Solution properties of ionomers. I. Counterion effect

The effect of counterions on the solution properties of two types of ionomers, one based on sulfonated polystyrene and the other based on styrene–methacrylic acid copolymer, was studied by viscosity and light scattering measurements. It was found that the order of counterion binding of ionomers in a polar solvent and the order of aggregation of ionomers in a low-polarity solvent were the same for the same ionomer system. However, the order for the sulfonated ionomer was Li < Na < K < Cs, whereas that for the carboxylated ionomer was the opposite. This can be explained by a difference in desolvation during anion–cation interaction and by considering site-binding in a polar solvent and the association of ion pairs in a low-polarity solvent. These findings for ionomer systems are parallel to the association behavior of small ions in water, cation affinity in crosslinked resins, and counterion binding of polyelectrolytes in water.     

Ionic aggregate structure in ionomer melts: effect of molecular architecture on aggregates and the ionomer peak

We perform a comprehensive set of coarse-grained molecular dynamics simulations of ionomer melts with varying polymer architectures and compare the results to experiments in order to understand ionic aggregation on a molecular level. The model ionomers contain periodically or randomly spaced charged beads, placed either within or pendant to the polymer backbone, with the counterions treated explicitly. The ionic aggregate structure was determined as a function of the spacing of charged beads and also depends on whether the charged beads are in the polymer backbone or pendant to the backbone. The low wavevector ionomer peak in the counterion scattering is observed for all systems, and it is sharpest for ionomers with periodically spaced pendant charged beads with a large spacing between charged beads. Changing to a random or a shorter spacing moves the peak to lower wavevector. We present new experimental X-ray scattering data on Na(+)-neutralized poly(ethylene-co-acrylic acid) ionomers that show the same two trends in the ionomer peak, for similarly structured ionomers. The order within and between aggregates, and how this relates to various models used to fit the ionomer peak, is quantified and discussed.     

Breakdown of hydration repulsion between charged surfaces in aqueous Cs+ solutions

Using a surface force balance, we have measured the normal and shear forces between mica surfaces across aqueous caesium salt solutions (CsNO(3) and CsCl) up to 100 mM concentrations. In contrast to all other alkali metal ions at these concentrations, we find no evidence of hydration repulsion between the mica surfaces on close approach: the surfaces appear to be largely neutralized by condensation of the Cs ions onto the charged lattice sites, and are attracted on approach into adhesive contact. The contact separation at adhesion indicates that the condensed Cs ions protrude by 0.3 +/- 0.2 nm from each surface, an observation supported both by the relatively weak adhesion energies between the surfaces, and the relatively weak frictional yield stress when they are made to slide past each other. These observations show directly that the hydration shells about the Cs(+) ions are removed as the ions condense into the charged surface lattice. This effect is attributed to the low energies-resulting from their large ionic radius-required for dehydration of these ions.     

Solution viscosity behavior of polystyrene-based cationic ionomers. Effects of ion content and solvent

Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (ε_r) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low ε_r, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (A_N), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high A_N value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc.     

离聚体的结构表征——Ⅴ.含氟离聚体中离子微区稳定性的研究

本文用DSC方法研究了羟酸型含氟离聚体中不同金属离子种类、可离子化基团含量、配位结构单元构型及离子微区大小对离聚体中离子微区稳定性的影响。实验表明:离聚体中金属离子配位能力愈强,羟酸含量愈高,离子微区尺寸愈大,则相应离聚体中离子微区稳定性愈大。铅高聚体>锌离聚体>钙离聚体>钠离聚体。     

Wettability of poly(styrene‐co‐acrylate) ionomers improved by oxygen‐plasma source ion implantation

