Conventional heterogeneous dispersion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersing media with the addition of interfacially active agents to stabilize the colloidal dispersion that forms. Successful stabilization of the polymer colloid during polymerization results in the formation of high molar mass polymers with high rates of polymerization. An environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations is described in which supercritical carbon dioxide (CO(2)) is used in conjunction with molecularly engineered free radical initiators and amphipathic molecules that are specifically designed to be interfacially active in CO(2). Conventional lipophilic monomers, exemplified by methyl methacrylate, can be quantitatively (>90 percent) polymerized heterogeneously to very high degrees of polymerization (>3000) in supercritical CO(2) in the presence of an added stabilizer to form kinetically stable dispersions that result in micrometer-sized particles with a narrow size distribution.

The high water repellence of superhydrophobic surfaces is attributed to the limited contact area between the solid and water which is manifested by a high static water contact angle (WCA) and a low sliding angle. The solid-liquid interfacial energy can be minimized by engineering not only the chemistry but also the topography of the solid surface. [1,2] For example, epicuticular wax on the lotus leaf is an intrinsically hydrophobic material.[3] However, when nano-sized crystals of wax cover a micron-level rough surface, as is the case on the lotus leaf, the WCA is further enhanced to 1608, which is defined as superhydrophobic. [4][5][6][7][8] In this case, the water droplet forms a three-dimensional, discontinuous, triphasic (water-air-solid) contact line [9] that is relatively longer and less stable than such a line on a macroscopically smooth surface. Moreover, a nonhydrophobic material can also be rendered hydrophobic with a WCA well above 1508 by chemical modification, for example, through the incorporation of fluorine or silicone, as well as by increasing the roughness. [9][10][11][12][13][14] Such an extreme water repellence is highly attractive for novel industrial and practical applications: continuously clean buildings, windows, and outdoor decorations, stain-resistant fabrics, antifouling marine structures, and oxidation-resistant surfaces. [2,8,10] Currently, the production of superhydrophobic surfaces is based on time-consuming, expensive, and/or nonversatile processes, such as controlled crystallization, lithography, etching, and templating. [9][10][11][12][13]15] To mimic the topography of the lotus leaf and to achieve a high WCA, we fabricated a polymeric film surface with a high degree of roughness through a simple and practical electrospinning process.[16] Electrospun films consist of a continuous, nonwoven web of fibers (with diameters in the order of 1-1000 nm) and, depending on processing conditions, with polymer droplets either as isolated spheres (> 1 mm in diameter) or strung along a fiber. [17][18][19][20][21][22] The electrospun film is produced by applying an electrical bias from the tip of a polymer solution-filled syringe to a grounded collection plate. Along the trajectory of the extruded polymer fiber, most of the solvent evaporates, such that a mat of randomly aligned fibers collects and form a thin film. In addition to surface roughness, the film properties were optimized by chemical modification, such as the addition of fluorine to enhance and stabilize WCA values and the incorporation of crosslinking for solvent resistance. Our ability to engineer both the physical and chemical properties of the electrospun films enables flexibility in tuning the degree of hydrophobicity.A thermoset polymer was synthesized by first reacting acrylonitrile (AN) and a,a-dimethyl meta-isopropenylbenzyl isocyanate (TMI) in N,N-dimethylformamide (DMF), and then mixing the resultant poly(AN-co-TMI) with a perfluorinated linear diol (fluorolink-D) and tin(ii) ethyl hexanoate (T2EH) in DMF. The solution w...

The aim of this study was to prepare non-woven materials from a biodegradable polymer, poly(epsilon-caprolactone) (PCL) by electrospinning. PCL was synthesized by ring-opening polymerization of epsilon-caprolactone in bulk using stannous octoate as the catalyst under nitrogen atmosphere. PCL was then processed into non-woven matrices composed of nanofibers by electrospinning of the polymer from its solution using a high voltage power supply. The effects of PCL concentration, composition of the solvent (a mixture of chloroform and DMF with different DMF content), applied voltage and tip-collector distance on fiber diameter and morphology were investigated. The diameter of fibers increased with the increase in the polymer concentration and decrease in the DMF content significantly. Applied voltage and tip-collector distance were found critical to control 'bead' formation. Elongation-at-break, ultimate strength and Young's modulus were obtained from the mechanical tests, which were all increased by increasing fiber diameter. The fiber diameter significantly influenced both in vitro degradation (performed in Ringer solution) and in vivo biodegradation (conducted in rats) rates. In vivo degradation was found to be faster than in vitro. Electrospun membranes were more hydrophobic than PCL solvent-casted ones; therefore, their degradation was a much slower process.

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Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers. The effects of copolymer composition and amount of PdCl 2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl 2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6-ene-1-yne-3-ol, DHL) in toluene at 90°C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current Pd/Al 2O3 catalyst.