China
Africa
Explore chapters and articles related to this topic
Bioresponsive Hydrogels for Controlled Drug Delivery
Published in Deepa H. Patel, Bioresponsive Polymers, 2020
Tamgue Serges William, Dipali Talele, Deepa H. Patel
The method of preparation will determine the polymeric constitution of hydrogels. Hydrogels can be classified into three groups: Homopolymeric Hydrogels: It is a polymeric network consisting of a single species of monomer, which is the basic structural unit comprising of any polymer network. Homopolymers may have cross-linked skeletal structure dependent on the nature of the monomer and polymerization method [13].Co-Polymeric Hydrogels: It is made up of two or more distinct monomer species with at least one hydrophilic component, assembled in a random, block or alternating configuration along the chain of polymer [14].Multi-Polymer or Interpenetrating Polymeric Hydrogel (IPN): It is made of two independent cross-linked synthetic and/or natural polymer components, confined in a network form [15].
Polymerization of 1,2-Epoxides
Published in F. E. Bailey, Joseph V. Koleske, Alkylene Oxides and Their Polymers, 2020
F. E. Bailey, Joseph V. Koleske
Anticipating Section IV.D, tacticity can come about because the initiator is enantiomorphic selective or because incoming monomer is controlled by the configuration of the terminal or penultimate structural unit of polymer. Stereospecific olefin polymerizations are generally of the latter type, while both types probably have been observed with the alkylene oxides. In the case of propylene oxide, where the crystalline polymer arises from enantiomorphic selectivity of the site for monomer coordination, the isotactic configuration is the more likely to occur. Syndiotactie polymer would result from perfectly alternating monomer selectivity during propagation. Stereoblock polymer, in which more extended sequences of one antipode monomer would be followed by an extended sequence of the other, would lead to crystalline, but optically inactive, polymer, from a racemic mixture of monomers (78).
Properties of Coal
Published in A. Williams, M. Pourkashanian, J. M. Jones, N. Skorupska, Combustion and Gasification of Coal, 2018
A. Williams, M. Pourkashanian, J. M. Jones, N. Skorupska
As a result of these studies it is generally accepted that coal is composed mainly of aromatic units arranged into a three-dimensional structure by covalent cross-links and hydrogen bonding. Heteroatoms are incorporated into the aromatic units and functional groups. Coal is thought to contain smaller molecules dispersed within the macromolecular network. Thus, any model coal chemical structure represents a statistically averaged picture. The information required to construct such a model apart from the elemental composition are therefore: Aromaticity and the average number of aromatic rings per “structural unit”Cross-link density; their natureFunctional groups; their number and nature
Emulsions of cross-linked polyacrylic ester for quick-drying yarn sizing
Published in The Journal of The Textile Institute, 2022
Jianhua Ma, Yanqin Shen, Miaomiao Zhang, Yaowu Wang, Hailiang Wu
The chemical structure of starch, PVA and PEA was shown in Figure 2a. It can be seen that the molecular structural unit of starch is α-D-glucopyranose, each of which has three hydroxyl groups, meanwhile PVA was mainly composed of 1,3-ethylene glycol, and each unit contains a hydroxyl group which forming a linear polymer, as observed in Figure 2b that the absorption peaks at 3300 cm−1 for starch and PVA is assigned to the C-OH stretching (Zhang & Li, 2003). For PEA, the primary synthetic monomer included methyl methacrylate, methacrylic acid, methyl acrylate, and ethyl acrylate, and according to Figure 2b, the absorption peak at 1723 cm−1 was the stretching vibration peak of C = O which indicated that the polyacrylate segment has been synthesized (Z. W. Zhu, Zhang et al., 2019). Among the composition of all molecular chains, only the methacrylic acid segment has a hydrophilic carboxyl functional group to ensure the stability of PEA sizing dispersion.
Synthesis and cytotoxicity of novel elastomers based on cholesteric liquid crystals
Published in Liquid Crystals, 2020
Weilong Xie, Ruoran Ouyang, Haoyu Wang, Na Li, Changren Zhou
According to the 1H-NMR spectrum in Figure 1(c), curve TriGCC shows the signal peak (g) at 3.61 ppm appeared as a multiplet form, which is assigned to the oxyethylene structural unit of oligo(ethylene glycol), whereas signals occurred at 3.67 ppm and 4.30 ppm are assignable to the proton peak (f, d) of the methylene group near the ester group. The peaks at 5.80–6.40 ppm are all assigned to the proton peaks (a, b, c) of C = C bond on ATriGCC terminated by acryloyl chloride, whereas new signals occurred at 4.97 ppm and 5.80 ppm are attributed to the proton peaks (a* and b*) on ATriGCC terminated by undecylenyl chloride. The resonance at 3.61–4.20 ppm is attributed to the main chain protons of triethylene glycol. This observation indicates that C = C is successfully attached to the cholesterol derivative. And the corresponding IR and 1H-NMR results of M1 and M2 are listed in Table 1. Moreover, C2, M3, and M4 also revealed similar 1H-NMR spectra, which are shown as Figure S1 in supporting information, and the corresponding value are listed in Table S1.
Photocatalytic performance of nitrogen-doped titanium dioxide nanostructures prepared by sol-gel method
Published in Inorganic and Nano-Metal Chemistry, 2023
Gao Ruqin, Lu Pan, Zhang Zichang, Yao Yingli, Liang Heng, Li Youyin, Li Guoting
At present, a considerable proportion of China’s oil fields have entered the tertiary oil recovery stage. With the extension of the exploitation period, the increase of water content in crude oil has led to difficulty in oil-water separation, and the discharge of oily sewage has increased rapidly. Polymer flooding and Alkaline–surfactant–polymer(ASP) flooding tertiary oil recovery technologies that improve oil recovery have emerged.[1] Polyacrylamide (PAM) is a linear polymer: the amide group contained in its structural unit readily forms hydrogen bonds with other compounds, so it demonstrates good water solubility and chemical activity. Branches can result in a variety of network or branched structure modified products, allowing PAM to be used to produce different derivatives with a variety of excellent properties that other polymers do not have. PAM has a certain viscosity after being dissolved in water, which reduces the water permeability of the oil layer, improves the oil-water mobility ratio, increases the sweep coefficient, adjusts the injection profile, expands the sweep volume, and improves oil recovery. The extensive application of mining has led to the production of a large amount of PAM flooding oil production wastewater. Due to the characteristics of PAM itself, the oil-water separation speed will be declined during the separation and electric dehydration process:[2] this will increase the thickness of the W/O and O/W mixed emulsification layer, which will affect the efficacy of demulsification of the demulsifier, in turn increasing the difficulty of electric dehydration. It is difficult to purify oil production wastewater using current conventional sewage treatment methods. The composition of oil production wastewater is complex, the discharge volume thereof is large, its treatment is difficult, wasteful in resource terms, polluting the environment, and cause great harm to water bodies.[3] With the severity of water scarcity and the improvement of popular awareness of environmental protection, how to deal with petrochemical wastewater has gradually become a focus of much research.