SynopsisThe objective of this work was to obtain primary amine groups on the surface of poly(viny1 alcohol) films by means of a reaction with hexamethylene diisocyanate. The reaction was run in such a way as to minimize the internal crosslinking by employing a large excess of hexamethylene diisocyanate in toluene and then hydrolyzing the unreacted isocyanate endgroup to primary amine. After dialyzing out the adsorbed hexamethylenediamine from the aqueous solution of reacted poly(viny1 alcohol), the extent of covalent bonding of hexamethylene diisocyanate onto the polymer was determined by measuring aminohexyl content through a fluorescence assay. This assay is based on the reaction of fluorescamine, 4-phenylspiro[furan-2(3H)-l~-phthalan]-3,3'-dione, with a primary amine to yield a fluorophor which will emit a strong fluorescence at 475-490 nm when excited a t 390 nm. Analyses show a range of 1.1 X 10-lo-3.6 X 10-lo mole of amines per cm2 of reacted poly(viny1 alcohol) film. When assuming 47% as degree of crystallinity approximated by IR spectroscopy for these polymer films, the availability of hydroxyl groups in amorphous region was estimated to be 3.7 X mole/cm2. The extent of reaction based on available hydroxyl groups was then in the range of 31-97%. The primary amine groups attached by this method can now he exploited for binding biomolecules such as heparin (anticoagulant) or fibrinolytic enzymes in an attempt to achieve biocompatible materials.
The static and fatigue strength properties of commercially pure VT1-00 (Russian standard) titanium and the Zr-2.5%Nb zirconium alloy have been studied after equal-channel angular pressing (ECAP). It is shown that the formation of submicrocrystalline (SMC) structure upon ECAP leads to significant strengthening, increases the service life in a high stress amplitude range and increases the fatigue strength relative to those typical of the annealed state. The specific features of the fatigue fracture mechanism in different structural states of materials are studied.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.