Characterization and degradation of some silicon-containing polyimides

PII:

Polymer Degradmon and Smbiliry 60 ( 1998) 16 I 168 c’ 1998 Elsevier Science Limited. All rights reserved Prmted m Northern Ireland 0141-3910/98/519.00

SO141-3910(97)00063-3

ELSEVIER

Characterization and degradation of some silicon-containing polyimides T. C. Chang* & K. H. Wu Department

of Applied Chemistry, (Received

8 November

Chung Cheng Institute

of Technology,

1996; revised version

received

Tahsi, Taoyuan,

6 January

Taiwan 33509, Republic of China

1997; accepted

20 January

1997)

Polysiloxaneimides (PSI) were synthesized by polycondensation of 3,3’,4,4’-benzophenone tetracarboxylic dianhydride (BTDA) with oxydianiline (ODA) and amino-terminated siloxanes of varying molecular weights. The structures of the PSI copolymers were characterized by infra-red (IR), 29Si and 13C nuclear magnetic resonance (NMR) spectroscopies. The dynamics in the interface of PSI copolymers were investigated by proton spin-spin relaxation measurements. The apparent activation energy for degradation of PSI copolymers both in nitrogen and air was studied by thermogravimetry and compared with that of the unmodified polyimide. The activation energies of the degradation process in nitrogen decreased approximately with increasing siloxane content, whereas those in air increased. @$ 1998 Elsevier Science Limited. All rights reserved

was reported first by Kuckertz.6 Thereafter, Greber reported the synthesis of a series of PSI copolymers with different siloxane backbones.7 However, McGrath et al. reported the most popular synthesis method based upon the incorporation of cr,w-aminopropyl polysiloxane oligomers with a variety of aromatic dianhydrides.8 Thermogravimetric analysis (TG) is widely used as a method to investigate the thermal decomposition of polymers and to determine their kinetic parameters.9-‘4 St. Clair et al. examined the thermal stability of PSI copolymers derived from aromatic, amine-terminated siloxane oligomers of varying and found that PSI have molecular weights, improved adhesive strengths and better thermal stability than LARC- 13. l5 Moreover, Lai et al. evaluated the apparent activation energy (E,) of thermal degradation for PSI copolymers.‘6 To understand the dynamics of the interface between the rigid PI segment and the flexible siloxane segment in PSI copolymers, we have measured the relaxation times of protons in the PI segments and the siloxane sequence, respectively. In this paper, PSI copolymers are synthesized from aminopropyl siloxane of varying molecular weight. Additionally, the effects of atmosphere, siloxane length and siloxane content on the degradation of PSI copolymers both in N2 and air have also been investigated by TG.

1 INTRODUCTION Polyimides (PIs) synthesized from aromatic monomers are of great interest for high-performance applications owing to their excellent high-temperature thermal properties. However, these polymers are often insoluble in organic solvents in fully imidized form, presenting serious processing difficulties. Therefore, much effort has been concentrated on synthesizing tractable PIs which maintain reasonable high strength and thermo-oxidative stability. Various successful attempts have been made to incorporate flexible bridging units or bulky side groups into the rigid PI backbone to enhance the chain mobility and processing.’ The polydimethylsiloxane repeating unit, -0Si (CHs)z-, is endowed with unusual properties such as high dynamic flexibility, high oxidative stability and excellent thermal stability.2 The incorporation of flexible polysiloxane into a PI backbone can yield processable polysiloxaneimide (PSI) copolymers, silicon-containing polyimides, with good thermal mechanical properties. Therefore, PSI copolymers are attractive for aerospace applications3 as membranes4 and for electrolysis.5 The flexible siloxane dimer incorporated into polyimide *To whom correspondence

should be addressed. 161

162

T. C. Chang, K. H. Wu

2 EXPERIMENTAL 2.1 Materials 3,3’,4,4’-Benzophenone tetracarboxylic dianhydride (BTDA) and oxydianiline (ODA) were obtained in high purity from the Tokyo Chemical Industry Co. and subjected to a general purification method.” Aminopropyl tetramethyl disiloxane was obtained from Htils-Petrach. Two a,w-aminopropyl polydimethylsiloxane oligomers (BY 16-353 and BYl6853B; Dow Corning), having a number-average molar mass of 1300 and 4400 g mol- ‘, respectively, were used in this study. Siloxane oligomers were used without any further purification. NJDimethylacetamide (DMAc; Aldrich) was distilled under vacuum, and toluene (Aldrich) was dried over 4 A molecular sieves. 2.2 Polymerization All the polymers were synthesized by the solution imidization method with a 33:l (v/v) DMAc/ toluene mixture. I8 Polymerization was conducted