The surfaces of poly(styrene‐co‐acrylic acid) copolymers and their Na‐ and Cs‐neutralized ionomers were modified by O₂‐plasma source ion implantation (PSII) treatment to improve the surface wettability. The changes in the surface wettability, composition, and structure upon the PSII treatment were examined with contact‐angle measurements and X‐ray photoelectron spectroscopy. The untreated surfaces of the acid copolymers and ionomers exhibited different surface energies; this implied clearly that the type of ion species affects the surface hydrophilicity. Also, the PSII treatment induced oxygen‐containing groups to reside on the surface and ionic groups to come out toward the surface; this made the surfaces of the ionomers more hydrophilic as compared with that of the acid copolymers. The ionomers also showed slow hydrophobic recovery. Thus, it was suggested that the reduced mobility of the polymer chain because of the presence of ionic aggregates results in restricted reorientation of oxygen‐containing groups. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1791–1797, 2003     

Aqueous NaCl and CsCl solutions confined in crystalline slit-shaped silica nanopores of varying degree of protonation

All-atom molecular dynamics simulations were conducted to study the dynamics of aqueous electrolyte solutions confined in slit-shaped silica nanopores of various degrees of protonation. Five degrees of protonation were prepared by randomly removing surface hydrogen atoms from fully protonated crystalline silica surfaces. Aqueous electrolyte solutions containing NaCl or CsCl salt were simulated at ambient conditions. In all cases, the ionic concentration was 1 M. The results were quantified in terms of atomic density distributions within the pores, and the self-diffusion coefficient along the direction parallel to the pore surface. We found evidence for ion-specific properties that depend on ion-surface, water-ion, and only in some cases ion-ion correlations. The degree of protonation strongly affects the structure, distribution, and the dynamic behavior of confined water and electrolytes. Cl(-) ions adsorb on the surface at large degrees of protonation, and their behavior does not depend significantly on the cation type (either Na(+) or Cs(+) ions are present in the systems considered). The cations show significant ion-specific behavior. Na(+) ions occupy different positions within the pore as the degree of protonation changes, while Cs(+) ions mainly remain near the pore center at all conditions considered. For a given degree of protonation, the planar self-diffusion coefficient of Cs(+) is always greater than that of Na(+) ions. The results are useful for better understanding transport under confinement, including brine behavior in the subsurface, with important applications such as environmental remediation.     

Self-organization of sulfopolystyrene ionomers in solutions: Dependence on the polarity of the solution and the content of ionogenic groups in chains

The self-organization of ionomers of sulfonated polystyrene containing different amounts of SO₃Na ionogenic groups (0.5, 1.35, and 2.6 mol %) in three solvents (benzene, toluene, and THF) is studied via the methods of neutron scattering. It is shown that, in toluene, ionogenic groups form “effective” chains of up to 10–20 macromolecules owing to aggregation. In benzene, chains of both the PS precursor and ionomers are surrounded by volume solvate shells in the form of ∼4-nm-dia tubes that hamper interaction between ionomers via ionogenic groups. The tendency of ionomer chains toward aggregation in benzene is enhanced as the content of polar groups in chains is increased to 2.6 mol %. The diameter of solvate shells around chains decreases to ∼1 nm, and chains associate to form denser structures. In this case, the degree of integration of macromolecules turns out to be smaller than that in toluene. In THF, the processes of solvation and structuring of PS precursor chains are well defined and compete with tendencies toward association through ionogenic groups in solutions of ionomers. The formation of developed supramolecular structures in THF is hindered by the shielding of the potentials of interaction between ion pairs because of a high dielectric constant of the solvent.     

