Methacrylic acid metallic salts

In a similar way, cross thermal coupling of binary salts of but-3-enoic acid and methacrylic acid (the salts were obtained by mixing equimolar amounts of the two acids with an equimolar amount of metal or alkaline metal earth salts) on heating gave the coupled product, which was isolated as the methyl ester, i.e. (E)-methyl-hex-l-ene-l,5-dicarboxylate (Scheme 31). 

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. 

Polymers with a sizable number of ionic groups and a relatively nonpolar backbone are known as ionomers. The term was first used for copolymers of ethylene with carboxylated monomers (such as methacrylic acid) present as salts, and cross-linked thermoreversibly by divalent metal ions. Such polymers are useful as transparent packaging and coating materials. Their fluorinated forms have been made into very interesting ion-exchange membranes (considered further below). 

Alternatively, esterification of carboxylic acid can be carried out in aqueous media by reacting carboxylic acid salts with alkyl halides through nucleophilic substitutions (Eq. 9.10).20 The reaction rate of alkyl halides with alkali metal salts of carboxylic acids to give esters increases with the increasing concentration of catalyst, halide, and solvent polarity and is reduced by water. Various thymyl ethers and esters can be synthesized by the reactions of thymol with alkyl halides and acid chlorides, respectively, in aqueous medium under microwave irradiation (Eq. 9.11).21 Such an esterification reaction of poly(methacrylic acid) can be performed readily with alkyl halides using DBU in aqueous solutions, although the rate of the reaction decreases with increasing water content.22... 

Ethylene ionomers consist of copolymers of ethylene and an organic add, such as methacrylic acid, the acid moieties of which have been neutralized to form a metal salt. The metal salts from neighboring chains tend to form clusters, such as the one shown schematically in Fig. 18.3. The net result is the overall structure shown in Fig. 18.2 g), in which the ionic clusters form weak crosslinks between adjacent chains. Ionomers also contain short and long chain branches, which are similar to those found in low density polyethylene. 

Ionomers are made in a two-stage process. In the first step, we copolymerize ethylene with small amounts of an organic acid containing a vinyl group, such as acrylic or methacrylic acid, in a high pressure reactor. In the second step, we neutralize the acid comonomers to form metal salts. We can create ionomers with a variety of metal salts, including sodium, calcium, and zinc. 

EMA ionomers (see Figure 4.30) are speciality thermoplastics copolymerized from ethylene and a small fraction of methacrylic acid, which is then transformed into the salt of sodium, zinc, lithium or another metal randomly distributed along the backbone. The backbone is identical to that of the polyolefins but the pendant groups are different, with a polar and ionic character. 

Heteropoly catalysts have significant activities for the oxidation of isobutane into methacrolein and methacrylic acid. The yield increased up to 6% by vanadium substitution or salt formation, as follows. With Cs2.5Ni0.08H0.34+JrPV,Mo12 - O40, the highest conversion and selectivity were observed at x 1 (355). Increases in the reaction temperature to 613 K led to increased yields, up to 9.0%. A similar increase in the yield resulted from the substitution of As for P as a heteroatom or from the addition of various transition metals (106, 356). 

Ionomers consist of statistical copolymers of a non-polar monomer, such as ethylene, with (usually) a small proportion of ioniz-able units, like methacrylic acid. Ethylene-co-methacrylic acid copolymers (-5% methacrylic acid) are used to make cut-proof golf balls (see Fascinating Polymers opposite). The protons on the carboxylic acid groups are exchanged with metal ions to form salts. These ionic species phase-separate into microdomains or clusters which act as crosslinks, or, more accurately, junction zones (Figure 6-4). (We discuss interactions in a little more detail in Chapter 8.)... 

The salts of poly(methacrylic acid) with Na, Li, K and Cs (CAS for Na salt 25086-62-8) decompose at approximately 350°, whereas the Mg and other alkaline earth metal salts decompose at 500°. The NH4 salt decomposes somewhat differently with elimination of NH3, H2O, and other fragments, at higher temperatures (500° C) forming some isocyanic acid and HCN [119], Some results on poly(methacrylic acid) thermal decomposition as reported in literature are given in Table 6.7.18 [6]. 

