Polyethylene-based ionomers

The best combination of properties of polyethylene-based ionomers, such as stiffness, strength, transparency, and toughness, are realized at partial degrees of conversion of about 40-50% [13]. The initial increase in properties is a result of the presence of ionic interactions, which strengthen and stiffen the polymer. There is, however, some loss of crystallinity as a result of the presence of the ionic groups. When the loss of crystallin-... 

The type of counterion present in an ionomer may, or may not, have a significant effect of properties. For polyethylene-based ionomers, where the presence of crystallinity has an appreciable effect on properties, the type of counterion present does not appear to have a significant effect on either modulus or tensile strength, as Fig. 4 indicates. However, in amorphous ionomers, the effects of changing the counterion from a monovalent one, as in Na or K, to a divalent one, such as Ca, may be appreciable. 

Lee JA, Kontopoulou M, Parent JS. Synthesis and characterization of polyethylene-based ionomer nanocomposites. Polymer 2005 46 5040-5049. 

The perfluorinated, carboxylated and sulfonated ionomer membranes form the ionic clusters of a few nm in size, as in the case of the hydrocarbon-based ionomers such as polyethylene,polystyrene and polybutadiene(9). The ionic clusters strongly affect physical properties of the membranes, e.g., the swelling behavior of the membranes (amount of water uptaken by the membranes, W and... 

This versatile technique is generally used where a ply of polyethylene or copolymer thereof is required in a structure. Other polymers may be used in specialized areas but the handling can become more difficult. The process is widely used within the Packaging Industry for the coating of paper, board, foils, cellulose film and thermoplastic films. The most common coating resin used is low-density polyethylene, but this now extends to copolymers such as Ethylene-vinyl acetate, ethylene-acrylic acid, polypropylene, high density polyethylene and ionomers (e.g. Surlyn). The acrylic acid-based materials and ionomers are used in areas in which enhanced adhesive strength is required, such as resistance to difficult environments. 

A wide range of ionomers based on other polymer backbones has also been stndied. Even thongh an extensive discnssion of properties of partly crystalline ionomers as well as the other ionomer famiUes is beyond the scope of the present review, it will be nsefiil to discnss veiy briefly the properties of some of them. In partly crystalline polyethylene-based and perfluorinated ionomers the degree of crystallinity makes the interpretation of experimental results difficult. 

On the basis of these measurements and related physicochemical studies, it is possible to process a structure for ethylene-based ionomers. The un-ionized acid copolymer is thought to consist of two phases a crystalline polyethylene phase and an amorphous phase consisting of polyethylene crosslinked by hydrogen-bonded carboxylic dimers. The ionized copolymers exhibit three distinct phases a crystalline polyethylene phase, an amorphous polyethylene phase, and a dispersed ionic phase consisting of ionic domains. 

Tables 2 and 3 give the results of haze reduction for the polymeric red and polymeric yellow dye, respectively, based on the type of analysis described for Figure 2. Haze reductions in both the red and yellow polymeric dye were observed with the addition of both polyethylene-based Zn ionomer and polypropylene-alt-maleic anhydride copolymer. The polypropylene-graft-maleic anhydride copolymers were not effective in reducing haze in the polymeric red, but did show haze reduction in the yellow, although relatively higher loadings of this wax were necessary to give similar results to the Zn ionomer or the PP-alt-MA materials. The polyethylene-graft-maleic anhydride copolymer, the succinic anhydride- terminated isotactic PP, and the PP homopolymer wax did not reduce haze with the polymeric red. The C30 a-olefin-alt-maleic anhydride copolymer and the polyethylene-based calcium ionomer both produced increases in haze when molded with the polymeric red.

The term ionomer was first introduced in the early 1960s, when DuPont developed Surlyn resins [36], salt forms (Na and Zn) of the copolymers of ethylene and a small amount (several mole percent) of methacrylic acid. Initially, Surlyn resin that was based on polyethylene was called an ionomer, but later all polymers that have a small amount of ionic groups (up to 10-... 

Pressures to introduce restrictive legislation in Europe have eased as the debate has moved from the political arena to focus on assessment and management of risk. The main health and environment issue centres on halogen-based FRs, for possible formation of dioxin-related products such as brominated dioxins/furans by polybrominated biphenyl ethers (PBBE) under combustion conditions. These are very effective flame retardants and are widely used in polystyrene, polyethylene and polypropylene. Only a few of 75 identified brominated dioxin ionomers and 135 brominated furan ionomers are toxic, and they are only present in low concentrations in combustion. Less-toxic furans tend to be formed more than dioxins, and brominated dioxine/furans are less toxic than their chlorinated counterparts. 

The word ionomer dates back to 1965, but materials of this type had been synthesized and investigated long before. Examples of early work include the investigation of Littman and Marvel in 1930, synthesis of an elastomer based on butadiene and acrylic acid in the early 1930 s, and the appearance in the 1950 s of du Font s Hypalon (sulfonated, chlorinated, and cross-linked polyethylene) [29]. 

Commercial ionomers are based on polyethylene with acidic groups as part of the backbone chain. These are neutralized by metallic counterions, typically Na" or... 

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