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. 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