes 017 Yes 043 Yes 056 Yes

Dlelectnc constantb

25 28 32 36

IX) IX)

en III 1/1 III ~ III ::l C.

Z (ij" :::T

Synthesis of Fluorinated Polyimides 89

CF3

02N-6sr

j Co /OM'

TFDB

Figure 9 SynthesIs route for TFDB (From Ref 15)

They found that the cham extenslOn began at temperatures between 200°C and 300°C, but optlmal mecharucal propertIes were not obtamed WIth curmg temperatures below 350°C FIgure 14 shows the synthesIs scheme used to prepare 6FDA/OFB poly ImIde

At 100 kHz, the dlelectnc constant of the dry 6FDA/TFPDA was 2 75 and that of 6FDAI OFB was 2 75 The glass transitIon temperatures of both of these polYlmldes were above 330°C

Perfluoro aromatic dlammes have poor reactivIty, so It IS necessary to optImIze the reac­tion condItions m order to obtam good fIlms on the polYlmldes prepared from perfluoro aro­matic dlammes

D. Fluorinated Polyimides Prepared from Benzotrifluoride-Based Diamines

Gerber et al [22] synthesIzed fluonnated polylmldes from 3,5-dlammobenzotnfluonde (35-DABTF) and rune dlanhydndes FIgure 15 shows the chemIcal structures of the polYlmldes prepared from 35-DABTF, and theIr charactenstIcs are shown m Table 11 Poly(amlc aCld)s

90

6FDA PMDA

Polymenzatlon

H 0 0 H I II II I N-C C-N

"R/

HO-C/ "'C-OH II II o 0

TFDB

'>01 Wilt DMA~ Temperature RT

F3C

ImldlzatIon , Temperature 150 tIC

rOO II II

F .... , /C, N R...... N ,./ ...... 1

C C II II o 0

Sasaki and Nishi

n

n

Figure 10 SynthesIs scheme for fluonnated polYlmldes from TFDB (From Ref 16)

prepared from 3S-DABTF had relatively hIgh mtnnsic VIscosIties, from 0 3 to 0.9 dl/g, and they produced good films Introducmg a tnfluoromethyl group mto diamme dId not affect the reactlVlty of the dtamme 3S-DABTF/6FDA poly ImIde had the lowest dlelectnc constant, 2.S8 at 10 GHz, among the mne polYlmldes prepared from 3S-DABTF and had a relatively hIgh glass transition temperature of almost 300°C

Buchanan et al [23] have synthesized fluonnated polYlmldes from CF3-substItuted oxy­dtamhne 4,4' -oxy-bls[3(tnfluoromethyl)benzenamme] (124-0BABTF), which was synthesized m two steps from 2-chloro-S-mtrobenzotnfluonde as descnbed by Makl and Inukat [1S]. Figure 16 shows the chemIcal structure of the fluonnated polYlmldes obtained from 124-0BABTF, and their charactenstIcs are shown m Table 12 Five poly(amlc aCId)s were prepared m the conventIOnal way TheIr mherent VIscosIties were above 1 0 dl/g m most cases despite the presence of the strongly electron-wtthdrawmg CF3 groups of 124-0BABTF. Thermal Iml­dlzatIOn of the PAAs produced polYlmlde films that were tough, clear, and nearly colorless The dlelectnc constants of these polYlmldes are of particular mterest The most highly fluon­nated PolYlffilde, l24-0BABTF/6FDA, had a dlelectnc constant of 2 76 at 1 MHz, and ItS glass tranSitIOn temperature was 29SoC

(

Table 8 Charactenstics of F1uonnated PolYImides

Monomers

DIanhydnde

PMDA 6FDA

Diamme

TFDB TFDB

ImidizatlOn COndItIons Solvent, temperature( °C)/tIme(h)

DMAc, 7012, 16011, 200/0 5, 35011 (Nz) DMAc, 7012, 16011,200/0 5, 350/1 (Nz)

"Inherent VISCOSItIes were measured With DMAc solutIon at 30°C bMeasurements were made at 23°C and 1 MHz under dry conditIons Source Ref 16

P AA VISCOSIty' (T] [dl/g))

1 79 100

(

Molecular weIght

Film formatIon

Yes Yes

Dielectnc constantb

32 28

!i :::J -:::J" CD o iir g, !! c: o ~. :::J a CD Q.

"0 o ~ 3 c: CD o

<0 .....

92 Sasaki and Nishi

70'C

IOO'C

120'C

150'C

200'C

250'C

300'C

350'C

Figure 11 l3C NMR proton-decoupled spectra of 6FDA/TFDB samples cured at vanous temperatures (From Ref 17)

104

'iii , ,0 ° Co , ~ 103 ,0' C 0" , , GI '0 , , 13 \ ,0 ~

, , , , , 0 , 9' U

102 , i!' I,

I, Ui ° 0 (,) <II

:> 10

0 100 200 300 120+300

Curing Temperature eel

Figure 12 VIscosIty coefficIents of 15 wt% DMAc solutIons of 6FDA/TFDB polYlmlde as a functIOn of cunng temperature (From Ref 17)

Synthesis of Fluorinated Polyimides

R PMDA, BTDA, ODPA DSDA 6FDA, BPDA

TFDB

m-cre~ol, l~oqull1ohne

refiuxmg

roo II II p. ......... /"C,

N R..... N \ /" ..... /

C c II II o 0 n

Figure 13 SynthesIs scheme for the fluonnated poiYImIdes from TFDB (From Ref 20)

93

IncorporatIOn of benzotnfluonde mOiety mto polYlmlde IS an effective way to lower the dlelectnc constant whIle mamtammg the glass transItion temperature