Benzophenone dianhydride

tetracarboxylic

(BTDA)

at room temperature under nitrogen with a concentration of 15% solids by weight in co-solvent. The general synthetic and imidization schemes for the polysiloxaneimide segmented copolymers are depicted in Scheme 1. A stoichiometric amount of the siloxane oligomer was first slowly added to a stirred solution of the BTDA dianhydride, effectively capping the siloxane oligomer through reaction of its amine end groups. The aromatic diamine ODA was then gradually added as a solution to the free dianhydride and anhydride-capped siloxane. The clear solution was stirred at room temperature for 24 h and then at 160°C for 8 h under nitrogen. Collected water was removed from the distillation trap with toluene. After cooling, the reaction mixture was poured into excess methanol. The precipitated polymer was collected by filtration, washed successively with methanol, and dried under vacuum at 80°C for 8 h. A yellow ochre solid (-90% yield) was obtained and characterized by infra-red (IR) and nuclear magnetic resonance (NMR) spectroscopies and TG. In addition, the unmodified PI homopolymer was synthesized via a similar procedure, by reacting BTDA with ODA,

BY 16-353, BY 16-853B or Aminopropyl tetramethyl-disiloxane DMAc and Toluene Room temperature 5 hours reaction time

Oxydianiline (ODA) 24 hours reaction time Poly (Siloxane Amic Acid)s Dehydration cyclozation by solution imidization Solvent azeotroping agent at 160°C for 8 hours

Polysiloxaneimrdes Scheme 1

Characterization

and degradation

of some silicon-containing

163

polyimides

for comparative purposes. Samples are designated so that, for example, PSI-1300(10) denotes a copolymer containing lOwt% of siloxane. that has a number-average molecular weight of 1300 g mol- ’ . 2.3 Characterization The solution-imidized copolymers and homopolymer were all soluble in dipolar, aprotic solvents such as N-methylpyrrolidinone (NMP) and DMAc. Imidization was confirmed by IR spectra (Bomem DA 3.002) of samples prepared as KBr pellets. The characteristic imide and siloxane peaks were observed as follows. IR (KBr): 17771780 cm-i (imide C = 0 symmetric stretching), 1720-l 723 cm-’ (imide C = 0 asymmetric stretch1382-l 384 cm-’ (C-N stretching), 717ing), 1013720 cm-i (imide ring deformation), 1015 cm-’ (Si-0-Si stretching) and 797-799 cm-’ 29Si- and i3C-NMR spectra of (Si-C stretching). the solid polymers were determined (Bruker MSL200). Proton spin-spin relaxation time (T2) was measured at room temperature via solid-state i3CNMR (Bruker MSL-200) by using the pulse sequence described by Tekely and co-workers. 19,20 The characteristics and kinetics of degradation of the polymers were measured with a Seiko SSC 5000 TG/DTA instrument. Heating rates (B) of 5, 10, 20 and 40”Cmin’ were used. The sample weight was about 10 mg, and the gas (nitrogen or air) flow rate was kept at 100mlmin’.

3 RESULTS

AND DISCUSSION

3.1 NMR spectral analysis The siloxane segments in PSI-276(20) copolymer have one electronic environment which is reflected in one broad peak (7.6ppm) in the 29Si-NMR the 29Si-NMR spectrum [Fig. l(a)]. However, spectra of PSI-l 300 copolymers show two peaks [Fig. l(bk(d)], which indicate two kinds of silicon with markedly different electronic environments. Therefore, the peaks at around 7.0 and -22.0ppm can be attributed to the silicon directly connected to PI and in the siloxane sequence, respectively.21’22 Moreover, the peak width at half-height (vi/z) for the former (153-97 Hz) is broader than that for the latter (62240Hz). The narrow 29Si-NMR peak width for silicon in the siloxane sequence suggests more motional narrowing. Furthermore, the values of u112for peaks in the 29Si-NMR spectra decrease

(e)

1.

