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Glove Selection for Work with Acrylates Including Those Cured by Ultraviolet, Visible Light, or Electron Beam
Published in Robert N. Phalen, Howard I. Maibach, Protective Gloves for Occupational Use, 2023
For some specific industrial, medical, or dental applications, the oligomers are manufactured in a more controlled synthetic route to a purer product with narrow molecular weight distribution. Moreover, purification steps may be added to remove impurities such as catalysts and other low-molecular-weight chemicals that will not be incorporated into the polymer network upon cure and/or that might be of toxicological concern.
Basic Physics and Recent Developments of Organic Random Lasers
Published in Marco Anni, Sandro Lattante, Organic Lasers, 2018
Ilenia Viola, Luca Leuzzi, Claudio Conti, Neda Ghofraniha
From an experimental point of view, different types of organic semiconductors are suitable for lasing. They are characterized by innovative optoelectronic properties, tunable with the chemical–physical structure, and are suitable both for nonconventional manufacturing procedures and substrates. Organic semiconductors, like all organic materials, are carbon-rich compounds with a structure tailored to optimize a particular function, such as luminescentproperties or charge mobility. Usually the semiconducting properties arise from the overlap of molecular orbitals of these conjugated molecules. Organic semiconductors are conventionally classified in small molecules, oligomers, and polymers. Small molecules refer to those compounds with a well-defined molecular weight. Oligomers are molecular complexes that consist of a few monomer units, while polymers are long-chain molecules consisting of an indeterminate number of molecular repeat units.
Quantum Mechanics of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
There are two wavefunctions and φ=0 is at a dimer position. The origin φ is shifted in the middle of the distance between two carbon atoms by the angle of 30°. A “dimer” is oligomer that consists of two monomers similar in structure. A dimer can be weak, strong, covalent or intermolecular. Oligomer is term that describes a molecular complex that consists of a few monomers. Oligomer is a counterpart of a polymer, for which the number of monomers (as constituents) is not limited.
The use of meta-analysis in food contact materials risk assessment
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Marzena Pawlicka, Paweł Struciński, Jacek Postupolski
Oligomers consist of 2 to 40 monomeric units and can be linear, branched or cyclic. They are formed as a result of either incomplete polymerization or subsequent degradation (thermal or hydrolytic) of polymeric material. The variety of possible oligomers is constantly increasing with the introduction onto the FCM market of new types of plastics made from novel monomers and monomer combinations. Such a diversity, accompanied by the lack of appropriate analytical standards, makes both qualitative and quantitative characterization of oligomeric migrants, as well as evaluation of their toxicity, a challenging task. Hoppe et al. (2016) stressed that oligomers are not specifically regulated in regulation EU 10/2011 and are, therefore, in practical terms located in a legal ‘gray area’. The permanent extension of the EU positive list with new co-monomers as a consequence of industrial developments principally gives rise to an exponentially growing amount of new oligomers which might be present in food contact polymers as potential migrants. Safety assessment for oligomers has been traditionally based on their respective monomers, since physiological degradation of oligomers to monomers is assumed. However, polycondensate-type cyclic oligomers may need to be considered separately; their susceptibility to hydrolysis in the gastrointestinal tract and their toxic properties are as yet incompletely understood.
Preparation of new low viscosity urethane dimethacrylates for dental composites
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Yuling Xu, Haibo Wang, Dong Xie
The synthesized oligomers were characterized by Fourier transform-infrared spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The proton NMR (1HNMR) spectra were obtained on a 500 MHz Bruker NMR spectrometer (Bruker Avance II, Bruker BioSpin Corporation, Billerica, MA) using deuterated dimethyl sulfoxide as solvent and FT-IR spectra were obtained on a FT-IR spectrometer (Mattson Research Series FT/IR 1000, Madison, WI).