- Email: [email protected]
Investigation on poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)]
Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 738–742 www.elsevier.com/locate/cclet
Investigation on poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] Fei Gao, Ling Ling Zhang, Fa Rong Huang *, Lei Du Key Laboratory for Specially Functional Polymeric Materials and Related Technology of the Ministry of Education, East China University of Science and Technology, Shanghai 200237, China Received 31 August 2009
Abstract Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagent with 1,3-dichlorotetramethyldisiloxane and dichloromethylsilane. The copolymer was characterized by FT-IR, 1H NMR, differential scanning calorimetry and thermogravimetric analysis. The results show that the copolymer exhibits good processability and cures at low temperatures. The cured copolymer shows high thermal stability. # 2009 Fa Rong Huang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Silicon-containing arylacetylene resin; Siloxane; m-Diethynylbenzene; Methylsilylene
There is current interest in polycarbosilanes containing acetylene groups in the main chain duo to their unique properties of excellent heat resistance, good electronic properties, low water absorption, and high char yields [1–2]. Research in our group has focused on the design and synthesis of various novel polymers that contain arylacetylene units and inorganic moieties in the main chain [3–4]. Recently, several investigations have been conducted on polymers containing siloxane, silarylene and acetylene units [5–7]. However, the arylacetylene polymer containing siloxane units and methylsilylene units in the main chain has not been previously reported. In this study, poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagent with 1,3-dichlorotetramethyldisiloxane and dichloromethylsilane and its properties were examined. 1. Experimental Unless otherwise noted, all syntheses were performed under an atmosphere of dry nitrogen. Tetrahydrofuran (THF) was refluxed over sodium with benzophenone and freshly distilled in nitrogen before use. 1,3-Dichlorotetramethyldisiloxane * Corresponding author. E-mail address: [email protected] (F.R. Huang). 1001-8417/$ – see front matter # 2009 Fa Rong Huang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2009.12.013
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
739
(DCTMDS)[8] was prepared following published procedures. m-Diethynylbenzene was supplied by Fine Chemical Institute of East China University of Science and Technology and used as received. 1 H NMR analysis was performed on a BRUKER AVANCE 500 (500 Mz) instrument. Fourier transform infrared (FT-IR) spectrum was obtained using a Nicolet 550 spectrometer. The molecular weight was determined by gel permeation chromatography (GPC) using a Waters GPC system. DSC was performed on a NETZSCH 200 PC module. TGA was performed on a TA Instruments SDT Q600 analyzer. Unless otherwise noted, all reactions were performed under an atmosphere of dry nitrogen. The mdiethynylbenzene magnesium reagent [3] (0.053 mol) was prepared following published procedures. The reaction flask was then cooled with an ice/water bath and a solution of DCMS (3.14 g, 0.036 mol) in THF (20 mL) was added dropwise to the m-diethynylbenzene magnesium reagent (0.053 mol) over 30 min. After complete addition, the ice/ water bath was removed and the reaction mixture was heated to 45 8C with an oil bath with stirring over 1 h. The flask was then cooled with an ice/water bath and a solution of DCTMDS (1.55 g, 0.012 mol) in THF (20 mL) was added dropwise over 30 min. After complete addition, the ice/water bath was removed and the reaction mixture was heated to 75 8C with an oil bath with stirring over 2 h. The flask was then cooled with an ice/water bath and a solution of acetic acid in toluene (50 mL) was added dropwise over 30 min, and then a 2% aqueous solution of hydrochloric acid (50 mL) was added dropwise over 30 min. The resulting oil phase was separated by using a separator funnel and washed with deionized water until neutral. Then toluene was distilled off and an orange product (8.67 g) was obtained with 89% yield. The synthesis route is shown in Scheme 1. Prior to cure, the copolymer was degassed at 100 8C/15 mm Hg. The copolymer was thermally cured according to the procedure: 150 8C for 2 h, 170 8C for 2 h, 210 8C for 2 h, 250 8C for 2 h, and 300 8C for 2 h. After that, the cured sample was allowed to cool slowly to room temperature. Shiny and void-free dark cured copolymer was obtained. 2. Result and discussion Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was prepared by Grignard method.[3] In a flask, dichloromethylsilane was allowed to react with the dimagnesium dibromide (BrMg–CC–Ph–CC–MgBr) to produce an intermediate {BrMg–[CC–Ph–CC– SiH(CH3)]x–CC–Ph–CC–MgBr}, and then the intermediate condensed with dichlorotetramethyldisiloxane to form a copolymer, poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] with –[SiH(CH3)–CC–Ph–CC]– unit and –[Si(CH3)2–O–Si(CH3)2–CC–Ph–CC]– unit. The copolymer was analyzed by 1H NMR, GPC, and FT-IR. The number molecular weight of the copolymer is 1731 (PDI: 1.53). FT-IR spectrum of the copolymer is shown in Fig. 1. It reveals a strong absorption at 2157 cm 1 which is attributed to –CC– and Si–H bonds. A strong and sharp absorption at 1256 cm 1 is for Si–CH3 and at 2962 cm 1 for –CH3 stretching mode. A sharp absorption at 3290 cm 1 belongs to C–H stretching vibration and the weak adsorption at 3065 cm 1 is due to the aromatic C–H stretching. A strong and broad absorption at 1050 cm 1 is due to the Si–O–Si stretching.
