Study on the dehydrofluorination of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer

Heterogeneous Transformation of Ginsenoside Rb1 with Ethanol Using Heteropolyacid-Loaded Mesoporous Silica and Identification by HPLC-MS

Rare ginsenosides with major pharmacological effects are barely present in natural ginseng and are required to be obtained by transformation. In the current study, ginsenoside Rb1 was chemically transformed with the involvement of ethanol molecules to prepare rare ginsenosides using the synthesized heterogeneous catalyst 12-HPW@MeSi. A total of 16 transformation products were obtained and identified using high-performance liquid chromatography coupled with multistage tandem mass spectrometry and high-resolution mass spectrometry. Ethanol molecules were involved in the production of 6 transformation products by adding to the C-20(21), C-20(22), or C-24(25) double bonds on the aglycone to produce ethoxyl groups at the C-25 and C-20 positions. Transformation pathways of ginsenoside Rb1 are summarized, which involve deglycosylation, elimination, cycloaddition, epimerization, and addition reactions. In addition, 12-HPW@MeSi was recyclable through a simple centrifugation, maintaining an 85.1% conversion rate of Rb1 after 3 cycles. This work opens up an efficient and recycled process for the preparation of rare ginsenosides with the involvement of organic molecules.

Synthesis and Properties of the Novel High-Performance Hydroxyl-Terminated Liquid Fluoroelastomer

Functional liquid fluoroelastomers are in high demand in new energy fields. And these materials have potential applications in high-performance sealing materials and as electrode materials. In this study, a novel high-performance hydroxyl-terminated liquid fluoroelastomer (t-HTLF) with a high fluorine content, temperature resistance, and curing efficiency was synthesised from a terpolymer of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), and hexafluoropylene (HFP). A carboxyl-terminated liquid fluoroelastomer (t-CTLF) with controllable molar mass and end-group content was first prepared from a poly(VDF-ter-TFE-ter-HFP) terpolymer using a unique oxidative degradation method. Subsequently, an efficient "one-step" reduction of the carboxyl groups (COOH) in t-CTLF into hydroxyl groups (OH) was achieved via the functional-group conversion method using lithium aluminium hydride (LiAlH₄) as the reductant. Thus, t-HTLF with a controllable molar mass and end-group content and highly active end groups was synthesised. Owing to the efficient curing reaction between OH and isocyanate groups (NCO), the cured t-HTLF exhibits good surface properties, thermal properties, and chemical stability. The thermal decomposition temperature (T_d) of the cured t-HTLF reaches 334 °C, and it exhibits hydrophobicity. The oxidative degradation, reduction, and curing reaction mechanisms were also determined. The effects of solvent dosage, reaction temperature, reaction time, and ratio of the reductant to the COOH content on the carboxyl conversion were also systematically investigated. An efficient reduction system comprising LiAlH₄ can not only achieve an efficient conversion of the COOH groups in t-CTLF to OH groups but also the in situ hydrogenation and addition reactions of residual double bonds (C=C) groups in the chain, such that the thermal stability and terminal activity of the product are improved while maintaining a high fluorine content.

Analysis of the chemical behavior at the molecular level of lined pipes with fluoropolymers in a sodium hypochlorite production line/bibliographic review

This case study is about finding the best fluoropolymer coating for pipes that resists the sodium hypochlorite continue production, which is one of the most aggressive chemical processes that can lead to molecular attack in reactors made by lined pipes. There are several types of coatings pipe such as fiberglass, polymers and elastomers, but the fluoropolymers which have unique properties that make them resistant to chemical attack. In this production process, the premature deterioration of coating pipes is common, due to the expansion of chlorine at the inlet of the reactor, caused by the reaction of chlorine–sodium hydroxide, this is the critical point of the process. Some problems that we find is the chemical attack in that some fluoropolymers coating suffer premature degradation caused by the chemical compatibility, in this case, we explain in detail the chemical and molecular composition of each of the fluoropolymers and how this change occurs at the molecular level. While the lined pipes are the best economical option for chemicals applications, however, it is important to know the correct coating to ensure a long lifetime and avoid piping changes due to premature degradation. Based on the findings of the chemical resistance of each fluoropolymer under study, it is determined which is the best fluoropolymer that resists continuous production of sodium hypochlorite. Results were obtained by a systematic review of the literature.

Strategically Altered Fluorinated Polymer at Nanoscale for Enhancing Proton Conduction and Power Generation from Salinity Gradient

Reverse electrodialysis (RED) generates power directly by transforming salinity gradient into electrical energy. The ion transport properties of the ion-exchange membranes need to be investigated deeply to improve the limiting efficiencies of the RED. The interaction between “counterions” and “ionic species” in the membrane requires a fundamental understanding of the phase separation process. Here, we report on sulfonated poly(vinylidene fluoride-co-hexafluoropropylene)/graphitic carbon nitride nanocomposites for RED application. We demonstrate that the rearrangement of the hydrophilic and hydrophobic domains in the semicrystalline polymer at a nanoscale level improves ion conduction. The rearrangement of the ionic species in polymer and “the functionalized nanosheet with ionic species” enhances the proton conduction in the hybrid membrane without a change in the structural integrity of the membrane. A detailed discussion has been provided on the membrane nanostructure, chemical configuration, structural robustness, surface morphology, and ion transport properties of the prepared hybrid membrane. Furthermore, the RED device was fabricated by combining synthesized cation exchange membrane with commercially available anion exchange membrane, NEOSEPTA, and a maximum power density of 0.2 W m⁻² was successfully achieved under varying flow rates at the ambient condition.

