Graft copolymerization of styrene onto poly(vinyl chloride) (PVC) and polypropylene (PP) was carried out in a supercritical CO2 medium using AIBN as a free radical initiator. The supercritical CO2 medium served as a reaction medium in addition to being a solvent for the styrene monomer and the free radical initiator. The reaction temperature and pressure were kept above the critical points of the solvent‐monomer mixture to form a homogeneous single‐phase medium. The resulting graft copolymers were characterized using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) techniques. The weight percent of grafting was determined using IR absorbance ratio technique. TGA results showed that the thermal stabilily of grafted copolymer of PVC was better than that of PVC, while grafted copolymer of PP had poorer thermal stability than PP. DSC results showed that glass transition temperatures (Tg's) of the grafted copolymers were higher than those of the starting polymers PVC and PP. The presence of polystyrene attached to the backbone polymer was confirmed by 1H NMR and 13C NMR analyses. 相似文献
A novel kind of gel polymer electrolytes (GPE) based on comb-like copolymers of poly(ethylene glycol) monomethylether (mPEG) grafted carboxylated butadiene-acrylonitrile rubber (XNBR) were prepared by introducing ionic liquids and LiClO4 into polymer framework. FTIR spectra confirmed the grafting of mPEG to XNBR as side chains, and the content of grafted mPEG were calculated from the integral area of related peaks in 1 H NMR spectra. Such grafted copolymer based GPE with ionic liquids as solvent showed higher ionic conductivity and reached a maximum ionic conductivity of 1.64?×?10?3?S/cm (30?°C) in the experimental range, because the copolymers performed better polymer chain flexibility, which could be concluded from the decrease of Tg and crystallinity through DSC analysis. The generated GPE exhibited high electrochemical stability and the unit cell of LiFePO4/GPE/Li could be cycled at room temperature. 相似文献
As part of a series of studies, effects of Na+ substitution on the thermal evolution of cesium‐based geopolymers on heating were studied. A series of sodium‐substituted cesium‐based geopolymers, Cs(1?x)NaxGPs (where x=0, 0.1, 0.2, 0.3, and 0.4), were prepared and treated at 1300°C for 2 hours to obtain the corresponding ceramic products. The thermal evolution process was disclosed by virtue of a variety of technical, including TG‐DTA, thermal shrinkage, XRD analysis, SEM, and TEM investigation. The results indicated that unheated Cs(1?x)NaxGPs was not completely amorphous after the substitution of Na+ and the crystallinity of Cs(1?x)NaxGPs gradually increased with the rise of sodium content. Meanwhile, the average particle sizes of Cs(1?x)NaxGPs also increased evidently with increases in sodium substitution. The final product after heat treatment mainly consisted of pollucite (CsAlSi2O6) and amorphous glass phase. The particle size of pollucite grain gradually decreased as more Cs+ were replaced maybe owing to the role of Na+ in the nucleation process of pollucite. Two forms of Na+ present in the final products: A small portion was present in the pollucite grains due to Na+ partial occupied the crystallographic sites of Cs+; and the rest were present in the amorphous glass phase among the pollucite grains. The average coefficient of thermal expansion (CTE) of resulting Cs(1?x)NaxGPs ceramics increased from 4.80×10‐6 K?1 (x=0) to 7.26×10?6 K?1 (x=0.4) with increases in sodium substitution, which could be due to the amorphous glass phase had a relatively higher CTE than that of pollucite. 相似文献
PVC, which was polymerized at atmospheric pressure (so called U-PVC) contains relatively high concentrations of defects contrary to normal PVC. The number of chain scissions in U-PVC determined by ozonolytic cleavage resulted in values between 0.026 and 0.058 per 100 monomer units (100 VC). The determination of allylic and tertiary chlorine was done by selective reaction of U-PVC with phenol and NMR-spectroscopic investigations of the phenolized polymers. The average ‘labile chlorine’ content amounts to 0.65/100 VC. Hydroxyl radicals formed during the decomposition of the initiator (K2S2O8) resulted in alcoholic endgroups in U-PVC, which were detectable in the IR-spectrum at 3580 