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In this investigation, chitosan (CS) is modified by propane sultone via a sulfonation reaction to create various degrees of sulfonation. The sulfonated chitosan (SCS) has a pendant alkyl sulfonic group dangling at the side chain, which can improve its hydrophilicity and water solubility. Elemental analysis, Fourier transform infrared spectroscopy (FTIR) and 13 C nuclear magnetic resonance ( 13 C NMR) were applied to identify the structure by determining the distribution of the substituents in the product. The degree of sulfonation in the SCS can be controlled and the hydrogen bonding interaction can be reduced by varying the degree of sulfonation. A solubility test proved that solubility increased with degree of substitution at over a wide range of pH values. X-ray diffraction patterns of SCS samples demonstrated that the crystallinity declined as the degree of sulfonation increased. Thermogravimetric analysis and modulated differential scanning calorimetry (MDSC) results indicated that thermal stability fell but water absorbance increased with the degree of sulfonation. More water-soluble SCS is thus obtained. The controllable different sulfonation degree of the CS polymer suggests new possibilities for the application of CS-based materials.

A high-performance, low-dielectric-constant polyimide (PI) nanocomposite from poly(amic acid) (PAA) cured with a reactive fluorine polyhedral oligomeric silsesquioxane (POSS) isomer was successfully synthesized. The features of this reactive fluorine POSS isomer [octakis(dimethylsiloxyhexafluoropropylglycidyl ether)silsesquioxane (OFG)] provided two important approaches (containing fluorine or being porous in the polymer matrix) of reducing the dielectric constant of PI. This reactive POSS isomer had an average of four epoxy groups and four fluorine groups on the POSS cage, and the epoxy groups could be cured with PAA to form a network framework of a PI/POSS nanocomposite. The PI/OFG nanocomposite had a high crosslinking density, high porosity (24.3%), high hydrophobicity, and low polarizability. These properties enhanced the thermal (glass-transition temperature $ 362 8C) and dielectric (dielectric constant $2.30) properties of PI more than other POSS derivatives introduced into the PI backbone. A large number of small POSS particles (<10 nm) were embedded inside the PI matrix when the OFG content was low, whereas interconnected POSS aggregation domains were observed when the OFG content was high. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5391-5402, 2006

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