E. Fluorinated Polyimides Prepared from O-Substituted Diamines

MIsra et al [24] have synthesIzed fluonnated polYlmldes from 6FDA and seven fluonnated dlammes WIth varymg structures m order to study the effect of dIfferent fluonnated segments upon the dlelectnc constant They synthesIzed the novel dlammes 4FBDA, DTDE, DTHE, and TFATDFDADP [25] FIgure 17 shows the synthesIs scheme for the fluonnated PolYlffildes, and theIr charactenstIcs are shown m Table 13 After the room temperature reactlOn, the PAAs

"'--' from BAT, BAO, and BDAF were hIghly VISCOUS, whereas thos~ from 4FBDAF, DTDE, DTHE, and TFATDFDADP showed no appreciable mcrease m solutlOn VISCOSIty After heatmg at lOOoe, the solutIOn VISCOSIty of the poly(amlc aCld)s from 4FBDAF, DTHE, and TFATDFDADP mcreased TheIr number average molecular weIghts are gIven m Table 13 The molecular weIght of 6FDAIDTDE was very low, those of 6FDA/BAT and 6FDAIDTHE were from 4000 to 9000, and those of 6FDA/TFATDFDADP, 6FDA/BAT, 6FDA/BAO, and 6FDA/BDAF were all above 15,000 MIsra et al [24] concluded that these were due to de­creased nucleophlhc reactIvIty of the amme caused by the presence of a strong electron-wlth­drawmg group artha to the ammo group (fluonne atoms m 4FBDAF, and fluonnated acryloxy or alkoxy groups m DTDE and DTHE) In addItion to thIS electromc effect, stenc hmdrance due to the presence of a bulky group artha to the ammo groups may also lower reaCtiVIty, causmg a decrease m molecular weIght, as m the case wIth poly ImIde from dlamme DTDE At 100 kHz, the dlelectnc constants of the polYlmldes prepared from dlammes DTHE and TFATDFDADP were 2 93 The correlatIOn between the dlelectnc constant and the fluonne content was weak because of the lack of systemIc vanatIOn m the polymer structures The

Table 9 CharactenStiCS of Fluonnated PolYlImdes

Monomers ImldlzatIon conditions Dmnhydnde Dmmllle Solvent, temperature(OC)/tIme(h)

PMDA TFDB Refluxlllg m-cresol (chemical) BTDA TFDB Refluxlllg m-cresol (chemical) ODPA TFDB Refluxlllg m-cresol (chemical) DSDA TFDB Refluxlllg m-cresol (chemical) 6FDA TFDB Refluxlllg m-cresol (chemical) BPDA TFDB Refluxlllg m-cresol (chemical)

"Inherent vISCOSItIes were measured with polYlmlde m-cresol solution at 30°C bASTM D-150 Source Ref 20

P AA VISCosltya Molecular (rj[dl/g]) weight

16 1 1 10 1 9 49

FIlm fonnatlOn

Yes Yes Yes Yes Yes Yes

Dlelectnc constantb

25

co .1:0

en II) !II II)

25: II) :::J C.

z (ii" =.

(

Table 10 Charactenstics of Fluonnated PolYImides

Monomers

Dianhydnde

6FDA 6FDA 6FDA PMDA BPDA BPDA BTDA

Diamme

TFPDA PDA OFB TFPDA TFPDA PDA TFPDA

ImidizatIOn COndItions Solvent, temperature(°C)/tIme(h)

NMP, room temp - 150, 350 NMP, room temp - 200, 350 NMP, 50 - 200, 350 NMP, room temp - 200, 350 NMP, 75 - 200, 350 NMP, room temp - 200, 350 NMP, room temp - 200, 350

"Number-average molecular weIghts by GPC of PAA III THF bMeasurements were made at 100 kHz under dry condItIons Source Ref 21

P AA VISCOSIty (T][dl/g])

003-0045

(

Molecular weighta

940 - 1381

1480

714 - 890

FIlm Dielectnc formatIOn constantb

Yes 275 Yes 29 Yes 275 No No Yes 29 No

(J) '< :J -::r CD U)

iii' 0 -:!! t:: 0 ::!, :J II) -CD c.. "tI 0 -< 3' c: CD U)

CD en

96

+

F F F F

H2N-O---O-NH2

F F F F

6FDA OFB

~lllullOIl PolYWIIJen,allOll

NMP (RT - l'iO"C)

H 0 0 H F

!-g~c~g-~ HO-C I # I # C-OH

F F F

II II 0 0

F

F

Solid-state ~ham extensIOn and IImdlzatlOn of dned oligomer film Slow ramp from RT to ViO"C

o 0 II F3C, /CF3 II F F F

l:crcCcC\ 'c ~ # l

II II F F F F 0 0

6FDA/OFB

n

n

Figure 14 SynthesIS scheme for 6FDA/OFB poly Imide (From Ref 21 )

R BTDA, 6FDA, ODPA, BPDA, IOPA, PMDA, SIDA, DSDA, BTSDA

n

Sasaki and Nishi

Figure 15 Chemical structure of the polYlmldes from 35-DABTF (From Ref 22)

Table 11 Charactenstlcs of Fluonnated PolYlmldes

Monomers ImldlzatlOn condItIons Dlanhydnde Dlamme Solvent, temperature(°C)/tlme(h)

BTDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (air) 6FDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (air) ODPA 35-DABTF DMAc, 100/1, 200/2, 300/1 (air) BPDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (air) IPDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (alf) PMDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (air) SIDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (alf) DSDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (air) BTSDA 35-DABTF DMAc, 100/1, 200/2, 300/1 (alf)

"Inherent vlscositles were measured wah 0 5 wt% DMAc solution at 35°C bMeasurements were made at 10 GHz Source Ref 22

P AA vIscosity" (11 [dllg])

053 070 034 089 053 093 064 051 037

(

Molecular Film weight formatIOn

Yes Yes Yes Yes Yes No No No Yes

Dlelectnc constantb

290 258 291 302

275

CJJ '< :::s -:::T CD (I) (jj"

o -!! c o ~" :::s a CD c. "'tJ o -< 3" a: CD (I)

<0 .....

