Thermoplastic and thermoset acrylic resins

Among methacrylic ester polymers, poly(methyl methacrylate) is the most important one industrially. Most of it is prepared by free-radical polymerizations of the monomer and a great deal of these polymerizations are carried out in bulk. Typical methods of preparation of clear sheets and rods consist of initial partial polymerizations in reaction kettles at about 90°C with peroxide initiators. This is done by heating and stirring for about 10 min to form syrups. The products are cooled to room 

Monomers that contribute rigidity Elexibilizing monomers Monomers used for cross-linking 

Methyl methacrylate Ethyl acrylate Acrylic acid 

Ethyl methacrylate Isopropyl acrylate Methacrylic acid 

Vinyl toluene i-Octyl acrylate Hydroxypropyl acrylate 

Poly(methyl methacrylate) intended for surface coatings is prepared by solution polymerization. The molecular weights of the polymers are about 90,000 and the reaction products that are 40-60% solutions are often used directly in coatings. 

A certain amount of poly(methyl methacrylate) is also prepared by suspension polymerization. The molecular weights of these polymers are about 60,000 and they are used in injection molding and extrusion. 

Thermosetting acrylic resins are used widely in surface coatings. Both acrylic and methacrylic esters are utilized and the term is applied to both of them. Often, such resins are terpolymers or even tetrapolymers, where each monomer is chosen for a special function. One is selected for rigidity, surface hardness, and scratch resistance another for ability to flexibilize the film, and the third for crosslinking it. In addition, not all comonomers are necessarily acrylic or methacrylic esters or acids. For instance, among the monomers that may be chosen for rigidity may be methyl methacrylate. On the other hand, it may be styrene instead, or vinyl toluene, etc. The same is true of the other components. Table 5.12 illustrates some common components that can be found in thermoset acrylic resins. 

The choice of crosslinking reaction may depend upon the desired application. Itmay also simply depend upon price, or a particular company that manufactures the resin, or simply to overcome patent restrictions. Some common crosslinking reactions will be illustrated in the remainder of this section. If the functional groups are carboxylic acids in the copolymer or terpolymer, crosslinking can be accomplished by adding a diepoxide. 

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Acrylics. Acrylic resins are the most widely used polymers in the paint and coating industry. The two principal forms of acrylic used in surface coatings are thermoplastic and thermoset. Thermoplastics form a film by the evaporation of the solvent present in the coating formation. Thermosets are cured at ambient or elevated temperatures by reacting them with other polymers. The following monomers are generally used in the synthesis of acrylic polymers (Table 7.6) [10]. 

CICH2CH20)2P00CH2CH20P0(0CH2CH2CI)2 Properties M.w. 472.02 Uses Flame retardant additive for flexible PU foams for the transportation, bedding, and furniture industries, and in thermoplastic and thermoset resins such as acrylates, polyolefins, PAN, styrene, ABS, polyesters, epoxies, and PET... 

A large mrmber of polymeric materials are involved in a web coating. These include poly-virtylchloride, polyurethanes (thermoplastic and thermoset solvent-based and water-based), natural, nitrile, chloroprene, and ethylene-propylene rabbers, silicones, polyethylene (chlorinated and chlorositifonated), polyamide, polyester, acrylic resins, polyvinylal-cohol, polytetrafluroethylene, and ethylene-vinyl acetate copolymer as the main matrix polymers of coating compositions. Most of these polymers are not plasticized or seldom... 

Commercial acrylic resins comprise a broad array of polymers and copolymers derived from esters of acrylic acid and methacrylic acid. They range from the homopolymer of methyl methacrylate to a variety of copolymers including both the thermoplastic and thermoset type and ranging from hard and stiff types to soft and elastomeric types. The most common of the thermoplastic acrylic resins are the poly(methyl methacrylate) homopolymer (PMMA) and the copolymers containing predominantly methyl methacrylate but with small amounts of methyl or ethyl acrylate, acrylonitrile, or styrene comonomers added for improved toughness. 

As mentioned above, both thermoplastic and thermosetting type acrylic resins are commercially available for coatings, elastomers, sealants and adhesive applications. These resins are supplied in many different delivery forms such as powders or pellets, solutions in organic solvents and aqueous dispersions. These resin types are briefly described below. 

The term solution acrylics refers to acrylic resins prepared by chain-growth polymerization using a solutionbased polymerization process. Here, acrylic monomers and initiators are slowly added to an organic solvent and polymerization is carried out at a predetermined temperature and inert atmosphere with efficient stirring. Both monomers and the polymer formed are miscible in the selected solvent. With the progress of polymerization, the solution viscosity will Increase and heat transfer becomes difficult, limiting the solid content of the final solution. Both thermoplastic and thermosetting solution acrylics can be prepared by this technique. 

Many alternatives exist and the choice between thermoplastic and thermosetting resins depends on the expected lifetime and maximum operating temperature. Styrene-butadiene block copolymers and acrylic resins can be used to produce low-end adhesives with an acceptable stability up to 100°C, whereas epoxy and silicone thermosets are preferred for their robustness at 150-200°C. In the most severe environments, poly(imide-siloxanes) and polyimides can sustain medium-term exposures to 250 and 300°C, respectively. Various conductive fillers are cited in the literature, including noble metals such as gold or silver, and low-cost metals such as copper, nickel, chromium, and soft solders. 