Scheme 1. Synthesis of the copolymer.
740
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
Fig. 1. FT-IR spectrum of the copolymer. 1
H NMR (CDCl3, ppm) spectrum of the copolymer is shown in Fig. 2. The dimethylsiloxy protons resonate at 0.40 ppm. The silicon methyl protons resonate at 0.55 ppm while the protons bonded to silicon resonate at 4.62 ppm. In addition, the aromatic protons resonate at 7.20–7.80 ppm and the protons of the terminal ethynyl groups resonate at 3.10 ppm. DSC curve of the copolymer measured under nitrogen is shown in Fig. 3. The copolymer shows a well-defined broad cure exotherm. The exotherm begins about 217 8C with a maximum at 233 8C. The amount of exthotherm is 282.9 J/g. The exotherm is attributed to the cross-linking reactions: (1) the Diels–Alder reaction between Ph–CC and CC and (2) the hydrosilylation reaction between the Si–H and CC proceed at 150–200 8C [9]. Small broad exotherm around 350 8C is also observed and is attributed to reaction of internal ethynyl groups [2]. Thermal stability of the cured copolymer is determined by TGA analyses in nitrogen at the heating rate of 10 8C/ min. As shown in Fig. 4, the decomposition temperature at 5% weight loss (Td5) of the cured copolymer is 670 8C. The decomposition residue at 1000 8C of the cured copolymer is 90.5%. It indicates that thermal Stability increases through incorporating methylsilylene unit into the polymer backbone.
Fig. 2. 1H NMR spectrum of the copolymer.
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
741
Fig. 3. DSC curve of the copolymer.
Fig. 4. TGA curve of the cured copolymer.
3. Conclusions Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagents with 1,3dichloroteramethyldisiloxane and dichloromethylsilane, and its structure was determined by FT-IR, 1H NMR, GPC, etc. The copolymer is soluble in common organic solvents. At elevated temperatures, the copolymer can be thermally transformed into highly crosslinked structure (cured copolymer). The cured copolymer shows high thermal stability with Td5 at 670 8C under nitrogen. Acknowledgments We gratefully acknowledged the financial support of the National High Technology Research and Development Program of China (No. 2002305205) and the National Basic Research Program of China (No. 51320006).
742
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
M. Itoh, K. Inoue, K. Iwata, Macromolecules 30 (1997) 694. S. Kuroki, K. Okita, T. Kakigano, Macromolecules 30 (1998) 2804. F. Wang, J. Zhang, J.X. Huang, Polym. Bull. 56 (2006) 19. Q. Li, Y. Zhou, X.D. Hang, Eur. Polym. J. 44 (2008) 2538. C.L. Homrighausen, T.M. Keller, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 88. C.L. Homrighausen, T.M. Keller, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 1334. C.L. Homrighausen, T.M. Keller, Polymer 43 (2002) 2619. M. Ishikawa, E. Toyoda, M. Ishii, Organometallics 13 (1994) 808. S. Kuroki, K. Okita, T. Kakigano, et al. Macromolecules 30 (1998) 2804.
