Surface Segregation-typed Polyimide Blends between Silicon-containing Polyimide and Polyimides of Varied Chain Flexibility Sunan Tiptipakorn, 1 Parkpoom Lorjai, 1 Shinji Ando, 2 and Sarawut Rimdusit 1 1 Faculty of Engineering, Department of Chemical Engineering, Chulalongkorn University, Bangkok, Thailand 2 Department of Chemistry and Material Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan Surface segregation behaviors of blending systems between polysiloxane-block-polyimide (SPI) and three polyimides with different chain flexibility (PMDA/ODA, s-BPDA/ODA, and ODPA/ODA) have been investigated. All film samples with 50 mm thickness were characterized by surface profilometer, atte- nuated total reflection infrared (ATR-IR), and ATR microscope. In this study, the films with various PSI contents were processed on a glass substrate. At low concentration of PSI (less than 10 phr), three types of the polyimides trended to migrate to the glass-side surface, while PSI component trended to migrate to the air-side surface. For high concentration of PSI (i.e., 10 phr and 30 phr), the glass-side surface was covered with the poly- imides, whereas the air-side surface showed two different colors. ATR microscope revealed PMDA/ODA blending system exhib- ited the highest segregation level. Keywords blends, phase-segregation, polyimide, silicon-containing polyimide INTRODUCTION Since the first commercialization of polyimides in the late 1960s by Du Pont, the advancement in the science and technology of the polymers, particularly in the field of aromatic polyimides, has led to a wide range of their utilization among in which the most relevant are in the microelectronic industries (as optical components or dielectric and passivation layers), [1 – 3] in the membrane industries, [4] as well as in the space application field. [5 – 11] Nowadays, s-BPDA/ODA (Upilex-R trademark from Ube Industries), and PMDA/ODA (Kapton trademark from DuPont), and ODPA/ODA are widely used in many applications such as microelectronic, and filtration fields. These three kinds of polyimide has been a dramatic increase in demand of polyimides. Therefore, PMDA/ODA, s-BPDA/ODA, and ODPA/ODA were chosen as a major component of polyimide blends in this study. Si-containing polymers such as poly(dimethyl siloxane), copolymer of poly(dimethyl siloxane) and polyimide, or poly- silsesquioxane have been reported to possess high UV stability, enhanced solubility, high impact resistance, modified surface properties, etc. [12 – 15] It has been well known that polyimide and Si-containing block copolyimide polymers are immiscible. Rimdusit et al. [16] studied the segregation behavior of the blends between s-BPDA/ODA and silicon-containing block copolyimide, and reported that the behavior of the blend confirms the surface segregation of gradient structure. As mentioned before, three types of polyimide, i.e., PMDA/ ODA, s-BPDA/ODA, and ODPA/ODA, have been used in this study because of their different chain structures. PMDA/ ODA includes only one benzene ring in each repeating unit; the structure of s-BPDA/ODA includes two benzene rings, and that of ODPA/ODA include ether group linked between two benzene rings. The conformation of ODPA/ODA is the most, while that of PMDA/ODA is the least. The differences of internal structures of these polyimides in the blends possibly lead to interesting different behavior of segregation. Due to the differences of the chain flexibilities among three polyimides (major component), the segregation degrees of the blends are expected to be different. The authors would like to acknowledge the Thailand Research Fund (TRF) and the Commission on Higher Education for the financial support through the Research Grant for Mid-Career University Faculty of fiscal year 2005 – 2007. The present research also receives partial financial support from the Foundation for the International Exchange of the Faculty of Engineering, Tokyo Institute of Technol- ogy. In addition, CU Graduate Thesis Grant of Chulalongkorn Univer- sity is also acknowledged. Additionally, the authors would like to thank Mettler-Toledo (Thailand) Co., Ltd. for the use of Thermogravi- metric Analysis. Received 8 June 2007; accepted 18 October 2007. Address correspondence to Sarawut Rimdusit, Faculty of Engin- eering, Department of Chemical Engineering, Chulalongkorn Univer- sity, Bangkok 10330, Thailand. E-mail: sarawut.r@chula.ac.th Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:248–255, 2008 Copyright # 2008 Taylor & Francis Group, LLC ISSN: 1553-3174 print /1553-3182 online DOI: 10.1080/15533170802023387 LSRT302506 LSRT_038_003 Techset Composition Ltd, Salisbury, U.K. 4/30/2008 248