Water reducible acrylic resins are available to the coatings formulator as both thermoplastic, and thermosetting types. The thermoplastic acrylics film form by simple solvent evaporation and, therefore, cosolvent and amine selection are important. One of the cosolvents used must be a true solvent for the system and be less volatile. It must evaporate more slowly than water. This is to minimise the potential for blushing or flocculation that could be caused by having water as the last solvent to leave the film. The amine should also be volatile at ambient temperatures to minimise the retained water solubility, or sensitivity of the film after drying. This is particularly important since there is no curing reaction with thermoplastics. 

A family of plastics technically known as polyacrylates. Derived from acrylic (or methacrylic) acid, the family includes a variety of materials, including thermoplastic and thermoset resins, textile fibers, paints, and adhesives. Polymethyl methacrylate (PMMA) is one of the most important. Another interesting member of this family is cyanoacrylate, better known as super glue. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Core-shell rubber (CSR) particles are prepared by emulsion polymerization, and typically exhibit two or more alternating rubbery and glassy spherical layers (Lovell 1996 Chapter 8). These core-shell particles are widely used in thermoplastics, especially in acrylic materials (Lovell, 1996), and have also been used to modify thermosets, such as epoxies, cyanates, vinyl ester resins, etc. (Becu et al., 1995). 

Thermoplastics in the form of a lacquer have poorer mechanical strength than the thermosetting resins but are more easily removed, should this prove necessary. Polyvinyl acetate and polyurethane are good examples of this class of consolidants, particularly on wrought iron artefacts. Many of the copper and copper-based alloys, such as bronzes and brasses recovered from the Mary Rose, were consolidated with a solution of acrylic resin dissolved in toluene (Incralac). 

Virtually all thermoplastics and some thermoset most common are commodity plastics such as PVC, PE, PP, and PS others include ABS, nylon, cellulosics, acrylics Several thermoplastics with PE (particularly ND, PE) having the largest volume others include PVC, PP, PS, ABS, acrylics, nylons, acrylonitrile, acetates, and PC PE, (highest volume) PP, PVC together account for almost all plastics used others include a number of engineering thermoplastics, including ABS, acetal copolymers, nylon (6 and 11), polycarbonate Almost all thermoplastics but most commonly used include ABS, PP, PS, PVC polyesters others include acrylics, polycarbonate, cellulosic, nitrile resins... 

Notable among the thermoplastic materials are polyethylene, polypropylene, polyvinyl chloride, the styrene synthetic rubber blends, the acrylics, and the fluorocarbons. Notable among the thermosetting reinforced materials are the polyesters, epoxy, and the furan resins as custom-made reinforced materials, and the phenolic and epoxy resins molded, filament-wound, and/or extruded with reinforcement. AU these materials are available as piping, sheet stock, and miscellaneous molded and fabricated items. These materials, particularly polyvinyl chloride, polypropylene, and reinforced polyesters, are now being used extensively for ventilating ductwork in handling corrosive fumes. They have proved to be economically improved over metals such as stainless steel, lead. 

CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Flame retardant, smoke suppressanL processing aid, water resist, aid, antistat for wire/cable, elec, insulators, printed circuit boards, potting resins, molded and extruded polyolefins, flooring compds., conveyor belting, fabric coatings, polyester and aciylic pultrusion compds., thermosetting resins (BMC, SMC), PVC, EVA, EPDM, XLPE, EEA, thermoplastic elastomers, silicone rubber, NR, SR, acrylic resins, unsat. polyesters... 

Engineering plastic n. (1) A broad term covering those plastics, with or without fillers and reinforcements that have mechanical, chemical, electrical, and/or thermal properties suitable for industrial applications. R. B. Seymour, an outstanding authority, defined them as polymers thermoplastic or thermosetting, that maintain their dimensional stability and major mechanical properties in the temperature range 0-100° C. He listed the big five (among neat resins) as nylons, polycarbonate, acetals, polyphenylene ether, and thermoplastic polyesters. Among many others are acrylics, fluorocarbons, phenoxy, acrylonitrile-butadiene-styrene terpolymer, polyaryl... 

At one time the definition of lacquer (as distinguished from other finishes) was limited so that the film-forming ingredient in a lacquer formulation was specified as cellulose nitrate or other cellulosics, but the definition has now been broadened to include other film formers as well. Typical lacquers include those based on nitrocellulose, other cellulose derivatives, vinyl resins, acrylic resins, and so forth. Although meant to describe only thermoplastic film formers, the term lacquer has been extended to thermosetting coatings as well. 

The adhesives used on tapes are either thermosetting or thermoplastic. The thermoset adhesives consist of rubber, acrylic, silicones, and epoxies, whereas the thermoplastic adhesives are generally acrylic or rubber. Tackifying resins are generally added to increase the adhesion. 

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