含不同金属离子的EPDM磺酸盐离聚物的研究

合成了含不同金属离子Na~+、Mg~(2+)、Zn~(2+)和Al~(3+)的四种乙丙三元共聚物(EPDM)磺酸盐离聚物, 红外光谱和氧瓶燃烧法测定了磺酸基的存在和含量。动态力学结果表明, 离聚物中碳酸盐基团可能以多重离子对形式聚集; 热重法指出, EPDM磺酸盐的热稳定性为钠盐>锌盐>镁盐>铝盐。考察了它们在二甲苯-正己醇混合溶剂中, 比浓粘度随浓度、温度变化的规律, 初步分析了各种金属盐的差异及其原因。     

How alkali metal ion binding alters the conformation preferences of gramicidin A: a molecular dynamics and ion mobility study

Here, we present a systematic study combing electrospray ionization-ion mobility experiments and an enhanced sampling molecular dynamics, specifically integrated tempering sampling molecular dynamics simulations (ITS-MDS), to explore the conformations of alkali metal ion (Na, K, and Cs) adducts of gramicidin A (GA) in vacuo. Folding simulation is performed to obtain inherent conformational preferences of neutral GA to provide insights about how the binding of metal ions influences the intrinsic conformations of GA. The comparison between conformations of neutral GA and alkali metal ion adducts reveals a high degree of structural similarity, especially between neutral GA and [GA + Na](+); however, the structural similarities decrease as ionic radius of the metal increases. Collision cross section (CCS) profiles for [GA + Na](+) and [GA + Cs](+) ions obtained from by ITS-MDS compare favorably with the experimental CCS, but there are significant differences from CCS profiles for [GA + K](+) ions. Such discrepancies between the calculated and measured CCS profiles for [GA + K](+) are discussed in terms of limitations in the simulation force field as well as possible size-dependent coordination of the [GA + K](+) ion complex.     

乙烯-丙烯共聚物磺酸盐离聚物的研究——Ⅱ.离聚物的合成和表征

通过氯磺化共聚物的水解合成了乙烯-丙烯共聚物磺酸钠离聚物,对离聚物的结晶度和其中硫、氯、钠元素的含量进行了表征.当离子含量达到5—7 mol％时,离聚物的LAXD曲线出现离子峰;DSC指出T_g急剧升高,而低于此离子浓度的离聚物均不出现这些现象.反映出此离子浓度下的离聚物,离子基因可能聚集形成离子簇结构.     

Modeling electrode polarization in dielectric spectroscopy: Ion mobility and mobile ion concentration of single-ion polymer electrolytes

A novel method is presented whereby the parameters quantifying the conductivity of an ionomer can be extracted from the phenomenon of electrode polarization in the dielectric loss and tan delta planes. Mobile ion concentrations and ion mobilities were determined for a poly(ethylene oxide)-based sulfonated ionomer with Li(+), Na(+), and Cs(+) cations. The validity of the model was confirmed by examining the effects of sample thickness and temperature. The Vogel-Fulcher-Tammann (VFT)-type temperature dependence of conductivity was found to arise from the Arrhenius dependence of ion concentration and VFT behavior of mobility. The ion concentration activation energy was found to be 25.2, 23.4, and 22.3+/-0.5 kJmol for ionomers containing Li(+), Na(+), and Cs(+), respectively. The theoretical binding energies were also calculated and found to be approximately 5 kJmol larger than the experimental activation energies, due to stabilization by coordination with polyethylene glycol segments. Surprisingly, the fraction of mobile ions was found to be very small, <0.004% of the cations in the Li(+) ionomer at 20 degrees C.     

IONIC THERMOPLASTIC ELASTOMERS: A REVIEW

The incorporation of small amount of ionic groups into hydrocarbon polymers results in unique physical properties and these polymers are called ionomers. They are effectively cross-linked through the association of ionic groups, forming multiplets or clusters. These associations are thermally labile to a greater or lesser extent depending on the composition of the ionic domains. In elastomeric ionomers, the thermolabile nature of the ionic domains permits the adequate flow at the processing temperatures, and hence the term ionic thermoplastic elastomers. Polar plasticizers are incorporated into ion-containing polymers in order to reduce the melt viscosity, resulting from the strong ionic associations, and to improve the processability. The introduction of ionic groups into the block copolymers improves their thermal stability and high temperature performance. The presence of ion-ion interactions in different rubber/plastic blends enhances the mechanical compatibility of the otherwise incompatible blends and thereby results in the formation of ionic thermoplastic elastomers, depending on the rubber to plastic ratios. In the absence of ionic groups the blend components are incompatible, as indicated by poor physical properties of the blends. However, the introduction of ionic groups onto the polymer chains causes a dramatic increase in compatibility between the rubbery and the plastic phases, as indicated by the synergism in physical properties. The present paper reviews the ionic thermoplastic elastomers based on elastomeric ionomers, block copolymer ionomers, and ionomeric polyblends.     