98

R 6FDA, ODPA, BPDA, PMDA,BTDA

Sasaki and Nishi

n

Figure 16 ChemIcal structure of the polYImides from 124-0BABTF (From Ref 23)

results also suggest that at comparable fluorme contents, fluorme bound to an aromatic nng lowers the dielectnc constant more than ahphatIc fluonne does (compare, for example, the polyimides from BAT and BAO WIth that from BDAF)

F. Fluorinated Polyimides Prepared from (Mono- or Bis­trifluoromethyl)benzenetetracarboxylic Dianhydrides

ThIS sectIOn descnbes a study of fluonnated polYImides wIth a ngid-rod structure. The mam purpose of thIS study was to obtam a low dielectnc constant and low thermal expansIOn

Matsuura et al [26] synthesIzed a senes of new fluonnated ngid-rod polYImides by the reactIOn of TFDB wIth 1 ,4-bIs(trifluoromethyl)-2,3,5,6-benzenetetracarboxyhc dmnhydnde (P6FDA), 1-(tnfluoromethyl)-2,3,5,6-benzenetetracarboxyhc dianhydnde (P3FDA), or PMDA Figure 18 shows the synthesIs route for P6FDA

FIgure 19 shows the synthesIs scheme for the fluonnated ngid-rod polYImides prepared from P6FDA and TFDB Table 14 shows the charactenstIcs of the fluonnated polYImides prepared from P6FDA and P3FDA. The mtrmsic VIscosItIes of P6FDA/TFDB, P3FDA/TFDB, and PMDA/TFDB poly(amic aCId)s were 0 6,0.7, and 1 8 dl/g, respectively, and these de­creased WIth mcreasmg number of tnfluoromethyl SIde chams m the dianhydnde umt Matsuura et al. [26] suggested two reasons for thIS behaVIor' It IS easy to open the dianhydnde nng by mtroducmg tnfluoromethyl group, and cham-cham mteracuon decreases WIth mcreasmg fluo­nne content All the poly(amic acid)s produced good films The coeffiCIents of thermal ex­pansion of P6FDA/TFDB, P3FDA/TFDB, and PMDA/TFDB were -0 5 x 10-5 °C-I, 2 8 X

10-5 °C-I, and 5.6 x 10-5 °C-I, respectIvely, and mcreased WIth the number of tnfluoromethyl SIde chains m the dianhydnde unit ThIS shows that the trifluoromethyl SIde group loosened the molecular packmg The dielectnc constants at 1 MHz of PMDA/TFDB, P3FDA/TFDB, and P6FDA/TFDB were 3.2, 28, and 2 6, respectIvely, and decreased as the fluorme con­tent increased.

ThIS study showed that fluonnated polyimides wIth a ngid-rod structure can have both a low dielectnc constant and low thermal expanSIOn, and that the posItIon of the tnfluoromethyl groups IS Important for a low CTE.

Table 12 CharactenstIcs of Fluonnated PolYlmldes

Monomers ImldlzatIon conditions Dlanhydnde Dlamme Solvent, temperatureCOC)/tlme(h)

ODPA 124-0BABTF DMAc, 100105, 20010 5, 300/1 (air) 6FDA 124-0BABTF DMAc, 10010 5, 200105, 300/1 (air) BPDA 124-0BABTF DMAc, 100105, 200105, 300/1 (air) PMDA 124-0BABTF DMAc, 10010 5, 200105, 300/1 (air) BTDA 124-0BABTF DMAc, 100105, 20010 5, 300/1 (air)

"Inherent VIscosItIes were measured WIth 0 5 wt% DMAc solutIOn at 35°C bMeasurements were made at 50 % RH and 1 MHz Source Ref 23

(

P AA VISCosltya Molecular Film (T)[dl/g]) weight formation

1 23 Yes 060 Yes 1 79 Yes 125 Yes 1 41 Yes

Dlelectnc constantb

3 14 276 320 3 16 322

en '< :l -;:r CD UI en' o -:!! c o :::!, :l III -CD Q.

'tI o -< 3' c: CD UI

co CO

100

6FDA

+ H2N-Ar-NH2

Ar 4FBDAF IHOE DTHE TFATOFDADP BAT BAO BDAF

NMP (RT - J(X)"C)

tHO OH t I II F3C, /CF3 II I N-CX),<:::::: 'ccc'<:::::: C-N-Ar

HO-C # # C-OH II II o 0 n

I ~O - 100"C

Figure 17 SynthesIs scheme for the fluonnated poJYlffiIdes (From Ref 24)

Sasaki and Nishi

G. Fluorinated Polyimides Prepared from Rigid Fluorinated Dianhydrides

Trof1menko [27] synthes1zed a new class of ng1d fluonnated monomers for polY1m1des based on a 9,9-d1SubstItuted xanthene core The mm was to obtam polY1m1des w1th a h1gh glass tran­sltlOn temperature, low coeffic1ent of thermal expanslOn, low d1electnc constant, and low water absorption all at the same time He synthes1zed two d1anhydndes, 9,9-b1stnfluoromethyl-2,3,6,7 -xanthenetetracarboxy hc dmnhydnde (6FCD A) and 9-phenyl-9-tnfluoromethy 1-2,3,6,7 -xanthenetetracarboxyhc dmnhydnde (3FCDA) F1gure 20 shows the synthes1s route for 6FCDA and 3FCDA

Auman [28] synthes1zed novel fluonnated polY1m1des from 6FCDA or 3FCDA and nme diammes mcludmg a ngid fluonnated d1amme hke TFDB. F1gure 21 shows the synthes1s scheme for the fluonnated polY1m1des from 6FCDA or 3FCDA, and the1r charactenstlcs are shown m Table 15 He used two methods to synthes1ze the polY1m1des synthes1s of the poly-

