Synthesis and Characterization of New Poly(arylene ether

Chapter 39

Synthesis and Characterization of New Poly(arylene ether oxadiazoles) Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 27, 2015 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1994-0537.ch039

Frank W. Mercer, Chris Coffin, and David W. Duff Corporate Research and Development, Raychem Corporation, Mail Stop 123/8512, 300 Constitution Drive, Menlo Park, CA 94025-1164

Considerable attention has been devoted to the preparation of fluorine-containing polymers because of their unique properties and high temperature performance (1). Recently we reported the preparation and characterization of novel fluorine-containing polyimides and polyethers which exhibit low moisture absorption and low dielectric constants (2, 3). Fluorinated polyimides absorb 1 wt% water and have dielectric constants of about 2.8 (all dielectric constants reported in this paper were measured at 10 kHz) whereas their non-fluorinated analogs absorb as much as 3 wt% water and have dielectric constants of about 3.2. Fluorinated polyarylethers, which are free of polar groups such as ketones, imides and sulfones, absorb as little as 0.1 wt% water and have dielectric constants less than 2.8. In our continuing effort to develop polymers with low dielectric constants and which exhibit low moisture absorption, we have prepared and characterized six new fluorinated polyarylethers (FPAE). FPAE 1, 2, 3, 4, 5, and 6 (depicted in Scheme 1) were prepared by reaction of decafluorobiphenyl with 4,4'(hexafluoroisopropylidene)diphenol (Bisphenol A F ) , 9,9-bis(4-hydroxyphenyl)fluorene, 1,1-bis(4-hydroxyphenyl)-1-phenylethane (Bisphenol AP), phenolphthalein, fluorescein, and methyl 3,5-dihydroxybenzoate, respectively. The properties of FPAE 1, 2, 3, 4, 5, and 6 make them useful for electronic applications. EXPERIMENTAL Reagents All reagents were reagent grade and were used without purification. Decafluorobiphenyl, phenolphthalein, fluorescein, 3,5-dihydroxybenzoic acid, cyclohexanone, dimethylacetamide (DMAc), g-butyrolactone (GBL), and potassium carbonate were obtained from Aldrich Chemical. Methyl 3,5-dihydroxybenzoate

0097-6156y94/0537-0546$06.00/0 © 1994 American Chemical Society

In Polymers for Microelectronics; Thompson, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

39. MERCER ET AL.

Synthesis of New Poly(arylene ether oxadiazoles) 547

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 27, 2015 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1994-0537.ch039

F

E •F +

F

FPAE1

F

F

HO—R—OH

F

R =

F P A E 2 Ft =

FPAE 3

R =

Scheme 1.


548

POLYMERS FOR MICROELECTRONICS

was prepared by esterification of 3,5-dihydroxybenzoic in methanol using sulfuric acid catalysis. Bisphenol AF, Bisphenol AP, and 9,9-bis(4-hydroxyphenyl)fluorene were obtained from Kennedy and Klim and used as received.


Measurements Dielectric constants were measured at 10 KHz using our previously described method (2). Tensile testing of compression molded films was conducted on an Instron tensile tester (ASTM D-882-64T). Moisture absorption was calculated following immersion of solution-cast films of the polymers in water for 16 hrs at 90 °C. Glass transition temperatures (Tg) reported in this paper were determined using differential scanning calorimetry (DSC). Both DSC and thermal gravimetric analyses (TGA) were performed on a Perkin-Elmer Series 7 D S C / T G A . Gel permeation chromatography was carried out on a HewlettPackard 1090 liquid chromatograph fitted with four Polymer Labs PL-Gel columns (500A, 100A, 103A, and 104A pore diameters), using tetrahydrofuran as the mobile phase and polystyrene molecular weight standards. Nuclear magnetic resonance analysis was performed on a Varian XL-300 NMR spectrometer. Gas chromatographic/mass spectral (GC/MS) analysis was performed on a Hewlett-Packard 5995 G C / M S . The percent gel in crosslinked polymers was determined by Soxlet extraction with DMAc for 16 hrs. Polymer Synthesis Polymerization of decafluorobiphenyl with the bisphenols was carried out using the following general procedure: to a 250 mL round bottom flask was added 11.36 g (0.034 mol) of decafluorobiphenyl, 11.54 g (0.033 mol) of 9,9bis(4-hydroxyphenyl)-fluorene, 105 g DMAc, and 12.2 g (0.090 mol) of potassium carbonate. The mixture was stirred at 120 °C under nitrogen for 17 hrs. The mixture was allowed to cool to room temperature and poured into a blender containing 300 mL of water to precipitate the polymer. The polymer was isolated by filtration, washed with water and dried to yield FPAE 2 as a white powder. RESULTS AND DISCUSSION A model reaction between 1 mole of decafluorobiphenyl and 2 moles of phenol was carried out in DMAc and followed by G C / M S . The reaction, depicted in Scheme 2, was near completion after 6 hrs at 150 °C. After 18 hrs, the reaction was worked up and the expected 4,4'-diphenoxyoctafluoro-biphenyl (4) was isolated as the exclusive product by F - N M R and G C / M S . Decafluorobiphenyl was subsequently reacted with aromatic diphenols in DMAc using potassium carbonate to give the fluorinated polyarylethers. Solutions of FPAE 1, 2, 3, 4, 5, and 6 containing up to 25 wt% polymer, were prepared in DMAc, tetrhydrofuran, bis(2-ethoxyethyl)ether, GBL, cyclohexanone, methyl isobutyl ketone, or mixtures of the above. Solutions of the polyethers in a 50/50 mixture of G B L and cyclohexanone (w/w) were spin-coated 19



