Epoxy chemistry

Originally developed commercially in the late 30 s by Castan, and early 40 s by Ciba A.G., then taken up for use in aircraft manufacture, epoxy (polyglycidyl ether) technology was introduced to the coatings industry in the late 1940 s. The excellent chemical and physical properties exhibited by epoxies has meant a sustained and continued growth in importance within the coatings industry to a level such that over 500,000 tonnes/year of epoxy resins were consumed by the industry in 1990. 

The variations produced by the above reaction are almost unlimited. Practically, however, the range of resins offered by the manufacturers are restricted to those most commercially viable. Although each manufacturer will have their own commercial names or codes for their products, in order to differentiate between the variants possible, most coatings technologies generally refer to the Epikote series of epoxy resins when discussing resin types. A brief example of the resins and their epoxy functionality are listed in Table 2-6. 

TABLE 2-6 EPOXY RESINS WHICH CAN BE USED IN INTERNAL LACQUERS 

Note that there are significant variations in the EEW (epoxy equivalent weight) or EGC (epoxy group content) between the same grades of epoxy resin (for example the EEW for a g type epoxy may range from 260 - 440). 

Higber Molecular Weight Bitphertol A Epoxy Resins 

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In a specific example of adhesive bonds between cold rolled steel and SMC adherends (Table II) an adhesive based on hydrolysis resistant epoxy chemistry (i.e., adhesive E) was compared with an adhesive based on hydrolysis prone urethane chemistry (i.e., adhesive C) in composite to cold rolled steel bonds. After corrosion testing, a significant difference in both retention of initial bond strength and locus of failure was observed. For bonds prepared with adhesive E, little if any reduction of the initial bond strength was observed after corrosion testing. The locus of failure for both the tested and untested bonds was largely in the... 

Similarly to UP resins, VE resins consist of an unsaturated oligomer dissolved in styrene. The unsaturated oligomer is based on the epoxy chemistry (Sec. 2.2.4). When one mole of a DGEBA monomer is reacted with 2 moles of (meth)acrylic acid, an a, oo-di(meth)acrylate oligomer is obtained ... 

We can prepare functionalized chromophore and crosslinking reagents in a thermosetting composition that is, the chromophores and crosslinking reagents can react to form a three-dimensional crosslinked polymer matrix. Thermosetting polyurethane, sol-gel, or epoxy chemistries are frequently used. Many variations on the above themes can be and have been executed for example,... 

One of the major advantages of epoxy chemistry is the wide latitude it provides the for-mulator for solving technical problems. Epoxies can be designed to be flexible or rigid high or low modulus homogeneous, filled, or foamed conductive or insulative fire-retardant and resistant to heat and chemicals. 

FIGURE 5.13 Polymercaptan-epoxy chemistry accelerated with a tertiary amine.20... 

A typical cationic uv adhesive formulation contains an epoxy resin, a cure-accelerating resin, a diluent (which may or may not be reactive), and a photoinitiator. The initiation step results in the formation of a positively charged center through which an addition polymerization reaction occurs. There is no inherent termination, which may allow a significant postcure. Once the reaction is started, it continues until all the epoxy chemistry is consumed and complete cure of the resin has been achieved. Thus, these systems have been termed living polymers. 

Epoxy adhesives have achieved their commercial success due in no small way to their processing capabilities. Epoxy chemistry is compatible with (1) a variety of formulating techniques and processes accessible to the adhesive manufacturer and (2) a variety of application and curing methods accessible to the end user. 

Since epoxy adhesive formulation represents a surprisingly broad area of technology, a road map to the use of this book may be valuable. Chapters 1 through 3 discuss the synthesis of raw materials, epoxy chemistry in general, and the physical and chemical properties that are important for an epoxy adhesive. These properties are important during the three primary phases or conditions of an adhesive (1) uncured, (2) during cure, and (3) fully cured. 

Epoxy structural adhesives have proven to be versatile and reliable compositions. Their widespread use and acceptance is in part due to the varied chemistry of the epoxy ring and the skill of scientists and adhesive formula-tors in developing high-quality compositions that can produce reliable, reproducible structural joints even when applied by relatively unskilled users. New compositions and chemical reactions continue to be disclosed, and it is certain that the knowledge of epoxy chemistry will continue to grow. Many of the new discoveries will find their way into new epoxy structural adhesives. 