-

Table 13 Charactenstlcs of Fluonnated PolYlmldes

Monomers ImldlzatlOn condItIons. Dlanhydnde Dlamme Solvent, temperature(°C)/ume(h)

6FDA 4FBDAF NMP, 70112, 100/2, 150/2,200/2,250/2,30011 6FDA DTDE NMP, 70112, 100/2, 150/2,200/2,250/2,30011 6FDA DTHE NMP, 70112, 100/2, 150/2,200/2,250/2,30011 6FDA TFATFDFDADP NMP, 70112, 100/2, 150/2,200/2,250/2,30011 6FDA BAT NMP, 70112, 100/2, 150/2,200/2,250/2,300/1 6FDA BAO NMP, 70112, 100/2, 150/2,200/2,250/2,30011 6FDA BDAF NMP, 70112. 100/2, 150/2,200/2,250/2,30011

"Number-average molecular weights by GPC of PAA III THF bMeasurements were made at 22°C, 50% RH and 100 kHz Source Ref 24

P AA vIscosity Molecular (TJ[dIlg]) (Mw) weight"

3964 417

8507 29,297 15,602 30,402 27,600

Film formatIOn

No No Yes Yes Yes Yes Yes

Dlelectnc constantb

2 93 300 295 295 299

102

CH'~CH'

CH,~CH'

I

CH'YyCH,

CH,VCH, I

CF,

CH'*I CH, CH, ~ CH,

F,

HOOC*CF. COOH

HOOC ~ I COOH F.

HIO./lz

CHJCOOH HzO H2~O. (100 203)

70"C I H

CI\II Cu I OMF

150"C ~() h

170"C.17h

Reflux 3 h

..

..

..

..

I

CH'YyCH,

CH3VCHa I

CF3

CH3*1 CH,

CH3 ~ CH. Fa

CF.

HOOC*I COOH

HOOC ~ COOH F3

~\=¢rCF' ,7 C ~ C

I r I ' o 0

'C ~ c' 1/ \\ o CF3 0

P6rDA

Figure 18 SynthesIs route for P6FDA (From Ref 26)

Sasaki and Nishi

(amlc aCid) with subsequent coatmg and thermal cunng, and direct synthesIs of the PolYlffilde in one pot by solutlOn Imldlzation m an NMP/N-cyclohexylpyrollidmone (CHP) solvent mix­ture at 180-190°C.

He found that combmmg ngld fluorinatmg dlanhydndes With a rodlike fluonnated dlamme like TFDB produced polyimlde films with an Ideal combmatlOn of low dlelectnc constant, low mOisture absorptlOn, and low CTE. The polyimide from 6FCDA and TFDB had a low dlelectnc constant of 24 at 1 MHz, low CTE of 6 ppm, low moisture absorptlOn of 1 2 wt% at 85% relative humidity (RH), and high glass translhon temperature of 420°C

The fluormated polYlmldes from 6FCDA or 3FCDA and a ngld fluor mated dlamme are very attrachve for electrorucs apphcatlOn

Auman and Trofimenko [29] have reported the synthesIs of fluorinated, high glass tran­sition temperature, soluble polYlmldes based on 12, 14-diphenyl-12, 14-bls(tnfluoromethyl)-12H, 14H -5,7 -dlOxapentacene-2,3, 9, lO-tetracarboxyhc dianhydnde (PXPXDA). The chemical structure of the fluorinated PolYlffildes IS shown m Figure 22, and their charactenshcs are shown

-

Synthesis of Fluorinated Polyimides

~\JQ=CF3 ,7 C ""'- C / I '" \ o 0

\C # /

" CF \\ 030

P6FDA

PolymellzatlOn

H 0 CF 0 H

~-gyYg-~

HO-C~C-OH II CF II o 3 0

1 FDB

,>"Ivent DMAc T"IllPCI,llUIL RT

F3C

P6FDA/TFDB Poly(amlL dud)

ImldlzatlOn , Temperdturc 350°C

"~CF3 " C././ C / r I \ N N \C ~ /

II II o CF3 0 F3C

P6FDAITFDB PolYlllllde

103

n

n

Figure 19 SynthesIs scheme for the fluormated polYlmldes from P6FDA and TFDB (From Ref 26 )

m Table 16 The polYlmlde synthesIs was earned out m the same two ways, as for 6FCDA and 3FCDA The molecular weights of the PAAs and polYlmldes were all high PXPXDAI TFDB had a low dlelectnc constant of 2 6 at I MHz and low CTE of 10 ppm

H. Fluorinated Polyimides Prepared from 2,2'­Bis(fluoroalkoxy)benzidines

The prevIous sectIOn showed that TFDB IS sUItable as a dlamme for fluorInated, ngld-rod polYlmlde Femng et al [30] have mvestlgated the synthesIs and properties of fluorInated polYlmldes prepared from novel 2,2'-bls(fluoroalkoxy)benzldmes. Figure 23 shows the syn­theSIS scheme for the poiYlmldes from 2,2'-bls(fluoroalkyoxy)benZldmes, and their character­IStiCS are shown m Table 17. The three new dlammes were synthesized from the correspond­mg 3-(f1uoroalkyoxy)mtrobenzenes by reductIOn, followed by benzldme rearrangement The fluonnated polYlmldes from the three dIammes (TFMOB, TFEOB, DFPOB) were synthesized

Table 14 CharactenstIcs of Fluonnated PolYImIdes

Monomers ImIdIzatIon condItions Dlanhydnde Dlamme Solvent, temperature(°C)/tIme(h)

PMDA TFDB DMAc, 70/2, 160/1,200/05, 350/1 (N2)

P3FDA TFDB DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

P6FDA TFDB DMAc, 70/2, 160/1, 200/05, 350/1 (Nz) PMDA DMDB DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

P3FDA DMDB DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

P6FDA DMDB DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

PMDA DPTP DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

P3FDA DPTP DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

P6FDA DPTP DMAc, 70/2, 160/1, 200/05, 350/1 (N2)

"Inherent VIscosItIes were measured With DMAc solutIon at 30°C bMeasurements were made at 23°C and 1 MHz under dry condilions Source Ref 26

(

P AA VISCOSIty' Molecular FIlm (T][dl/g]) weIght Yes/No formatIOn

1 8 Yes 07 Yes 06 Yes 27 Yes 1 3 Yes 07 Yes 1 3 Yes 03 Yes 02 Yes

(

Dlelectnc constantb

32 28 26

..... g

en DI UI DI ~ DI ::J Q.

