Chirality analysis of helical polymers

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Tamaki Nakano ◽  
Adriana Pietropaolo ◽  
Masahiro Kamata
Keyword(s):  
Optical Rotation ◽  
Polymeric Materials ◽  
Helical Conformation ◽  
Cd Spectra ◽  
Chiroptical Properties ◽  
Helical Polymers ◽  
Exciton Coupling ◽  
Related Information ◽  
Unit Model ◽  
Wide Range

AbstractOptically active macromolecules, having a preferred- or single-handed helical conformation, play important roles in polymeric materials and in life. This article presents how helical polymers can be assessed from a view of chirality. These assessments, based on optical rotation (OR) and circular dichroism (CD) spectral measurements with associated information, include theoretical spectral calculations as well as chromatographic resolution. Specific applied examples are discussed for poly(9,9-dioctylfluorene-2,7-diyl) and derivatives, stereoregular polyolefins bearing centers of chirality in the side chain, isotactic poly(triphenylmethyl methacrylate), and π-stacked poly(dibenzofulvene). For more convincing establishment of a helix, it is important to correlate chiroptical properties with related information such as molar-mass effects, temperature effects, and chemical transformation effects on the properties. Helices of the polyolefins and poly(TrMA) were confirmed considering these aspects. In addition, comparison of chiroptical properties between the polymer in question and a monomeric unit model compound generally helps to confirm a helix. There are no general, reliable methods to quantify helical sense excess. On the other hand, absolute helical sense can be determined by comparing experimental and theoretical CD spectra as well as considering exciton coupling effects in CD spectra. The former method can be more generally applied for a wide range of polymers as far as a good model for calculations is designed, while the latter can be more conveniently and empirically applied for a certain class of polymer structures that are suited to exhibit exciton coupling without using computers.

scholarly journals Recent Advances in Fabrication of Non-Isocyanate Polyurethane-Based Composite Materials

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3497
Author(s):  
Piotr Stachak ◽  
Izabela Łukaszewska ◽  
Edyta Hebda ◽  
Krzysztof Pielichowski
Keyword(s):  
Raw Materials ◽  
Synthesis Method ◽  
Polymeric Materials ◽  
Original Research ◽  
Significant Group ◽  
Oh Groups ◽  
New Class ◽  
Hazardous Chemical ◽  
Wide Range

Polyurethanes (PUs) are a significant group of polymeric materials that, due to their outstanding mechanical, chemical, and physical properties, are used in a wide range of applications. Conventionally, PUs are obtained in polyaddition reactions between diisocyanates and polyols. Due to the toxicity of isocyanate raw materials and their synthesis method utilizing phosgene, new cleaner synthetic routes for polyurethanes without using isocyanates have attracted increasing attention in recent years. Among different attempts to replace the conventional process, polyaddition of cyclic carbonates (CCs) and polyfunctional amines seems to be the most promising way to obtain non-isocyanate polyurethanes (NIPUs) or, more precisely, polyhydroxyurethanes (PHUs), while primary and secondary –OH groups are being formed alongside urethane linkages. Such an approach eliminates hazardous chemical compounds from the synthesis and leads to the fabrication of polymeric materials with unique and tunable properties. The main advantages include better chemical, mechanical, and thermal resistance, and the process itself is invulnerable to moisture, which is an essential technological feature. NIPUs can be modified via copolymerization or used as matrices to fabricate polymer composites with different additives, similar to their conventional counterparts. Hence, non-isocyanate polyurethanes are a new class of environmentally friendly polymeric materials. Many papers on the matter above have been published, including both original research and extensive reviews. However, they do not provide collected information on NIPU composites fabrication and processing. Hence, this review describes the latest progress in non-isocyanate polyurethane synthesis, modification, and finally processing. While focusing primarily on the carbonate/amine route, methods of obtaining NIPU are described, and their properties are presented. Ways of incorporating various compounds into NIPU matrices are characterized by the role of PHU materials in copolymeric materials or as an additive. Finally, diverse processing methods of non-isocyanate polyurethanes are presented, including electrospinning or 3D printing.

scholarly journals Originals of operating images for generalized problems of unsteady heat conductivity

2019 ◽  
Vol 14 (4) ◽  
pp. 77-86 ◽  
Author(s):  
E. M. Kartashov
Keyword(s):  
Mathematical Models ◽  
Bessel Functions ◽  
Applied Mathematics ◽  
Operational Calculus ◽  
Polymeric Materials ◽  
Thermal Reaction ◽  
Heaviside Step Function ◽  
External Influences ◽  
Wide Range ◽  
Variable Function

