129Xe NMR as a probe of polymer blends

The miscibility of two-component polymer blends has been investigated using xenon-129 (¹²⁹Xe) nuclear magnetic resonance (NMR) to probe the phase morphology. The chemical shift of ¹²⁹Xe dissolved in a given polymer is unique, thus heterogeneous blends with large domain sizes exhibit two ¹²⁹Xe NMR lines. When a single resonance is obtained, the data are consistent with miscibility, yielding an upper bound on the domain size. The temperature dependence of the relative solubilities and chemical shifts of ¹²⁹Xe dissolved in the pure components may allow a determination of the phase morphology in blends exhibiting a single resonance. The method is used to demonstrate that polychloroprene and 25% epoxidized 1,4-polyisoprene form a miscible blend.     

Proton NMR investigation of the local dynamics of PEO in PEO/PMMA blends

Longitudinal relaxation of proton magnetisation was used to characterize the molecular motions of PEO chains in compatible PEO (hydrogenated)/PMMA (deuterated) blends. Both the temperature and the PEO concentration, Φ, were varied. A maximum in the spin–lattice relaxation rate was observed and its properties were analyzed as a function of Φ. For Φ ≤ 0.50, the maximum is observed below the glass transition temperature of the blend; this shows that PEO chains dispersed in a matrix of PMMA remain highly mobile on a local scale even below T_g(Φ). A frequency–temperature correspondence procedure, applied to the measurements performed at two Larmor frequencies, 32 and 60 MHz, leads to a characteristic correlation time for PEO molecular motions. Its temperature dependence obeys a WLF free volume relation above the glass transition of the blends. The PEO free volume fraction and its thermal expansion are strongly reduced by the presence of the PMMA chains. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1095–1105, 1997     

Enhanced ionic conductivity in PEO/PMMA glassy miscible blends: Role of nano‐confinement of minority component chains

AC impedance spectroscopy was used to investigate the ionic conductivity of solution cast poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends doped with lithium perchlorate. At low PEO contents (below overlap weight fraction w^*), ionic conductivities are almost low. This could be due to nearly distant PEO chains in blend, which means ion transportation cannot be performed adequately. However, at weight fractions well above w^*, a significant increase in ionic conductivity was observed. This enhanced ionic conductivity mimics the PEO segmental relaxation in rigid PMMA matrix, which can be attributed to the accelerated motions of confined PEO chains in PMMA matrix. At PEO content higher than 20 wt % the conductivity measured at room temperature drops due to crystallization of PEO. However by increasing temperature to temperatures well above the melting point of PEO, a sudden increase of conductivity was observed which was attributed to phase transition from crystalline to amorphous state. The results indicate that some PEO/PMMA blends with well enough PEO content, which are structurally solid, can be considered as an interesting candidate for usage as solid‐state electrolytes in Lithium batteries. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2065–2071, 2010     

~(129)Xe-NMR在沸石结构研究中的应用

本文主要采用~(129)Xe-NMR,并结合~(29)Si-与~(27)Al-NMR技术,探讨了在ZSM-5沸石上引入的锌及NaY沸石上引入的稀土阳离子的存在状况,高温焙烧过程对HZSM-5骨架结构的影响。     

129Xe and 131Xe nuclear magnetic dipole moments from gas phase NMR spectra

³He, ¹²⁹Xe and ¹³¹Xe NMR measurements of resonance frequencies in the magnetic field B₀ = 11.7586 T in different gas phase mixtures have been reported. Precise radiofrequency values were extrapolated to the zero gas pressure limit. These results combined with new quantum chemical values of helium and xenon nuclear magnetic shielding constants were used to determine new accurate nuclear magnetic moments of ¹²⁹Xe and ¹³¹Xe in terms of that of the ³He nucleus. They are as follows: μ(¹²⁹Xe) = ?0.7779607(158)μ_N and μ(¹³¹Xe) = +0.6918451(70)μ_N. By this means, the new ‘helium method’ for estimations of nuclear dipole moments was successfully tested. Gas phase NMR spectra demonstrate the weak intermolecular interactions observed on the ³He and ¹²⁹Xe and ¹³¹Xe shielding in the gaseous mixtures with Xe, CO₂ and SF₆. Copyright © 2015 John Wiley & Sons, Ltd.     