Z iii" :t'

Synthesis of Fluorinated Polyimides 105

0'

In",,,,," X CF.

HOOC~COOH

HOOC)lAO~coOH

Dehydrauon

o 0 \\:dXxX CF. II

l I ~ I ~ \ o l 'c # # C

II 0 \\ o 0

X=CF3 6FCDA X=Ph lFCDA

Figure 20 SynthesIs route for 6FCDA and 3FCDA (From Ref 27)

usmg the conventlOnal polymenzatlOn and one-pot solutlOn polymenzatIon. The polYImides had high molecular weIghts and gave good films. Tnfluoromethoxy substitutlOn was shown to gIVe propertIes sImilar to tnfluoromethyl substitution. The polyimide from 6FCDA and TFMOB had a low dielectnc constant of 2 8 at 1 MHz, low CTE of 10 ppm, low moisture absorption of 08 wt% at 85% RH, and hIgh glass transItIon temperature of 375°C.

I. Fluorinated Polyimides Prepared from a Diamine Based on Trifluoroacetophenone

Rogers et al. [31] have synthesIzed very hIgh glass transition temperature, soluble polyimides from a diamme based on tnfluoroacetophenone. 1,1-bIs(4-ammophenyl)-1-phenyl-2,2,2-tn­fluoroethane (3Fdiamme) was prepared usmg the procedure of Kray and Rosser [32] as shown in FIgure 24. Figure 25 shows the synthesIs scheme for the polYImides prepared from PMDA, 3Fdiamme, and phthalIc anhydride Their charactenstics are shown in Table 18.

106 Sasaki and Nishi

o 0 \\ riJO:CF3 1/ c/ I "<:::::: I "<:::::: \0 'c ~ ~ /

+ H2N-R-NH2

1/ 0 \\ o 0

X=Cf3 6FCDA X=Ph 3FC'DA

R MPD, PPD, DAD, TPDR DMDR 4,4'-ODA, 15-DAN 1 4'-ODA 4,4'-6F

NMP or NMP/CHP RT

tHO OH t I II

xXXxX CF3 II I

N-C C-N-R

I ~ 1"<::::::

# ~ HO-C 0 C-OH

II II o 0 n

I Coat

2 Dry, thermally

IIll1dlZe, 150't

or I Solullon Imldlzc

180 - 190't 2 Coat

1 Dry. 150"C

t- \riJO:CF3 ; t / I "<:::::: I "<:::::: \ N N---R \ ~ ~ / C C II 0 \\ o 0 n

Figure 21 SyntheSIS scheme for the fluonnated polYlmldes from 6FCDA or 3FCDA (From Ref 28 )

A calculated amount of phthalic anhydnde was added to the prepared dIamme solutIon to afford nonreactive end groups and controlled molecular weIghts The mtnnsIc VISCOSIties of the three polYlmIdes from PMDA, 6FDA, and BPDA were 0 65, 0 36, and 0 47 dl/g, respec­tively These polyimIdes were soluble m NMP, and tough films could be formed from the polYlmlde solutions The PMDA/3Fdiamme poly ImIde exhibIted a glass transItion temperature exceedmg 420°C

Soluble polYlmldes with high glass transItIon temperature could be synthesIzed from 3Fdiamme.

III. FLUORINATED POLYIMIDES FOR OPTO-ELECTRONICS

OptIcal polymers are expected to be used for optIcal communications. Such optical polymers reqUIre thermal stabihty above 300°C as well as good transparency because they must be

(

CJ)

Table 15 CharactenstIcs of Fluonnated PolYImIdes '< ::l -:r

Monomers (1)

ImIdlZatIOn condItIons P AA VISCOSIty Molecular FIlm Dlelectnc III 0"

DIanbydnde Dmmme Solvent, temperarure(°C)/tIme(h) (Tj[dl/g]) weIght formatIOn constantd 0 -6FCDA 4,4'-ODA NMP,350/- 250,000' Yes 28 :!! 6FCDA 3,4'-ODA NMP,350/- 207,000' Yes 29 c

0 6FCDA MPD NMP,350/- 147,000' Yes ::::!"

::l 6FCDA PPD NMP,350/- 117,000' Yes III -6FCDA 4,4'-6F NMP,350/- 143,000' Yes (1)

Q. 6FCDA DAD NMP,350/- 203,000' Yes "0 6FCDA TFDB NMP,350/- 215,000' Yes 0

-< 6FCDA DMDB NMP,350/- 251,000' Yes §" 3FCDA 4,4'-ODA NMP,350/- 325,000' Yes is: 3FCDA 3,4'-ODA NMP,350/- 241.000' Yes (1)

III 3FCDA MPD NMP,350/- 229,000' Yes 3FCDA PPD NMP,350/- 266,000' Yes 3FCDA 4,4'-6F NMP,350/- 277,000' Yes 3FCDA DAD NMP,350/- 387,000' Yes 3FCDA 1,5-DAN NMP,350/- 177,000' Yes 3FCDA TFDB NMP,350/- 396,000' Yes 3FCDA DMDB NMP,350/- 298,000' Yes 6FCDA 4,4'6F NMP/CHP, 180-190 (chemIcal) 102,000b Yes 23 3FCDA 4,4'-ODA NMP/CHP, 180-190 (chemIcal) 327,000c Yes 28 3FCDA 3,4'-ODA NMP/CHP, 180-190 (chemIcal) 167,000c Yes 28 3FCDA MPD NMP/CHP, 180-190 (chemIcal) 204,000c Yes 27 3FCDA 4,4'-6F NMP/CHP, 180-190 (chemIcal) 321,000c Yes 25 3FCDA DAD NMP/CHP, 180-190 (chemIcal) 228,000b Yes

"Number-average molecular weIghts by GPC of PAA m DMAc/LIBr/H3P04/THF at 35°C bNumber-average molecular weIghts by GPC of polYlmlde m DMAc at 135°C cNumber-average molecular weIghts by GPC of poly ImIde m DMAc/LIBr/HcPO/THF at 35°C dMeasurements were made at 0 % RH and I MHz Source Ref 28 .....

