Methacrylic esters, chemical resistance

These same rules apply to other resins such as the family of unsaturated polyesters. In these, the reactive diluents dilute the ester groups. A reduction in ester group concentration can be achieved by using more rigid skeletal structures and employing only terminal ester groups (vinyl ester resins) or urethane links (vinyl urethanes, urethane methacrylates). The chemical resistance of these resins is summarized in Table 3.6. 

Vinyl lacquers are used mainly where a high degree of chemical resistance is required these lacquers are based on vinyl chlorides and vinyl acetates. Acrylic lacquers are based on methyl methacrylate and methyl acrylate polymers and copolymers. Other esters of acrylic and methacrylic acid also may be used to make nonconvertible film formers. Judicious selection of these acrylic acid or methacrylic acid esters allows one to produce film formers with specifically designed properties such as hardness, flexibility, gloss, durability, heat, and chemical resistance. Acrylic lacquers, however, are not noted for their water resistance. The principal uses of acrylic-type lacquers are fluorescent and metallic paints, car refinish applications, clear lacquers and sealers for metals, and protective coatings for aircraft components and for vacuum-deposited metals, as well as uses in pigmented coatings for cabinets and appliances. 

Vinyl ester resins (VERs, epoxy methacrylates) are a major class of styrenated, free radically curable, corrosion- and chemical-resistant thermoset resins. They are largely used in fiber-reinforced structural applications, and they have a substantial history of long-term service in numerous environments at elevated temperatures and pressures, usually under load. 

Poly (methyl methacrylate) is characterized by crystal-clear hght transparency, unexcelled weatherability, and good chemical resistance and electrical and thermal properties. It has a useful combination of stiffness, density, and moderate toughness. PMMA has a moderate Tg of 105°C, a heat deflection temperature in the range of 74 to 100°C, and a service temperature of about 93°C. However, on pyrolysis, it is almost completely depolymerized to its monomer. The outstanding optical properties of PMMA combined with its excellent environmental resistance recommend it for applications requiring light transmission and outdoor exposure. Poly (methyl methacrylate) is used for specialized apphcations such as hard contact lenses. The hydroxyethyl ester of methaciyhc acid is the monomer of choice for the manufacture of soft contact lenses. Typical applications of poly(methyl methacrylate are shown in Table 15.6. 

Contact lenses are the most common polymer product in ophthalmology. The basic requirements for this type of materials are (T)excellent optical properties with a refractive index similar to cornea good wettability and oxygen permeability ( ) biologically inert, degradation resistant and not chemically reactive to the transfer area ( ) with certain mechanical strength for intensive processing and stain and precipitation prevention. The common used contact lens material includes poly-P-hydroxy ethyl methacrylate, poly-P-hydroxy ethyl methacrylate-N-vinyl pyrrolidone, poly-P-hydroxy ethyl methacrylate, Poly-P-hydroxy ethyl methacrylate - methyl amyl acrylate and polymethyl methacrylate ester-N-vinyl pyrrolidone, etc. The artificial cornea can be prepared by silicon rubber, poly methyl... 

Esters of Epoxy Resin and Methacrylic Acid. Epoxy resins can also be reacted with methacrylic acid on heating. The resulting methacrylate ester resins are dissolved in polymerizable solvents and catalyzed with peroxides (e.g., Derakane, Dow Chemical). These catalyzed resins are applied as thick-layer laminates in combination with glass fibers, fabrics, or mats. The laminates are generally cured at ca. 60 C and have extremely good chemical resistance they are therefore used in the chemical industry for the internal lining of reactors and storage tanks [2.127]-[2.130). 

Within the different types of epoxies, are found epoxy diacrylates or vinyl ester resins, used to produce specific corrosion and chemical resistant composite systems. Vinyl ester resins are produced by either reacting epoxy resins of glycidyl derivatives with methacrylic acid, or from BPA and glycidyl methacrylates, where an active monomer (usually styrene) as crosslinker, hardener (usually organic peroxides), accelerators (cobalt) are added to the system. In the thermoset epoxy systems, there are also the mould releasers , which can be either internal such as, lecithin, or stearates of zinc and calcium, certain organic phosphates that are mixed in the resin, or, external - such as, fluorocarbons, silicone oil, and certain waxes, that are directly laid on the mould. 

Vinyl esters are thermosetting resins that consist of a polymer backbone with an acrylate or methacrylate termination. The backbone component of vinyl ester resins can be derived from epoxide, polyester or urethane but those based on epoxide resins have most commercial significance. Bisphenol A epoxy formed vinyl esters were designed for chemical resistance and commonly formulated for viscosity for use in filament winding of chemical containers. Typically styrene is used as a reactive dilutent to modify viscosity. Phenolic novolac epoxies are used to produce vinyl esters with higher temperature capability and good solvent resistance, particularly in corrosive environments, and their FRP composites have demonstrated initial economy and better life cycle costs compared with metals. 

Some polymerizable esters can be used as a copolymerizable internal plasticizer in technical applications. The best known of the group is diallyl phthalate (DAP), which is used to replace styrene, divinyl benzene, or methyl methacrylate in unsaturated polyester resins. It has a very low vapour pressure (300°C boiling point), leading to significant reduction in loss through evaporation. It considerably improves properties such as hardness, chemical resistance, hydrolysis resistance, electrical properties, and product life. It is particularly used in electrical applications, can be employed (after suitable preparation) in cold-cure systems, and shows high affinity to glass fibre. DAP can also be used as a reactive plasticizer with PVC resins. 

Chemical Properties. The chemical-resistance properties of methacrylic ester polymers are even higher than those of the acrylic esters. Methacrylic esters imdergo a lower degree of hydrolysis in either acidic or alkaline media than acrylics. Both acrylics and methacrylics easily outperform vinyl acetate-containing polymers which are well known to be susceptible to hydrolysis of the side-chain ester. There are marked differences in the chemical-resistance properties of different forms of PMMA. The syndiotactic (alternating) form of PMMA is the most chemically inert. The rate of hydrolysis for syndiotactic PMMA is lower than that for isotactic (26) radical polymerizations generate large portions of syndiotactic PMMA and benefit in terms of stability. 

A non-epoxy-based vinyl ester is simply a methacrylate terminated polyester. It has a reduced resistance to caustic and acids and can be used as a plastic composite binding resin in applications where high chemical resistance is not critical. Epoxy vinyl ester resins have not penetrated the automotive market because relatively inexpensive polyesters can meet most of the performance needs except chemical resistance. However, it is possible to imagine the introduction of epoxy vinyl ester resins into more corrosive or severe applications near the engine, batteries, external body parts, and so forth. 

In VE resins, the ester bond is located at the end of each polymer chain and results exclusively from the reaction of an unsaturated monocarbonic acid with the epoxy group of an epoxy resin. The reactive points have a methacrylate or acrylate structure and are located at the end of the polymer chain. Due to the methyl group branching of the methacrylic acid, the ester bond has spatial protection against hydrolytic and chemical attacks, which explains its high chemical resistance. 

These thermoplastic resins are obtained by the polymerization or copolymerization of acrylic and methacrylic esters. Acrylic resins may be combined with melamine, epoxy, alkyd, acrylamide, etc., to produce systems that bake to a film with excellent resistance to water, acids, alkalies, chemicals, and other corrosives. Acrylic resins are used in coatings for all types of appliances, cans, and automotive parts and for all types of metals. 

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