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Polymer International 40 (1996)275-279
Polyimide-Polysi loxane Block Copolymers
Synthesized from a, a-(3-Aminophenoxy)
Terminated Poly[Oxy(dimethylsilyl)-1,4phenylene(dimethylsilylene) ] s
Petr Sysel* & David Oupicky
Department of Polymers, Institute of Chemical Technology, Technicka 5,16628 Prague 6, Czech Republic
(Received 25 August 1995; revised version received 17 November 1995; accepted 8 March 1996)
Abstract: A method has been worked out for the synthesis of u,o-(3-aminophenoxy) terminated poly[oxy(dimethylsilyl)-1,4-phenylene(dimethylsilylene)]
oligomers with controlled molecular weight. From these oligomers were synthesized polyimide-polysiloxane block copolymers via a transimidization route,
with polyimide moieties based on 2-aminopyridine terminated 5,5'-oxybis-1,3isobenzofuranedione - 44-[l,4-phenylenebis(1-methylethylidene)]bisaniline oligomers. The copolymers obtained show higher thermooxidative stability in comparison with copolymers having siloxane moiety based on upaminopropyl or
u,w-arylamine terminated poly(dimethylsi1oxane)oligomers.
K e y words: polyimides, u,w-(3-aminophenoxy) terminated poly[oxy(dimethylsilyl)-l,4-phenylene(dimethylsilylene)] oligomers, polyimide-polysiloxane block
copolymers, thermooxidative stability.
INTRODUCTlO N
On the other hand, the thermooxidative stability of
this type of copolymer is reduced in comparison with
p~lyimides.~
Incorporation of a,w-aminopropyl terminated
poly(dimethylsi1oxane) oligomers (Fig. lakfrequently
utilized as the precursor of the polysiloxane moiety-is
considered to be a reason for the lower thermooxidative
stability of PI-PSX due to the primary splitting of
C(methy1ene)-Si
bonds.3
Because the dissociation energy of the C(aryl+Si
bond (370 kJ mol- ') is higher than that of the
C(methylene+Si bond (304 k J m ~ l - ' ) , ~a logical
assumption about the higher thermooxidative stability
of PI-PSX based on a,w-arylamine terminated
poly(dimethylsi1oxane) oligomers (Fig. 1b) was formed.
But this assumption was confirmed only in the case that
terminated siloxane dimers (x = 1 in Fig. la, b) were
utilized for this purpose.6 If polysiloxane oligomers with
longer polymer chains (x > 1) are built into the copolymers, it has been found that the type of endgroup
Aromatic polyimides, a class of high-performance polymers, possess a number of excellent properties. Their
thermal stability, dielectric and mechanical properties,
chemical resistance and planarization ability make them
suited for applications in (micro) electronics, the aviation industry and aerospace investigation.'
The considerable disadvantage of classic polyimides
is their insolubility and infusibility (without degradation
of main polymer chains), and thus poor processability.'
The tractability of polyimides (PI) can be improved
by incorporation of flexible polysiloxane (PSX) segments into their b a ~ k b o n e .Polyimide-polysiloxane
~
copolymers (PI-PSX) show the majority of the properties of polyimides, and in addition enhanced solubility,
reduced moisture sorption and higher toughness and
impact resistance?
* To whom all correspondence should be addressed.
275
Polymer International 0959-8103/96/$09.000 1996 SCI. Printed in Great Britain
276
P . Sysel, D. Oupickj
I
1
I
I
H~N-(CH~)~-S~-(O-S~-),(CH&YNH~
a)
b)
Fig. 1. Terminated polysiloxane oligomers. (a) apAminopropy1 terminated poly(dimethylsi1oxane); (b) aparylamine terminated
poly(dimethylsi1oxane);(c) a,w-(3-aminophenoxy)terminated PSPS.
decides neither their thermal stability under an inert
atmosphere' nor their thermooxidative stability in air.'
The tendency to establish a temperature-dependent
equilibrium between linear polysiloxane chains and
low-molecular weight cyclic siloxanes probably plays an
important role. In spite of their relatively high dissociation energy (480 kJmol-') the Si-0 bonds are split
primarily via formation of low-molecular weight cyclic
components, preferred from the energetic point of
view.g
The equilibrium low-molecular weight cycles-linear
polymer can be shifted in favour of the latter as a consequence of incorporation of bulky groups into the polysiloxane chains. Thus, the authors" studying the
thermooxidative stability of poly[oxy(dimethylsilyl)-1,4phenylene(dimethylsilylene)] (PSPS) found the weight
loss to be 4*8wt% (lOh, 305°C) in comparison with
poly(dimethylsi1oxane) (22 wt%) under identical experimental conditions.