Structure formation of PVDF/PMMA blends studied

Conformational formation and crystallization dynamics of miscible PVDF/at-PMMA and PVDF/iso-PMMA polymer blends from the molten state were studied by the simultaneous DSC/FT-IR measurement. Formation of TGTG' conformation occurred before starting crystallization exothermic peak in the PMMA content (_PMMA) range from 0 to 0.4 for both blends. The formation rate of TGTG' conformation, crystal growth rate and surface free energy of PVDF crystal in blends depended linearly on _PMMA for PVDF/at-PMMA, however, those rates for PVDF/iso-PMMA slightly influenced by _PMMA. These results suggested that the former was miscible blend in molecular level, however, the latter was a miscible blend with large concentration fluctuation or a partially segregated system.     

The dependence on temperature and concentration of 129Xe NMR chemical shift values of organoxenon(II) salts [RXe][Y] and of the parent molecule XeF2

The dependence of the 129Xe NMR chemical shift value of XeF2 on temperature and concentration was determined in a variety of prototypic media: in acidic (anhydrous HF, aHF), nonprotic but polar (dichloromethane), and basic (CD3CN-EtCN, 1:3 v/v) solvents. The 129Xe NMR spectra of a representative series of organoxenon(II) salts [RXe][Y] (R = C6F5, heptafluoro-1,4-cyclohexadien-1-yl (cyclo-1,4-C6F7), pentafluoro-1,4-cyclohexadien-3-on-1-yl (cyclo-3-O-1,4-C6F5), CF2=C(CF3), (CF3)2CFC[triple bond]C, C4H9C[triple bond]C; Y = BF4, AsF6) in aHF showed, compared with XeF2-aHF, a quantitatively less distinct but qualitatively related dependence of delta(129Xe) vs temperature. The dependence of their delta(129Xe) values on concentration in aHF is negligible. An explanation for the different behavior of [RXe][Y] and XeF2 is offered.     

MCM-41分子筛的合成及129Xe核磁共振的研究

ＭＣＭ４１中孔分子筛是１９９２年由Ｍｏｂｉｌ公司的科学家Ｋｒｅｓｇｅ［１］等人首次合成的,并在《自然》杂志发表。这种中孔分子筛具有六角形孔径,孔径２ｎｍ～１０ｎｍ,这种分子筛的孔径可以通过水晶模板来控制［２］。已报道的合成ＭＣＭ４１,孔径一般在２．０ｎｍ～３．５ｎｍ,使用的水晶模板一般是单一或两种阳离子季铵盐表面活性剂［３,４］。本论文通过引入第二种扩孔模板,与阳离子季铵盐协同作用,合成了孔径５．２ｎｍ（ＢＥＴ法测）的ＭＣＭ４１。通过氮气的吸脱附,测定了分子筛的比表面和孔径等性质。Ｊ．Ｆｒａｉｓｓａｒｄ…     

Positron annihilation and differential scanning calorimetry investigations in poly(methylmethacrylate)/low molecular weight poly(ethylene oxide) polymer blends

Positron annihilation lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC) measurements were performed in atactic poly(methylmethacrylate) and low molecular weight poly(ethylene oxide) (PEO) polymer blends, prepared by codissolution in acetonitrile, covering the full range of composition. Results from the two techniques indicate that a “window of miscibility” is attained at around 20–30 wt % of the semicrystalline PEO. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1045–1052, 2000     

Characterization of 6FDA‐based hyperbranched and linear polyimide–silica hybrid membranes by gas permeation and 129Xe NMR measurements

