Hydrophobic recovery behavior of PMMA and PEA ionomers treated with PSII

The surfaces of poly(methyl methacrylate) (PMMA)‐based and poly(ethyl acrylate) (PEA)‐based ionomers were treated either with plasma or with plasma source ion implantation (PSII), and their hydrophobic recovery behavior was studied by measuring water contact angles. It was found that the hydrophobic recovery of the plasma‐treated and PSII‐treated surfaces of PMMA ionomers was much slower than that of the acid‐form copolymers. This was due to the presence of hydrophilic ionic groups on the ionomer surface. In addition, in the case of the PMMA ionomers, a slow hydrophobic recovery behavior for a long period of time was observed. In the case of the PEA ionomer, the water contact angle values were found to be larger than those for the PMMA ionomers. When the contact angle values of the PMMA and PEA ionomers were compared to those of polystyrene (PS) ionomers, it was found that the order of ionomers showing higher angle value at comparable aging time was as follows: PS ionomer > PEA ionomer > PMMA ionomer. This was due to the difference in polarity and matrix glass transition temperature of the ionomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3100–3106, 2003     

Dynamic mechanical properties of weakly clustered poly(styrene-co-sodium citraconate) ionomers

Summary The properties of poly(styrene-co-citraconate) ionomers were investigated dynamic mechanically. It was found that the loss tangent peak for the matrix glass transition decreased with increasing content of ionic units, while the loss tangent peak for the cluster glass transition was barely detectable. However, the ionic modulus values of the citraconate ionomers as a function of the amount of ionic units were comparable to those of well-clustered methacrylate ionomers. Thus, it was postulated that the ionic modulus was affected by both clustering due to the overlapping of regions of restricted mobility and strong physical cross-links originated from the ionic association of ca. 4 ion pairs. Received: 16 March 2001/Revised version: 25 April 2001/Accepted: 27 April 2001     

Dynamic mechanical properties of three different combinations taken from styrene-co-itaconate, styrene-co-methacrylate, and styrene-co-sulfonate ionomers

Dynamic mechanical properties of three different styrene-based ionomer blends containing ca. 5 mol% of ionic repeat units were investigated; the three ionic units were itaconate (ITANa), methacrylate (MANa), and styrenesulfonate (SNa). For SNa-MANa ionomers, it was observed that this ionomer system showed only two loss tangent peaks, implying that this ionomer system resembles a typical miscible system. When the ion content increased, however, the ionomer blend showed two cluster loss tangent peaks, indicating the presence of phase-separated cluster regions. This suggests that, with increasing ion content, the role of ionic units becomes more important than that of host non-ionic units to determine ionomer properties. In the case of ITANa-MANa and ITANa-SNa ionomers, however, it was suggested that the multiplets of the MANa and SNa ionomers might be disrupted upon the addition of the ITANa ionomers. In addition, the SEM images showed that the fracture surfaces of ionomers changed upon blending.     

Acrylic ampholytic ionomers

In a continuing study of the preparation of ampholytic ionomers from the polymerization of ion-pair comonomers (cationic-anionic monomer pairs) with nonionic comonomers, the preparation of such ionomers from methyl methacrylate and n-butyl acrylate is described. For both systems, ionomers of varying ion contents were obtained. In the n-butyl acrylate system, a linear relationship of T_q vs. mol % ion content was found, but this did not occur for the methyl methacrylate ionomers. The solubilities of these materials in a wide variety of solvents is discussed. It appears that for n-butyl acrylate ionomers of high ion content in aqueous solution, a new form of polymeric surfactant is obtained.     

The effect of hydrophobicity in alkaline electrodes for passive DMFC

The effect of hydrophobicity in alkaline electrodes has been investigated in an effort to improve their performance in passive direct methanol fuel cells. Two approaches have been used to increase the hydrophobicity within the electrodes. One is using a more hydrophobic ionomer, and the other is introducing polytetrafluoroethylene (PTFE) into the catalyst layer. Two types of anion exchange ionomers with different hydrophobicity have been synthesized for this study. The effect of ion exchange capacity, ionic conductivity, and water uptake of the ionomers on the electrode performance has been studied using a half-cell test. The use of a hydrophobic ionomer resulted in enhanced cathode performance even though the ionic conductivity was lower than the more hydrophilic ionomer. Also, the addition of PTFE improved both the cathode and anode performance. The improved alkaline electrode performance was compared to a traditional acid electrode using Nafion as the ionomer. The performance increased threefold as a result of higher hydrophobicity in alkaline electrode.     

