Morphology of Sulfonated Random Ionomers Based on Hydrogenated Styrene–Butadiene Copolymer Studied by SAXS

Abstract

KEY WORDSMorphology 1 Small-Angle X-Ray Scattering I Ionomer I Styrene-Butadiene I Ionomer Peak I Hydrogenation I During the past three decades, extensive studies have been performed to improve our understanding of the morphology and properties of ionomers. It is generally accepted that ionic groups form aggregates, called multiplets. 1 The Eisenberg-Hird-Moore (EHM) model, a recent model of the morphology of random ionomers, postulates that polymer chains surrounding the multiplets undergo reduction in mobility. 2 At very low ion content, only multiplets are present. As the number density of the multiplets increases with ion content, the regions of restricted mobility start to overlap and form large contiguous regions of reduced mobility. When the dimensions of these regions exceed ca. 100 A, they are called clusters. 2 In this state, the ionomer exhibits two glass transitions: one for the matrix regions is found at lower temperatures, while that for the cluster regions is located at higher temperatures.In general, clustered ionomers exhibit small-angle peaks in small-angle X-ray scattering (SAXS) profiles. The poly(styrene-co-cesium methacrylate) ionomer containing ca. 7 mol% of ions exhibits the maximum in the SAXS peak at q=ca. 0.32A -1 (q=4nsin8fJ,, where e is half the scattering angle and Jc is the X-ray wavelength). 3 q corresponds to a Bragg spacing (dsragg) of ca. 20 A.Bragg spacing is thought to reflect the distance between multiplets. 4 • 5 The poly(styrene-co-cesium styrenesulfonate) ionomer (ca. 5 mol% of ions) shows the maximum of the SAXS peak at qmax=ca. 0.15A -1 (dsragg=ca. 42 A). 6 Another interpretation of the SAXS profile, the so-called core-shell model, has also been proposed. 7 The dynamic mechanical properties of sulfonated poly(styrene-co-ethylene-co-butylene) (SPSEB) random ionomers have been investigated. 8 Thus, as a follow-up work, the present study explores the morphology of the SPSEB ionomers. The comparison of the results obtained in this study with those from the sulfonated polystyrene ionomers is also made. Among the results obtained in the present study, the answers to the following two questions are of most importance; 1) what type of morphology does this ionomer system have? 2) what is the effect of the matrix Tg on the multiplet formation?t To whom correspondence should be addressed. EXPERIMENTAL Polymer SynthesisThe preparation and sulfonation of a hydrogenated poly(styrene-co-butadiene) random copolymers, i.e., poly(styrene-co-ethylene-co-butylene) (PSEB), are described elsewhere. 8 The PSEB copolymer is composed of 73 mol% of ethylene, 8 mol% of butylene, and 19 mol% of styrene. The polymer was sulfonated using a modification of the sulfonation method of Thaler. 9 The sulfonation level was determined by titration of the sulfonated PSEB (SPSEB) sample with standard methanolic NaOH to the phenolphthalein end point. Sample PreparationThe copolymers were dissolved in a mixture of xylenefl-butanol (3/1 vfv, for ionomers of low ion contents) or in a mixture of methanolftetrahyd...

Synthesis and mesomorphic properties of side‐chain liquid crystalline ionomers containing sulfonic acid groups

“…As the number density of the multiplet increased with ion content, the regions of restricted mobility started to overlap and formed large contiguous regions of reduced mobility. 23 In this state, the ionic clusters and LC phase were coexistent. The ionic clusters and the LC segments may be dispersed each other to form multiple blocks.…”

Gummy Nanoparticles with Glassy Shells in Electrostatic Nanocomposites

“…A model by Eisenberg et al invoking clusters of ionic groups 46 was to explain the SAXS of some ionomers. 47 Viscoelastic properties also depend on the nature of the counterions, which are trapped within these clusters. 45,48 The nanocomposite prepared here differs in that half of the charge is balanced by triflate ions and half by PSS, which presumably bridge aggregated nanoparticles.…”

Blends of styrene-butadiene-styrene triblock copolymer with random styrene-maleic anhydride copolymers

“…In particular, these results were tentatively explained11 on the basis of entanglement formation between the two components upon mixing, although no experimental confirmation of such hypothesis was presented. An even more pronounced improvement of the thermal behavior could be observed if polar groups were inserted into the PS domains of the triblock copolymer either by direct chemical modification13–17 or by blending processes 18. In particular, the sulfonation reaction of styrene‐ethylene/1‐butene‐styrene (SEBS) triblock copolymer with consequent neutralization of the sulfonic acid moieties represents a convenient route to introduce ionic interactions in the PS “hard” phase 13.…”