30

I.

I.

I

20

10

0

*

I

-10

*

8.

I

-20

-30

.,

40

~hwm)

Fig. 1. CP-MAS 29Si-NMR spectra for (a) PSI-276(20), (b) PSI-1300(10), (c) PSI-1300(20), (d) PSI-1300(30) and (e) PSI4400(20) copolymers.

with increasing siloxane content and siloxane length (Table 1). On the other hand, the percentages of the integrated peak intensities in the 29Si spectra should represent the percentages of the two kinds of silicon, because the cross-polarization rate for both peaks is almost the same.2’x22 The relative peak intensity ratios of 1(-22.0)/1(7.0) increase with increasing siloxane content (Table 1). In comparison with the 29Si-NMR spectrum of PSI1300(20) copolymer [Fig. 1(c)l, the chemical shift at around 7.0ppm for PSI-4400(20) is not observed [Fig. l(e)]. This result suggests that the percentage of the silicon in the siloxane sequences for PSI4400(20) copolymer is much larger than that directly connected to PI. The 13C-NMR spectra of PSI copolymers are nearly identical. A narrow peak for carbons in the siloxane segments [-OSi(CH3)2-] is observed at around l.Oppm. Moreover, the value of ulj2 for this peak carbons decreases with increasing siloxane content and siloxane length (Table 1). The results reveal that the motion of the siloxane segments’ carbons increases with increasing siloxane content and siloxane length. On the other hand, the value of ul12 for -OSi&H3)2in PSI copolymer is larger than that in polydimethylsiloxane/ methacrylate) block copolymer poly(methy1 (PDMS-b-PMMA).22 The same situation is observed in the 29Si-NMR spectrum. This broadening of the carbon and silicon resonances suggests that the effect of rigid-chain PI on the mobility of siloxane chains is larger than that of PMMA.23

164

T. C. Chang, K. H. Wu

Table 1. Chemical shifts (6), peak width at half-height (u~,~)and percentage peak areas (numbers in parentheses from NMR integration) for solid polysiloxaneimides Polymer

29Si-NMR

6 (wm)

“I :2 (Hz)

7.6 (100) 7.0 (45) 7.3 (39) 7.2 (28)

PSI-276(20) Ps1-1300(10) PSI-l 300(20) PSI-1300(30) PSI-4400(20)

153 136 117 97

Polymer

175 190 187 180 219 202

165.7 166.4 165.8 165.9 66. I 165.7

3.2 NMR relaxation times NMR experiments on PSI copolymers were performed at room temperature. At this temperature the rigid PI segments are in the glassy state, whereas the flexible siloxane segments are well above their glass transition and melting temperatures. Therefore, the two segments exhibit very different chain mobility, which should result in very different nuclear magnetic relaxation properties. Figure 2 shows the correlation between the logarithmic intensities of the 166ppm peak (imide

4.0

3.5

--3-

PI

-o-

PSI-

-A-

PSI-1300

(20)

--CL

PSI-4400

(20)

276 (20)

3 3.0

d k. x c E s .r

“1.2

W.4

-22.1 (55) -22.4 (61) -22.3 (72) -22.2 (100)

62 49 40 40

1.0 1.4 1.4 1.4 1.0

200 170 107 66 78

13C-NMR

PI PSI-276(20) PSI- I 300( 10) PSI-1300(20) Ps1-1300(30) PSI-4400(20)

s

6 (ppm)

2.5

2.0

.z 1.5

1.0 I

0

I

I,

I.

200

400

I

600

,

1,

800

I,

1000

1,

1.

1200

1400

I

160 0

TZ (ps2)

Fig. 2. Logarithmic intensity (arbitrary units) of the CP-MAS ‘3C-spectra of PI in PSI copolymers versus square of proton relaxation period, 7*.