Effects of compositional inhomogeneity on the mechanical properties and morphology of styrene-co-methacrylate random ionomer mixtures

A series of poly(styrene-sodium methacrylate) SMANa ionomers of varying ion contents was synthesized, and mixtures of the ionomers were made to artificially broaden the compositional inhomogeneity of the SMANa ionomers at a constant ion content of 7.3 mol%. The mechanical properties of the unblended SMANa ionomer containing 7.3 mol% of ions and the ionomer mixtures were compared. It was found that the ionic moduli of the unblended ionomer and ionomer mixtures were very similar to each other, indicating that the mixing process did not change the degree of clustering. However, the slope of ionic plateau became steeper as the difference in the ion contents of two ionomers in the ionomer mixture increased, suggesting that the inhomogeneity of the matrix and cluster phases increased. It was also observed that the difference between the matrix and cluster T_gs increased as the divergence of the ion contents of two ionomers in the ionomer mixture became wider. In addition, it was found that when the difference of the two ion contents exceeded over 6 mol%, the ionomer mixture started to show a trace of phase-separation. At ca. 9 mol% of ion content difference, the ionomer mixture exhibited a third loss tangent peak, possibly due to the presence of the phase-separated matrix regions. The SAXS study showed that, even though the three-dimensional arrangement of multiplets in an ionomer matrix was not changed upon mixing two ionomers, the matrix phase became inhomogeneous.     

Mechanical and thermal properties of potassium salts of poly(ethylene‐co‐ethylacrylate): Polyolefin ionomers in the absence of acid groups

The thermal and mechanical properties of ionomers prepared by partial saponification of poly(ethylene‐co‐ethylacrylate) (EEA) with potassium were investigated by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The Vicat softening temperature (VST) and bending modulus were also evaluated. Molecular design of the present EEA‐based ionomers eliminates acid groups, which affect ionic aggregates for conventional ionomers. The DSC results showed that the melting enthalpy and main crystallization temperature decreased as the ion content increased, whereas on the other hand, the crystal melting temperature at about 360 K did not depend on the ion content, and a secondary exothermal peak was observed in the cooling process. The variance of the VST increased as the crystallinity decreased. The temperature‐dependent curves of DMA data of the EEA‐based potassium ionomers with a higher ion content showed elastic plateau even at temperatures above their crystal melting points. Our results indicate the existence of strong cross‐linking mediated by ion aggregates. The quadratic increase of stiffness as a function of ion content, increasing VST with decreasing crystallinity, and elastic plateau of temperature‐dependent moduli above crystal melting temperature are significant characteristics of the EEA‐based potassium ionomers, which contain ionic aggregations without acid group presence. POLYM. ENG. SCI., 55:1843–1848, 2015. © 2014 Society of Plastics Engineers     

Redox-active liquid-crystalline ionomers: 1. Synthesis and rheology

Liquid-crystalline (LC) copolymers with redox-active groups were prepared by copolymerization of mesogenic and ferrocene-containing monomers (up to 10%). In these copolymers the ferrocene groups can be oxidized reversibly to prepare ionomers, while retaining the LC phase. It is thus possible to vary the amount of ionic groups in the ionomers by a redox reaction. The oxidized (charged) polymers show a strong excess X-ray scattering at small angles. This is typical for ionomers and is assigned to the scattering of ionic aggregates. Dynamic mechanical measurements show that these aggregates are effective as crosslinking points. Thus an oxidation-reduction reaction can be used to transfer an uncrosslinked polymer (reduced ferrocene groups, uncharged) reversibly into an oxidized polymer that acts like a weakly crosslinked gel.     