Analysis of carrageenans by matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. I. kappa-Carrageenans.

Matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectra of small kappa-carrageenans are reported and discussed. MALDI spectra can be obtained in both positive and negative ion mode. In the absence of extraneous metal ions, positive ions are formed by the attachment of one Na(+) ion to the carrageenan, whereas for negative ions one Na(+) ion is detached from the sulfate group. Multiply charged species are not observed in MALDI. Intense ESI spectra can be obtained in negative ion mode and now multiply charged species are seen. Alkali exchange experiments show that in these small carrageenan anions one, but only one, alkali metal ion is bound in a bidentate coordination with two ionic sulfate groups. G2-type ab initio calculations on model ions HO(-) [M(+)] (-)OH (M = Li, Na, K, Cs), as well as arguments based on a simple Coulombic interaction model, show that the bidentate stabilization energy drops rapidly as the size of the alkali cation increases. Exchange of Na(+) with Li(+) leads to expulsion of the Na(+) ion generating, in ESI, intense multiply charged anions. An attempt is made to rationalize this behavior in terms of hydration effects.     

Influence of major cations of sea water on the desorption of137Cs from marine sediments

Desorption studies of¹³⁷Cs from marine sediments by artificial sea water and artificial sea water devoid of individual major cations such as Na, K, Ca, Mg and Sr indicated that only Na and K were effective in the desorption of¹³⁷Cs. Studies with various ionic strengths ranginf from 0.01 to 1.6M KCl and NaCl solutions showed that KCl desorbs constantly about 45%¹³⁷Cs at and above an ionic strength of 0.1. In case of NaCl, the percent desorption increases linearly with ionic strength. The difference in desorption by K and Na is attributed to the contraction of the clay mineral layers by K ion and expansion of the layers by Na ion.     

Light-scattering study of the coil-to-globule transition of linear poly(N-isopropylacrylamide) ionomers in water

The coil-to-globule transition of two poly(N-isopropylacrylamide) (PNIPAM) ionomers with different ionic contents (0.8 and 4.5 mol %), but similar weight average molar masses, in deionized water was investigated by a combination of static and dynamic light scattering. In spite of the large difference in their ionic contents, both the ionomers have a nearly same lower critical solution temperature (LCST, ∼ 32.5°C). At temperatures higher than the LCST, the ionomer chains undergo a simultaneous intrachain coil-to-globule transition and interchain aggregation to form nanoparticles thermodynamically stable in water. The average size of the nanoparticles decreases respectively as the ionic content increases and the ionomer concentration decreases. The interchain aggregation can be completely suppressed in an extremely dilute ionomer solution (< ∼ 5 × 10⁻⁶ g/mL), so that the intrachain coil-to-globule transition leads to the collapse of the ionomer chains into individual single-chain nanoparticles. Our results clearly indicate that there is a hysteresis in the colling process (the globule-to-coil transition). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1501–1506, 1998     

Side‐chain functionalized liquid crystalline polymers and blends, 2. Phase behavior of comb‐shaped liquid crystalline ionomers containing ions of alkaline metals