Physical and gas transport properties of novel hyperbranched polyimide–silica hybrid membranes were investigated and compared with those of linear‐type polyimide–silica hybrid membranes with similar chemical structures. Hyperbranched polyamic acid, as a precursor, was prepared by polycondensation of a triamine, 1,3,5‐tris(4‐aminophenoxy)benzene (TAPOB), and a dianhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). 6FDA‐TAPOB hyperbranched polyimide–silica hybrids were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) by sol–gel reaction. 5% weight‐loss temperature of the 6FDA‐TAPOB hyperbranched polyimide–silica hybrids determined by TG‐DTA measurement considerably increased with increasing silica content, indicating effective crosslinking at polymer–silica interface. CO₂, O₂, N₂, and CH₄ permeability coefficients of the 6FDA‐based polyimide–silica hybrids increased with increasing silica content. In addition, CO₂/CH₄ selectivity of the 6FDA‐TAPOB–silica hybrids remarkably increased with increasing silica content. From ¹²⁹Xe NMR analysis, characteristic distribution and interconnectivity of cavities created around polymer–silica interface were suggested in the 6FDA‐TAPOB–silica hybrids. It was indicated that size‐selective separation ability is effectively brought by the incorporation of silica for the 6FDA‐TAPOB hyperbranched polyimide–silica hybrid membranes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 291–298, 2006     

129Xe NMR法研究醇二元混合溶液

129Xe NMR可以作为研究液体结构状态的探针．甲醇是一个与水结构差别最小的有机溶剂．本文研究了129Xe在甲醇-丁醇,甲醇-戊醇,甲醇-辛醇,甲醇-癸醇混合溶剂中化学位移随组成的变化,并测定了混合溶剂的密度和折射率．129Xe化学位移随混合溶剂的摩尔分数的变化为四条曲率很近的曲线,而化学位移随混合溶剂的体积分数的变化为斜率随多碳醇碳原子数增加的直线．这表明甲醇-多碳醇二元混合溶剂中不存在疏溶剂作用,而构成分子均匀分布的体系．129Xe在甲醇-丁醇,甲醇-癸醇中的化学位移与混合溶剂折射率的一种函数的关系为两条斜率很接近的直线,表明Xe在溶液中主要受范德华力作用．     

MCM-41分子筛的合成及129Xe核磁共振的研究

Purely siliceous MCM-41 with a narrow pore-size distribution, different pore size, high surface area was synthesized . As prepared, calcined and catalytically tested MCM-41 materials have been comprehensively characterized by N₂ adsorption/desorption at 77K and ¹²⁹Xe NMR. By adding mesitylene during the synthesis, the pore size of MCM-41 was enlarged to 5.2nm. The chemical shift in ¹²⁹Xe NMR spectroscopy of adsorbed xenon indicates that the MCM-41 is one dimensional pore channels .     

结晶-非晶共混体系的结晶行为研究——PEO/PMMA与PEO/PVA共混物

用DSC和傅里叶红外(FTIR)光谱表征PEO/PMMA和PEO/PVA共混体系的结晶行为。发现PEO/PVA体系的结晶度与其组成的变化是一致的;而PEO/PMMA体系的结晶度随非晶组分增加而下降的速度,从与组成变化一致到比后者快,但又随时间而改变。对此结晶/非晶共混体系的结晶度随组成和时间而变化的现象,可用体系的玻璃化转变温度(T_g)来解释。     

Miscibility of PVC/PMMA blends by vicat softening temperature, viscometry, DSC and FTIR analysis

 This paper deals with the miscibility of polyvinyl chloride (PVC) with polymethyl methacrylate (PMMA). Blends of variable compositions from 0 to 100 wt% were prepared in the presence (15, 30 and 50 wt%) and in the absence of di ethyl- 2 hexyl phtalate as plasticizer. Their miscibility was investigated by using various analytical methods: determination of the Vicat softening temperature, a viscometry method based on the criterion of polymer–polymer miscibility, differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The results show that the plot of Vicat temperature against composition is a continuous curve, indicating the miscibility of the blend. The viscometry method and DSC find that the two polymers are miscible up to about 60 wt% of PMMA. This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (C=O) of PMMA and hydrogen from (CHCl) groups of PVC, as evidenced by FTIR spectroscopy. The two-band deconvolution shows an increase in associated groups percentage in the domain of miscibility.     

