Sheng Shu Hou

Function and performance of silicone copolymer. Part IV. Curing behavior and characterization of epoxy–siloxane copolymers blended with diglycidyl ether of bisphenol-A

Abstract In this research, a siloxane-type epoxy resin (SG copolymer), which has pendant epoxide rings on the side chain of the polysiloxane polymer backbone, was synthesized by the hydrosilylation reaction of poly(methylhydrosiloxane) with allyl glycidyl ether. The polymer structures were characterized by 1H NMR. The SG resin was then blended with a commercial epoxy resin (diglycidyl ether of bisphenol-A, DGEBA) at various ratios, using dicyandiamide (DICY) as a curing agent. The curing behaviors were studied by DSC. It was found that the initial curing temperature (Ti) and peak curing temperature (Tp) were increased by the addition of SG copolymer to the epoxy resin. Their morphology, mechanical properties and the stability of the cured piece were investigated using SEM, DMA and TGA, respectively. The results show that the addition of SG copolymer increases the mobility of the crosslinked network, and increases the thermal stability.

Poly(ethylene oxide)-co-poly(propylene oxide)-based gel electrolyte with high ionic conductivity and mechanical integrity for lithium-ion batteries

Using gel polymer electrolytes (GPEs) for lithium-ion batteries usually encounters the drawback of poor mechanical integrity of the GPEs. This study demonstrates the outstanding performance of a GPE consisting of a commercial membrane (Celgard) incorporated with a poly(ethylene oxide)-co-poly(propylene oxide) copolymer (P(EO-co-PO)) swelled by a liquid electrolyte (LE) of 1 M LiPF6 in carbonate solvents. The proposed GPE stably holds LE with an amount that is three times that of the Celgard-P(EO-co-PO) composite. This GPE has a higher ionic conductivity (2.8×10(-3) and 5.1×10(-4) S cm(-1) at 30 and -20 °C, respectively) and a wider electrochemical voltage range (5.1 V) than the LE-swelled Celgard because of the strong ion-solvation power of P(EO-co-PO). The active ion-solvation role of P(EO-co-PO) also suppresses the formation of the solid-electrolyte interphase layer. When assembling the GPE in a Li/LiFePO4 battery, the P(EO-co-PO) network hinders anionic transport, producing a high Li+ transference number of 0.5 and decreased the polarization overpotential. The Li/GPE/LiFePO4 battery delivers a discharge capacity of 156-135 mAh g(-1) between 0.1 and 1 C-rates, which is approximately 5% higher than that of the Li/LE/LiFePO4 battery. The IR drop of the Li/GPE/LiFePO4 battery was 44% smaller than that of the Li/LE/LiFePO4. The Li/GPE/LiFePO4 battery is more stable, with only a 1.2% capacity decay for 150 galvanostatic charge-discharge cycles. The advantages of the proposed GPE are its high stability, conductivity, Li+ transference number, and mechanical integrity, which allow for the assembly of GPE-based batteries readily scalable to industrial levels.

High performance of transferring lithium ion for polyacrylonitrile- interpenetrating crosslinked polyoxyethylene network as gel polymer electrolyte

A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06-8.21 mS cm(-1)) than that of the commercial Celgard M824 separator (0.45-0.90 mS cm(-1)) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes.

Synthesis and characterization of amphiphilic graft copolymers based on poly(styrene-co-maleic anhydride) with oligo(oxyethylene) side chains and their GPC behavior

Abstract A series of amphiphilic graft copolymers were synthesized based on poly(styrene-co-maleic anhydride) (SMAs) (backbone copolymers) and methoxypolyethylene glycols (MPEGs) (grafts) in this study. Selection of proper reaction conditions using p-toluenesulfonic acid (PTSA) as catalyst and toluene as solvent in the present research can prevent crosslinking reactions which may occur due to the presence of di-functional polyethylene glycol in the commercial MPEGs. The structures and compositions of the graft copolymers were determined by gel permeation chromatography (GPC) and 1H NMR analysis. It is noteworthy that the GPC behavior of these graft copolymers follows the rule of thumb for GPC, i.e. the higher molecular weight copolymers have lower retention volumes. This is very different from the GPC behavior of similar graft copolymers reported previously in the literature. Also, differential scanning calorimetry (DSC) characterization shows that there are two transition temperatures for some of these amphiphilic copolymers owing to the existence of another aggregation phase of MPEG grafts.