A series of operating (Laplace) non-standard images, the originals of which are absent in well-known reference books on operational calculus, are considered. By reducing one of the basic images to the Riemann-Mellin contour integral for the modified Bessel functions and analyzing the corresponding inversion formula using the approaches of the complex variable function theory, an analytical form of the original original is found, which is abrupt in nature with a break point. It is shown that analytical solutions of the corresponding mathematical models using the found originals have a wave character, which is expressed by the presence of the Heaviside step function in the solutions. The latter means that at any time there is a region of physical disturbance to the point of discontinuity and an unperturbed area after the point of discontinuity. The images studied are included in the operational solutions of mathematical models in many areas of applied mathematics. physics, thermomechanics, thermal physics, in particular in the theory of thermal shock of viscoelastic bodies, in the study of the thermal reaction of solids based on the classical Maxwell-Cattaneo-Lykov-Vernott phenomenology, taking into account the final rate of heat propagation. These models are needed to study the thermal reaction of relatively new consolidated structurally sensitive polymeric materials in structures exposed to high-intensity external influences. The analytical relations obtained for the originals and the original improper integrals resulting from them, containing combinations of Bessel functions, can be used in the general methodology of constructing and applying various mathematical models in a wide range of external influences on materials in many fields of science and technology.

Polymer characterization

2004 ◽  
Author(s):  
Ian L. Hosier ◽  
Alun S. Vaughan
Keyword(s):  
Molecular Weight ◽  
Electrode Materials ◽  
Polymeric Materials ◽  
Optical Nonlinearity ◽  
Polymer Science ◽  
New Materials ◽  
Wide Range ◽  
Step Growth ◽  
Step Growth Polymerization ◽  
Increasing Demand

Polymer science is, of course, driven by the desire to produce new materials for new applications. The success of materials such as polyethylene, polypropylene, and polystyrene is such that these materials are manufactured on a huge scale and are indeed ubiquitous. There is still a massive drive to understand these materials and improve their properties in order to meet material requirements; however, increasingly polymers are being applied to a wide range of problems, and certainly in terms of developing new materials there is much more emphasis on control. Such control can be control of molecular weight, for example, the production of polymers with a highly narrow molecular weight distribution by anionic polymerization. The control of polymer architecture extends from block copolymers to other novel architectures such as ladder polymers and dendrimers. Cyclic systems can also be prepared, usually these are lower molecular weight systems, although these also might be expected to be the natural consequence of step-growth polymerization at high conversion. Polymers are used in a wide range of applications, as coatings, as adhesives, as engineering and structural materials, for packaging, and for clothing to name a few. A key feature of the success and versatility of these materials is that it is possible to build in properties by careful design of the (largely) organic molecules from which the chains are built up. For example, rigid aromatic molecules can be used to make high-strength fibres, the most highprofile example of this being Kevlar®; rigid molecules of this type are often made by simple step-growth polymerization and offer particular synthetic challenges as outlined in Chapter 4. There is now an increasing demand for highly specialized materials for use in for example optical and electronic applications and polymers have been singled out as having particular potential in this regard. For example, there is considerable interest in the development of polymers with targeted optical properties such as second-order optical nonlinearity, and in conducting polymers as electrode materials, as a route towards supercapacitors and as electroluminescent materials. Polymeric materials can also be used as an electrolyte in the design of compact batteries.

scholarly journals Leveraging Conversational Technology to Answer Common COVID-19 Questions

2020 ◽  
Author(s):  
Mollie McKillop ◽  
Brett R South ◽  
Anita Preininger ◽  
Mitch Mason ◽  
Gretchen Purcell Jackson
Keyword(s):  
Health Information ◽  
Information Needs ◽  
One Health ◽  
Conversational Agents ◽  
Governmental Agencies ◽  
Related Information ◽  
Wide Range ◽  
The Mean ◽  
Pandemic Response ◽  
Conversational Turns

