scholarly journals Stability of SG1 nitroxide towards unprotected sugar and lithium salts: a preamble to cellulose modification by nitroxide-mediated graft polymerization

2013 ◽  
Vol 9 ◽  
pp. 1589-1600 ◽  
Author(s):  
Guillaume Moreira ◽  
Laurence Charles ◽  
Mohamed Major ◽  
Florence Vacandio ◽  
Yohann Guillaneuf ◽  
...  
Keyword(s):  
Graft Polymerization ◽  
Polymer Chains ◽  
Lithium Salts ◽  
Organic Media ◽  
Cellulose Derivatives ◽  
Cellulose Modification ◽  
Model Study ◽  
The Stability ◽  
Grafting From ◽  
Intramolecular Hydrogen

The range of applications of cellulose, a glucose-based polysaccharide, is limited by its inherently poor mechanical properties. The grafting of synthetic polymer chains by, for example, a “grafting from” process may provide the means to broaden the range of applications. The nitroxide-mediated polymerization (NMP) method is a technique of choice to control the length, the composition and the architecture of the grafted copolymers. Nevertheless, cellulose is difficult to solubilize in organic media because of inter- and intramolecular hydrogen bonds. One possibility to circumvent this limitation is to solubilize cellulose in N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA) with 5 to 10 wt % of lithium salts (LiCl or LiBr), and carry out grafted polymerization in this medium. The stability of nitroxides such as SG1 has not been studied under these conditions yet, even though these parameters are of crucial importance to perform the graft modification of polysaccharide by NMP. The aim of this work is to offer a model study of the stability of the SG1 nitroxide in organic media in the presence of unprotected glucose or cellobiose (used as a model of cellulose) and in the presence of lithium salts (LiBr or LiCl) in DMF or DMA. Contrary to TEMPO, SG1 proved to be stable in the presence of unprotected sugar, even with an excess of 100 molar equivalents of glucose. On the other hand, lithium salts in DMF or DMA clearly degrade SG1 nitroxide as proven by electron-spin resonance measurements. The instability of SG1 in these lithium-containing solvents may be explained by the acidification of the medium by the hydrolysis of DMA in the presence of LiCl. This, in turn, enables the disproportionation of the SG1 nitroxide into an unstable hydroxylamine and an oxoammonium ion. Once the conditions to perform an SG1-based nitroxide-mediated graft polymerization from cellobiose have been established, the next stage of this work will be the modification of cellulose and cellulose derivatives by NMP.

scholarly journals Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2942
Author(s):  
Bhausaheb V. Tawade ◽  
Ikeoluwa E. Apata ◽  
Nihar Pradhan ◽  
Alamgir Karim ◽  
Dharmaraj Raghavan
Keyword(s):  
Energy Density ◽  
Polymer Nanocomposites ◽  
High Performance ◽  
Breakdown Strength ◽  
Polymer Nanocomposite ◽  
High Energy ◽  
Polymer Chains ◽  
High Energy Density ◽  
Grafted Nanoparticles ◽  
Grafting From

The synthesis of polymer-grafted nanoparticles (PGNPs) or hairy nanoparticles (HNPs) by tethering of polymer chains to the surface of nanoparticles is an important technique to obtain nanostructured hybrid materials that have been widely used in the formulation of advanced polymer nanocomposites. Ceramic-based polymer nanocomposites integrate key attributes of polymer and ceramic nanomaterial to improve the dielectric properties such as breakdown strength, energy density and dielectric loss. This review describes the ”grafting from” and ”grafting to” approaches commonly adopted to graft polymer chains on NPs pertaining to nano-dielectrics. The article also covers various surface initiated controlled radical polymerization techniques, along with templated approaches for grafting of polymer chains onto SiO2, TiO2, BaTiO3, and Al2O3 nanomaterials. As a look towards applications, an outlook on high-performance polymer nanocomposite capacitors for the design of high energy density pulsed power thin-film capacitors is also presented.

scholarly journals Investigation of Hydrothermally Stressed Silicone Rubber/Silica Micro and Nanocomposite for the Coating High Voltage Insulation Applications