C=O) in the 13C-NMR spectra of polymers and the square of the transverse proton relaxation period (t2). It is found that the carbons in PI segments exhibit a Gaussian fast decay, expressed as &(fast) = exp[-(t/7’2)2/2],‘” with similar spin-spin relaxation time T2 values (~18 ps) in PSI copolymers (Table 2). They are very close to the T2 value of the PI homopolymer (17.7 ps). The results reveal that the spin-spin relaxation of the rigid-chain PI protons is not affected by the presence of the flexible siloxane segments in the PSI copolymers. On the other hand, the siloxane segments [-OSi(CH&; PSI-l 300 and PSI-44001 have a Lorentzian slow decay, Zo(slow) = exp[-t/T2],19 with two different relaxation times T2 (Fig. 3) indicating that the siloxane protons can be found in two environments. The slopes of the straight lines in Fig. 3 yield the parameters T2(fast) and T2(slow) (Table 2). For the siloxane segments in PSI copolymers, there first occurs a fast decay (19-29 ps), close to that of the ‘H free-induction decay of the PI segments (-18 ps), followed by a slow decay (67-102~s). The fast and slow decaying components can be attributed to siloxane units in the interface and in the sequence, respectively. For each type of carbon, the Y-axis intercepts in Fig. 3 are proportional to the percentage of proton atoms’9,20 to be found in each component (Table 2). However, PSI-276(20) copolymer has one kind of silicon that connects directly to PI segments. Thus, the siloxane segment in PSI-276(20) copolymer has only single T2 (19 ps) as expected, and that is very close to the value for PI segments (17.8 ps). The result indicates that motion of the disiloxane

Characterization and degradation of some silicon-containing polyimides

165

Table 2. Chemical shifts (S), proton spin-spin relaxation times ( T2) and fractions of different domains in different segmented copolymers Polymer

PI phase 6 (ppm)

PI PSI-276(20) PSI-1300(20) PSI-1 300(30) PSI-4400(20)

DMS phase T2

165.7 166.4 165.9 166.1 165.7

chains is seriously PI segments.24

(PS)

17.7 17.8 18.1 18.5 17.0

restricted

T2

6 (wm)

19 21 29 22

1.0 1.4 1.4 1.0

by bonding

Fraction

(~1

to the rigid

3.3 Thermal properties The TG curve of PI under nitrogen indicates one main reaction stage (Fig. 4) which is reflected in one peak in the differential thermogravimetric (DTG) curve (Fig. 5). PI is stable up to approximately 530°C and loses about 42% of its weight. However, PSI copolymers start to lose weight around 430°C and their degradation in N2 shows two stages of weight loss (Fig. 5). The weight loss in the first stage increases with increasing siloxane content, and that in the second stage decreases (Fig. 6). Therefore, the former is subjected to the decomposition of siloxane, while the latter is due to the degradation of ODA.25 Qualitative characterization of the degradation process is illustrated by the 5% weight loss temperature and the temperature of maximum rate in weight loss, T5 and T,,,.

(%)

T2

100 26 14 13

Fraction

(w)

102 79 67

(%)

74 86 87

The characteristic temperatures of degradation for these polymers, both in N2 and air at a heating rate of lO”Cmin-‘, are listed in Table 3. Comparing the T5 and T,,, of the PSI copolymers with those of the PI homopolymer in N2, the lower thermal stability of the former is obvious. The explanation for this result may be because thermal degradation begins at the aliphatic n-propyl segments linking the siloxane segments to the PI matrix.15T26 Accordingly, the overall thermal stability is decreased as the siloxane segment molecular weight is decreased and the concentration of n-propyl linkages in the PSI increases. Thus, PSI276(20) has the lowest T,,, (55oOC) in thermal degradation. Thermo-oxidative degradation of PSI occurs at lower temperatures as the siloxane content and siloxane length increase. However, the T,,, and char yield (Y,) in thermo-oxidative degradation are proportional to the siloxane content (Table 3). This suggests that silicate-type structures are the principal degradation product in an air atmosphere.5

5.0 L

4.5

-

4.0

-

3.5

-

3.0

-

2.5

-

2.0

100 -o-

PSI-

276 (20)

+

PSI-I 300 (20)

+

Ps14wl(20)

60 Fg v

50-

= .$

40 -

3

-

30 1.5

1.0

-

20

-

PI

----

PSI-

276(20)

.‘..-.-. PSI-1300

(20)

-.-.-.-

(20)

PSI4400

; i i i

-

i :t in Air %:u ‘;::yy:y_:,:, ---_____

10 -

-

r 0.5”

0

’

’

10

’

’ 20

’

’

.