Magnetism and nuclear magnetic resonance of hectorite and montmorillonite layered silicates

The temperature and magnetic-field (H) dependencies of the bulk dc magnetization (M) and the M∕H ratio of montmorillonite (MMT), hectorite (HCT), and synthetic mica-montmorillonite (SMMT) clays have been measured and compared with the signal intensity of H1 and Si29 nuclear magnetic resonance (NMR) spectra. MMT exhibits Langevin paramagnetism with an effective magnetic moment of 5.5±0.1μB per Fe ion whereas SMMT has diamagnetic properties. At 300K, M∕H of HCT measured in a magnetic field of H⩽1kOe is larger than that of MMT, whereas in a field of 50kOe, the inverse situation is observed. The difference arises because the magnetization of HCT is dominated by a contribution from ferromagneticlike impurities. The H1 and Si29 NMR signals of MMT are broadened beyond detectability due to the paramagnetic effect. Although HCT contains ferromagneticlike components that result in a large M∕H in low field, it yields H1 and Si29 NMR spectra with signal intensities similar to those of diamagnetic SMMT. Our data highl...

NMR studies on effects of tetraalkylammonium bromides on micellization of sodium dodecylsulfate.

The effects of tetraalkylammonium bromides (TAABs) on the micellization of sodium dodecylsulfate (SDS) are studied using pyrene solubilization and several nuclear magnetic resonance (NMR) techniques. Two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) experiments confirm that tetraalkylammonium (TAA(+)) ions associate with SDS to form mixed micelles. TAA(+) ions attach to the surface of the mixed micelles and become inserted into the hydrophobic core of the mixed micelles. Because TAA(+) ions appear in the hydrophobic interior of the TAA-SDS mixed micelles, the micropolarity inside the mixed micelles sensed by pyrene might not reflect the true hydrophobicity of the micellar core. Using proton chemical shift analysis, the degree of hydration on the surface of the mixed micelles is determined from the chemical shift change of SDS α-CH2 protons. The self-diffusion coefficients of SDS and TAA(+) ions in the TAAB/SDS/D2O solutions are measured by using pulse-field gradient NMR, and the fraction of TAA(+) ions associated with the SDS to form the mixed micelles is calculated from the self-diffusion data. Moreover, secondary micelle formation for SDS and TAA(+) ions is observed on the basis of (1)H chemical shift analysis and the self-diffusion data. The 2D NOESY experiments also reveal unusual tumbling behavior of SDS alkyl protons. For Pr4NBr/SDS and Bu4NBr/SDS solutions, positive and negative nuclear Overhauser effects are simultaneously observed among the SDS alkyl protons.

Intermolecular association and supramolecular structures of PNVF–LiPFN and PVP–LiPFN complexes in the aqueous phase

A new polymer–surfactant system, the poly(N-vinylformamide) (PNVF)–lithium perfluorononanoate (LiPFN) system, has been studied by a combination of the surface tension method and two-dimensional 1H-19F heteronuclear Overhauser effect NMR spectroscopy (2D 1H-19F HOESY). Using the surface tension method, we found that the critical aggregation concentration (cac) of LiPFN in the presence of PNVF is ca. 2 mM. In addition, the association behavior between LiPFN and PNVF is similar to that between poly(vinylpyrrolidone) (PVP) and LiPFN. The supramolecular structure of the PNVF–LiPFN complex in the aqueous phase is revealed by means of the 2D 1H-19F HOESY experiment. On the basis of the intermolecular cross-relaxation between the PNVF protons and the LiPFN fluorines, we could conclude that the PNVF chain do penetrate into the LiPFN aggregate. The semi-quantitative analysis of the internuclear distance indicates that the PNVF chain is not located at the center core of the LiPFN aggregate, but the PNVF chain thread itself through the surface shell of the LiPFN aggregate instead. PNVF protons are nearest to the fluorines next to the carboxyl group, suggesting that the interaction between PNVF and LiPFN is mainly due to the dipole-ionic attraction. Moreover, we have reinvestigated the supramolecular structure of PVP–LiPFN complex and have found that the PVP chain also penetrates into the LiPFN aggregate. In contrast with the PNVF–LiPFN complex, the PVP chain in the PVP-LiPFN complex is rather close to the middle part of the LiPFN molecules which constitute the polymer-bound aggregate. This indicates that the formation of PVP–LiPFN complex involves more or less fluorophilic interactions.