In this work the a,o-(3-aminophenoxy) terminated
PSPS (T-PSPS) (Fig. lc) were therefore synthesized and
characterized, and subsequently were utilized for the
synthesis of polyimide-polysiloxane block copolymers
(this designation is used in the text although the term
'polysiloxane' is not quite appropriate in this case). Preliminary tests of the thermooxidative stability of such
copolymers were also performed.
EXPERIMENTAL
5,5'-0xybis-1,3-isobenzofuranedione (4,4'-oxydiphthalic
anhydride, ODPA) (Chriskev) was heated overnight to
180°C in a vacuum before use. 1,4-Bis(4-amino-l,ldimethylbenzy1)benzene (Bisaniline P, BIS P) (Kennedy
and Klim) was used as received. 2-Aminopyridine (2AP) (Aldrich) was recrystallized from a mixture of
chloroform/petroleum ether. 3-Aminophenol (3-AP)
(Aldrich) was sublimed under vacuum. 1,4-Bis(hydroxydimethylsily1)benzene (BHDMSB) (Petrarch), 2-ethyl-
hexanoic acid, 1,1,3,3-tetramethylguanidine and zinc
acetate dihydrate (all Aldrich) were used as received.
N-Methyl-2-pyrrolidone (NMP), 1,2-dichlorobenzene
(DCB) and chlorobenzene (CB) (all Fisher) were distilled
under vacuum over phosphorus pentoxide and stored in
an inert atmosphere. Benzene (Fisher) was distilled
under atmospheric pressure over sodium.
Synthesis of a,w- (3-aminophenoxy) terminated
poly[oxy(dimethylsilyl)- 1,4-phenylene(dimethylsilylene)] oligomers with controlled
molecular weight
A typical example of the synthesis of this type of oligomer (with theoretical molecular weight A, =
3000gm01-~) is as follows: l o g (0.044 17mol)
BHDMSB, 0.71768 (0.006 57mol) 3-AP, 1 wt% of a
catalyst (prepared from 2-ethylhexanoic acid and 1,1,3,
3-tetramethylguanidine' ') and 36.8 ml benzene were
charged to a three-necked round-bottomed flask
equipped with a magnetic stirrer, a nitrogen inlet, a
thermometer and an azeotrope trap with condenser and
drying tube. The reaction mixture was heated for 5 h at
80°C and benzene was then distilled off. Heating was
prolonged for 4 h at 140°C and l h at 150°C under
vacuum. The solid product was dissolved in benzene,
precipitated into methanol and dried to constant weight
in a vacuum oven.
The oligomers were characterized by 'H NMR
analysis (Bruker 400) in &chloroform, and their molecular weight, A,, determined by conductometric titration
(Radelkis, Hungary); solvent+hloroform,
titrating
agent4.025 M hydrobromic acid in glacial acetic acid.
Intrinsic viscosities were measured in toluene at 25°C.
2-Aminopyridine terminated ODPA-BIS P polyimide oligomers were synthesized by a published procedure.12 All glassware for the synthesis of oligomers
was dried in the oven at 120°C for 4 h before use.
A typical example of the synthesis of this type of oligomer (with theoretical A, = 6000gmol-l) is as
follows: 7g (0.02256mol) ODPA was dissolved in
-
POLYMER INTERNATIONAL VOL. 40. NO. 4, 1996
277
Polyimide-polysiloxane block copolymers
59.8 ml NMP in a 250ml four-necked flask equipped
with a mechanical stirrer, a nitrogen inlet and a condenser with drying tube. 0.4269 g (0.004 54 mol) 2-AP
was added (weighing dish + funnel rinsed with 10ml of
NMP) and allowed to react with the ODPA for 2h.
6.9924 g (0.020 30 mol) Bis P was added to the reaction
mixture (10ml of NMP used for rinsing). The reaction
was allowed to proceed for 24 h at room temperature.