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3567
Author(s):  
Faiza Faiza ◽  
Abraiz Khattak ◽  
Safi Ullah Butt ◽  
Kashif Imran ◽  
Abasin Ulasyar ◽  
...  
Keyword(s):  
Silicone Rubber ◽  
Structural Changes ◽  
Polymer Chains ◽  
Hydrothermal Conditions ◽  
Silica Filler ◽  
Before And After ◽  
Aging Conditions ◽  
The Stability ◽  
Micro Silica ◽  
Applied Stresses

Silicone rubber is a promising insulating material that has been performing well for different insulating and dielectric applications. However, in outdoor applications, environmental stresses cause structural and surface degradations that diminish its insulating properties. This effect of degradation can be reduced with the addition of a suitable filler to the polymer chains. For the investigation of structural changes and hydrophobicity four different systems were fabricated, including neat silicone rubber, a micro composite (with 15% micro-silica filler), and nanocomposites (with 2.5% and 5% nanosilica filler) by subjecting them to various hydrothermal conditions. In general, remarkable results were obtained by the addition of fillers. However, nanocomposites showed the best resistance against the applied stresses. In comparison to neat silicone rubber, the stability of the structure and hydrophobic behavior was better for micro-silica, which was further enhanced in the case of nanocomposites. The inclusion of 5% nanosilica showed the best results before and after applying aging conditions.

scholarly journals Electro-responsive polyelectrolyte-coated surfaces

2017 ◽  
Vol 199 ◽  
pp. 335-347 ◽  
Author(s):  
V. Sénéchal ◽  
H. Saadaoui ◽  
J. Rodriguez-Hernandez ◽  
C. Drummond
Keyword(s):  
Electric Field ◽  
Smart Materials ◽  
Electrical Stimulus ◽  
Colloidal Dispersions ◽  
Polymer Chains ◽  
Molecular Response ◽  
Coated Surfaces ◽  
The Stability ◽  
Induced Changes ◽  
Applied Fields

The anchoring of polymer chains at solid surfaces is an efficient way to modify interfacial properties like the stability and rheology of colloidal dispersions, lubrication and biocompatibility. Polyelectrolytes are good candidates for the building of smart materials, as the polyion chain conformation can often be tuned by manipulation of different physico-chemical variables. However, achieving efficient and reversible control of this process represents an important technological challenge. In this regard, the application of an external electrical stimulus on polyelectrolytes seems to be a convenient control strategy, for several reasons. First, it is relatively easy to apply an electric field to the material with adequate spatiotemporal control. In addition, in contrast to chemically induced changes, the molecular response to a changing electric field occurs relatively quickly. If the system is properly designed, this response can then be used to control the magnitude of surface properties. In this work we discuss the effect of an external electric field on the adhesion and lubrication properties of several polyelectrolyte-coated surfaces. The influence of the applied field is investigated at different pH and salt conditions, as the polyelectrolyte conformation is sensitive to these variables. We show that it is possible to fine tune friction and adhesion using relatively low applied fields.

scholarly journals Synthesis and Complexation Properties of 2-Hydroxy-5-methoxyphenylphosphonic Acid (H3L1). Crystal Structure of the [Cu(H2L1)2(Н2О)2] Complex

2021 ◽  
Vol 91 (11) ◽  
pp. 2176-2186
Author(s):  
G. S. Tsebrikova ◽  
Yu. I. Rogacheva ◽  
I. S. Ivanova ◽  
A. B. Ilyukhin ◽  
V. P. Soloviev ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Methoxy Group ◽  
Protonation Constants ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Stability ◽  
Intramolecular Hydrogen ◽  
Oxygen Atoms

Abstract 2-Hydroxy-5-methoxyphenylphosphonic acid (H3L1) and the complex [Cu(H2L1)2(H2O)2] were synthesized and characterized by IR spectroscopy, thermogravimetry, and X-ray diffraction analysis. The polyhedron of the copper atom is an axially elongated square bipyramid with oxygen atoms of phenolic and of monodeprotonated phosphonic groups at the base and oxygen atoms of water molecules at the vertices. The protonation constants of the H3L1 acid and the stability constants of its Cu2+ complexes in water were determined by potentiometric titration. The protonation constants of the acid in water are significantly influenced by the intramolecular hydrogen bond and the methoxy group. The H3L1 acid forms complexes CuL‒ and CuL24‒ with Cu2+ in water.