0 ......

108

t) 'c 1/ o

R ODA, PPD, DAD, TFDB

Sasaki and Nishi

°t II

:>-R \\ o n

Figure 22 ChemIcal structure of the polyimides from PXPXDA (From Ref 29)

compatible WIth conventIOnal Integrated circUit (lC) fabricatIon, As a consequence, conven­tIonal optical polymers, such as poly(methyl methacrylate) and polycarbonate, cannot be used in these applIcations because of theIr poor thermal stabIlIty __

On the other hand, conventIonal polYImides lIke Kapton are reddIsh-brown In color and have not been used In optoelectrOnIcs applIcatIOns Some fluonnated poly 1m Ides are transpar­ent, so they look very prOmISIng as optical polymers In thIS sectIOn we first dISCUSS an evalu­atIon of fluorinated polYImides WIth a hexafluorOisopropylidene group as an optIcal waveguIde matenal, and then dISCUSS the synthesIS and properties of several new fluonnated polYImides for optoelectrOnIcs

A. Fluorinated Polyimides with Hexafluoroisopropylidene Groups as an Optical Waveguide Material

Reuter et al [33] Investigated the optIcal propertIes of three fluonnated PolYlffiIdes from 6FDA These polyimides are all advertised as haVIng good optical propertIes a PyralIn product (Du Pont) prepared from 6FDA and ODA, SIXEF-44 (Amencan Hoechest) prepared from 6FDA and 4,4-6F, and SIXEF-33 (Amencan Hoechest) prepared from 6FDA and 3,3-6F FIgure 26 shows the chemIcal structures of the polYImides In theIr expenment, planar wavegUides were produced by spin casting films onto glass substrates, and the optIcal losses were measured usmg a 633-nm He-Ne laser. The relatIonshIp between optical loss and cunng condItions was In-veStigated. __

They found that the IntroductIOn of a hexafluorOisopropylIdene group Into the polYImide umt greatly Improved the optical transparency of polyimides The optical losses ranged from very hIgh for PMDA/ODA polYImide film through moderate for 6FDA/ODA polYImide film to low for 6FDA/4,4-6F polYImide film and 6FDA/3,3-6F polYImide film The 6FDA/4,4-6F poly Imide film, after drYIng for 1 h at 90°C, has optIcal losses below 0 1 dB/cm at 633 nm. The low loss below 0 5 dB/cm ws retaIned at temperatures up to 200°C but the loss Increased to more than 25 dB/cm WIth heatIng to 300°C They pOInted out two poSSIble causes for the observed wavegUide losses. ordenng wIth or wIthout charge transfer complex forma­tion, and VOids or pInholes.

For waveguide applIcatIOn It IS Important to know the optIcal losses of typical fluonnated polYImides. The values are 0 5 dB/cm after 200°C annealIng and 2 5 dB/cm after 300°C annealIng

Table 16 Charactenstlcs of Fluonnated PolYlmldes

Monomers ImldlzatlOn conditions P AA vIscosity Dlanhydnde DIamme Solvent, temperarure(°C)/tlme(h) (11 [dl/g))

PXPXDA 4,4'-ODA NMP/CHP, 180-190 (chemical) PXPXDA PPD NMP/CHP, 180-190 (chemical) PXPXDA DAD NMP/CHP, 180-190 (chemical) PXPXDA TFDB NMP/CHP, 180-190 (chemical)

"Number-average molecular weights by GPC of polyumde III DMAc at 135°C bNumber-average molecular weights by GPC of polyumde III DMAc/LIBr/H3POiTHF at 35°C cNumber-average molecular weights by GPC of PAA III DMAc/LIBr/H3P04/THF at 35°C dMeasurements were made at 0% RH and 1 MHz Source Ref 29

Molecular weight

44,000', 68,4oob 53,600' 38,lOOC 68,4oob

Film fonnatlon

Yes No Yes Yes

Dlelectnc constantd

28

25 26

CJ) '< :::J -:::T C1l (I)

Ii;' S. !! c o ... S' I» -C1l a. 'tJ o -< 3' c: C1l (I)

..... o CO

110

R 6FCDA 1FCDA BPDA. PMDA

f Coat

2 DIY. thermally IIll1dlze. ~50"C

I Solvent RT

or

ORI

RI

Rf=CF3 TFMOB Rf=CF2CFiH TFEOB Rf=CF2CFHOCF2CF2CF3 DFPOB

RIO

I SolutIon IIll1dlze

180 - f90"C 2 Coat ~ Dry. ViO"C

n

n

Sasaki and Nishi

Figure 23 SynthesIs scheme for the polylmldes from 2,2'-bls(fluoroalkoxy)benzldmes (From Ref 30)