This apparatus with the solution of polyamic acid
was additionally equipped with an azeotrope trap (filled
with DCB) and a thermometer. After adding 14.5ml
DCB the reaction mixture was heated to 170°C (in an
oil bath) for 24 h. The solution was cooled to room temperature, diluted with NMP and precipitated into methanol. The collected polyimide was dried to constant
weight in a vacuum oven ( 200°C for 24 h).
Polyimide-polysiloxane block copolymers were prepared via a transimidization route.' A typical example
of the synthesis of this type of copolymer (with theoretical A, = 40000 gmol-l) is as follows: 7 g of the
2-AP terminated polyimide oligomer based on ODPABis P with A,, = 6000gmol-' was dissolved in
70ml CB at 120°C (in an oil bath) in a 250ml fournecked flask equipped with a mechanical stirrer, a nitrogen inlet, a condenser with drying tube and a
=
thermometer. 3.5103g of the T-PSPS with A,,
3400 g moland 100ppm zinc acetate dihydrate
(catalyst) were added (rinsed with 15-5ml CB). Then the
reaction was run for 3 h at 125°C. The solution was
cooled to room temperature, diluted with CB and precipitated into methanol. The collected copolymer was
dried to constant weight in a vacuum oven (- 150°C for
24 h).
Copolymers were characterized by 'H NMR analysis
in &chloroform. Their intrinsic viscosities were measured in chloroform at 25°C. Molecular weights were
determined by means of a Waters 150 C gel permeation
chromatograph (RI and viscometric (VISCOTEK 100)
detectors, a Styragel column set 500-lo3-lo4-lo5
mobile phase-tetrahydrofuran, 1ml min- ').The thermooxidative stability was evaluated by means of isothermal thermogravimetric analysis in air at 300°C on a
Perkin-Elmer TGA-7 instrument.
-
-
-
'
-
Fig. 2. Synthesis of cr,o-(3-aminophenoxy)terminated PSPS.
The molecular weight, A,, of T-PSPS was controlled
by the molar ratio of BHDMSB and 3-AP. The best
agreement between theoretical and obtained values of
R, was reached by using a three-step reaction procedure (5 h/SOOC, 4 h/140"C, 1h/150"C + vacuum). If a
vacuum was used already during the second step, markwere reached in comparison
edly higher values of A,,
with the theoretical values, probably because a considerable portion of unreacted 3-AP had sublimed off
from the reaction mixture.
The 'H NMR spectrum of T-PSPS is shown in Fig.
3. The signal at 0.3 ppm is assigned to the methyl group
protons, the signal at 3-5ppm to the amino group
protons and the signals at 7.4-7-7ppm to the aromatic
protons. Signals at 6.2 and 6.9ppm are due to the
protons of phenoxy groups. The values of A, (Table 1)
were obtained from the integral ratio of the protons of
the methyl groups to the protons of the amino endgroups. However, this method of A,,determination
becomes less accurate when oligomers with a higher
molecular weight are prepared owing to the unfavourable signal-to-noise ratios at 3.5 ppm. The molecular
weights obtained by conductometric titration are thus
regarded as closer to the real values. All data, including
the intrinsic viscosity values [ q ] , are summarized in
Table 1.
RESULTS AND DISCUSSION
Synthesis and characterization of a,w- (3-aminophenoxy) terminated poly[oxy(dimethylsilyl)- I ,4phen ylene (dimethylsilylene)] oligomers (T-PSPS)
The oligomers were synthesized by the catalysed polycondensation reaction of 1,4-bis(hydroxydimethylsilyl)
benzene (BHDMSB) in the presence of 3-aminophenol
(3-AP) (Fig. 2). The catalyst used (1 wt%) was an adduct
of 1,1,3,3-tetramethylguanidine and 2-ethylhexanoic
acid.'
POLYMER INTERNATIONAL VOL. 40. NO. 4, 1996
I--l
8.
Fig. 3. 'H NMR spectrum of a,w-(3-aminophenoxy)terminated
PSPS.
278
P. Sysel, D. Oupickj
TABLE 1. Characterization of a,o-(3-aminophenoxy) terminated
PSPS
Sample
3.4K T-PSPS
6'6K T-PSPS
7.2K T-PSPS
-
-
M n , theor.
M n , CTd
M n , NMR
(g mol-')
(g mol-l)
(g mol-')
3000
6000
7000
3400
6600
7200
3600
7000
-
Crll
(rnl g-')
12
16
19
By conductometric titration.
