Sulfonation Level Research Articles

A Study on Morphology and Properties of IPP/Zinc-Neutralized Sulfonated EPDM Blends

Abstract The effect of zinc-neutralized sulfonated EPDM (Zn-SEPDM) on the compatibility and the crystallizing behavior of isotactic polypropylene (IPP), and also the morphology of the blend were studied through WAXD, DSC, TEM, and mechanical properties test. The results show that addition of Zn-SEPDM decreases both the melting point and the crystallizing temperature of IPP. The widths at half-height of the melting peak and the crystallizing peak become narrower; the d-spacings of the crystal planes are unchanged, revealing the existence of interactions between Zn-SEPDM and the amorphous region of IPP. The higher the sulfonation level, the smaller the average distances across the IPP phase and the EPDM phase. As Zn-SEPDM content exceeds 20%, Zn-SEPDM in the blend becomes continuous and an abrupt change in impact strength is incurred therefrom. Owing to the incorporation of ionic groups into EPDM, the strong interactions between the chains make both the impact and the tensile strength of IPP remarkably higher.

Viscoelastic behavior of lightly sulfonated polystyrene ionomers

The linear viscoelastic behavior of sulfonated polystyrene ionomers with as few as one sulfonate group per 1000 styrene repeat units was studied by dynamic mechanical analysis. Interactions of the sulfonate groups shifted the terminal flow region to lower frequency and produced a new low-frequency relaxation that was not present in the unmodified polystyrene. The observation of the low-frequency relaxation at very low sulfonation levels suggests that even for 0.11 mol % sulfonation, ionic clusters formeven though, no SAXS peak has been resolved for ionomers with that low a sulfonation level. The effect of the ionic groups on the viscoelastic properties can be varied for a fixed sulfonation level by weakening the ion-dipole strength of the ion pair. This can be achieved by substituting ammonium (NH4+) cations for metal cations such as Na+.

Preparation and thermal characterization of the glass transition temperatures of sulfonated polystyrene‐metal ionomers

AbstractThe glass transition temperatures and heat capacity changes in the transition region are reported for six sulfonated linear polystyrenes in the hydrogen form, H‐SPS, in the 3.4–20.1 mol % sulfonation range and 76 metal SPS ionomers in the 3.4–12.8 mol % range. The metals are those which interact predominantly ionically and include +1, +2, and +3 ions of the alkali metal, alkaline earth, and rare earth (lanthanide) series. The results show the effect of H2O or coordinating ligands on glass transition temperatures (Tg) and the importance of eliminating it to obtaining reproducible values for Tg and ΔCp. The Tg values of dry M‐SPS ionomers depend only on the sulfonation level despite wide variation in metal ion charge and size. The variation of ΔCp with sulfonation level is interpreted as showing that at high levels a few unsulfonated styrene units adjacent to sulfonated ones are constrained, presumably by clustering, from participation in the polystyrene‐like cooperative rearrangements in the transition region.

Influence of polymer composition on the thermal characteristics of sulfonated EPDM ionomers

AbstractDetailed thermal characterization of sulfo‐EPDM ionomers was carried out. The endotherms observed via differential scanning calorimetry (DSC) and multiple inflections observed via thermal mechanical analysis (TMA) are speculated to be due to associated ionic species in the polymers. A large time dependence of the DSC endotherm was observed, suggesting substantial variations in the nature of the ionic species over this period. The influence of ionomer composition on thermal characteristics was probed with whole polymers and polymer fractions. In general, trends in the DSC and TMA data paralleled those expected on the basis of the anticipated effect of polymer sulfonation level, molecular weight, and counterion type on the strength of the physical crosslinking of these polymers. Both the DSC endotherms and the TMA inflection regions are rationalized in terms of a previously developed ionic‐bond exchange model.

Properties and biological interactions of polyurethane anionomers: effect of sulfonate incorporation.