39.

Synthesis of New Pofy(arylene ether oxadiazoles) 549

MERCER ET AL.

Scheme 2.

onto glass and dried 15 min at 100 °C, 15 min at 200 °C, and 30 min at 350 °C. The resulting tough, flexible films were about 10 microns thick. The dielectric constants of the FPAE polymers were measured at 0% relative humidity (RH) and at 60% R H and are listed in Table 1. Moisture absorption of the FPAE polymers was measured and is also listed in Table 1. FPAE 1, 2, 3, 4, 5, and 6 have glass transition temperatures of 189 °C, 260 °C, 208 °C, 243 °C, 285 °C, and 148 °C, respectively, and show excellent thermal stability. Thermal gravimetric analysis of FPAE 1 and FPAE 2 reveals that the polymers exhibit initial weight losses in air at 500 °C (scan rate = 20 °C/min). FPAE 2 has improved thermal stability over FPAE1 and FPAE 4, revealing only a 3.6% weight loss after 3 hr in air at 450 °C, whereas FPAE1 and FPAE 4 exhibit 19.8% and 50% weight loss, respectively, after similar treatment. The results of T G A analysis for FPAE1, FPAE 2, and FPAE 4 are listed in Table 2. FPAE 1 and FPAE 2 can be compression molded at 260 °C and 315 °C, respectively, to yield transparent, flexible films. Tensile specimens were prepared from from the resulting films of FPAE 1 and FPAE 2. The mechanical properties of these films are listed in Table 3. The molecular weight of FPAE polymers was controlled by addition of an excess of decafluorobiphenyl. The GPC analysis of several FPAE polymers having differing levels of excess decafluorobiphenyl are listed in Table 4. Attempts to prepare FPAE polymers with an excess of bisphenol always led to crosslinked polymer eels and no soluble polymers were obtained. The 282.3 MHz F spectrum for FPAE 2 prepared using a 3% molar excess of decafluorobiphenyl was recorded. The peaks in the spectrum were referenced externally to a,a,a-trifluorotoluene at -63.7 ppm. The spectrum is dominated by the peaks centered at -139.0 and -153.7 ppm corresponding to the F2 and F l fluorine atoms, respectively, in FPAE 2 (Scheme 1). These assignments were confirmed by examining the F spectrum of the model compound, 4,4'-diphene 9

19



550


Table 1. Dielectric Properties and Moisture Absorption of FPAE Polymers Polymer FPAE FPAE FPAE FPAE FPAE FPAE

1 2 3 4 5 6

Dielectric Constant 0% R H 60% R H 2.50 2.60 2.60 2.75 2.80 3.10

Moisture Absorption (wt. %) 0.10 0.15 0.10 0.45 0.50

2.60 2.70 2.70 3.00 3.10 3.35

—

Table 2. T G A Analysis of FPAE 1,2, and 4 Property T G A Weight Loss Onset in Air (°C) Onset in Nitrogen (°C) Maximum Weight Loss @1000°C(%) Isothermal Weight Loss in Air 3Hoursat400°C(%) 3Hoursat450°C(%)

FPAE 1

FPAE 2

FPAE 4

500 510

500 540

450

60

37.5

98

2.5 19.8

2.7 3.6

—

—

50



M E R C E R ET A L .