30

’ 40

.

’ 50

.

’

11 :’ :: :I

1

60

r (KS)

Fig. 3. Logarithmic intensity (arbitrary units) of the CP-MAS 13C-spectra of siloxane in PSI copolymers versus proton relaxation period, T.

300

400 Temperature

500

600

700

I

(‘C)

Fig. 4. TG thermograms of polymers PI, PSI-276(20), PSI1300(20) and PSI-4400(20) in N2 and air at the heating rate of lO”Cmin-‘.

166

T. C. Chang, K. H. Wu I

1

Consequently, the flammability improved for siloxane-modified

7-PI 6-

----

PSI-

resistance polymers2’

will be

276(20)

----~---PSI-1300

(20)

-.--.-

(20)

PSI-4400

3.4 Kinetics of degradation

5-

.lI 100

’

’

’

’

200

’

*

300

’

3

400

Temperature

Fig. 5. DTG traces and PSI-4400(20)

’

3

500

*

’

600

1

’

700

800

(‘C)

of polymers PI, PSI-276(20), PSI-l 300(20) in N2 at the heating rate of 10°C min-‘.

-

9

90 -

70 g F

-

-....-.-

PSI-1300

(30) .E E 3

60-

.o, 2

50-

-4

101 100

’

’

’

200

’

’ 300

’

3

400

’

’

500

’

3

600

700

c3 L

The relationship between logarithm of the heating rate (log B) and reciprocal temperature (l/7’) for each value of a! (CY,the degree of conversion= weight loss at a given temperature/total weight loss of the degradation) is shown in Fig. 7 for PSI1300(30) copolymer. Apparent activation energies (E,) are calculated from the slopes of the lines.28 A wide variation of E, with degree of conversion is shown in Figs 8 and 9. The results are as expected, owing to the continuous change of degradation mechanism. Although the complex degradation is outside Ozawa’s theory, we may be able to discuss the complexity of the degradation and trends by using such E, values. The average activation energies of thermal and thermo-oxidative degradation for PI in this work are 330 and 210kJmolV’, respectively. The effect of siloxane content on the activation energies of PSI copolymers is shown in Fig. 8. It is found that the activation energies of thermal degradation for PSI- 1300( 10) and PSI-l 300(20) increase with increasing conversion in the range O.lOLa50.40. After 40% conversion, the activation energies of thermal degradation for PSI1300( 10) and PSI-1300(20) are about 310 and 270 kJ mol-‘, respectively. Moreover, the activation energy of thermal degradation decreases with

1

’

800 16

(‘C)

Temperature

Fig. 6. TGA and DTG thermograms of polymers PSI1300(10), PSI-1300(20) and PSI-I 300(30) in Nz at the heating rate of lO”Cmin-‘.

Table

3. Thermal

properties’ of polysiloxaneimides 10°C min-’ heating rate

Polymer

at

Air

N2

0.8

T5 k-276(20) Ps1-1300(10) PSI-I 300(20) PSI-I 300(30) PSI-4400(20)

458 547 434 435 434 434

TllXiX

Yc

T5

645 550 626 620 626 615

43 58 54 53 51 46

422 483 414 402 394 397

Tr,,,,

606 592 604 610 620 598

Yc

05 3 7 11 8

“T,=a 5% weight loss temperature (“C) observed in TGA; T,,,,, = maximum polymer decomposition temperature (“C); Y, = char yield (wt%) at 800°C.

0.6 u= 08 I

1.1

0706 I

12

05

04

,

I

13

03

02

,

I

1.4

01 *

I

15

.