B. Fluorinated Polyimides from Bis(trifluoromethyl)diaminobiphenyl as an Optical Material

In Sec II.B we saw that the fluonnated polYlmlde prepared from 6FDA and TFDB has high transparency, so It IS expected to be useful as an optical matenal The optical loss of 6FDA/ TFDB polYlmlde film after high-temperature cunng (350°C) was 0 7 dB/cm at the wavelength of 633 nm [34] ThiS value IS much lower than that for 6FDA/4,4-6F polYlmlde films after 300°C curmg (see Sec. lILA) Optical matenals must have a controllable refractive mdex as well as bemg transparent. Matsuura et al [35] have syntheSized polYlmlde copolymers from 6FDA, PMDA, and TFDB III order to control the refractive mdex Figure 27 shows the syn­theSIS scheme for the copolYlmldes from 6FDA, PMDA, and TFDB The refractive mdex at the wavelength of 589 3 nm of 6FDA/TFDB was 1.556, and that of PMDA/TFDB was 1 647 Thus, the refractive Illdex can be controlled between 1 556 and 1 647 by the copolymenza­tlOn of 6FDA, PMDA, and TFDB (Figure 28) r36]

Table 17 CharactenStiCS of Fluonnated PolYimides

Monomers ImidizatlOn conditions Dtanhydnde Dlamme Solvent, temperature(°C)/time(h)

6FCDA TFDB NMP/CHP, 180-190 (chemical) 6FCDA TFMOB NMP/CHP, 180-190 (chemical) 6FCDA TFEOB NMP/CHP, 180-190 (chemical) 6FCDA DFPOB NMP/CHP, 180-190 (chemical) 3FCDA TFDB NMP/CHP, 180-190 (chemical) 3FCDA TFMOB NMP/CHP, 180-190 (chemical) 3FCDA TFEOB NMP/CHP, 180-190 (chemical) BPDA TFDB NMP/CHP, 180-190 (chemical) BPDA TFMOB NMP/CHP, 180-190 (chemical) BPDA TFEOB NMP/CHP, 180-190 (chemical) BPDA DFPOB NMP/CHP, 180-190 (chemical) PMDA TFDB NMP/CHP, 180-190 (chemical) PMDA TFMOB NMP/CHP, 180-190 (chemical) PMDA TFEOB NMP/CHP, 180-190 (chemical) PMDA DFPOB NMP/CHP, 180-190 (chemical)

"Number-average molecular weights by GPC of polyumde III DMAc at 13SoC bMeasurements were made at 0% RH and I MHz Source Ref 30

P AA ViSCOSity (Y][dl/gD

Molecular Film weight" formatlOn

126,000 Yes 107,000 Yes 88,800 Yes 52,900 Yes

208,000 Yes 149,000 Yes 98,200 Yes

315,000 Yes 165,000 Yes 113,000 Yes 65,900 Yes

107,000 Yes 87,400 Yes

121,000 Yes 61,300 Yes

Dielectnc constantb

24 28 30 25 27 26 3 1 29 27 33 27 26 26 33 25

en '< ::s -::r CD til Ii;-0 -!! c: 0 :::!. ::s Q) -CD c. 'tI 0 -< 3' c: CD til

... ... ...

112

CF,COCI + o

0-0

~ # C-CF,

PhNH2

PhNH2· HCI rcnux

Figure 24 SynthesIs route for 3FdJamme (From Ref 32)

Sasaki and Nishi

These polyumdes had good transparency In the near-Infrared region as well as In the vIsible region. Matsuura et al [37] fabncated optical ndge wavegUIdes for optical commUnIcatIOn components from these copolYlmldes, and at the wavelength of 1 3 /lm, the optical loss of these waveguides was 0 3 dB/cm These polyimldes wavegUIdes have been used In optoelectronIc multIchlp modules [38,39] In additIOn, single-mode optical wavegUIdes made from these flu­orinated polyimides were recently fabncated [40]

BeSides waveguides, several other optical components such as optical filters [41] and optiCal waveplates [42] have been fabncated USIng optical polYlmides made from 6FDA, PMDA, and TFDB.

c. Perfluorinated Polyimides

Although the fluorInated polYlmides from 6FDA,PMDA, and TFDB have excellent proper­ties as optical matenals, there are some absorption peaks In the near-mfrared regIOn due to the harmOnICs of the carbon-hydrogen bonds [34] For optical commUnIcatIOn use, Ando et al [43,44] proposed perfluormated polYlmldes, m which fluorme-carbon bonds were substi­tuted for hydrogen-carbon bonds, because these should have no absorptIOn peaks between 1 0 and 1.7 /lm They first Investigated the synthesIs of the perfluonnated polyumdes USIng P6FDA, which IS the only dlanhydnde without carbon-hydrogen bonds, and five perfluoro dlammes

Synthesis of Fluorinated Polyimides

o 0 \\ II

(/~c'o + \c~/ II \\ o 0

NMP Rl,24 h

H 0 0 H

I " " I N-CXXC-N HO-C I # C-()H

o II

~\ ~/

\\ o

" " o 0

o 0

" " /CXXC" N I N

" # / C C

" " o 0

NMP/o-d,chlorobcnzene(80/20) 16'i"C -24 h

n

Figure 25 SyntheSIS scheme for the polYImIdes from 3FdIamme (From Ref 26)

113

(FIg 29) The conventIOnal two-step reactIOn was unable to produce a continuous fIlm of perfluonnated poly ImIde

The pnmary reason for gettmg noncontmuous film was thought to be the poor reaCtivIty of perfluoro diammes and the hIgh ngidity of the polymer cham Therefore, they next syn­thesIzed a novel perfluonnated dianhydnde WIth a flexIble ether hnkage, 1 ,4-bIS(3 ,4-dicarb­oxytnfluorophenoxy) tetrafluorobenzene dianhydnde (IOFEDA), VIa a three-step reaction (FIg 30) An estimation of the reactivIty of the five perfluonnated diammes by the reactIOn wIth phthahc anhydnde, and 15N and IH NMR study showed that tetrafluoro-m-phenylenediamme (4FMPD) was the most reactive among the five diammes [44], Perfluonnated polyimide was synthesIzed from lOFEDA and 4FMPD, and a fleXIble film was formed (Fig 31) The per­fluonnated polyimide had a hIgh glass transItIOn temperature (301°q, and hIgh ImtIal poly­mer decompOSItion temperature (407°q The lOFEDA/4FMPD poly ImIde film cured at 200°C was soluble m polar orgamc solvents Then, usmg the lOFEDA/4FMPD polYImide dIssolved m acetone-d6, the visible-near-mfrared absorptIon spectrum was measured (FIg 32), The sohd