Chinese Chemical Letters 21 (2010) 738–742 www.elsevier.com/locate/cclet
Investigation on poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] Fei Gao, Ling Ling Zhang, Fa Rong Huang *, Lei Du Key Laboratory for Specially Functional Polymeric Materials and Related Technology of the Ministry of Education, East China University of Science and Technology, Shanghai 200237, China Received 31 August 2009
Abstract Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagent with 1,3-dichlorotetramethyldisiloxane and dichloromethylsilane. The copolymer was characterized by FT-IR, 1H NMR, differential scanning calorimetry and thermogravimetric analysis. The results show that the copolymer exhibits good processability and cures at low temperatures. The cured copolymer shows high thermal stability. # 2009 Fa Rong Huang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Silicon-containing arylacetylene resin; Siloxane; m-Diethynylbenzene; Methylsilylene
There is current interest in polycarbosilanes containing acetylene groups in the main chain duo to their unique properties of excellent heat resistance, good electronic properties, low water absorption, and high char yields [1–2]. Research in our group has focused on the design and synthesis of various novel polymers that contain arylacetylene units and inorganic moieties in the main chain [3–4]. Recently, several investigations have been conducted on polymers containing siloxane, silarylene and acetylene units [5–7]. However, the arylacetylene polymer containing siloxane units and methylsilylene units in the main chain has not been previously reported. In this study, poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagent with 1,3-dichlorotetramethyldisiloxane and dichloromethylsilane and its properties were examined. 1. Experimental Unless otherwise noted, all syntheses were performed under an atmosphere of dry nitrogen. Tetrahydrofuran (THF) was refluxed over sodium with benzophenone and freshly distilled in nitrogen before use. 1,3-Dichlorotetramethyldisiloxane * Corresponding author. E-mail address: [email protected] (F.R. Huang). 1001-8417/$ – see front matter # 2009 Fa Rong Huang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2009.12.013
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
739
(DCTMDS)[8] was prepared following published procedures. m-Diethynylbenzene was supplied by Fine Chemical Institute of East China University of Science and Technology and used as received. 1 H NMR analysis was performed on a BRUKER AVANCE 500 (500 Mz) instrument. Fourier transform infrared (FT-IR) spectrum was obtained using a Nicolet 550 spectrometer. The molecular weight was determined by gel permeation chromatography (GPC) using a Waters GPC system. DSC was performed on a NETZSCH 200 PC module. TGA was performed on a TA Instruments SDT Q600 analyzer. Unless otherwise noted, all reactions were performed under an atmosphere of dry nitrogen. The mdiethynylbenzene magnesium reagent [3] (0.053 mol) was prepared following published procedures. The reaction flask was then cooled with an ice/water bath and a solution of DCMS (3.14 g, 0.036 mol) in THF (20 mL) was added dropwise to the m-diethynylbenzene magnesium reagent (0.053 mol) over 30 min. After complete addition, the ice/ water bath was removed and the reaction mixture was heated to 45 8C with an oil bath with stirring over 1 h. The flask was then cooled with an ice/water bath and a solution of DCTMDS (1.55 g, 0.012 mol) in THF (20 mL) was added dropwise over 30 min. After complete addition, the ice/water bath was removed and the reaction mixture was heated to 75 8C with an oil bath with stirring over 2 h. The flask was then cooled with an ice/water bath and a solution of acetic acid in toluene (50 mL) was added dropwise over 30 min, and then a 2% aqueous solution of hydrochloric acid (50 mL) was added dropwise over 30 min. The resulting oil phase was separated by using a separator funnel and washed with deionized water until neutral. Then toluene was distilled off and an orange product (8.67 g) was obtained with 89% yield. The synthesis route is shown in Scheme 1. Prior to cure, the copolymer was degassed at 100 8C/15 mm Hg. The copolymer was thermally cured according to the procedure: 150 8C for 2 h, 170 8C for 2 h, 210 8C for 2 h, 250 8C for 2 h, and 300 8C for 2 h. After that, the cured sample was allowed to cool slowly to room temperature. Shiny and void-free dark cured copolymer was obtained. 2. Result and discussion Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was prepared by Grignard method.[3] In a flask, dichloromethylsilane was allowed to react with the dimagnesium dibromide (BrMg–CC–Ph–CC–MgBr) to produce an intermediate {BrMg–[CC–Ph–CC– SiH(CH3)]x–CC–Ph–CC–MgBr}, and then the intermediate condensed with dichlorotetramethyldisiloxane to form a copolymer, poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] with –[SiH(CH3)–CC–Ph–CC]– unit and –[Si(CH3)2–O–Si(CH3)2–CC–Ph–CC]– unit. The copolymer was analyzed by 1H NMR, GPC, and FT-IR. The number molecular weight of the copolymer is 1731 (PDI: 1.53). FT-IR spectrum of the copolymer is shown in Fig. 1. It reveals a strong absorption at 2157 cm 1 which is attributed to –CC– and Si–H bonds. A strong and sharp absorption at 1256 cm 1 is for Si–CH3 and at 2962 cm 1 for –CH3 stretching mode. A sharp absorption at 3290 cm 1 belongs to C–H stretching vibration and the weak adsorption at 3065 cm 1 is due to the aromatic C–H stretching. A strong and broad absorption at 1050 cm 1 is due to the Si–O–Si stretching.