I

16

1000/l (1/K)

Fig. 7. Dependence of the logarithm of heating rate (log B) on reciprocal temperature (1 /r) for the Ozawa method at indicated conversions ((Y) of decomposition of PSI-1300(30) in nitrogen.

Characterization

Air

and degradation

N?

-w-o--c-c---c-r?L--

PSI-1300 (10) PSI-1330 (20) PSL13ca (30)

250

t 150 t

t 100 t 50 1 0

I

I

#

I

I

I

I

I

I

10

20

30

40

50

60

70

60

90

Degree of Conversion,

a (%)

Fig. 8. Effect of siloxane content on E, of degradation copolymers.

for PSI

increasing siloxane content. This may be associated with the higher heat capacity and thermal conductivity for the siloxane segments which may favor degradation of the aliphatic n-propyl segments. However, the activation energy of thermal degradation for PSI- 1300(30) after 60% conversion is slightly greater than that for PSI-l 300(10) and PSI- 1300(20) copolymers. Apparently, a weight percentage of siloxane segment larger than 30% in PSI-l 300 copolymers has a retarding effect on chain scission of the PI segment. The result may be due to formation of protective silicon dioxide coatings on the surface.29 500 450 400

t

Air N, --m----o--

PI

d----o-&--A----

PSI- 276 (20) PSI-1300 i2oj

--F--~---

PSI4400

(20)

I

~ ___... -D------O

.____

350 300 250 200 150

-

100

-

I

I

I

I

I

I

I

1

I

0

I

10

20

30

40

50

60

70

60

90

Degree

Fig. 9. Effect of siloxane

of Conversion,

u (%)

length on E, of degradation copolymers.

for PSI

of some silicon-containing

polyimides

167

The apparent activation energies of the thermooxidative degradation for PSI copolymers in the initial stage are around 175 kJmol_‘. Moreover, the E, of thermo-oxidative degradation for PSI copolymers decreases with increasing conversion and increases with siloxane content. The greater E, for PSI-1300(30) may be rationalized on the basis of the formation of thermally stable structures. It is believed to be associated with the oxidative crosslinking via the methyl groups that has been reported for polydimethylsiloxane.30 Figure 9 displays the relationships between siloxane length and activation energies of PSI copolymers. It is found that the activation energies of thermal degradation for PSI copolymers decrease with decreasing siloxane length, and E, in thermo-oxidative degradation is less influenced by siloxane length. E, of PSI-276(20) in thermal degradation decreases with increasing conversion in the range 0.105~~~0.40 and is close to 100 kJmolli after 40% conversion. The E, of thermo-oxidative degradation for PSI- 1300(20) and PSI-4400(20) decreases with increasing conversion. However, the E, of PSI-276(20) in thermooxidative degradation decreases with increasing conversion up to 20%, and increases again in the range 0.20<(;~10.40. After 40% conversion, E, of thermo-oxidative degradation for PSI copolymers decreases with increasing conversion.

4 CONCLUSIONS The structures of synthesized polysiloxaneimide (PSI) copolymers were confirmed thorough IR, 13C-NMR and 29Si-NMR characterization. 29SiNMR spectra of PSI copolymers showed two kinds of silicon, which may be assigned to siloxane sequences and siloxane units directly attached to PI. Moreover, it was found that the values of peak width at half-height (vi,*) for peaks of siloxane segment carbon and silicon in NMR spectra decreased with siloxane length and siloxane content. The spin-spin relaxation of protons in the rigid PI segments was not affected by the presence of the flexible siloxane segments in the PSI copolymer, whereas the motion of the siloxane chains was restricted by bonding to the rigid PI segments. A three-phase structure for PSI-l 300 and PSI-4400 copolymers was observed by proton spin-spin relaxation measurements, while a two-phase structure was found for PSI-276. The apparent activation energies (E,) in thermal degradation for PSI

168

T. C. Chang, K. H. Wu

copolymers increased with increasing conversion, and decreased with increasing siloxane content in the range O.lO
9. Sauerbrunn, 26, 29.

