ladder like polysiloxane hybrid films

Materials Letters 64 (2010) 2710–2713

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Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t

Preparation and characterization of polyimide/ladder like polysiloxane hybrid films Yuzhong Feng, Shengli Qi, Zhanpeng Wu, Xiaodong Wang, Xiaoping Yang, Dezhen Wu ⁎ State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, 100029, Beijing, China

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Article history: Received 4 May 2010 Accepted 26 August 2010 Available online 31 August 2010 Keywords: Polyimide Ladder like Polyphenylsilsesquioxane Thermal properties Mechanical properties

a b s t r a c t Novel polyimide (PI)/ladder like polyphenylsilsesquioxane (PPSQ) hybrid films was prepared. PI was made from poly(amide acid) of 4, 4′’-diaminodiphenylether and pyromellitic dianhydride. PPSQ was prepared from phenyltrimethoxysilane through sol–gel process. The chemical structure of PPSQ was characterized by Fourier transform infrared and nuclear magnetic resonance. The coefficients of thermal expansion for the hybrid films decrease with the increasing content of PPSQ. The thermal and mechanical properties of the hybrid films were essentially similar to the neat PI. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.

1. Introduction Organic–inorganic nanocomposites with well defined architectures have attracted a great deal of attention as they not only have synergistic properties, but can also be tailored to specific technical applications [1,2]. One class of inorganic component-polyphenylsilsesquioxane (PPSQ), which is a special type of double-stranded polymer possess much higher resistance to chemical, thermal and biological degradation, relative to the common single chain polymers. Because of their capacity for attaching different functional groups and high solubility in many organic solvents, PPSQ molecules can form covalent bonds with themselves or organic monomers [3–5]. PPSQ molecules are typically stable up to 450 °C, higher than the thermal degradation temperatures of most polymers. Their incorporation into some polymers has led to enhancements in thermal stability and mechanical properties. For instance, PPSQ molecules have been successfully incorporated into polyethylene [6]. Polyimide (PI) is widely used in microelectronic industries because of their outstanding characteristics, such as excellent tensile strength and modulus, good thermal stability and dielectric property, and good resistance to organic solvents [7–12]. With the miniaturization of integrated circuit, applications such as circuit-printing films and semiconductor coatings however require the PI to possess lower coefficient of thermal expansion, higher glass transition temperature and better thermal mechanical strength to avoid debonding between PI and inorganic substrate [13]. Incorporation of inorganic materials such as clay and silica nanoparticles has been proved very effective in providing enhancements in thermal and mechanical properties [14–

⁎ Corresponding author. Tel./fax: + 86 10 64421693. E-mail address: [email protected] (D. Wu).

17]. Nevertheless, there is little research focusing on the coefficient of thermal expansion properties. In this study, we intend to prepare PI/PPSQ hybrid films with low coefficient of thermal expansion by γ-aminopropyl triethoxysilane (APTS) to provide bonding between the PPSQ and polyimide through a sol–gel process. The thermal, mechanical properties of hybrid films were also studied in detail. 2. Experimental section 2.1. Materials All of the reagents and solvents were commercially available and analytical grade. Toluene, hydrogen chloride and dimethylacetamide (DMAc) (analytical pure,) were provided by Tianjin Fu Chen Chemicals Reagent Company and used without further purification. Potassium hydroxide and methanol were bought from Beijing Chemical Factory and used as received. Phenyltrimethoxysilane (PTM) and γ-aminopropyl triethoxysilane (APTS) were purchased from Alfa Aesar and used as received. Pyromellitic dianhydride (PMDA) and 4, 4′-diaminodiphenylether(ODA) were obtained from Shanghai Research Institute of Synthetic Resins. 2.2. Charecterization FTIR was performed on a Nicolet Nexus 670 FTIR spectrometer using potassium bromide as a nonabsorbent medium. 1H nuclear magnetic resonance (NMR), 13C-NMR and 29Si-NMR measurements were carried out on AV 600 with deuterated chloroform (CDCl3) as solvent. Chemical shifts were reported in ppm. The surface morphology was observed on a Hitachi S-4700 field emission scanning electron microscope (SEM) after samples coated with a ca. 5 nm