129Xe NMR study of the localization of PdCl2 supported on carbon nanotubes

Localization of PdCl₂ clusters supported on multi-wall carbon nanotubes (MWCNT) has been investigated using ¹²⁹Xe NMR of adsorbed xenon. As-made MWCNTs with channels initially inaccessible for adsorption and ball-milled MWCNTs with the totally accessible internal surface were used as supports. The observed ¹²⁹Xe NMR spectra were determined by the dynamics of xenon exchange between the aggregate pores and nanotube channels. No considerable changes of the ¹²⁹Xe NMR spectrum with the concentration of supported PdCl₂ were observed for the as-made MWCNT, while an additional resonance appeared for the ball-milled nanotubes. The ¹²⁹Xe NMR experiments evidenced the supported species to be localized on the internal surface of the ball-milled MWCNT.     

固体NMR研究PAA/PEO共混物中氢键相互作用与结构演化

分子间相互作用是决定材料结构和性能的关键因素之一,而如何在分子水上实现对复杂相互作用分子的检测仍然是一个挑战性课题。本工作首先在不同p H值条下以聚丙烯酸/聚环氧乙烷(PAA/PEO)的混合水溶液制备了系列的固体薄膜,然后采用多种基于连续相调制多脉冲技术的一维和二维~1H多脉冲去耦(CRAMPS)固体NMR新技术,并结合高分辨~(13)C交叉极化魔角旋转(CPMAS)、~(23)Na多量子(MQ)等多核固体NMR实验,对PAA/PEO聚合物共混物的微观结构和动力学进行了原位和系统的研究。通过不同类型的~1H高分辨CRAMPS实验检测到共混物中包含多种不同类型质子:通过氢键相互作用形成二聚体的COOH基团、自由COOH基团、与水结合的COOH基团和主链基团。随着p H值的升高,除主链质子外,大部分其它区域的信号都明显降低,这是由于PAA与PEO以及水的氢键作用减弱所致。这些CRAMPS NMR技术也被用来阐明不同p H值制备的样品中不同基团的分子运动性。此外,二维~1H-~1H自旋交换NMR实验提供了关于聚合物PAA与PEO大分子链间、以及水与聚合物的相互作用。~1H自旋扩散实验表明,在这些共混物中明显存在相微观相分离的结构,并且测定的分散相区尺寸约为17 nm。~(23)Na MQMAS实验揭示了在共混物中存在两种类型~(23)Na位,一种是自由的钠离子,另一种是与大分子相互作用的Na离子。特别是通过~1H-检测的~(23)Na-~1H CPMAS实验揭示了Na~+离子的位置远离PEO而与PAA临近。上述这些SSNMR实验结果在分子水平上提供了氢键相互作用对PAA/PEO共混物微观结构和动力学影响的详细信息,可以获得不同p H值对PAA与PEO的氢键作用、相容性、微观结构、水-聚合物相互作用和不同组分分子运动性的影响。在上述核磁共振研究的基础上,我们提出了一种新的PAA/PEO共混物的结构模型,该模型首次成功地揭示了不同的p H值对PAA/PEO共混物中微观结构和动力学的影响。本工作清楚地表明,固态核磁共振是在分子水平上研究具有复杂相互作用的多相聚合物材料的有力工具。本文的研究工作对于探索检测聚合物弱相互作用的新方法和发展基于氢键相互作用的聚合物新材料的开发具有重要意义。     

Phase behavior and a modified Kwei equation for ternary polymer blends containing stereoregular PMMA