The polyimide-polysiloxane block copolymers were
prepared via a transimidization reaction (Fig. 4). In the
presence of the catalyst (about 100ppm zinc acetate
dihydrate') the reaction rate was markedly higher in
comparison with the non-catalysed reaction. All copolymers were synthesized with the target value of M,,=
40OOO g mol- by offsetting the stoichiometry and using
the polyimide oligomer in excess.
The 'H NMR spectrum of this type of copolymer is
shown in Fig. 5. The integral ratio of the signal at
1.7 ppm (protons of the methyl groups of the polyimide
moiety) to the signal at 0.4ppm (protons of the methyl
'
groups of the polysiloxane moiety) reflects the final
composition (Table 2). Results of the viscometric and
GPC analyses are also given in Table 2. The molecular
weights obtained are in very good agreement with the
target values. The data of both 'H NMR and GPC
analysis confirm that copolymers close to the chosen
composition and molecular weight were prepared.
The uniform theoretical values of the molecular
weight of copolymers, it?,, = 40OOO g mol- ', enable us
to make reasonable conclusions regarding their relative
thermooxidative stability. In this connection it is important that it was possible to compare their thermooxida-
Fig. 4. Synthesis of polyimide-polysiloxane block copolymers via a transimidizationroute.
TABLE 2. Characterization
Sample
6KP1-3'4KPSPS3
8KPI-7'2KPSPS
4'7KPI3'4KPSPS
4.7KPI-6.6KPSPS
3KPI-7.2KPSPS
40KPI CONTROL
of
polyimide-polysiloxane
copolymers
pspsthaor.
pspsexp.8
Mnb
(wt%)
(wt%)
(g mol-l)
31
39
42
52
72
31
37
41
49
68
-
-
-
36 000
-
3 4 000
35 000
40 000
block
Crll
(rnl g-l)
46
48
53
49
46
53
eFrom ' H NMR.
By GPC.
Copolymer based on PI oligorner with M n= 60009 mol-' and T-PSPS oligorner with M, = 3400g rnol-'.
POLYMER INTERNATIONAL VOL. 40. NO. 4, 1996
279
Polyimide-polysiloxane block copolymers
I
L
F
(-Si-0-Si-)).
It is apparent that the copolymer
based on T-PSPS is more stable against thermooxidative attack than the other copolymers tested, and its stability is close to that of the polyimide control
(homopolymer with theoretical fin= 40000gmol- I).
These results support the former conclusion^^^^ that the
type of endgroup in the polysiloxane oligomers
employed does not play a key role in the stability of
polyimide-polysiloxane copolymers.
A more detailed study of thermooxidative stability of
these copolymers will be presented in future work. We
would also like to use copolymers of this type to test
their membrane properties.
Fig. 5. 'H NMR spectrum of polyimide (ODPA-BIS P)polysiloxane (PSPS) block copolymer.
ACKNOWLEDGEMENTS
tive stability with polyimide-polysiloxane copolymers
based on a,w-aminopropyllZ and a,w-arylamine terminated poly(dimethylsi1oxane) oligomers.' Figure 6 shows
the results of isothermal thermogravimetric analyses of
copolymers with the same type of polyimide moiety
(ODPA-BIS P), differing in the composition of the
incorporated polysiloxane moiety (but containing an
identical amount (22-23 wt%) of 'pure' siloxane portion
-r ' -
REFERENCES
-100
d.
UI
0
.-I
98
U
m
-
.
.
I
f
96
-
0
This work was started during Petr Sysel's stay at the
Department of Chemistry and the NSF Center for High
Performance Polymeric Adhesives and Composites of
the Virginia Polytechnic Institute and State University,
Blacksburg. The William and Mary Greve Foundation,
Inc., New York, fellowship to Petr Sysel is acknowledged.
500
1000
1500
t i m e (minutes)
Fig. 6. Thermograms of (A) polyimide control, and
polyimide-polysiloxane copolymers with siloxane moiety
based on (B) apaminopropyl terminated poly(dimethy1si1oxane)s (kindly provided by M. E. Rogers"); (C) a p a r y l amine terminated poly(dimethylsiloxane)s;s (D) a,w-(3aminophenoxy)terminated PSPS in air, 300°C.
POLYMER INTERNATIONAL VOL. 40. NO. 4, 1996
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