Methyl methacrylate , 413 Table

The major one-carbon feedstock is methane and it serves as the feedstock to a number of important monomers including hexamethylene tetramine and melamine, used in the synthesis of a number of cross-linked thermosets as well as vinyl acetate, ethylene, ethylene glycol, and methyl methacrylate (Table 17.1). 

Anionic poiymerization. Anionic polymerization is an addition polymerization in which the growing chain end bears a negative charge. The monomers suitable for anionic polymerization are those that have substituent groups capable of stabilizing a carbanion through resonance or induction. TVpical monomers that can be polymerized by ionic mechanisms include styrene, acrylonitrile, and methyl methacrylate (Table 14.20). 

Swelling of polymethyl methacrylate latex particles with methyl methacrylate. Table IV lists the swelling ratios and interfacial tensions for the different-size polymethyl methacrylate latexes with added Aerosol MA and sodium dodecyl sulfate emulsifiers. Comparison of the data with the theoretical curves from Model I (Figure 2) defines an apparent interaction parameter of 0.45 and the semi-empirical equation ... 

The kp value for phenyl methacrylate (Table 7) is smaller than that for methyl methacrylate (Table 8), although phenyl methacrylate is more likely to be attacked by a free radical than methyl methacrylate (see copolymerization data96 97 ). Accordingly, it is clear that the propagating radical of methyl methacrylate is more reactive than that of phenyl methacrylate. This is because the phenyl methacrylate radical is more likely to form the radical-solvent complex, which is consistent with the above-mentioned proposal by Henrici-01iv6 et al.67-71 and Bamford et al.2 . 

For the common nomenclature the usual practice is to name a polymer according to its source, i.e., the monomer(s) used in its synthesis, and the generic term used is poly monomer , whether or not the monomer is real. The prefix poly is added on to the name of the monomer to form a single word, e.g., polyethylene, polystyrene, and polyacrylonitrile (see Table 1.1). However, when the monomer has a multiworded name, the name of the monomer after the prefix poly is enclosed in parentheses, e.g., poly(vinyl chloride), poly(vinyl alcohol) and poly (methyl methacrylate) (Table 1.1). 

Because of the attraction and repulsion forces, the conventionally determined intrinsic viscosity of mixtures of different polymers may appear higher or lower than that calculated from Equation (9-125) from the mass contributions w, and intrinsic viscosities [17], of the components. Examples of this are the values for mixtures of poly(styrene) and poly(methyl methacrylate) (Table 9-5). 

In principle, the chemical reactions of macromolecules should be similar to those of low-molecular-weight substances. Experimentally, however, either degradation is found to occur at very much lower temperatures or, occasionally, there is degradation into different products. The decomposition of poly(ethylene), for example, begins at 200°C lower than that of hexadecane. At 450°C, poly(methyl methacrylate) will be almost completely depolymerized into monomer, methyl methacrylate (Table 23-2). At this temperature, on the other hand, low-molecular-weight primary esters decompose into olefins and acids. The nature of the product also depends on whether the experiment is carried out at atmospheric pressure under nitrogen or under high vacuum (Table 23-3). 

PROBLEM 14.6 Methyl methacrylate (Table 14.1) can be polymerized by catalytic amounts of n-butyllithium at -78°C. Using eqs. 14.17 and 14.18 as a model, write a mechanism for the reaction. Show how the intermediate carbanion is resonance-stabilized. 

Selected physical properties of various methacrylate esters, amides, and derivatives are given in Tables 1—4. Tables 3 and 4 describe more commercially available methacrylic acid derivatives. A2eotrope data for MMA are shown in Table 5 (8). The solubiUty of MMA in water at 25°C is 1.5%. Water solubiUty of longer alkyl methacrylates ranges from slight to insoluble. Some functionalized esters such as 2-dimethylaniinoethyl methacrylate are miscible and/or hydrolyze. The solubiUty of 2-hydroxypropyl methacrylate in water at 25°C is 13%. Vapor—Hquid equiUbrium (VLE) data have been pubHshed on methanol, methyl methacrylate, and methacrylic acid pairs (9), as have solubiUty data for this ternary system (10). VLE data are also available for methyl methacrylate, methacrylic acid, methyl a-hydroxyisobutyrate, methanol, and water, which are the critical components obtained in the commercially important acetone cyanohydrin route to methyl methacrylate (11). 

Table 5. A2eotropic Mixtures with Methyl Methacrylate ...

Woddwide production capacity is shown in Table 6. Economic conditions in the late 1980s and eady 1990s led to global overcapacity of methyl methacrylate, which caused many plants to be operated at less than optimum levels. 