An effective way to synthesize liquid crystalline ionomers by an exchange reaction between the acid groups of functionalized LC polymers and a metal acetate was examined. A number of LC ionomers containing ions of the alkaline metals Na and Rb (1.2–18.3 mol‐%) were obtained. The introduction of small amounts (1.2–5 mol‐%) of metal ions into a functionalized LC polymer matrix leads to significant changes in the phase state of copolymers – the nematic phase is replaced by a SmA phase; an increase of the content of alkaline metal ions causes linear growth of clearing temperatures. The influence of the nature of the metal ions on the phase behavior of LC ionomers was determined. To describe the peculiarities of the LC ionomers' phase behavior a model based on the assumption that an ion multiplet is formed was proposed. Here, the rigidity of the functionalized LC copolymer chains used as a matrix for the preparation of LC ionomers was taken into consideration.     

Influence of ionic association on the nonisothermal crystallization kinetics of sodium sulfonate poly(butylene succinate) ionomers

We evaluated the relationship between the ionic substituents and nonisothermal crystallization behavior in poly(butylene succinate) (PBS) ionomers, synthesized by the introduction of sulfonated dimethyl fumarate (SDMF) with sodium sulfonate. In addition, we investigated the effect of sodium ions on the molecular structure of the PBS backbone by solid‐state ²³Na NMR analysis. Sodium ion aggregates (multiplets) was predominately created with the ionic group concentration, and melt rheology and dynamic melt analysis results showed that multiplet formation induced not only remarkable heterogeneity, but also a high degree of clustering in the PBS chains. At low ionic group concentration, well dispersed multiplets behaved as effective nuclei during the crystallization of the PBS ionomer and accelerated the rate of crystallization. As ionic group concentration grew higher, crystallization rates decreased due to hindered chain mobility by clusters consisting of numerous multiplets. A combined Ozawa and Avrami equation proved to be more effective than the Ozawa equation in describing the nonisothermal crystallization kinetics of PBS and its ionomers. The observed nucleation activity indicates that the nonisothermal crystallization rate is not directly proportional to the ionic group concentration. Superior nucleation activity was observed in PBS ionomer containing 1 mol % SDMF. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 925–937, 2008     

SAXS study on ionic aggregates of styrene‐isoprene‐sulfonated isoprene terpolymer ionomer

The small‐angle X‐ray scattering profile of styrene‐isoprene‐sulfonated isoprene terpolymer ionomers was studied to clarify the structure of ionic aggregates at ambient temperature as a function of the degree of neutralization of Na or Mg cations. An ionic cluster peak was observed for ionomers with a degree of neutralization greater than 25%. The ionic cluster peak was analyzed by the modified hard sphere model proposed by Yarusso and Cooper [Macromolecules, 1983, 16, 1871], and the size of the ion cluster, the closest approach distance between the clusters, and the average system volume per ion cluster were evaluated by a curve‐fitting method. The size of the ion clusters of the ionomer with monovalent Na cation increased with the degree of neutralization, but for divalent Mg cation slightly changed. The number of ion clusters of the styrene‐isoprene‐sulfonated isoprene ionomer with Na and Mg cations characteristically increased with the neutralization. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1307–1311, 2000     

含离子聚合物体系的动力学

离子作用的可逆性赋予了含离子聚合物丰富的力学和电学性能,使其广泛应用在高抗冲材料、记忆材料、自修复材料和智能响应材料等新兴领域.本专论结合作者近年的研究工作,介绍了含离子聚合物体系的构效关系和分子流变学,从3个方面展开:第1部分介绍了对于含离子聚合物的离子聚集状态的调控,和离聚物与聚电解质的相互转化;第2部分介绍了离子高度聚集的无规离聚物丰富的线性黏弹性,重点介绍了非缠结体系在链均一个离子浓度附近区域的溶胶凝胶转变以及缠结体系在平均每个缠结链段一个离子浓度附近区域的单平台到双平台模量的转变;第3部分介绍了如何进行分子设计,使得含离子聚合物成为有效的离子传输介质.最后总结了该研究领域的科学问题和面临的挑战.