Abstract The rapidly evolving science about the Coronavirus Disease 2019 (COVID-19) pandemic created unprecedented health information needs and dramatic changes in policies globally. We describe a platform, Watson AssistantTM (WA), which has been used to develop conversational agents to deliver COVID-19 related information. We characterized the diverse use cases and implementations during the early pandemic and measured adoption through number of users, messages sent, and conversational turns (i.e., pairs of interactions between users and agents). Thirty-seven institutions in nine countries deployed COVID-19 conversational agents with WA between March 30 and August 10, 2020, including 24 governmental agencies, seven employers, five provider organizations, and one health plan. Over 6.8 million messages were delivered through the platform. The mean number of conversational turns per session ranged between 1.9 and 3.5. Our experience demonstrates that conversational technologies can be rapidly deployed for pandemic response and are adopted globally by a wide range of users.

scholarly journals Molecular Modeling Investigations of Sorption and Diffusion of Small Molecules in Glassy Polymers

Membranes ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 98 ◽  
Author(s):  
Niki Vergadou ◽  
Doros N. Theodorou
Keyword(s):  
Small Molecules ◽  
Molecular Simulation ◽  
Glassy Polymer ◽  
Polymeric Materials ◽  
Gas Separations ◽  
Polymeric Systems ◽  
Wide Range ◽  
Multiscale Problem ◽  
Polymer Configurations ◽  
And Diffusion

With a wide range of applications, from energy and environmental engineering, such as in gas separations and water purification, to biomedical engineering and packaging, glassy polymeric materials remain in the core of novel membrane and state-of the art barrier technologies. This review focuses on molecular simulation methodologies implemented for the study of sorption and diffusion of small molecules in dense glassy polymeric systems. Basic concepts are introduced and systematic methods for the generation of realistic polymer configurations are briefly presented. Challenges related to the long length and time scale phenomena that govern the permeation process in the glassy polymer matrix are described and molecular simulation approaches developed to address the multiscale problem at hand are discussed.

scholarly journals Fabrication of photothermally active poly(vinyl alcohol) films with gold nanostars for antibacterial applications

2018 ◽  
Vol 9 ◽  
pp. 2040-2048 ◽  
Author(s):  
Mykola Borzenkov ◽  
Maria Moros ◽  
Claudia Tortiglione ◽  
Serena Bertoldi ◽  
Nicola Contessi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Vinyl Alcohol ◽  
Near Infrared ◽  
Polymeric Materials ◽  
Photothermal Effect ◽  
Poly Vinyl Alcohol ◽  
Broad Application ◽  
Gold Nanostars ◽  
Wide Range ◽  
Spherical Gold Nanoparticles

The unique photothermal properties of non-spherical gold nanoparticles under near-infrared (NIR) irradiation find broad application in nanotechnology and nanomedicine. The combination of their plasmonic features with widely used biocompatible poly(vinyl alcohol) (PVA) films can lead to novel hybrid polymeric materials with tunable photothermal properties and a wide range of applications. In this study, thin PVA films containing highly photothermally efficient gold nanostars (GNSs) were fabricated and their properties were studied. The resulting films displayed good mechanical properties and a pronounced photothermal effect under NIR irradiation. The local photothermal effect triggered by NIR irradiation of the PVA-GNS films is highly efficient at killing bacteria, therefore providing an opportunity to develop new types of protective antibacterial films and coatings.

Materials Compatibility With Pyrolysis Biofuel

2001 ◽  
Author(s):  
D. W. Kirk ◽  
Z. R. Li ◽  
D. Fuleki ◽  
P. C. Patnaik
Keyword(s):  
Stainless Steel ◽  
Alloy Steel ◽  
Polymeric Materials ◽  
304L Stainless Steel ◽  
Chromium Alloy ◽  
Stainless Steel 316L ◽  
Diesel Fuels ◽  
Wide Range ◽  
Elastomeric Materials ◽  
Pyrolysis Oils

