Ethylene ionomers physical properties

For the sake of brevity detailed tables of all tests performed are shown for duPont ionomer resins only (Tables II, III, IV, VI to X). The other ethylene copolymers were similarly treated and evaluated. The effects of increasing radiation dosages on certain physical properties of selected duPont ionomers are shown graphically in Figures 1, 2, and 3. 

Sulfonation is very useful chemical modification of polymer, as it induces high polarity in the polymer changing its chemical as well as physical properties. Sulfonated polymers are also important precursors for ionomer formation [75]. There are reports of sulfonation of ethylene-propylene diene terpolymer (EPDM) [76, 77], polyarylene-ether-sulfone [78], polyaromatic ether ketone [79], polyether ether ketone (PEEK) [80], styrene-ethylene-butylene-styrene block copolymer, (SEBS) [81]. Poly [bis(3-methyl phenoxy) phosphozene] [82], Sulfonated polymers show a distinct peak at 1176 cm"1 due to stretching vibration of 0=S=0 in the -S03H group. Another peak appears at 881 cm 1 due to stretching vibration of S-OH bond. However, the position of different vibrational bands due to sulfonation depends on the nature of the cations as well as types of solvents [75, 76]. 

Recent studies in our laboratories have been concerned with the physical properties of sulfonated ionomers such as sulfonate ethylene/propylene/ethylidene norbornene terpolymers (4, or lightly sulfonated polystyrene (S-PS) (11). These ionomers exhibit pronounced ion pair association (at sulfonate levels > 15 milli-equivalents/100 g polymer) to a degree that they appear crosslinked covalently. These interactions can be dissipated by the addition of a polar additive, thereby showing that such associations are indeed physical and do not arise due to covalent crosslinking. 

Metal sulfonate-containing ethylene-propylene-diolefin ter-polymers (EPDM) were plasticized with stearic acid and derivatives for the reduction of the melt viscosities of these ionomers through interaction with the very strong ionic associations. Substantial improvements in melt flow were achieved with stearic acid and the zinc, lead, and ammonium stearates, while other metal stearates were ineffective. Zinc stearate and lead stearate not only markedly improved melt flow but, remarkably, also enhanced the mechanical properties of the plasticized systems. These unique additives were fully compatible with the EPDM ionomers and provided thermoelastic systems with excellent physical properties and ready processability. 

T he type of counterion used in an ion-containing polymer can have a substantial effect on the physical properties of the material. Many studies have been made in the past comparing the properties of metal- or ammonium-neutralized ionomers two recent books on ion-containing polymers present a comprehensive review of the literature (1,2). There is a wealth of information comparing different metal counterions in neutralized or partially neutralized ethylene-carboxylic acid copolymers. Rees and Vaughan studied the melt flow and tensile properties of... 

In this section, the metal-cationic salts of copoly(ethylene-methacrylic acid) are called the ethylene ionomers. This ethylene ionomer is one of the well-known commercial ionomers, marketed under the trade name Surlyn by DuPont. Many ethylene ionomers have crystalline and amorphous phases of ethylene chain units as well as polyethylene. Therefore, there is a three-phase structure, with crystalline, amorphous, and ionic aggregate phases this is a unique characteristic of ethylene ionomers compared with other ionomers. Although the ionic aggregate structure of the ethylene ionomer has not been fully established, its structural model is represented5 as shown in Fig. 1. In ethylene ionomers, therefore, it is necessary that some physical properties should be considered by correlating to not only the ionic aggregates but also the crystalline phases. 

The characteristics of the physical properties and ionic aggregates in the ethylene ionomers have been outlined in the previous sections. The application of solid-state high-resolution l3C NMR spectroscopy to the structural analysis of ethylene ionomers33-37 is described in this section. One of the advantages of l3C NMR is to simultaneously obtain information from all phases of ethylene ionomers, i.e. crystalline, amorphous, and ionic aggregate phases. 

Some physical properties of polyethylene ionomers are compared with those of polyethylene and the acid copolymer, poly(ethylene-co-methacrylic acid) in Table 5.15. lonomer is generally tougher and, as shown in Table 5.15, relative to the acid copolymer, its tensile strength is increased by 27—53% and its stiffness is nearly tripled. 

An early, and widely used, commercial example of side-chain functionalities inducing interactions between polymer chains are ionomers, hydrocarbon macromolecules bearing, for example, carboxylic acid groups [e.g., poly(ethylene-co-methacrylic acid)], which are partially or fuUy neutralized with metal or quaternary ammonium ions. These ionomers are thermoplastic ionic polymers boasting unique physical properties such as enhanced impact strength, toughness, and thermal reversibility. They were developed and commercialized by DuPont, and have recently attracted attention due to their self-healing properties. ... 

Copolymerization of ethylene with polar comonomers results in such resins as ethylene-co-vinyl acetate, ethylene-co-vinyl alcohol, and ethylene-co-metha-crylic acid copolymers. The polar side groups so incorporated may interact with each other to endow the product with specific physical properties, or they may be used as sites for subsequent chemical reactions. A major family of polymers falling into this category are ionomers, which consist of ethylene-co-vinyl acid copolymers, the acid functions of which have been neutralized to form metal salts. 

The ionic aggregates present in an ionomer act as physical crosslinks and drastically change the polymer properties. The blending of two ionomers enhances the compatibility via ion-ion interaction. The compatibilisation of polymer blends by specific ion-dipole and ion-ion interactions has recently received wide attention [93-96]. FT-IR spectroscopy is a powerful technique for investigating such specific interactions [97-99] in an ionic blend made from the acid form of sulfonated polystyrene and poly[(ethyl acrylate - CO (4, vinyl pyridine)]. Datta and co-workers [98] characterised blends of zinc oxide-neutralised maleated EPDM (m-EPDM) and zinc salt of an ethylene-methacrylic acid copolymer (Zn-EMA), wherein Zn-EMA content does not exceed 50% by weight. The blend behaves as an ionic thermoplastic elastomer (ITPE). Blends (Z0, Z5 and Z10) were prepared according to the following formulations [98] ... 

Neutralization of ethylene copolymers containing up to 5%-10% acrylic or methacryUc acid copolymer with a metal salt such as the acetate or oxide of zinc, magnesium, and barium yields products referred to as ionomers. (Commercial products may contain univalent as well as divalent metal salts.) lonomers are marked by Du Pont under the trade name Surlyn. These have interesting properties compared with the nonionized copolymer. Introduction of ions causes disordering of the semicrystalline structure, which makes the polymer transparent. lonomers act like reversibly cross-linked thermoplastics as a result of microphase separation between ionic metal carboxylate and nonpolar hydrocarbon segments. The behavior is similar to the physical cross-linking in thermoplastic elastomers (see Chapter 1 of Industrial... 

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