Thermoplastic elastomers ionomers

DuPont Acetal EVA Nylon 6, 6/6, 6/12, Mineral Filled 6/6, Industrial PBT PET Polyethylene Modified Thermoplastic Elastomer Ionomer Liquid Crystal Polymer ... 

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

Butadiene—Methacrylic Acid Ionomers. Carboxyl groups can readily be introduced into butadiene elastomers by copolymerization, and the effects of partial neutralization have been reported (63—66). The ionized polymers exhibit some degree of fluidity at elevated temperatures, but are not thermoplastic elastomers, and are very deficient in key elastomer properties such as compression set resistance. 

It may also be argued that plasticised PVC may be considered as a thermoplastic elastomer, with the polymer being fugitively cross-linked by hydrogen bonding via the plasticiser molecules. These materials were, however, dealt with extensively in Chapter 12 and will not be considered further here. The ionomers are also sometimes considered as thermoplastic elastomers but the commercial materials are considered in this book as thermoplastics. It should, however, be kept in mind that ionic cross-linking can, and has, been used to fugitively crosslink elastomeric materials. 

Upaeglis A. and O Shea F.X., Thermoplastic elastomer compounds from sulfonated EPDM ionomers. Rubber Chem. TechnoL, 61, 223, 1988. 

Antony P., Bandyopadhyay S., and De S.K., Thermoplastic elastomers based on ionomeric polyblends of zinc salts of maleated polypropylene and maleated EPDM rubber, Polym. Eng. Sci., 39, 963, 1999. Weiss R.A., Sen A., Pottick L.A., and Willis C.L. Block copolymer ionomers. Thermoplastic elastomers possessing two distinct physical networks, Polym. Commun., 31, 220, 1990. 

Ionomer-type elastomers, containing small amounts (less than 5%) of metal carboxylate or sulfonate groups, have potential as a new class of thermoplastic elastomers. Carboxylic acid groups are introduced into polymers such as polybutadiene by copolymerization with a monomer such as acrylic or methacrylic acid. 

Thermoplastic elastomers (TPE), 9 565-566, 24 695-720 applications for, 24 709-717 based on block copolymers, 24 697t based on graft copolymers, ionomers, and structures with core-shell morphologies, 24 699 based on hard polymer/elastomer combinations, 24 699t based on silicone rubber blends, 24 700 commercial production of, 24 705-708 economic aspects of, 24 708-709 elastomer phase in, 24 703 glass-transition and crystal melting temperatures of, 24 702t hard phase in, 24 703-704 health and safety factors related to, 24 717-718... 

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] ... 

Since infrared (IR) spectroscopy is one of the most widely used techniques for the identification of materials at the molecular level, it has been extensively used to characterise the rubbery materials. In this chapter the rubbery materials encompass PE, plasticised PVC, thermoplastic elastomers and ionomers. 

Duvdevani(40) have been directed at modification of ionomer properties by employing polar additives to specifically interact or plasticize the ionic interactions. This plasticization process is necessary to achieve the processability of thermoplastic elastomers based on S-EPDM. Crystalline polar plasticizers such as zinc stearate can markedly affect ionic associations in S-EPDM. For example, low levels of metal stearate can enhance the melt flow of S-EPDM at elevated temperatures and yet improve the tensile properties of this ionomer at ambient temperatures. Above its crystalline melting point, ca. 120°C, zinc stearate is effective at solvating the ionic groups, thus lowering the melt viscosity of the ionomer. At ambient temperatures the crystalline additive acts as a reinforcing filler. 

Table II shows the values of Em (the modulus corresponding to the ultimate Maxwell element), and Me (the molecular weight of the network chain) for the samples dried at a low temperature. It is clear from the table that McexP/Mccal is larger than 1, which means that some of the 3-arm PIB ionomers function as difunctional polymers, i.e. some of the ions are present as free pairs. It is also seen that the higher the temperature, the more of the polymer chains act as difunctional units. This result confirms that ionic aggregates are disrupted by increasing the temperature, a phenomenon fundamental to the use of these materials as thermoplastic elastomers. Moreover, this result parallels the finding of Neppel et al. (5-6) who showed that clusters decompose progressively to multiplets as the temperature is increased.

These differences in sulfonate and carhoxylate associations are believed to be important factors in potential applications involving these ionomers, such as thermoplastic elastomers (8), elastic foams (14), solution applications (13), and related uses (6). 