cm?1. The termination with hydroxyradicals also led to structures at the chain ends changing into ß-chloraldehyde groups accompanied by HCl-elimination. The corresponding signal in the IR-spectrum appeared at 1720 cm?1. U-PVC raw material contained about two branch points per 100 VC. The CCl4 extracts of the same polymers revealed the ten-fold content of branching. The olefinic structures ? CH?CH? CHCl? and ? CHCl? CH?CH2 were determined by NMR-spectroscopy. The concentrations of each ranged from 0.25 to 0.3/100 VC. A typical double bond for U-PVC at the chain ends represented the structure ? CH?CH? CH2Cl, which was preferably present in the low molecular weight material. 相似文献
Silver ions are bound on polystyrene containing ? CH2Cl groups with a distribution coefficient of about 100 ml/g, but they are not bound on polystyrene itself. This indicates direct interaction between Ag+ ions and the chlorine atoms of the ? CH2Cl groups in the sense of formation of a 1:1 complex. In presence of 0.1 mol/l of ammonium ions somewhat smaller distribution coefficients are found in the range from pH 4 to pH 6. In presence of 10?3 mol/l of Na2S2O3 the distribution coefficients are only about 6 ml/g. From solutions, however, containing 1 mol/l of NaCl or 0.1 mol/l of Na2S2O3 or 10?3 mol/l of NaCN, silver is not sorbed in measurable amounts, because complexation in solution predominates. 相似文献
Measurements have been made of the depression of the freezing point of fused KSCN by Na2S, Na2S4.4 and K2S5.9. Na2S gives a freezing point depression corresponding to three region particles. These are believed to be 2Na+ and CN?, the cyanide ion being formed by reaction of S2? with the solvent. Na2S4.4 and K2S5.9 give opaque solutions in KSCN which are initially dark blue-green, and which slowly lose sulphur vapour and change colour to blue and finally to pale yellow. The initial freezing point depressions correspond to 4 and 2 foreign particles respectively, but when sulphur evolution is complete the final depressions correspond to 2 and 0 foreign particles. The following schemes are consistent with the observations 相似文献
A series of Na-montmorillonite (Na+-MMT) modified acrylic impact modifiers (mAIM) were prepared by seeded emulsion polymerization. These mAIM modifiers were characterized by XRD. A 0.24?nm of increased interlayer distance of Na+-MMT was an indication of polymer chains intercalation within interlayer spacing. The notched Izod impact tests proved that the impact strength of the PVC/AIM composites prepared by melt blending was 43?J/m, markedly higher than the impact strength of pure PVC. Furthermore, with increasing content of AIM, the composites exhibited changes from brittle fracture to ductile fracture, with the impact strength increasing from 200 to about 1,000?J/m. The impact strength of PVC/mAIM also showed the same trend, although there were drops in some values. The impact strength of PVC/mAIM composites decreased with the increases in Na+-MMT content, but the yield strength and modulus of the composites increased with higher Na+-MMT content. The result also showed that the tensile strength of mAIM with 2 wt?% Na+-MMT is lower than that of mAIM with 0.8 and 1 wt?% contents, but still sufficiently large in comparison to the tensile strength of mAIM with 0 wt?% Na+-MMT. The dynamic mechanical analysis (DMA) result showed that the glass transition temperature (Tg) of mAIM did not show obvious changes and the elasticity of mAIM was reduced with the additional Na+-MMT content. 相似文献
The (K1-xNax)2Mo2O7 (0.0?≤?x?≤?0.3) ceramics with ultra-low sintering temperatures were prepared by a modified solid-state reaction method. Polyvinyl ethanol (PVA) binder was replaced by ethanol and isostatic pressing technology was used, which improved the density of the ceramics effectively and avoided the side effect of the residual PVA. When x?≤?0.3, the (K1-xNax)2Mo2O7 ceramics are with a triclinic phase and all components can be sintered well at 450?°C. The substitution of Na+ at the K-site modified the dielectric properties of K2Mo2O7 ceramic and in particular increased the Q?×?f value. Among all the components, the (K0.8Na0.2)2Mo2O7 ceramic exhibited the best microwave dielectric properties with a permittivity of 8.7, a Q?×?f value of 50 300?GHz and a temperature coefficient of ?64?ppm/°C. The (K1-xNax)2Mo2O7 (0.0?≤?x?≤?0.3) ceramics are very potential candidates for ultra-LTCC devices and the modified solid-state reaction method is an excellent substitution for the conventional solid-state method. 相似文献