Hydrophobic properties of ethylene–vinyl alcohol copolymer treated with plasma source ion implantation

The industrial use of ethylene–vinyl alcohol copolymer (EVOH) film is limited because it is easily degraded by moisture. The plasma source ion implantation (PSII) technique with CF₄ or CH₄ gas was used for the EVOH film to improve the surface hydrophobic properties. Variables examined in implantation were ion energy (0–10 keV), treatment time (5 s–5 min), and ion species. The hydrophobic properties of EVOH films were greatly enhanced after a CF₄ PSII treatment, as evidenced by an increased contact angle from 66° to above 100° at ‐5 keV, and remained relatively unchanged during the period of 28 days. X‐ray photoelectron spectroscopy, atomic force microscopy, and O₂ permeability were used to characterize the surface properties of EVOH films treated with PSII. The improved hydrophobic properties were closely related to the formation of fluorine‐containing functional groups such as CF, CF_2, and CF₃ on the modified surface. The percentage distribution of carbon functional groups supports the role of CF₂ and CF₃ groups in surface modification. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2069–2075, 2004     

Multiblock sulfonated poly(arylene ether sulfone)s with fluorenyl hydrophilic moieties for PEMFC applications

Multiblock sulfonated poly(arylene ether sulfone) (MB-SPAES) ionomers containing fluorenyl hydrophilic moieties were synthesized and converted into proton exchange membranes (PEMs) through solution casting, as well as other two types of MB-SPAES membranes containing hydrophilic biphenyl and hexafluoroisopropyl diphenyl moieties for the comparison. Chemical structures of the MB-SPAES ionomers were confirmed by ¹H NMR spectrometer. Fundamental physical properties were characterized based on the ionic group content, the hydrophilic/hydrophobic block structure and length, including ion exchange capacity (IEC), water uptake, size change, mechanical property, proton conductivity, hydrolytic stability and fuel cell performance. All the obtained MB-SPAES membranes were transparent and mechanical ductile, suitable for PEM applications. Water uptake and size change results showed that the MB-SPAES membranes containing fluorenyl hydrophilic moieties absorbed less water and swelled smaller in water than the other two types at similar IECs, indicating their better dimensional stability. Proton conductivity and hydrolytic stability results indicated that the fluorenyl hydrophilic moieties were also favorable to gain better proton conductivity and hydrolytic stability.     

Disruption of the multiplets in poly(styrene-co-methacrylate) ionomers by the addition of aliphatic diacid salts

Dynamic mechanical properties and morphology of poly(styrene-co-sodium methacrylate) ionomers containing disodium salts of aliphatic diacid were investigated. It was found that upon the addition of diacid salts to the ionomers, the position of the matrix loss tangent peak remained constant, but the cluster loss tangent peak shifted to lower temperatures; the size of the matrix loss tangent peak increased, but that of the cluster peak decreased. In addition, the ionomers containing diacid salts showed X-ray diffraction patterns at relatively wide angles but no DSC melting peak. Thus, it was postulated that the organic salts prohibit the ionic groups of the ionomer from forming multiplets, and that the ionic groups of the ionomer, not forming the multiplets, participate in the formation of ionic aggregates with the ionic groups of the diacid salts.     

Zum kautschukelastischen verhalten von polyurethan-ionomeren

Dispersions of cationic and anionic ionomers of polyurethanes were prepared by the acetone method. Characteristic changes of the viscosity were observed during the addition of water. This change was studied with a cationic ionomer. The ionomers are mainly associated dimeric species in solution of acetone. During the addition of water the ions are solvated while the hydrophobic segments are increasingly associated. At the maximum of the observed viscosity the apparent molecular weight M_max ≈ 3 M_min. In the absence of solvents the ionomers behave like crosslinked materials even if no covalent crosslinks are present. The modulus at small elongations is a linear function of the square of the concentration of the cations. It is concluded that two ionic centers are required per crosslink. The anionic ionomers were also chemically crosslinked since an excess of isocyanate was used. A linear increase of the modulus was observed with increasing amount of chemical crosslinks, while the concentration of ions and hydrogen bonds was constant. The crosslinks formed by ions can be suspended by swelling with water. The portion of the modulus caused by ionic crosslinking can be computed from the difference of the moduli in the dry and swollen state.     