S. and Gill, P., American

Laboratory,

1994,

IO. Wendlandt, W. W., Thermal Analysis. Wiley, New York, 1986. II. Chang, T. C., Chiu, Y. S., Chen, H. B. and Ho, S. Y., Polym.

Degrad.

12. Chang,

Stab.,

1995, 47, 375.

T. C., Chiu, Y. S., Chen,

Pol_ym. Degrad.

13. Chang,

Stab.,

T. C., Chen,

Polymer,

H. B. and Ho, S. Y.,

1995, 49, 353.

Y. C., Ho, S. Y. and Chiu, Y. S.,

1996, 37, 2963.

14. Chang, T. C. and Wu, K. H., Polym. Degrad.

Stab.,

1997,

57, 325.

15. Clair,

ACKNOWLEDGEMENTS

A. K. St., Clair, T. L. St. and Ezzell, S. A., in Chemistry, ed. L. H. Lee. Plenum Press, New York, 1984, p. 467. 16. Lai, J. Y., Lee, M. H., Chen, S. H. and Shyn, S. S., Polym. Adhesive

We thank the National Science Council of the Republic of China for financial support (CS 8602 10-D-007-006 and NSC 86-2113-M-O 14-003) and Miss S. Y. Fang for help in carrying out the NMR measurements.

J., 1994, 26, 1360.

17. Bott, R. H., Summers, J. D., Arnold, C. A., Taylor, L. T., Ward, T. C. and McGrath, J. E., J. Adhes., 1987, 23, 67. 18. Chun, B. W., Polymer, 1994, 36, 4203. 19. Tekely, P., Nicole, D., Brondeau, J. and Delpuech, J. J., J. Phys. Chem., 1986, 90, 5608. 20. Tekely, P., Canet, D. and Delpuech. J. J.. Mol. Phys., 1989, 67, 81.

REFERENCES 1. Mittal,

K. L. (Ed.),

tion and Application,

Polyirnides:

Vols

Synthesis,

Characteriza-

I and 2. Plenum

Press, New York, 1984. 2. Clarson, S. J. and Semlyen, J. A., Siloxane Polymers. Ellis Horwood-PTR Prentice Hall, New Jersey, 1993, pp. 72.-134.

93, 273. 5. Tian, S. B., Pak, Y. S. and Xu, G., J. Polym. Sci. Part B. 1994, 32, 2019. Kuckertz, V. H., Makromol. Chem., 1966, 98, 101. Greber, G., Angew. Makromol. Chem., 1968, 415, 212.

6. 7. 8. Arnold,

1984, 25, 1633.

24. Sohami,

R., Laupretre,

Polymer,

F., Monnerie,

L. and Krause,

S.,

1995, 36, 275.

25. Lee, Y. D., Luo, C. C. and Lee, H. R., J. Appl. Polym.

3. Pater, R. H., SAMPE J., 1994, 30, 29. 4. Lai, J. Y., Li, S. H. and Lee, K. R., J. Memb. Sci., 1994. Polym.

21. Feng, H., Shi, L., Feng, Z. and Shen, L., Makromol. Chem., 1993, 194, 2257. 22. Chang, T. C., Chen, H. B., Chen, Y. C. and Ho, S. Y., J. Polym. Sci. Part A: Polym. Chem., 1996, 34, 2613. 23. Ebdon, J. R., Hourston, D. J. and Klein, P. G., Polymer,

Phys.,

C. A., Summers, J. D.. Chen, Y. P., Bott, R. H., Chen, D. and McGrath. J. E., Polymer, 1989, 30, 986.

Sci.,

1988, 41, 877.

26. Tsutsumi,

N., Tsuji, A., Honie,

Eur. Polym. J.,

C. and Kiyotsukuri,

T.,

1988, 24, 8-37.

H. J. and Smith, S. A., J. Appl. 1981, 26, 847. 28. Ozawa. T., Bull. Chem. Sot. Jpn, 1965, 38, 1881, 29. Yilgor, I. and McGrath, J. E., Adv. Polym. Sci., 1988, 86, 1. 30. Clarson, S. J. and Semlyen, J. A., Polymer. 1986, 27, 91. 27. Kambour, Polym.

Sci.,

R. P., Klopfer,