Increa sing the bulkiness of the alkyl group from the esterifying alcohol in the ester also restricts the motion of backbone polymer chains past each other, as evidenced by an increase in the T within a series of isomers. In Table 1, note the increase in T of poly(isopropyl methacrylate) over the / -propyl ester and similar trends within the butyl series. The member of the butyl series with the bulkiest alcohol chain, poly(/-butyl methacrylate), has a T (107°C) almost identical to that of poly(methyl methacrylate) (Tg = 105° C), whereas the butyl isomer with the most flexible alcohol chain, poly( -butyl methaciylate), has a T of 20°C. Further increase in the rigidity and bulk of the side chain increases the T. An example is poly(isobomyl methacrylate)... 

Electrical Properties. Poly(methyl methacrylate) has specific electrical properties that make it unique (Table 4). The surface resistivity of poly(methyl methacrylate) is higher than that of most plastic materials. Weathering and moisture affect poly(methyl methacrylate) only to a minor degree. High resistance and nontracking characteristics have resulted in its use in high voltage appHcations, and its excellent weather resistance has promoted the use of poly(methyl methacrylates) for outdoor electrical appHcations (22). 

Table 4. Electrical Properties of 6.35-mm Thick Poly(methyl methacrylate) Sheet ...

The chemical resistance and excellent light stabiUty of poly(methyl methacrylate) compared to two other transparent plastics is illustrated in Table 5 (25). Methacrylates readily depolymerize with high conversion, ie, 95%, at >300° C (1,26). Methyl methacrylate monomer can be obtained in high yield from mixed polymer materials, ie, scrap. 

Table 5. Relative Outdoor Stability of Poly(methyl methacrylate) ...

Chain transfer to solvent is an important factor in controlling the molecular weight of polymers prepared by this method. The chain-transfer constants for poly(methyl methacrylate) in various common solvents (C) and for various chain-transfer agents are Hsted in Table 10. 

Plastic Sheet. Poly(methyl methacrylate) plastic sheet is manufactured in a wide variety of types, including cleat and colored transparent, cleat and colored translucent, and colored semiopaque. Various surface textures ate also produced. Additionally, grades with improved weatherabiUty (added uv absorbers), mat resistance, crazing resistance, impact resistance, and flame resistance ate available. Selected physical properties of poly(methyl methacrylate) sheet ate Hsted in Table 12 (102). 

Fig. 15. Oxygen permeability versus 1/specific free volume at 25 °C (30). 1. Polybutadiene 2. polyethylene (density 0.922) 3. polycarbonate 4. polystyrene 5. styrene-acrylonitrile 6. poly(ethylene terephthalate) 7. acrylonitrile barrier polymer 8. poly(methyl methacrylate) 9. poly(vinyl chloride) 10. acrylonitrile barrier polymer 11. vinyUdene chloride copolymer 12. polymethacrylonitrile and 13. polyacrylonitrile. See Table 1 for unit conversions.

In principle, A can be any polymer normally regarded as a hard thermoplastic, eg, polystyrene, poly(methyl methacrylate), or polypropylene, and B can be any polymer normally regarded as elastomeric, eg, polyisoprene, polybutadiene, polyisobutylene, or polydimethylsiloxane (Table 2). 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

The properties of three types of poly(methyl methacrylate) (sheet based on high molecular weight polymer, lower molecular weight injection moulding material and a one-time commercial copolymer) are given in Table 15.1. 

As may be expected of an amorphous polymer in the middle range of the solubility parameter table, poly(methyl methacrylate) is soluble in a number of solvents with similar solubility parameters. Some examples were given in the previous section. The polymer is attacked by mineral acids but is resistant to alkalis, water and most aqueous inorganic salt solutions. A number of organic materials although not solvents may cause crazing and cracking, e.g. aliphatic alcohols. 

Rather more recently Rohm and Haas GmbH have introduced Plexidur plus which is a copolymer of acrylonitrile and methyl methacrylate. It is best considered as a glazing material for use in schools, sports halls and vehicles. The material also has good clarity, rigidity and surface hardness. Some typical properties compared with PMMA are given in Table 15.2. 

Table 15.2 Some properties of a methyl methacrylate-acrylonitrile copolymer compared with a general purpose poly(methyl methacrylate) compound at 23°C and 50% R.H (German DIN tests)...

Mechanical properties are typical of a rigid plastics material and numerical values (Table 30.2) are similar to those for poly(methyl methacrylate). Although thermosetting, it has a low heat distortion temperature ( 80°C) and is not particularly useful at elevated temperatures. 

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