Preparation of an ionic/nonionic polyurethane-silicone dispersion (PUSD) with a high solid content and low viscosity using complex soft segments

A series of ionic/nonionic polyurethane-silicone dispersions (PUSDs) with a high solid content and low viscosity were prepared using isophorone diisocyanate as the hard segment, polytetrahydrofuran polyether diol (PTMG) and polysiloxane diol (PESI) as the complex soft segments and an ionic/nonionic low molecular weight polyether diol (DPSA) as the hydrophilic, chain-extending agent. The morphologies and rheological properties of the ionic/nonionic PUSD were examined using particle-size, TEM, and viscosity analyses. The hydrophobic and mechanical properties of the dispersions were also tested. It was found that under the conditions of a constant NCO/OH ratio (2/1) and weight percentage of DPDA (6%), the PUSD dispersions with higher PESI contents possessed higher average particle diameters and wider particle-size distributions. Particles in the PUSD dispersions are generally spherical and have a typical core–shell structure due to the use of complex soft segments. However, the solid content of the ionic/nonionic PUSD increased first and then decreased as the weight ratio of PESI to PTMG increased. When the ratio ranged from 4/10 to 6/10, the max solid content of the ionic/nonionic PUSD reached up to 58%, but the viscosity of the PUSD was less than 400 mPa.s^?1. Meanwhile, the water contact angle of the films increased due to the formation of a crosslinking structure on the side of the PUSD macromolecule, and when the weight ratio of PESI to PTMG varied from 3/10 to 7/10, the water contact angle of the films increased from 48.3° to 72.3°. In addition, both the freeze-thaw and thermal stabilities of the PUSD dispersions were enhanced as the weight ratio of PESI to PTMG increased. The PUSD coating had good mechanical properties as well.     

Imidazolium poly(butylene terephthalate) ionomers with long-term antimicrobial activity

Imidazolium poly(butylene terephthalate) ionomers with ionic groups located randomly along the polymer chain or selectively as end-groups (telechelic) have been prepared in order to determine their antimicrobial (AM) activity. Two different approaches have been followed for the linkage of the imidazolium to the polymer backbone: a covalent bond and an ionic aggregation to sulfonated groups covalently bonded to the polymer. The ionic groups have been linked to the polymer in order to improve the long-term AM activity since the low molecular weight additives commonly used tends to migrate toward the surface during use. We have found that imidazolium ionomers present AM activity comparable with that of commercial antimicrobial agents such as Triclosan. The AM activity depends on the polymer architecture, the telechelic approach being more active compared to the random approach. We have proved that imidazolium ionomers retain their high AM activity even after 6 days in water at 60 °C while Triclosan consistently loses his activity.     

New polyisobutylene-based model elastomeric ionomers: RheoLogical behavior

The rheological behavior of sulfonated polyisobutylene based elastomeric ionomers has been studied. The effects of molecular architecture, type of cation, and addition of excess neutralization agent were investigated. The effect of temperature was studied to a limited extent. In a specific case, the influence of an ionic plasticizer, zinc stearate was also examined. It was found that in these telechelic ionomers where the ionic groups are located exclusively at the chain ends, significant Ionic interactions may persist even at 180°C. The zinc-neutralized ionomers had the lowest viscosity as compared to the corresponding potassium- or calcium-neutralized ionomers. The covalent character of zinc is believed responsible for this behavior. Other factors being constant, the triarm based ionomers are more viscous than the monofunctional ionomers. A mixture of monofunctional ionomers with the triarm, species is a model for dangling chain ends, and results in a slight lowering of the viscosity under the conditions studied. Zinc stearate acts as an ionic plasticizer. Upon the addition of 15 percent by weight of zinc-stearate to the ionomer, the low shear rate viscosity drops by several orders of magnitude and renders the ionomer thermally processable at moderate temperatures.     

Effect of organic amine type on the structure and properties of the complex Zn(II) salts of ethylene–methacrylic acid copolymer with organic amines

The complex Zn(II) salts of ethylene–methacrylic acid copolymer (EMAA) were synthesized by using various organic amines from monoamines to polyamines, from primary amines to tertiary amines, and from molecular amines to polymer amines. Thermal analyses by differential scanning calorimetry (DSC), and the measurement of stiffness, melt flow rate (MFR), and dielectric properties were employed for the complex salts. It was found that the valence, strength of base, rigidity and flexibility, and bulkiness of the organic amines affect the degree of crystalline order of the ionic crystallites, which governs the stiffness of the complex ion ionomers. The stiffness is higher for the complex salts which form the higher orderliness in the ionic aggregates. The organic amines with two or more primary aliphatic amino groups and higher boiling temperatures from more rigid ionic crystallites in the complex ion ionomers leading to the enhanced modulus. Monoamines or polyamines with amino groups attached to flexible chains such as polyether and polysiloxane scarcely develop ionic crystallites and preferentially solvate the amorphous region including ionic groups leading to the decreased modulus. These results provide us with the fundamental information to control the modulus of ionomers.     