In order to investigate the factors affecting the interaction of polyurethanes and blood, a series of poly(tetramethylene oxide)-based polyurethane block copolymers was synthesized with systematically varying levels of ion incorporation in the hard segment block. A bimolecular nucleophilic substitution reaction was used to replace up to 20% of the urethane hydrogens with propyl sulfonate groups. Bulk and surface characterization was performed, and a canine ex vivo arteriovenous shunt was used to monitor initial platelet and fibrinogen deposition on these surfaces. The microphase separation and bulk physical properties were found to vary with ionic content. Surface analysis using both in vacuo (ESCA) and water-equilibrated (contact angle) methods indicated that these polymers, and especially the highly sulfonated materials, could rearrange to minimize their interfacial tension, depending on the contacting environment. Platelet deposition onto these materials decreased as the level of sulfonation increased, with the highly sulfonated polymer showing substantially less platelet spreading and activation than previously seen in the same experiment with other polymers.

Counterion and solvent effects on the dilute solution viscosity of polystyrene ionomers

AbstractWe present an analysis of data on the intrinsic viscosity [η] of sulfo‐polystyrene ionomers in several solvents for a variety of sulfonation levels and counterions. For solvents of low dielectric constant, 2 < ε < 18, [η] decreases from the base polymer value [η]0 with increasing substitution level. This behavior was attributed to intramolecular association of ionic dipoles. The ratio [η]/[η]0 was found to depend on a single reduced variable αAαSx, where x is the fractional substitution, αA depends only on the counterion, and αS ∝ ε−1 depends only on the solvent. For solvents of high dielectric constant, 36 < ε < 47, [η] increases approximately as x3, and counterion effects are small. This behavior was attributed to ionic dissociation, giving rise to a polyelectrolyte effect. Implications of the low ε results are discussed in relation to association‐induced gelation behavior and possible generalizations of the reduced variables approach.

Quasielastic light scattering and viscometric measurements on dilute ionomer solutions

The hydrodynamic radius and intrinsic viscosity of a number of dilute solutions containing lightly sulfonated polystyrene ionomers and its unmodified analog have been measured in both polar and nonpolar solvents. Since these ionic interactions are known to significantly modify the physical properties of a polymer through relatively strong intra- and intermolecular interactions, it is important to examine how the individual chain characteristics of a charged polymer are influenced with changes in solvent quality and sulfonation level. In a polar solvent, such as dimethylsulfoxide, a short and a long correlation time is observed indicative of at least two relaxation processes. The long correlation time is attributed to the translational motion of the entire polymer chain, while the short relaxation process is correlated with the motion of the polystyrene segments situated between ionic groups. This result may be due to the ability of dimethylsulfoxide to dissolve lightly sulfonated polystyrene, but not its nonionic analog. On the contrary, in a relatively nonpolar solvent, such as cyclohexanone, only a single correlation function is noted. Again correlation with viscometric measurements shows that this is entirely due to translational motion of the individual coil. In this particular solvent, both polystyrene and sulfonated polystyrene are soluble. These results are useful as a basis for interpreting similar measurements in the semidilute region where the ‘‘universal’’ solution characteristics of associating polymers more specifically ionomers, may be observed.

Far‐infrared studies of microphase separation in sulfonated ionomers

AbstractFar‐infrared spectra of a series of un‐neutralized and neutralized lightly sulfonated polystyrenes with varying sulfonation levels have been investigated to seek spectroscopic evidence for microphase separation known to control the physical properties of these polymers. Broad, strong absorbance bands, not found in the spectrum of unmodified polystyrene, are observed in the spectra of the sulfonated analogs. The effects on the far‐infrared spectra both of sulfonation level and of the mass and charge of the neutralizing cation are discussed in terms of cation motion and the formation of ion‐rich domains.