The thermoplastic IPNs utihze physical cross-hnks, rather than chemical crosshnks. Usually, these materials wiU flow when heated to sufficiently high temperature (hence the terminology thermoplastic), but behave as thermosets at ambient temperature, with IPN properties, often possessing dual phase continuity. Most often, physical crosshnks are based on triblock copolymers (thermoplastic elastomers being the leading material), ionomers, or semi-crystalhne materials. 

Although much of early work on ionomers had focused on non-elastomeric materials, attention has recently been shifted to elastomeric ionomers as potential thermoplastic elastomers(TPE), i.e. elastomers which flow at high temperatures yet retain their network structure at ambient temperatures. For a materid to fiinction as a useful elastomer, the polymer chains must be interconnected in a three-dimensional network. Classically, such crosslinked elastomers cannot flow readily. However, if an elastomer is physically crosslinked via strong ionic bonds, this may lead to a potential TPE. The ionic bonds form physical crosslinks between the polymer chains and thus promote good elastomeric character, yet at higher temperatures they become sufficiently labile to allow the material to flow and be processed as a TPE. 

FIGURE 13.2 Structures of commercially important thermoplastic elastomers HS = hard segment, SS =soft segment, (a) SBS (b) MDI-BD-PTMO polyurethane (c) PTMT and PTMO ct lyester (d) nylon 66 and PTMO copolyamide and (e) random o lymer ionomer E-MAA neutralized with sodium. 

Free radical copolymerization is used to produce ionomers that are used commercially as thermoplastic elastomers. There are two types of TPE ionomers copolymers of ethylene and methacrylic acid, and copolymers of ethylene and acrylic acid. The mole fraction of the acid monomer is typically 5% or less. The property difference between the two types of copolymers is... 

Numerous nylon blends prepared by compatibilization or reactive blending are commercially successful. The modifiers fiequenfly utilized in commercial nylon blends include polyolefin, thermoplastic polyolefin, thermoplastic polyunethane, ionomer, elastomer, ethylene-propylene rubber, nitrile mbber, polyftetrafluoroethylene), poly (phenylene ether), poly(ether amide), silicone, glass fiber, and carbon fiber. The nonpolar modifiers such as polyolefin, maleic anhydride or a polar vinyl monomer such as acrylic acid, methaciylic acid and fimiaric acid is fiequently incorporated to introduce reactive sites in nylon. 

Interesting polymeric materials such as thermoplastic elastomers based on PIB, associative amphiphiles based on poly(vinyl ethylene) (PVE), and telechelic ionomers have been prepared by cationic polymerization. A major drawback of cationic polymerization is the fact that in order to avoid termination and chain transfer reactions, the whole procedure has to take place at very low temperatures from -80 °C down to-100°G. 

The next two decades saw the development of new polymers such as thermoplastic PU (1961), aromatic polyamides, polyimides (1962) polyaminimides (1965), thermoplastic elastomers (styrene-butadiene block copolymers in 1965), ethylene-vinyl acetate copolymer, ionomers (1964), polysulfone (1965), phenoxy resins, polyphenylene oxide, thermoplastic elastomers based on copolyesters, poly butyl terephthalate (1971) and polyarylates (1974). 

In Table 2.2, the polymer-impregnated wood has reduced porosity, and hence is more water resistant. It is also stronger. The ionomers are included in Table 2.3, because they phase-separate like the block copolymers, and represent the limiting case of polymer I/polymer II having opposite chemical properties. One may consider these products block copolymers where the block consists of a single mer. The thermoplastic elastomers utilize the... 

Thermoplastic elastomers based on blends of a silicone rubber (cross-linked during processing) with block copolymer thermoplastic elastomers have also been prodnced (36,37). Other types that have been stndied (38) include graft copol5uners and elastomeric ionomers, but these have not become commercially important. 

Vargantwar PH, Shankar R, BCrishnan AS et al (2011) Exceptional versatihty of solvated block copolymer/ionomer networks as electroactive polymers. Soft Matter 7 1651-1655 Vargantwar PH, Oz9am AE, Ghosh TK et al (2012) Prestrain-free dielectrie elastomers based on acrylic thermoplastic elastomer gels a morphological and (electro)mechanical property study. Adv Funct Mater 22 2100-2113... 

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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