Dotsevi Y. Sogah

Chain-End Functionalized Nanopatterned Polymer Brushes Grown via in Situ Nitroxide Free Radical Exchange

The patterning of biologically active materials has been accomplished by the use of imprint lithography of functional photopolymer resins to create controlled nanoscale patterns of a cross-linked photopolymer containing embedded initiator groups. Functionalized polymer brushes consisting of polystyrene and poly(N,N-dimethylacrylamide) were grown from these patterned layers by nitroxide-mediated polymerization. Chain-end functionalization of the brush layer was accomplished by nitroxide radical exchange during the polymerization. Accordingly, brush layers terminated by pyrene and biotin functional groups were obtained by exchange with the appropriate alkoxyamines. The presence of pyrene functionality at the chain ends of the brushes was confirmed by fluorescent emission measurements. Fluorescently labeled streptavidin protein was selectively attached with high selectivity to the patterned biotinylated brush layer through biotin-streptavidin interactions. The functionalized polymer grafted surfaces and nanopatterns have been successfully characterized using a fluorescence spectrophotometer, AFM, SEM, confocal microscopy, and water contact angle measurements.

Molecular dynamics study of the intercalation of diblock copolymers into layered silicates

Polymer-layered silicate nanocomposites may be formed by annealing layered silicate particles with a polymer melt. Polymer molecules flow from a bulk melt into the galleries between silicate sheets, swelling the silicate structure. The use of an amphiphilic intercalant raises possibilities of forming novel structures and enhancing the intercalation kinetics relative to the case of homopolymer intercalants. We perform molecular dynamics simulations of the flow of a symmetric diblock copolymer from a bulk melt into a slit whose surfaces are modified by grafted surfactant chains, and whose walls are maintained at a constant pressure to permit the slit to open as polymer intercalates. Intercalation kinetics are examined for a variety of polymer–surface and interblock interactions and for thermodynamic states in which the bulk polymer occupies either a lamellar or disordered phase. Comparison to previous simulations of homopolymer intercalation demonstrates that diblock copolymers may be used to intercalate a ...

A novel silk‐based segmented block copolymer containing GlyAlaGlyAla β‐sheets templated by phenoxathiin

A novel segmented block copolymer, containing polyethylene glycol segment and GlyAlaGlyAla sequence derived from B. mori silk, has been prepared as a model for silk-based materials using both solution and interfacial techniques. Inherent viscosity, size exclusion chromatography, and light-scattering measurements gave molecular weight between Mw 34,000–39,000. Evidence for phase separation was provided by differential scanning calorimetry, which gave two Tgs at −57 °C and 111 °C, and transmission electron microscopy, which showed a morphology in which the peptide domain, estimated to be about 20–50 nm, was dispersed in the continuous polyether phase. Solid-state FTIR spectroscopic results showed that the polymer contained both parallel and antiparallel β-sheet stacks, and that the solution-polymerized material has the higher β-sheet content. This was further confirmed by 13C NMR, which gave about 80% total β-sheet content for the solution-polymerized product and about 40% for the polymer obtained by interfacial polymerization.

HIGHLY ISOTACTIC OPTICALLY ACTIVE METHACRYLATE POLYMERS BY FREE RADICAL CYCLOPOLYMERIZATION

Abstract Isospecific free radical cyclopolymerization of tartrate-based monomers gives polymers with very high optical rotations. Circular dichroism and polarimetric measurements suggest the polymers are rigid and ordered. Their high resistance to solvolysis suggests potential applications in chiral chromatography.

Facile alkylation of 2-methyl-2-oxazoline : synthesis of novel 2-substituted-2-oxazolines

Abstract The synthesis, mechanism of formation and purification of new oxazolines containing binaphthyl and biphenyl moieties based on alkylation of 2-methyl-2-oxazoline with alkyl halides are described. Yields up to 87 % have been realized, and the method is applicable to the syntheses of other 2-substituted-2-oxazolines.

A positive, chemically amplified, aromatic methacrylate resist employing the tetrahydropyranyl protecting group

In this article we describe the synthesis, properties, and lithographic behavior of a new class of chemically‐amplified, positive‐tone, aromatic methacrylate resists incorporating the tetrahydropyranyl protecting group bound to base‐solubilizing carboxylic acid moieties. Copolymers containing equimolar amounts of benzyl methacrylate and tetrahydropyranyl methacrylate were prepared by free radical and group transfer polymerization (GTP). Photogenerated sulfonic acids formed from covalent ester or ionic salt precursors were used to remove the acid labile tetrahydropyranyl (THP) group by heating after exposure. The resulting copolymers of benzyl methacrylate (BMA) and methacrylic acid (MAA) are extremely soluble in aqueous base solutions when the MAA concentration exceeds 38 mol %, thus affording positive tone patterns. We have studied these copolymer resists and find them to have high sensitivity (<30 mJ/cm2) when formulated with aromatic sulfonate or trifluoromethyl sulfonate sensitizers. Contrast is greater than 2 and submicrometer patterns in 1 μm thick films are resolved. Resolution is significantly influenced by the sensitizer, post exposure heating and development conditions. Molecular weight distribution appears to have little effect on the lithographic properties. Resolution presently is limited by resist adhesion which remains to be optimized. Plasma etching resistance to conditions used to etch Al is 1.8 times less than for hard‐baked HPR‐206 photoresist, but can be improved to a value of 1.5 by postexposure thermolysis. Improvements are needed before this type of chemically‐amplified resist is able to meet all deep‐UV lithographic requirements. However, it appears quite promising for other lower resolution (≫1 μm), thick‐film‐imaging applications which will be the subject of future papers.

Perfluoroalkylation of Polyurethane Membranes and Their Surface Characteristics

Two fluoroalkylating agents, 2-aminomethyl-1,1,2,3,3,4,4-H-perfluorodo- decanol and perfluorodecanoic acid, were used to modify the surfaces of polyurethane membranes and their fluoroalkylation efficiencies were compared. X-ray photoelectron spectroscopy showed that all the modified samples contained fluorine and that the amino alcohol-treated polyurethane had a slightly higher surface fluorine content than the perfluorodecanoic acid-treated one. Both the modifier concentration and the treatment time had no significant effect on the amount of fluorine incorporated. Evidence for fluorine incorporation was also provided by reflection infrared spectroscopy. Contact angle measurements indicated that the modified microporous membranes were both water- and oil-repellent and may, therefore, be used in protective clothing applications where good liquid barrier properties are desirable.