Structure, preparation and properties of liquid fluoroelastomers with different end groups

In order to design and prepare liquid fluoroelastomers with different end groups, and reveal the relationship between the molecular chain structure and properties, we studied on the oxidation degradation method and functional group conversion method to prepare carboxyl-terminated and hydroxyl-terminated liquid fluoroelastomers, respectively. The reaction mechanisms were also deduced. Furthermore, the curing system was created for liquid fluoroelastomers, and systematically analyzed their properties. The sequence type and content of the –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C– and oxygen-containing groups in the samples were measured and characterized by attenuated total reflectance/Fourier transform infrared (ATR-FTIR) spectroscopy, ¹H nuclear magnetic resonance (¹H-NMR), ¹⁹F-NMR spectroscopy and chemical titration, the molecular weights of liquid fluoroelastomers were measured by gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the thermal properties, while a viscometer was used to measure the dynamic viscosity of the liquid fluoroelastomers. Then the mechanical and surface properties of the cured samples were examined by universal testing machine and contact angle measurement instrument, respectively. The results show that carboxyl-terminated liquid fluoroelastomer with 2.71 wt% carboxyl terminal groups can be prepared by oxidation degradation method. When lithium aluminium hydride (LiAlH₄) was used as the reducing agent, it can efficiently convert carboxyl group to hydroxyl group with a conversion rate of more than 95%. In addition, it can be seen that the dynamic viscosity of the liquid fluoroelastomers were all decreased with the increase of temperature, and it is similar to about 10 Pa s at 70 °C. Compared with carboxyl-terminated liquid fluoroelastomers, hydroxyl-terminated liquid fluoroelastomers has higher curing reactivity, higher glass transition temperature (T_g) and thermal decomposition temperature (T_d), and better mechanical properties of cured samples. The two types of liquid fluoroelastomers with distinct end groups presented distinct hydrophilicity.

Liquid fluoroelastomers with carboxyl and hydroxyl end groups were prepared by the oxidation degradation method and the functional group conversion method, the relationship between the structure and properties of them was clarified.

Reduction of liquid terminated-carboxyl fluoroelastomers using NaBH4/SmCl3

Using a simple one-pot method, the reduction of liquid terminated-carboxyl fluoroelastomers (LTCFs) by sodium borohydride and samarium chloride (NaBH₄/SmCl₃) was successfully realized and liquid terminated-hydroxyl fluoroelastomers (LTHFs) were obtained. The structure and functional group content of LTCFs and LTHFs were analyzed by FTIR, ¹H-NMR, ¹⁹F-NMR and chemical titration. The results showed that –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C– and carboxyl groups of LTCFs were reduced efficiently, the reduction rate reached 92% under optimum reaction conditions. Compared with other frequently-used metal chlorides, SmCl₃ with a high coordination number could increase the reduction activity of NaBH₄ more effectively and the reduction mechanism was explored.

A facile method using NaBH₄/SmCl₃ allows for reduction of liquid terminated-carboxyl fluoroelastomers (LTCFs) in excellent yields and provides an attractive potential scheme for the reduction of other carboxyl organic compounds.

Hot nitric acid diffusion in fluoroelastomer composite and its degradation

Fluoroelastomers (FKM) are vital sealing materials in acidic environment and their failure can cause severe safety problems. Therefore, investigation of the degradation behavior and mechanism of FKM materials is of great significant. Herein, we investigate a diffusion model of an acidic solution into an FKM composite and its degradation behavior upon immersion in hot nitric acid solution. The results indicate that the diffusion process of the HNO₃ solution into the FKM composite conforms to the Fick diffusion model at a low concentration of nitric acid solution. Besides, the concentration of HNO₃ solution affects the diffusion process of solvent molecules and the dissolution process of the filler particles to some extent. SEM showed that the surface topography of the FKM was significantly altered after it was immersed in HNO₃ solution. The structural and chemical changes of the FKM were studied using ATR-FTIR, SEM-EDS and MAS NMR, which demonstrated the occurrence of decrosslinking via hydrolysis of the crosslinks and backbone cleavage by dehydrofluorination. This was also manifested by the decrease in crosslinking degree and mechanical properties. The present study is helpful for revealing the chemical changes in FKM in hot HNO₃ solution.

The degradation of fluoroelastomers in hot HNO₃ solution included the decrosslinking via hydrolysis of crosslinks and backbone cleavages by dehydrofluorination.