Ethylene-acid copolymers

Crystallinity of Ionomers. Ionomers are much less hazy than the ethylene acid copolymers from which they are derived. Studies w ith optical and electron microscopes have shown that this is due to suppression of the spherulitie structure by the metal ions. Surprisingly, x-ray diffraction has shown that polyethylene crystallinity is present in the ionomers. A typical level of crystallinity is 305 . 

Ethylene-acid copolymer resins n. Resins that are flexible, specialty thermoplastics created by high-pressure copolymerization of ethylene (E) and methacrylic acid (MAA) or acrylic acid (AA). 

Nucrel, Ethylene-acid copolymers, DuPont Nulok, Treated clay, Harwich Standard Distribution... 

Eihns of EAA are used in skin packaging, adhesive lamination, and flexible packaging of meat, cheese, snack foods, and medical products. Extrusion coating applications of EAA include coated paperboard, aseptic cartons, composite cans, toothpaste tubes, and food packages. The resin is compatible with LD, LED, and HDPE. PDA regulations permit the use of ethylene acid copolymers containing up to 25 percent acrylic acid, and 20 percent methylacrylic acid in direct food applications. 

A higher service temperature product assembly adhesive can be formulated by using an ethylene acid copolymer such as Elvax II 5550. These adhesives approach the higher service temperature of polyamide adhesives, and thus are a low cost alternative in many applications. A typical formulation is shown in Table 16. 

The FAMI compositions discussed in this paper were prepared by in-sim melt blending and neutralization of the ethylene acid copolymer, the fatty acid, and the neutralizing agent in a twin screws extruder. The FAMI... 

Commercial LDPE, PX22004 from Pemex with an MFR of 0.4 g/lOmin, was used. Two different coupling agents were used a eommercial zinc neutralized carboxylate ionomer, made from ethylene-acid copolymer, in which the acid groups are partially neutrahzed with zinc ions, Surlyn 1652 from DuPont with an MFR of 5.8 g/lOmin, density of 0.94g/em, 6.5 wt% of methacrylic acid, ion type zinc and a commercial LLDPE-g-MA, with 0.9% of MA, CXA4107 from DuPont. An a quaternary aimnonium salt modified clay (Closite 20A) from Southern Clay Products Co. was used. 

Ionomer resins consisting of ethylene—methacrylic acid copolymers partially neutralized with sodium or zinc were commercially introduced in 1964 by Du Pont under the Sudyn trademark (1). More recently, a similar line of products, sold as Hi-Mdan resins, has been commercialized by Mitsui—Du Pont in Japan. lolon ionomeric resins, based on ethylene—acrylic acid, are produced by Exxon in Belgium. Ionomers containing about 1 mol % of carboxylate groups are offered by BP in Europe as Novex resins. Low molecular weight, waxy Aclyn ionomers are produced and sold by AHiedSignal. 

Similar mechanical data for a series of ionomers derived from a single ethylene—acryflc acid copolymer have appeared (13) (Table 3). Comparison of the data from Tables 2 and 3 shows that the substitution of acryflc acid for methacrylic acid has only minor effects on properties. 

Melt Viscosity. As shown in Tables 2 and 3, the melt viscosity of an acid copolymer increases dramatically as the fraction of neutralization is increased. The relationship for sodium ionomers is shown in Figure 4 (6). Melt viscosities for a series of sodium ionomers derived from an ethylene—3.5 mol % methacrylic acid polymer show that the increase is most pronounced at low shear rates and that the ionomers become increasingly non-Newtonian with increasing neutralization (9). The activation energy for viscous flow has been reported to be somewhat higher in ionomers than in related acidic... 

Ethylene—Dicarboxylic Acid Copolymers. Partial neutralization of copolymers containing carboxyls in pairs on adjacent carbons, eg, ethylene—maleic acid, has been described (11). Surprisingly, there is no increase in stiffness related to neutralization. Salts with divalent metal cations are not melt processible. The close spacing of the paired carboxyl groups has resulted in ionic cluster morphology which is distinct from that of the commercial ionomer family. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

In most ionomers, it is customary to fully convert to the metal salt form but, in some instances, particularly for ionomers based on a partially crystalline homopolymer, a partial degree of conversion may provide the best mechanical properties. For example, as shown in Fig. 4, a significant increase in modulus occurs with increasing percent conversion for both Na and Ca salts of a poly(-ethylene-co-methacrylic acid) ionomer and in both cases, at a partial conversion of 30-50%, a maximum value, some 5-6 times higher than that of the acid copolymer, is obtained and this is followed by a subsequent decrease in the property [12]. The tensile strength of these ionomers also increases significantly with increasing conversion but values tend to level off at about 60% conversion. 

In a partially crystalline homopolymer, nylon 6, property enhancement has been achieved by blending with a poly(ethylene-co-acrylic acid) or its salt form ionomer [24]. Both additives proved to be effective impact modifiers for nylon 6. For the blends of the acid copolymer with nylon 6, maximum impact performance was obtained by addition of about 10 wt% of the modifier and the impact strength was further enhanced by increasing the acrylic acid content from 3.5 to 6%. However, blends prepared using the salt form ionomer (Sur-lyn 9950-Zn salt) instead of the acid, led to the highest impact strength, with the least reduction in tensile... 

Ethylene-acrylic acid copolymer neutralized with amines such as triethanol amine or N-methyl diethanol amine enhances anti-settling properties [1198, 1554]. 

We can incorporate short chain branches into polymers by copolymerizing two or more comonomers. When we apply this method to addition copolymers, the branch is derived from a monomer that contains a terminal vinyl group that can be incorporated into the growing chain. The most common family of this type is the linear low density polyethylenes, which incorporate 1-butene, 1-hexene, or 1-octene to yield ethyl, butyl, or hexyl branches, respectively. Other common examples include ethylene-vinyl acetate and ethylene-acrylic acid copolymers. Figure 5.10 shows examples of these branches. 

We make polyethylene resins using two basic types of chain growth reaction free radical polymerization and coordination catalysis. We use free radical polymerization to make low density polyethylene, ethylene-vinyl ester copolymers, and the ethylene-acrylic acid copolymer precursors for ethylene ionomers. We employ coordination catalysts to make high density polyethylene, linear low density polyethylene, and very low density polyethylene. 

Ethylene-acrylic acid copolymers are converted to ethylene ionomers in a separate, postpolymerization reaction. 

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