Table 18 Charactenstics of fluonnated polYImides

Monomers ImidizatIOn condItIons DIanhydnde DIamme Solvent, temperature( °C)/tlme(h)

PMDA 3Fdiamme NMPIDCB, 165 (chemIcal) BPDA 3Fdiamme NMP/DCB, 165 (chemIcal) 6FDA 3FdIamme NMPIDCB, 165 (chemIcal)

"Inherent VIscosIties were measured WIth NMP solution at 25°C DCB, O-dichiorobenzene Source Ref 31

PI VISCOSIty' Molecular FIlm (T] [dl/g]) weIght formatIOn

065 Yes 047 Yes 036 Yes

Dielectnc constant

..... ..... ~

en DI (II DI ~ DI :::l a. Z iii' :::r

Synthesis of Fluorinated Polyimides 115

6FDNODA

6FDN4,4-6F

6FDN3,3-6F

Figure 26 Chemical structures of the fluormated polYlmldes as an optical wavegUide matenal (From Ref 33)

lIne Indicates the absorbance of IOFEDA/4FMPD and the dashed lIne Indicates that of par­tially fluorInated polYlmlde (6FDA/TFDB) Except for a small absorptIOn peak (at 1.4 11m) due to moisture, the perfluorInated polYlmlde has no substantial absorptIOn peak over the wide wavelength range from I 0 11m to I 65 [44].

Perfluonnated polYlmlde with high transparency at the wavelengths of optical commum­cations, 1 0-1 7 11m, IS a promisIng matenal for optical commumcatlOn applIcations.

IV. SUMMARY

FluorInated polYlmldes have been extensively Investigated maInly for electromcs use SInce their first syntheSIS by Cntchley et al In 1972, many new fluorInated polYlmldes have been reported If the fluormated polyimldes from 6FDA are considered the first-generatIOn fluon­nated polYlmlde, the ones currently bemg developed should be called second-generatIOn flu­onnated polYlmides. These fluormated polylmldes for electromcs use reqUire several proper­ties. such as low dlelectnc constant, low thennal expansion coeffiCient, and high glass transition

116

o 0

\\ " clC~\o 'c~cl It \\ o 0

PMDA I-x 11101

CopolymellzallOn DMAL RT

o 0 II II

NH-C~C-f,\H

OH-C~C-oH II II o 0

Inlldlzalton 150"C

1 0 0

i~~'N 'c~c' II II o 0

TFDB 111101

I-x

Sasaki and Nishi

I-x

Figure 27 SynthesIs scheme for the copoJYlmldes from 6FDA, PMDA, and TFDB (From Ref 35 )

166

1.64

~ 162 v '0 .s v 160 ~ (,)

J:l 158 ~

156

1 54 0 20 40 60 80 100

6FDA Content (%)

Figure 28 Refractive mdex of copoJYlmldes from 6FDA, PMDA, and TFDB as a function of 6FDA content (From Ref 36)

Synthesis of Fluorinated Polyimides 117

t<:*~ "I )N--t. II II o F3 0 n

Rf TFPDA. OFB, 4FMPD, 8FODA, 8FSDA

Figure 29 Structure of perfluormated polYlmldes from P6FDA (From Ref 43)

temperature, all at the same tIme. InvestIgations of fluorinated polYImides for optoelectronics use have also started recently These can be called the third-generation fluormated polYImides.

A few dIfficult problems still pose challenge to the synthesIs of the fluormated polYImides. The mam problem IS the low reactiVIty of diammes caused by the mtroductIon of a fluorinated substitute, WhICh has a strong electron-attractmg force and causes a steric effect. To solve thIS problem, one must select a fluonnated diamine that has hIgh nucleophIhc reactivIty or find a new method of synthesIzmg fluonnated poly ImIde from a low-reactIvIty diamme. It IS also

F

NC~F + NCYF

F

Figure 30 SynthesIs route for lOFEDA (From Ref 43)

118

lOFEDA I + DMAc

F H2N¢NH. + I

F AlP F

F

4FMPD

o K 0 H H

~~OVO~~-~~~ HOOCYF F F FVCOOH FYF

F F F

! 200-350"0

F

lOFEDA/4FMPD

Sasaki and Nishi

Figure 31 SynthesIs scheme for perfluormated polynmde from lOFEDA and 4FMPD (From Ref 43 )

Important to know the reaction mechanism In order to synthesIze hIgh-molecular-weight flu­orinated polYImides. Some of the fluorInated polYImides are soluble In certain solvents, and this characteristic has been used to determine the reactIOn mechanism of fluonnated POlYlffilde synthesIs by NMR measurements

0.04 211C/>CH I

I I

-- 10FEDA/4FMPD I I I

6FDAfTFDB I 0.03 I

I

(dissolved In acelone-d6) I G) I U I C I

I as I

€ 0.02 \ I \

0 \ \

1/1 ~ \

.a \ as \

\ 001 \ ,

\ , " ...... _----

0.6 0.8 1.0 1.2 1.4 16

wavelength (Ilm)

Figure 32 VlSlble-near-mfrared absorption spectra of lOFEDA/4FMPD and 6FDA/TFDB polYlmldes dissolved m acetone-d6 (From Ref 44)

Synthesis of Fluorinated Polyimides 119

In the future, fluorInated polYlmlde studIes wIll receIve more attentIOn, and fluorInated polYlmldes desIgned for both electncal and optelectncal applIcatIons are expected to become a key matenal, for example, In Integrated commUnIcatIOn systems

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