Scheme 1. Synthesis of the copolymer.
740
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
Fig. 1. FT-IR spectrum of the copolymer. 1
H NMR (CDCl3, ppm) spectrum of the copolymer is shown in Fig. 2. The dimethylsiloxy protons resonate at 0.40 ppm. The silicon methyl protons resonate at 0.55 ppm while the protons bonded to silicon resonate at 4.62 ppm. In addition, the aromatic protons resonate at 7.20–7.80 ppm and the protons of the terminal ethynyl groups resonate at 3.10 ppm. DSC curve of the copolymer measured under nitrogen is shown in Fig. 3. The copolymer shows a well-defined broad cure exotherm. The exotherm begins about 217 8C with a maximum at 233 8C. The amount of exthotherm is 282.9 J/g. The exotherm is attributed to the cross-linking reactions: (1) the Diels–Alder reaction between Ph–CC and CC and (2) the hydrosilylation reaction between the Si–H and CC proceed at 150–200 8C [9]. Small broad exotherm around 350 8C is also observed and is attributed to reaction of internal ethynyl groups [2]. Thermal stability of the cured copolymer is determined by TGA analyses in nitrogen at the heating rate of 10 8C/ min. As shown in Fig. 4, the decomposition temperature at 5% weight loss (Td5) of the cured copolymer is 670 8C. The decomposition residue at 1000 8C of the cured copolymer is 90.5%. It indicates that thermal Stability increases through incorporating methylsilylene unit into the polymer backbone.
Fig. 2. 1H NMR spectrum of the copolymer.
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
741
Fig. 3. DSC curve of the copolymer.
Fig. 4. TGA curve of the cured copolymer.
3. Conclusions Poly[(methylsilylene ethynylene phenylene ethynylene)-co-(tetramethyldisiloxane ethynylene phenylene ethynylene)] was synthesized by polycondensation reaction of m-diethynylbenzene magnesium reagents with 1,3dichloroteramethyldisiloxane and dichloromethylsilane, and its structure was determined by FT-IR, 1H NMR, GPC, etc. The copolymer is soluble in common organic solvents. At elevated temperatures, the copolymer can be thermally transformed into highly crosslinked structure (cured copolymer). The cured copolymer shows high thermal stability with Td5 at 670 8C under nitrogen. Acknowledgments We gratefully acknowledged the financial support of the National High Technology Research and Development Program of China (No. 2002305205) and the National Basic Research Program of China (No. 51320006).
742
F. Gao et al. / Chinese Chemical Letters 21 (2010) 738–742
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
M. Itoh, K. Inoue, K. Iwata, Macromolecules 30 (1997) 694. S. Kuroki, K. Okita, T. Kakigano, Macromolecules 30 (1998) 2804. F. Wang, J. Zhang, J.X. Huang, Polym. Bull. 56 (2006) 19. Q. Li, Y. Zhou, X.D. Hang, Eur. Polym. J. 44 (2008) 2538. C.L. Homrighausen, T.M. Keller, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 88. C.L. Homrighausen, T.M. Keller, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 1334. C.L. Homrighausen, T.M. Keller, Polymer 43 (2002) 2619. M. Ishikawa, E. Toyoda, M. Ishii, Organometallics 13 (1994) 808. S. Kuroki, K. Okita, T. Kakigano, et al. Macromolecules 30 (1998) 2804.