Allylsulfone in Free Radical Reaction

Abstract A sulfonyl radical induced addition-cyclization reaction of vinylcyclopropane and 1,6-diene by using allylsulfone as sulfonyl radical precursor to give functionalized cyclopentane is described.

Interaction between hydrophobically modified 2-hydroxyethyl cellulose and sodium dodecyl sulfate studied by viscometry and two-dimensional NOE NMR spectroscopy

Interaction between an anionic surfactant, sodium dodecyl sulfate (SDS), and a nonionic polymer, 2-hydroxyethyl cellulose (HEC) hydrophobically modified with benzoyl chloride (bmHEC), is studied by viscometry and two-dimensional nuclear Overhauser effect NMR spectroscopy (2D NOESY) in a semidilute regime of bmHEC. The hydrophobicity of bmHEC was varied with different substitution of benzoyl group to HEC macromolecules. In general, the low-shear viscosity of 1 wt % bmHEC aqueous solution is increased with added SDS surfactant having concentration from 0 to 0.5 wt %, and then decreased significantly with a further addition of surfactant to 3 wt %. The activation energy of transient network formation in 1 wt % bmHEC aqueous solution present with SDS surfactant is found to be dependent with SDS concentration, which varies from 32.7 to 69.80 kJ/mol. The maximum activation energy takes place when 0.5 wt % SDS is added, which coincides with that of the maximal viscosity. The 2D NOESY displays that the surfactants actually interact with bmHEC not only on the hydrophobes, namely benzoyl groups, but also the polymer backbone, i.e., glucose units. In contrast, no interaction is revealed by 2D NOESY in the aqueous system containing SDS surfactant and HEC polymer.

Structure and molecular dynamics of sodium dodecylsulfate micelles modified with hydrophilic short-chain imidazolium salts in aqueous solution

This study uses pyrene solubilization and NMR experiments to investigate the effects of two hydrophilic short-chain ionic liquids (ILs), 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) and 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) on the micellization of sodium dodecylsulfate (SDS) in the aqueous phase. The results of the pyrene solubilization experiments indicate that the added short-chain ILs not only promote the micellization of SDS but also modify micelle properties. For NMR studies, the present study focuses on (1) the compositions and spatial arrangements of component molecules and (2) the molecular dynamics of DS(-) in the Rmim-modified SDS micelle. Using pulsed field gradient (PFG) NMR measurements, the composition of the Rmim-modified SDS micelle was calculated by the diffusion data and was found to be correlated with the [SDS]. Two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) experiments confirm that the 1-alkyl-3-methylimidazolium cation (Rmim(+)) is located inside the Rmim-modified SDS micelle. Corresponding to the microstructure of the Rmim-modified SDS micelle, in terms of (1)H T1 relaxation, the fast motion of SDS α-CH2 and β-CH2 segments are markedly restricted by the attached Rmim(+) to the sulfate group of DS(-), whereas the central carbons and the terminal CH3 group of DS(-) are only slightly affected. The chemical shift analysis indicates that the surface of the Rmim-modified SDS micelle is dehydrated by the absorbed Rmim(+) and becomes more hydrophobic than that of the pure SDS micelle. Insertion of Rmim(+) into the Rmim-modified SDS micelle appears to be driven through the hydrophobic interaction, and it is shown to combine with SDS molecules to constitute the hydrophobic part of the Rmim-modified SDS micelle.