A NaS battery having the configuration is described. This cell, operating just above the melting point of Na, utilizes sodium polysulfides (Na2Sn) dissolved in an organic solvent as the cathode. Use of this cathode system allows operation at a lower temperature than in the Na/molten Na polysulfide battery. In order to find a suitable solvent for the cathode, solubility and stability data for Na2S and Na2S4 were obtained in 26 organic solvents at 150°C. The solvent meeting the optimum requirements of high boiling point, polysulfide solubility, thermal stability and chemical compatibility with Na2Sn is N,N-dmethylacetamide (DMAC). Charge—discharge data for cells incorporating an Na2S4/DMAC cathode are presented. Discharge to at least S?22 appears possible. On recharge, a long chain, soluble Na polysulfide is formed rather than elemental S. This avoids possible problems due to separation of two phases as in the high temperature NaS battery. 相似文献
The monomer, 4-acrylamidobenzenesulfonamide (ABS), was synthesized via reaction of acryloyl chloride with 4-aminobenzenesulfonamide in acetone at 0 °C. This monomer was then grafted onto chitosan using solution containing 2% acetic acid and mixture of K2S2O8 and Na2SO3 as the redox promoter. An optimal G% of 150% was obtained when the process is conducted at 60 °C for 3 h employing 3.0 × 10?3 M K2S2O8 and 1.5 × 10?3 M Na2SO3. The graft copolymers, chitosan-g-poly(4-acrylamidobenzenesulfonamide), were characterized by using FTIR, XRD, and SEM. The results were shown that the crystallinity of chitosan is enhanced by increasing the monomer content through the grafting process. Potential Antimicrobial activities of the permethyl ammonium salt forms of chitosan and its grafted copolymers against selected microorganisms were evaluated. The results show that the graft copolymers display better inhibitory effects on the growth of bacteria and some fungi than does chitosan. 相似文献
The reaction rate of crosslinking of PVC with dithioltriazine has been studied by following gel formation and changes in the molecular weight distribution (MWD). Compounding was performed on a roll mill at 145°C and crosslinking by heat treatment at 180 or 90°C. In this system crosslinking is executed by the thiolate anion, formed in situ by reaction with MgO. We have studied the catalyzing effect of several polyols in order to achieve a more efficient reaction. Most likely, these catalysts work by chelating the Mg2+ ions, thus increasing the nucleophilic character of the thiolate. With the most efficient ones, ditrimethylolpropane and HO(CH2CH2)6-7H, complete crosslinking can be obtained in 3 min at 180°C, i.e., at processing temperatures. We also followed the changes in the MWD before gelation at a considerably lower temperature, 145°C, and found an extensive molecular enlargement even after 5-10 min. Most surprisingly, μMn increased up to 100% without formation of insoluble material. By 1H-NMR measurements on low molecular weight extracts, we have shown this to be due to a fast and selective reaction with allylic chlorine in the unsaturated end groups, ~ CH2? CH?CH? CH2Cl, formed in the mechanism of chain transfer to monomer. Due to this reaction, formulations with too high reactivity may crosslink during processing, which calls for a careful balancing of the reactivity for each processing case. 相似文献
The paper illustrates the graft emulsion polymerization of methylmethacrylate onto polybutadiene in two steps. In the first butadiene is polymerized using two radical initiators (AIBN and (NH4)2S2O8), whose ratio does not influence the relative amount of 1,2-, 1,4-trans and 1,4-cis structures. The second step uses AIBN only: the grafting yield is very high. Grafting mechanism is discussed. The grafted polymer has good mechanical properties and its blends with PVC present very high impact strength. The mechanical properties are discussed. A statistical copolymer of butadiene and methylmethacrylate was prepared and compared with the grafted polymer. The copolymer is also a very good additive for PVC to elevate its impact strength. 相似文献