Interactions of a sulfonated ionomer with surfactant in nonaqueous media

AbstractThe viscometric behavior of dilute solutions of the sodium salt of sulfonated polystyrene (0–6 mol % sulfonation level), with and without surfactant, is investigated to determine the extent of interaction as the structure of the solvent surfactant, and polymer concentration is varied. Reduced viscosity measurements confirm that formation of a polymer–surfactant complex in a relatively polar solvent is controlled to a large extent by charge–charge and hydrophobic forces. The magnitude of these specific interactions is dependent upon the relative polarity of the solvent medium. In a polar solvent, such as dimethylsulfoxide, the hydrophobic forces are strong enough to prevent expansion of the polymer chain at all surfactant concentrations studied. However, in a less polar medium (as in dimethylformamide) the hydrophobic forces are weaker and cannot prevent some chain expansion. It is interesting to note that in this solvent the polystyrene–cationic surfactant complex exhibits a polyelectrolyte effect. Finally, in a lower‐polarity medium (cyclohexanone) where the hydrophobic forces are weak, solution behavior is dominated by the interaction of the surfactant with the intramolecular sulfonate ion‐pair aggregates.

Synthesis and characterization of sulfonated poly(acrylene ether sulfones)

AbstractIonic groups incorporated into a polymer have a decided effect on its physical properties. A number of ionomers and polyelectrolytes have been widely applied. In particular, sulfonated bisphenol‐A polysulfone (SPSF) has been used as a composite or single‐component membrane for the desalination of water. In this article, the synthesis and physical characteristics of sulfonated polysulfone are addressed. A detailed synthesis route is provided and methods that yield determinable levels of sulfonation are described. These ion‐containing polymers retain an excessive amount of residual salts, which, of course, are impurities to the system. Therefore, before any analyses were made the polymers were subjected to a thorough soxhlet extraction process with boiling water, which appeared to be quite effective. The degree of sulfonation was assessed by several methods such as 1H NMR and FT‐IR. A new 1H NMR method was derived because the method cited in the literature proved to be too inconsistent for our work. The new 1H NMR method used a quaternary ammonium counterion [N(CH3)4]. These methyl protons are easily measured and may be ratioed against the isopropylidene protons in the polymer backbone that act as an internal standard. Characterization of the physical properties of SPSF consisted of water uptake, differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and solubility studies. Its physical appearance and mechanical behavior were improved by the solution procedure. Also addressed were the effects of different counterions (Na+ & Mg++) with SPSFs of low levels of sulfonation. The variation in physical properties between the divalent and monovalent counterions is dramatic, especially when observed by TMA in the rubber plateau above the apparent glass temperature.

Viscoelastic properties of sulfonated ethylene–propylene terpolymer neutralized with zinc cation

AbstractStress–relaxation measurements in uniaxial extension, in the terminal zone, were made of sulfonated ethylene–propylene terpolymer (EPDM), neutralized with zinc cation. The sulfonation levels were 15 to 20 meq/100 g polymer (0.47 and 0.62 mol %), and for each level the effect of the ionic plasticizer, zinc stearate, was investigated. For all the polymers, the decay of the modulus with elapsed time was gradual and featureless, reflecting a broad distribution of relaxation times. Sensitivity of the ionomers' structures to thermal history before an experiment was suggested by irreproducibility in the magnitudes, but not the distribution, of relaxation times at a given temperature. For polymers containing zinc stearate measured at 80°C, the amount of permanent set was low for relaxation up to about 20h, but increased rapidly with additional hours of stretch. Time–temperature superposition did not apply. Composite curves were constructed by matching the stress–relaxation response at short times; moduli measured at long times fell above the composite curve. The shapes of the composite curves were similar, regardless of the level of EPDM sulfonation or the presence of zinc stearate. The apparent Arrhenius activation energy for short‐time relaxation at similar levels of the modulus was about 35 kcal/mol at 140°C for the unplasticized polymers and about 70 kcal/mol at 90°C for the polymers containing zinc stearate, in contrast to the usual effect of plasticizer on the rate of relaxation of amorphous polymers except near the glass transition temperature.