0167-577X/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.08.067

Y. Feng et al. / Materials Letters 64 (2010) 2710–2713

platinum layer prior to measurement. Cross-sectional transmission electron micrograph (TEM) was taken with a Hitachi H-800 transmission electron microscope. Thermal gravimetric analysis was performed with a Netzsch TG 209 system heating at 10 k min− 1. Mechanical properties were evaluated using an instron-1185 system. The coefficient of thermal expansion (CTE) values on the temperature scale was between 50 and 250 °C. The thickness of film for all tests performed was about 30 μm. 2.3. Preparation of PPSQ A solution of 10 ml of phenyltrimethoxysilane dissolved in 50 ml toluene was slowly stirred in an ice bath for about 30 min, followed by dropping 15 ml ultra-pure water containing 0.151 ml hydrogen chloride into the solution. After being stirred for further 24 h at 0– 10 °C, the reaction mixture was separated into an organic solvent phase and an aqueous phase. The lower aqueous layer was removed by a separating funnel and the organic layer was collected. The collected organic solution was washed with ultra-pure water three times or more until the impurities such as chloride and hydrogen ions were completely removed. Finally, the phenyltrihydrolysiloxane was obtained. The phenyltrihydrolysiloxane was transferred into a flask, and then 3 ml of nucleophilic reagent (Potassium hydroxide concentration: 1 g/l methanol) was added. The mixture was stirred at 20 °C for 3 h followed by heating at 80 °C for 9 h to get the final products. The released water was removed by azeotropic distillation under reduced pressure. The final reaction solution was purified by ultra-

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pure water three times or more until the impurities such as potassium and hydroxyl ions were removed completely. After that the solution was concentrated to about 15 ml and then precipitated with 60 ml of methanol. The white precipitate was gained by filtration, washed with methanol, and dried under a vacuum to collect a white powder of polyphenylsilsesquioxane with a yield of 60%. FTIR (KBr): 3622 cm− 1 (―Si―OH), 3050, 1589, and 1433 cm− 1 (―C6H5), 1133 cm− 1 (―Si―O―Si―), 736, and 692 cm− 1 (Si―C6H5). 1H-NMR (270 MHz, CDCl3, δ): 7.00–8.00 ppm (br, ―C6H5), 2.40 ppm (br, ―Si―OH). 13C-NMR (125 MHz, CDCl3, δ): 125 ~ 135 ppm (―C6H5). 29Si-NMR (99 MHz, CDCl3, δ): −79 ppm (―Si―C6H5), − 69 ppm (―Si―OH). 2.4. Preparation of PI/PPSQ hybrid films The PI/PPSQ hybrid films were prepared by a two-step polymerization process depicted in Fig. 1. PMDA powders were added into a DMAc solution of ODA and LPPSQ under a nitrogen atmosphere, and then the mixtures were stirred for 2 h. And then 0.44 ml APTS were added into the system. After 2 h, 0.132 ml hydrochloric acid (PH = 3) were added into the system. The resulting solution was stirred at room temperature for 6 h to yield homogeneous yellowish poly (amic acid) (PAA) containing PPSQ solution. The solid concentration of poly (amic acid) was kept at about 10 wt.%. The PAA containing PPSQ solution was then cast onto glass plates and then thermally imidized by over 1 h to135°C and holding 1 h, heating to 200 °C over 2 h and remaining constant at 300 °C so as to produce strong, flexible, and dense hybrid films with about 30 μm thickness. The chemical

Fig. 1. Schematic representation of the preparation of PMDA/ODA PI/PPSQ hybrid film.

