Highly porous polymeric hollow nanofibers were developed using a method based on coaxial electrospinning with inner silicon oil and outer polymer solutions. This method was verified by the fabrication of polymeric hollow fibers, whose diameter and wall thickness could be varied by controlling the coelectrospinning parameters, such as the dielectric constant of the solvents, concentration of the polymer solution, molecular weights of the polymers and viscosity of the inner silicon oil phase. The entire diameter and wall thickness of the hollow fibers could be varied from 5 to 15 µm and 180 to 900 nm, respectively. Highly porous polymeric hollow nanofibers were fabricated by coaxial electrospinning with a highly volatile solvent. The interior surface was quite smooth without pores. Therefore, pore formation occurred at the outer surface of the hollow fibers due to rapid solvent evaporation because the jet only occurred between the surface of the polymer solution and air. The smooth interior and highly porous outer surface, circular crosssection and uniform size of the hollow polymer nanofibers are expected to have attractive applications in areas, such as catalysis, optoelectronics, nanofluidics, drug delivery or biosensorics.

New supported catalysts on the basis of cyclopentadienylindenylzirconium dichloride (CpIndZrCl,) anchored on silica with a trisiloxane spacer (ZATS) and a pentamethylene spacer (ZAPM) were prepared and used for ethylene polymerization with modified methylaluminoxane (MAO) as cocatalyst. ZATS and ZAPM produce polyethylene with lower molecular weight but show higher activity than silica-supported CpIndZrCl, which was prepared by reacting zirconocene directly with silica, i. e., the activity of silica-supported CpIndZrCl, is enhanced by introducing a spacer between silica surface and metallocene species.

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Melt blending of polylactic acid (PLA) and a chain-extended polyethylene glycol (CE-PEG) have been performed in an effort to toughen the PLA without significant loss of modulus and ultimate tensile strength. The chain-extended PEG was prepared with melt condensation of a low molecular weight PEG and 4,4 0 -methylenebis(phenylisocyanate) (MDI) for enhancement of the molecular weight of PEG. The thermal and mechanical properties, miscibility and phase morphologies of blends were investigated. By using thermal and fracture surface analysis, the blends were found to be a partially miscible system with shifted glass transition temperatures. The addition of CE-PEG leads to slight decrease in tensile strength and modulus, while the elongation at break is characterized by an important increase (540%), compared with neat PLA and PLA/PEG (low molecular weight PEG, M n ¼ 35,000). The relative ductility of PLA/CE-PEG is 40 times higher than that of neat PLA. The brittle fracture of neat PLA was transformed into a ductile fracture by the addition of CE-PEG.