Previously, poly(methyl methacrylate) (PMMA) was found to be almost immiscible with poly(vinyl acetate) (PVAc) regardless of tacticity of PMMA and casting solvent. Poly(vinyl phenol) (PVPh) was found successful previously in making immiscible atactic PMMA/PVAc miscible. In this investigation, tacticity effect of PMMA on a ternary composed of PMMA, PVAc and PVPh was studied. Isotactic PMMA ternary was shown to be miscible in all the studied compositions on the basis of single T_g observation. However, syndiotactic PMMA ternary demonstrated immiscibility at ca. 25% PVPh and miscibility was observed at higher PVPh concentrations. A modified Kwei equation based on the binary interaction parameters was proposed to describe the experimental T_g of the miscible ternary almost quantitatively.     

Investigating the effect of nanolayered silicates on blend segmental dynamics and minor component relaxation behavior in poly(ethylene oxide)/poly(methyl methacrylate) miscible blends

Polymer–silicate nanocomposites based on poly (ethylene oxide), PEO, poly(methyl methacrylate), PMMA, and sodium montmorillonite clay were fabricated and characterized to investigate the effect of nanolayered silicates on segmental dynamics of PEO/PMMA blends. X‐ray results indicate the formation of an exfoliated morphology in the nanocomposites. At low silicate contents, an enhancement in segmental dynamics of blend nanocomposites and also PEO, minor component in blend, is observed at temperature region below blend glass transition. This result can be attributed to the improvement of the confinement effect of rigid PMMA matrix on the PEO chains by introducing a low amount of layered silicates. On the other hand, at high silicate contents, an enhancement in segmental dynamics of blend nanocomposites and PEO is observed at temperature region above blend glass transition. This behavior could be interpreted based on the reduction of monomeric friction between two polymer components, which can facilitate segmental motions of blend components in nanocomposite systems. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Electrospinning of Gelatin/PEO Blends: Influence of Process Parameters in the Nanofiber Properties

Summary: Results of electrospinning of gelatin/PEO blends from aqueous solutions are presented. The effects of applied electric field (15–25 kV), flow rate (0.25–0.75 mL/h) and gelatin concentration in the final fiber diameter were studied. It was observed that the resulting fiber system presented high polydispersity, where fiber diameters ranged from 150 nm to 1.3 µm. In some cases an adequate fibrous system were not obtained. It was observed that the average diameter decreased mainly when the flow rate and gelatin concentration decreased.     

Enantiopure cryptophane-129Xe nuclear magnetic resonance biosensors targeting carbonic anhydrase

The (+) and ( ? ) enantiomers for a cryptophane-7-bond-linker-benzenesulfonamide biosensor (C7B) were synthesised and their chirality was confirmed by electronic circular dichroism spectroscopy. Biosensor binding to carbonic anhydrase II (CAII) was characterised for both enantiomers by hyperpolarised (HP) ¹²⁹Xe NMR spectroscopy. Our previous study of the racemic ( ± ) C7B biosensor–CAII complex [Chambers, J.M.; Hill, P.A.; Aaron, J.A.; Han, Z.H.; Christianson, D.W.; Kuzma, N.N.; Dmochowski, I.J. J. Am. Chem. Soc.2009, 131, 563–569] identified two ‘bound’ ¹²⁹Xe@C7B peaks by HP ¹²⁹Xe NMR (at 71 and 67 ppm, relative to ‘free’ biosensor at 64 ppm), which led to the initial hypothesis that (+) and ( ? ) enantiomers produce diastereomeric peaks when coordinated to Zn²⁺ at the chiral CAII active site. Unexpectedly, the single enantiomers complexed with CAII also identified two ‘bound’ ¹²⁹Xe@C7B peaks: (+) 72, 68 ppm and ( ? ) 68, 67 ppm. These results are consistent with X-ray crystallographic evidence for benzenesulfonamide inhibitors occupying a second site near the CAII surface. As illustrated by our studies of this model protein–ligand interaction, HP ¹²⁹Xe NMR spectroscopy can be useful for identifying supramolecular assemblies in solution.