The conversion of biomass such as wood and wood byproducts via pyrolysis into a liquid fuel is important in maximizing the use of material resources and in providing alternative and renewable sources of energy. Pyrolysis oils (or biofuels) have good combustion characteristics but are compositionally different from conventional diesel fuels. This difference requires that materials in contact with the biofuel be tested for compatibility. Three types of biofuels were tested for compatibility with a variety of polymeric materials and metal alloys. The test temperatures were set at 80°C to represent aggressive field usage conditions. The tests were conducted using coupons, which were fully immersed in the fluid for periods up to 15 days. These tests revealed that the metals 304L stainless steel, 316L stainless steel, 430 stainless steel and 20M04 stainless steels had corrosion rates of less than 0.007 mm/y and are suitable for use with the oils tested. A non-traditional low chromium alloy steel, MASH, was also examined and was found to be highly susceptible to all fuels at the high temperature tested and corroded at rates up to 3.7 mm/y. At room temperature, the alloy showed good resistance with a corrosion rate less than <0.009 mm/y. The polymeric materials showed a wide range of properties in the oils tested. Non-elastomers such as polytetrafluoroethylene, polypropylene and high-density polyethylene in general showed little swelling or staining in the oils. The elastomeric materials were much more susceptible to swelling, weight gain and change of surface properties. The attack on elastomeric materials was quite rapid with significant volume expansion seen within 24 hours. Viton, Buna-N and EPDM had volume changes up to 100% during a 10-day test and were not considered suitable seal materials for these oils. Multiple day tests for the low alloy steel at 80°C revealed that the corrosion attack was linear in nature leaving a corrosion scale, which slowed but did not prevent further attack. Details of the material degradation will be discussed.

scholarly journals Helix-sense-selective Polymerization of 3,5-bis(hydroxymethyl)phenylacetylene Rigidly Bearing Galvinoxyl Residues and Their Chiroptical Properties

Polymers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1877 ◽  
Author(s):  
Shi ◽  
Wang ◽  
Teraguchi ◽  
Aoki ◽  
Kaneko
Keyword(s):  
Main Chain ◽  
Helical Structure ◽  
Intramolecular Hydrogen Bonding ◽  
Catalyst System ◽  
Static Stability ◽  
Cotton Effect ◽  
Helical Conformation ◽  
Cd Spectra ◽  
Cotton Effects ◽  
Intramolecular Hydrogen

Four kinds of newly synthesized achiral phenylacetylenes bearing a phenylhydrogalvinoxyl residue at 4-position were polymerized by using a chiral rhodium catalyst system, [Rh(nbd)B(C6H5)4] or [Rh(nbd)Cl]2 catalysts in the presence of chiral (R)-(+)- or (S)-(–)-1-phenylethylamine ((R)- or (S)-PEA) cocatalysts. Poly(m-HGDHPA) and poly(m-HGTHPA) in THF showed Cotton signals at the absorption regions of the main chain and hydrogalvinoxyl in the circular dichroism (CD) spectra. It indicated that excess of one-handed helical polyacetylene backbone was induced by helix-sense-selective polymerization (HSSP) under the asymmetric conditions despite the achiral monomer, and the hydrogalvinoxyl moieties were also arranged to form one-handed helical structure. However, there was no Cotton effect for poly(p-HGDHPA) and poly(p-HGTHPA) because the intramolecular hydrogen bonding did not act well to stabilize the helical conformation. The hydrogalvinoxyl units of poly(m-HGDHPA) and poly(m-HGTHPA) were converted to the corresponding galvinoxyl radicals after treatment with PbO2. In the CD spectra of the polyradicals, the Cotton effects decreased depending on their static stability of helical conformation, suggesting that reversal conformation of the polymer chain arose.

scholarly journals Fabrication and Characterization of Polylactic Acid Electrospun Scaffolds Modified with Multi-Walled Carbon Nanotubes and Hydroxyapatite Nanoparticles

Biomimetics ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 43
Author(s):  
Athanasios Kotrotsos ◽  
Prokopis Yiallouros ◽  
Vassilis Kostopoulos
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanotubes ◽  
Polylactic Acid ◽  
Physical And Mechanical Properties ◽  
Polymeric Materials ◽  
Cost Effective ◽  
Electrospinning Process ◽  
Wide Range ◽  
Multi Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

The solution electrospinning process (SEP) is a cost-effective technique in which a wide range of polymeric materials can be electrospun. Electrospun materials can also be easily modified during the solution preparation process (prior SEP). Based on this, the aim of the current work is the fabrication and nanomodification of scaffolds using SEP, and the investigation of their porosity and physical and mechanical properties. In this study, polylactic acid (PLA) was selected for scaffold fabrication, and further modified with multi-walled carbon nanotubes (MWCNTs) and hydroxyapatite (HAP) nanoparticles. After fabrication, porosity calculation and physical and mechanical characterization for all scaffold types were conducted. More precisely, the morphology of the fibers (in terms of fiber diameter), the surface properties (in terms of contact angle) and the mechanical properties under the tensile mode of the fabricated scaffolds have been investigated and further compared against pristine PLA scaffolds (without nanofillers). Finally, the scaffold with the optimal properties was proposed as the candidate material for potential future cell culturing.

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