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Y. Feng et al. / Materials Letters 64 (2010) 2710–2713

Table 1 Sample designation and composition of the PMDA/ODA PI/PPSQ hybrid films. Sample code

PMDA (g)

ODA (g)

PPSQ (g)

DMAc (ml)

APTS (ml)

PI a b c d

2.2 2.2 2.2 2.2 2.2

2.0 2.0 2.0 2.0 2.0

0 0.108 0.221 0.467 0.741

40 40 40 40 40

0 0.44 0.44 0.44 0.44

compositions of the PI/PPSQ hybrid films prepared in this paper were listed in Table 1. 3. Results and discussion The SEM and TEM images for the hybrid films with PPSQ content of 15 wt.% are shown in Fig. 2. The SEM micrograph in Fig. 2 (a) shows that the PPSQ particles with an average diameter size of 50–100 nm are well dispersed in the film surface. The TEM micrograph in Fig. 2 (b) reveals that the PPSQ particles with an average diameter size of 1 μm are uniformly dispersed in the polyimide substrate. Both SEM and TEM micrograph reveal the same morphology of uniform distribution of PPSQ domains in the continuous PI phase. The main

(a)

Fig. 3. The coefficients of the thermal expansion of the PI/PPSQ hybrid films.

reason may be due to the PI blocks chemically bonding with the APTS, which can bond with PPSQ to form PPSQ domains. The CTEs of the PI/PPSQ hybrid films are shown in Fig. 3. The CTEs for the PI/PPSQ hybrid films decrease with the increasing content of PPSQ. The CTEs of the pure PI and the PI/PPSQ hybrid films with 5 wt.% PPSQ are 58.6 × 10− 6 K− 1 and 43.7 × 10− 6 K− 1, respectively. When the content of the LPPSQ increases to 15%, the CTE of the hybrid film decreases to 36.1 × 10− 6 K− 1, which is less than 62% of the CTE of pure PI. The decrease in CTE could be attributed to the increase in crosslinking density and the low CTE of rigid PPSQ. It is also observed that the reduction of CTE is significant at the lower content of LPPSQ. With an increase of PPSQ content, the CTE decreases slowly and then level off. Fig. 4 shows the thermal properties of the pure PI and the PI/PPSQ hybrid films. The decomposition temperatures determined by 5% mass loss temperature (T5). From Fig. 3, we can see that the T5 of the pure PI was 575 °C, meanwhile the T5 of the hybrid film with 15% PPSQ was 556 °C. Because the PPSQ and the phenyl groups with good thermal stability and the stable covalent bonds between two components limit the continuous decomposition of the PI phase. The hybrid films exhibit good thermal stability and their T5's are all above 550 °C. The tensile strength, the modulus and the elongation at break of the neat PI and PI/PPSQ hybrid films are listed in Table 2. The results show that the tensile strength and elongation of the hybrid PI at break

(b)

Fig. 2. (a) SEM and (b) TEM images for the hybrid films with PPSQ content of 15 wt.%.

Fig. 4. TG curve of the pure PI and different content PPSQ in the hybrid films: (a) 2.5 wt.%; (b) 5 wt.%; (c) 10 wt.%; (d) 15 wt.%.

Y. Feng et al. / Materials Letters 64 (2010) 2710–2713 Table 2 The mechanical properties of pure PI and PI/PPSQ hybrid films (The weight ratios of PPSQ and PAA in sample a, b, c, and d are 2.5%, 5%, 10%, and 15%, respectively). Sample code

Strength (MPa)

Modulus (MPa)

Elongation at Break (%)

PI a b c d

110 105.4 110.0 108.4 112.4

1076 1035 1156 1403 1332

44.3 44.2 43.1 32.0 40.4

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Acknowledgment The research was supported by the National High Technology Research and Development of China (863 Program, Project No. 2007AA03Z537), and the National Natural Science Foundation of China (NSFC, Project 51073230) and Innovative Research Team in the University (PCSIRT, IRT0706). References

change slightly, but their tensile modulus increases with increasing of PPSQ content because of the incorporation of rigid PPSQ. 4. Conclusion PI/PPSQ hybrid films were successfully prepared by a two-step polymerization process. The resulting PI/PPSQ hybrid films exhibit low CTE, which can reach to 36.1 × 10–6 K− 1 and is less than 62% of pure PI, when the content of the PPSQ increases to 15%. Meanwhile, compared with the neat PI films, the composite films possess nearly the same excellent thermal properties and mechanical properties and may be accepted as integrated circuit materials.

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