The addition of a copolymer has been shown to be a method of improving the mechanical properties of polyethylene/polyamide blends. One copolymer which has had particular success is poly(ethylene-co-methacrylic acid) (EMA) where the acid groups are partially neutralized by metal ions (EMA-salt). 

Many initiator-accelerator systems that contain accelerators other than amine have been suggested for vinyl pol3rmerization, but only a few have been employed in dental resins. Substitution of p-toluenesulfinic acid, alpha-substituted sulfones and low concentrations of halide and cupric ions for tertiary amine accelerators, yields colorless products (43-48). Most of these compounds have poor shelf-life. They readily oxidize in air to sulfonic acids which do not activate polymerization. Lauroyl peroxide, in conjunction with a metal mercaptide (such as zinc hexadecyl mercaptide) and a trace of copper, has been used to cure monomer-pol3rmer slurries containing methacrylic acid (49-50). Addition of Na salts of saccharine to monomer containing an N,N-dialkylarylamine speeds up pol)rmerization (51). 

However, attempts to find similar relationships for mixed-metal heteropoly compounds such as molybdovanadophosphates have not been successful. This has been due to the low thermal stability of these compounds. For example, PMohVO40 and PM010V2O40 decomposed to PM012O40 and VOx above 200 lC [4]. We attempted to stabilize the heteropolyanions by forming their cesium salts. Although the possibility of slight decomposition could not be excluded, high yields were obtained for the conversion of isobutyric acid to methacrylic acid (MAA) as shown in Fig. 1 [5]. 

Ionomers of practical interest have been prepared by two synthetic routes (a) copolymerization of a low level of functionalized monomer with an olefinically unsaturated monomer or (b) direct functionalization of a preformed polymer. Typically, carboxyl containing ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene and similar comonomers by free radical copoly-merization. Rees (22) has described the preparation of a number of such copolymers. The resulting copolymer is generally available as the free acid which can be neutralized to the degree desired with metal hydroxides, acetates and similar salts. Recently, Weiss et al.(23-26) have described the preparation of sulfonated ionomers by copolymerization of sodium styrene sulfonate with butadiene or styrene. 

The vapor phase synthesis of methacrylic acid from propionic acid and formaldehyde was studied [42]. In particular, the choice of alkali metal cation and loading were evaluated for their effect on the activity and selectivity of silica supported catalysts. Experiments were carried out in 0.5 in. (o.d.) quartz reactors equipped with 0.125 in. thermowells. Alkali metal cations supported on silica are effective base catalysts for the production of methacrylic acid. Silica surfaces exchanged with alkali metal cations are capable of chemisorbing propionic acid yielding surface-bound silyl propionate esters and metal propionate salts. The alkali metal cation influences the temperature at which desorption of the ester occurs (Cs < Na < Li < support). For silica catalysts of equimolar cation loading, activity and selectivity to methacrylic acid show the opposite trend, Cs > K. > Na > Li. Methacrylic acid selectivity reaches a maximum at intermediate cation loadings where interaction of adjacent silyl esters is minimized [42]. 

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. 

Poly(2-alkyl oxazoline)s having methacrylate or acrylate end groups were prepared by two methods [182]. a) Living polyoxazoline chains, prepared using methyl p-toluene sulphonate as initiator, were end-capped by reaction with metal salts or tetraalkylammonium salts of acrylic or methacrylic acid or a trialky-lammonium salt or trimethylsilyl ester of methacrylic acid (functional termination). b) The living polymers were terminated with water in the presence of Na2C03 to provide hydroxyl-terminated chains. Subsequent acylation with acry-loyl or methacryloyl chloride in the presence of triethylamine led to the formation of the macromonomers. The procedures are outlined in the following Scheme 51. 

Haller, R. Feder, M. Hatzakis, and E. Spiller, Copolymers of methyl methacrylate and methacryhc acid and their metal salts as radiation sensitive resists, 7. Electrochem. Soc., 126,154 (1979) M. Hatzakis, PMMA copolymers as high sensitivity electron resists, J. Vac. Sci. Technol. 16,1984 (1979). 

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