Theory of the stabilization of colloids by adsorbed polymer

1974 ◽  
Vol 337 (1611) ◽  
pp. 509-516 ◽  
Keyword(s):  
Plane Surface ◽  
Analytic Form ◽  
Polymer Chains ◽  
Contour Length ◽  
Link Length ◽  
Excluded Volume Effects ◽  
Adsorbed Polymer ◽  
Random Flight ◽  
The Stability ◽  
Simple Analytic Form

The configurational free energy of random flight polymer chains adsorbed by one end onto a plane surface as a function of the distance from a parallel plane surface is expressed to a good approximation in simple analytic form. The result is used to discuss the stabilization of a colloid suspension by adsorbed polymer. According to this theory two types of aggregation of colloid particles may occur. If LI < AS/2π 3 NkT , where l is the link length and L the contour length of a polymer chain, A is the Hamaker constant, N /S is the number of adsorbed polymer chains per unit area and kT is the Boltzman constant multiplied by temperature, the particles adhere closely, but if AS/2π 3 kT < IL < AS/nkT lg 2N a looser association is formed. It is expected that the presence of excluded volume effects would greatly increase the stability against the looser association.

Hollow polymer nanocapsules with ferrocenyl copolymer shell

2021 ◽  
Author(s):  
Moumita Dhara ◽  
Somdatta Rudra ◽  
Nilanjan Mukherjee ◽  
Tushar Jana
Keyword(s):  
Silica Nanoparticles ◽  
Polymer Chains ◽  
One Pot ◽  
Grafting From

Hollow polymer nanocapsules (HPN) consist of ferrocenyl shell have been developed by crosslinking the polymer chains grafted over silica nanoparticles (SiNP) which were synthesized via one pot grafting from surface...

scholarly journals A Novel Hydrogel Based on Renewable Materials for Agricultural Application

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Silvie Durpekova ◽  
Kateryna Filatova ◽  
Jaroslav Cisar ◽  
Alena Ronzova ◽  
Erika Kutalkova ◽  
...  
Keyword(s):  
Citric Acid ◽  
Water Uptake ◽  
Agricultural Product ◽  
Cellulose Derivatives ◽  
Gravimetric Analysis ◽  
Renewable Materials ◽  
Swelling Properties ◽  
Arable Farming ◽  
Swelling Capacity ◽  
The Stability

This study details the design and characterization of a new, biodegradable, and renewable whey/cellulose-based hydrogel (i.e., agricultural hydrogel). This was formulated from cellulose derivatives (carboxymethylcellulose (CMC) and hydroxyethylcellulose (HEC)) and acid whey cross-linked with citric acid, with the aim to obtain an agricultural product with a high swelling capacity to uphold the quality of soil and conserve water resources. With regard to the swelling behaviour of the prepared hydrogels, the authors initially assessed the swelling ratio and capacity for water uptake. Evaluating the chemical structure of the hydrogel and its thermal and viscoelastic properties involved performing Fourier transform infrared spectroscopy, differential scanning colorimetry, thermal gravimetric analysis, and rheological measurement of the hydrogel films. According to preliminary results, sufficient swelling capacity and stiffness were observed in a hydrogel prepared with 3% CMC and HEC, cross-linked with 5% citric acid. Moreover, the kinetics of water uptake revealed a promising capacity that was sustainable after 5 drying and swelling cycles. The results confirmed that the stability of the hydrogel was enhanced by the presence of the citric acid. As a consequence, it is necessary to utilize an appropriate cross-linking concentration and abide by certain conditions to ensure the swelling properties of the prepared hydrogel are sufficient. Further investigation of the topic, especially in relation to applications in soil, could confirm if the whey-cellulose-based hydrogel is actually suitable for agricultural use, thereby contributing to the advancement of sustainable arable farming.

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