Organic/inorganic hybrid materials prepared by the sol-gel approach have rapidly become a fascinating new field of research in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental understanding of the sol-gel process and the development and applications of new organic/inorganic hybrid materials. In this review, a brief summary of the research activities in the field of organic/inorganic nanocomposite materials and a general background of the sol-gel chemistry are first given. The emphasis of this report, however, is placed on the synthesis, structureproperty response, and potential applications of the organic/inorganic hybrid networks that possess chemical bonding between the organic and inorganic phases, particularly those systems that were developed in our laboratory since 1985.

The implications of the entanglement concentration (C e) on the electrospinning process for a series of linear and branched poly(ethylene terephthalate-co-ethylene isophthalate) (PET-co-PEI) copolymers with weight-average molecular weights (M w) ranging from 11 700 to 106 000 g/mol and branching index values (g‘) from 1.0 to 0.43 were investigated. Analyzing the dependence of specific viscosity (ηsp) on concentration enabled the determination of the semidilute unentangled, semidilute entangled, and concentrated regimes for the PET-co-PEI solutions. Linear and branched copolymers were electrospun from semidilute unentangled, semidilute entangled, and concentrated solutions under identical conditions to determine the effects of concentration regime and molecular topology on electrospun fiber morphology. The dependence of the fiber diameter and morphology on the zero shear rate viscosity (η0) and normalized concentration (C/C e) was determined. For copolyesters with molecular weights well above the entanglement molecular weight, C e was the minimum concentration required for electrospinning of beaded fibers, while 2−2.5 times C e was the minimum concentration required for electrospinning of uniform, bead-free fibers. When the concentration was normalized with C e, the influence of chain length and topology on the electrospinning process was removed, and the fiber diameter universally scaled with the normalized concentration to the 2.6 power.

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