Telechelic ionomeric poly(butylene terephthalate): Synthesis,characterization and comparison with random ionomers

Telechelic poly(butylene terephthalate) (PBT) ionomers have been prepared by melt synthesis using a new polycondensation process that involves a pre-reaction of sulfobenzoic acid sodium salt with butanediol. No side reaction occurs and the incorporation of the ionic groups is quantitative. The addition of a buffer agent, such as Na₃PO₄, to the catalyst reduces the THF formation and improves the polycondensation rate. The comparison of the thermo-mechanical and physical properties between random and telechelic ionomers is also reported. The ionic groups act as chain-extension reversible electrostatic links for telechelic ionomers while act as cross-links in random ionomers. Therefore, random ionomers present a consistently higher melt viscosity compared to telechelic ionomers and to PBT and for this reason high molecular weight random ionomers cannot be obtained by melt polycondensation. Thermal and hydrolytic stabilities of telechelic ionomers are comparable with those of commercial PBT and consistently higher respect to those of random ionomers. The presence of ionic groups decreases the translation mobility of the polymer chains thus lowering the crystallization rate.     

Viscoelastic study of ionomers

Stress-relaxation curves were obtained for ionomers containing different cations, per cents of ionization, and thermal treatments. Differences in the rheological behavior were found to depend more on the ionization level than on the ion. A recently proposed model for ionomers is discussed and found to be consistent with these results. In terms of this model the degree of ionization in the polymer acts as a regulator for the growth of small oriented lamellar (crystalline) regions. In the most general terms, the mechanical behavior and strength of ionomers appears dominated by the existence of “hard” regions interspersed among “soft” regions. In the polymers studied here there was some slight crystallinity; however, similar effects and explanations are probably suitable for amorphous “ionomers.” Toughness was also found in some completely amorphous carboxylcontaining copolymers without added ionic salts. The same explanation of “hard” regions interspersed among soft regions is also valid here. The “blocky” nature of the copolymerization may play a role in setting up this type of structure.     

Evaluation of polymer hydrophobic recovery behavior following H2O plasma processing

Inductively coupled radio frequency (rf) H₂O vapor plasma was used to modify a range of polymers to better elucidate the dependence of hydrophobic recovery on polymer composition and structure. Freshly modified and aged samples were examined using scanning electron microscopy, (SEM), X‐ray photoelectron spectroscopy, (XPS), and water contact angle (wCA) goniometry. Initially, wettability was increased on each polymer surface due to the implantation of polar oxide groups, an effect exacerbated by increased surface roughness with plasma treatment. Polypropylene and polystyrene exhibit nearly complete hydrophobic recovery as polar groups are subsumed as samples age. High‐density polyethylene and polycarbonate exhibit minimal hydrophobic recovery, owing to plasma‐induced cross‐linking and intrinsic thermal stability, respectively. Overall, the hydrophobic performance following H₂O plasma modification is similar to other oxidizing plasmas, suggesting that recovery behavior is intrinsic to the polymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41978.     

Viscoelastic properties of poly(styrene-co-vinylphosphonate) ionomers

Viscoelastic properties of neat and glycerol plasticized poly(styrene-co-diethyl vinylphosphonate) ionomers were investigated. Nanophase separation of a polar phase occurred due to hydrogen bonding or ionic interactions in the acid derivatives and the metal salts, respectively. Metal–phosphonate ion–dipole interactions were much stronger and more temperature persistent than the hydrogen bonding in the phosphonic acid derivatives, which were manifested by a much broader rubbery region in their viscoelastic behavior. The phosphonate interactions were thermally stable up to >250 °C, and the physically crosslinked network produced suppressed viscous flow of the ionomers to very high temperatures. Time–temperature superposition was not applicable for the SVP ionomers even at an ion content as low as 2.4 mol%. The addition of a polar plasticizer, e.g., glycerol, preferentially solvated the ionic associations and diminished the extent of the rubbery plateau of the ionomer and substantially decreased the terminal relaxation time.