Synthesis and Characterization of UV-Curable Ladder-Like Polysilsesquioxane Seung–Sock Choi, 1,2 Albert S. Lee, 1 He Seung Lee, 1 Hyeon Yeol Jeon, 1 Kyung–Youl Baek, 1 Dong Hoon Choi, 2 Seung Sang Hwang 1 1 Nano Hybrids Research Center, Korea Institute of Science Technology, Seongbuk-gu, Seoul 136-791, Korea 2 Department of Chemistry, Korea University, Seongbuk-gu, Seoul 136-701, Korea Correspondence to: S. S. Hwang (E-mail: sshwang@kist.re.kr) Received 5 June 2011; accepted 11 August 2011; published online 12 September 2011 DOI: 10.1002/pola.24942 ABSTRACT: Various ladder-like structured poly(phenyl-co-meth- acryl silsesquioxane)s (LPMSQ)s with high molecular weight (M w ¼ 10,000  40,000) were synthesized by direct hydrolysis and poly- merization in the presence of base catalyst at 25  C. Synthesized LPMSQs mainly showed ladder-like structure and photo-cure reac- tion by 100 mW/cm 2 (360 nm) for 10 s without any photo-cure initia- tors. Chemical composition and structural analysis of the obtained LPMSQs were characterized using 1 H NMR, 29 Si NMR, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatog- raphy (GPC), and X-ray diffraction (XRD). Physical properties of LPMSQs before and after photcuring were analyzed by Nanoinden- tation. Surface modulus increased to 8GPa and hardness of thin films increased from 100 to 400 MPa. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 5012–5018, 2011 KEYWORDS: materials science; organic-inorganic hybrid com- posite; organic-inorganic hybrid material; photochemistry; sil- sesquioxane; UV-curable material INTRODUCTION Recently, photocurable polymers have been in the limelight due to its myriad of advantages over conven- tional water and solvent-based thermal drying processes, of which include increased production speed, reduction of rejection rates, enhanced scratch and solvent resistance, while facilitating superior crosslinking. 1,2 For example, acryl or methacryl polymer resins have been applied to various areas, such as electronic components, 3 functional hardcoating materials, 4 and microlithography. 5 However, fully organic photocurable polymers have had dis- advantages such as low heat resistance, low oxidative resist- ance, yellow discoloration, as well as the required excessive use of photoinitiators. 6 To overcome these shortcomings, or- ganic–inorganic hybrid materials are one of the best substi- tutive candidates. Functional silicon sol-gel derived materials have been the most researched among the various organic– inorganic hybrid materials. Preparation of photocurable hybrid films using the silicon sol-gel method can be summar- ized in three steps. 7 First, the photocurable functional groups attached to the silane monomer are hydrolyzed and con- densed in acid or basic aqueous solution, with Si-OH groups remaining in the precursor polymer. These precursors are prepared by coating with photoinitiators on the substrate such as plastic, silicon wafer, or glass, followed by a thermal treatment process to necessitate the further condensation of the remaining Si-OH groups. Finally, through the adequate ultraviolet (UV) curing, functional hybrid films can be prepared. Compared with the organic polymer resins, the sol-gel derived materials such as those described by of Bae and co- workers exhibited superior surface hardness and thermal stability. 8 However, the thermal curing at temperatures exceeding 100  C required for secondary thermal condensa- tions between the many uncondensed Si-OH groups lead to a great amount of shrinkage and relatively high concentration of photoinitiators required are two significant drawbacks of the aforementioned sol-gel derived materials. To overcome the drawbacks of silicon sol-gel resins, structur- ally well-defined polysilsesquioxanes have been extensively researched. 8,9 Compared with silicon sol-gel derived materi- als, these structurally sound polysilsesquioxanes can be said to be well-defined in structure, contain very few unstable Si- OH groups, while exhibiting superior properties such as chemical resistance, thermal stability making it a very appro- priate material candidate as a organic–inorganic hybrid pho- tocurable polymer. These polysilsesquioxanes can be divided into two major groups, polyhedraloligosilsesquioxanes (POSS) and ladder-like Polysilsesquioxanes (LPSQ) (Fig. 1). POSS compounds are oligomers with molecular weight between 1 and 3 K and have a closed cage structure consist- ing of SiAOASi bonds with the R functionality located on the vertices of the polyhedron. 10,11 LPSQ compounds are V C 2011 Wiley Periodicals, Inc. 5012 JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2011, 49, 5012–5018 ARTICLE WWW.POLYMERCHEMISTRY.ORG