Synthesis of New Poly (arylene ether oxadiazoles)

Table 3. Mechanical Properties of FPAE 1 and 2 Property Thermal Coefficient of Expansion (ppm/°C) Ultimate Tensile Strength (Kpsi) Elongation at Break (%) Elastic Modulus (Kpsi)

FPAE 1

FPAE 2

76 8.3 85.0 245

65 10.7 36.0 295

Table 4. GPC Analysis of FPAE Polymers Polymer FPAE FPAE FPAE FPAE

1 1 2 4

Mole % Excess Decafluorobiphenyl

Mn

Mw

2 3 3 4

24,250 18,560 17,090 13,990

955,000 56,140 78,970 49,190


552


xyoctafluorobiphenyl, mentioned above. The predominance of these two fluorine environments suggests the FPAE 2 is linear with little or no branching. The F N M R spectrum also contains three spectral features centered at -138.3, -151.0 and -161.4 ppm corresponding to the F3, F5 and F4 fluorine atoms, respectively, in the nonafluorobiphenyl endcapper (Figure 1). Peaks corresponding to the fluorine atoms FJ and F' of the ether-substituted ring of the end cap have essentially the same chemical shifts as the fluorine atoms F l and F2 in F P A E 2. These assignments were confirmed by examining the F spectrum of the model compound 4-phenoxynonafluoro-biphenyl (5). Expansion of the spectral region centered at -151.0 ppm in the F N M R spectrum of FPAE 2 corresponds to the F5 fluorine atoms in 4-phenoxy-nonafluorobiphenyl. Integrating this F N M R spectral region of FPAE 2 and either the spectral region centered at -139.0, or that centered at -153.7 ppm, of FPAE 2 yields a DP of ~ 29 which is consistent with the DP of 32 calculated using the stoichiometric ratio of the reactants. FPAE polymers can be crosslinked by heating in air between 300 and 450 °C or heating in nitrogen using a peroxide crosslinker, such as dicumyl peroxide. Crosslinking leads to a themoset material having improved solvent resistance, and is necessary to prevent solvent induced stress cracking of the FPAE polymers when coatings or films of the polymers are exposed to polar aprotic solvents. Table 5 lists the gel content of FPAE 1 crosslinked by heating in air. The results of crosslinking of FPAE 1 and FPAE 2 with peroxides are listed in Table 6. 19

2


19

19

19

CONCLUSION FPAE polymers were prepared by reaction of decafluorobiphenyl with bisphenols. These polymers exhibit low dielectric constants, low moisture absorption, and excellent thermal and mechanical properties. Tough, transparent films of the polymers were prepared by solution casting or compression molding. These polymers may be useful in electronic applications. Synthesis and characterization of other polymers containing perfluoroaryl units is continuing.

Figure 1. Nonafluorobiphenyl endcapper.


39. MERCER ET AL.

Synthesis of New Pofy(arylene ether oxadiazoles)


Table 5. Crosslinking FPAE 1 by Heating in Air Cure Temperature (°C)

Cure Time (min)

300 400 400 400 400

30 15 30 60 105

, fcGel

c

55 79 80 86 92

Table 6. Peroxide Crosslinking of FPAE Polymers* Polymer FPAE FPAE FPAE FPAE FPAE FPAE FPAE FPAE FPAE

1 1 1 1 1 2 2 2 2

Peroxide — dicumyl peroxide dicumyl peroxide benzoyl peroxide benzoyl peroxide dicumyl peroxide benzoyl perodixe cumene hydroperoxide t-butyl perbenzoate

wt % Peroxide — 5 10 5 10 10 10 10 10

%Gel 3.0 68.8 69.2 31.9 50.7 94.0 49.4 81.3 75.8

* A l l samples cured at 400°C for 30 min. under nitrogen.

REFERENCES 1. Cassidy, P.E.; Aminabhavi, T.M.; Farley, J.M. J. Macromol. Sci.-Rev. Macromol. Chem. Phys., 1989, C29(2 & 3), 365. 2. Mercer, F.M.; Goodman, T.D. High Perf. Polymers, 1991, 3(4) 297. 3. Mercer, F.M.; Goodman, T.D., Polymer Preprints, 1991, 32(2), 188. 4. Richardson, G.A.; Blake, E.S. Ind. Eng. Chem. Prod. Res. Dev., 1968, 7, 22, . 5. The model compound, 4-phenoxynonafluorobiphenyl, was prepared upon treatment of decafluorobiphenyl (15 mmol) with phenol (15 mmol) in the presence of K2CO3 (43 mmol) in DMAc. The product was isolated following treatment of the reaction mixture with water. Subsequent preparative thin– layer chromatography of the crude product on silica gel with heptane elution afforded 4-phenoxynonafluorobiphenyl which crystallized upon standing, mp 110.5-111.5 °C. The F N M R spectrum of the purified model compound consisted of resonances centered at -138.3, -139.1, -151.1, -153.8 and -161.4 ppm. 19

Received December 30, 1992


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Synthesis and Characterization of New Poly(arylene ether

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