Epoxy chemistry is complex. Most epoxy resins are made by reaction of epichlorohy-drin with bisphenol A. 

Vinyl ether and epoxy chemistry established more than 50 years ago finally found its way into radiation curing technology. These compounds have been demonstrated to be reactive monomers in curing processes photoinitiated by iodonium and sulfonium salts. In particular, vinyl ethers are known to be among the most reactive monomers in photocuring chemistry. 

Room temperature acid catalysis involving cationic acetylacetone salts of Si, B, Ge and P have been used successfully in modern epoxy chemistry. 

Epoxy alkyds typically have 5—45% resins based on epoxy chemistry. Bisphenol A along with other phenols is used with epichlorohydrin. The epoxy groups of the resin are esterified with unsaturated fatty acids of soybean and tall oils. These resins oflFer better performance than a simple alkyd with excellent chemical-resistance and strong adherence to a wide variety of materials. 

Oriented PLC thermosets based on epoxy chemistry and with the mesogens in the backbone chain have been prepared by aligning an oligoether prepolymer either mechanically or in a magnetic field (13.5 T) prior to and during curing [135]. The temperature associated with a drop in order parameter increased with increasing crosslink density. Samples with few crosslinks showed a drop in order parameter at 130 C... 

Diffusion vs. Reaction Controlled Kinetics Contrast curves obtained from e-beam experiments at the lithographically usefiil doses at 90 °C and 110 °C for different PER times show a very characteristic behavior for this epoxy chemistry based chemically amplified resist. The gel dose does not change in this PER temperature and time range whereas the contrast increases in the higher temperature and time regime (Figures 7 and 8). 

It has been the experience of the authors that the cutting edge of important new technology in epoxy chemistry is mainly found in the trade literature of the suppliers. Patents and papers include much information, but the technology which works in the practical sense comes from those developments which are made available as new raw materials. 

One of the most important monomers in epoxy chemistry is the diglycidyl ether of bisphenol A (9a) ... 

Most work has been with free-radical systems but other chemistries can be used. Begishev etal. studied frontal anionic polymerization of e-caprolactam [18, 19], and epoxy chemistry has been used as well [20-23]. Mariani ctal. demonstrated frontal ring-opening metathesis polymerization [17]. Fiori et al. produced polyacrylate-poly(dicydopentadiene) networks frontally [24], and Pojman etal. studied epoxy-acrylate binary systems [25]. Polyurethanes have been prepared frontally [13,14, 26]. Frontal atom transfer radical polymerization has been achieved [16] as well as FP with thiol-ene systems [27]. Recent work has been done using FP to prepare microporous polymers [28-30], polyurethane-nanosilica hybrid nanocomposites [31], and segmented polyurethanes [32]. 

Brown, J.M., CurUss, D., Vaia, R.A., 2000. Thermoset-layered silicate nanocomposites. Quaternary ammonium montmorillonite with primary diamine cured epoxies. Chemistry of Materials 12, 3376-3384. 

Pfeil et al. received a patent in 2003 on Mortar Composition, Curable by Frontal Polymerization, and a Method for Fastening Tie Bars. Chemical anchors are adhesives, usually based on epoxy chemistry that are used to secure rods in holes drilled in concrete. Their approach is to use multifunctional acrylates with silica and quartz fillers and thermal initiators as the frontally cured chemical anchor. 

The resin matrix is usually a formulated thermoset system (i.e. a reactive matrix, which on the application of heat and pressure, chemically reacts to form an infusible reinforced laminate). The thermosetting matrices are most often based on epoxy chemistries although there are plenty of examples of phenolic, bismaleimide and polyimide matrices (for example, the HexPly range from Hexcel Composites) and a few where the resin is based on cyanate esters. Thermoplastic matrices are also encountered (i.e. matrices that can change from a solidus to a liquidus form by tbe application of heat and pressure and then revert to the solid state on cooUng) which are usually, but not exclusively, based on polysulphone, polyetbersulphone or polyether ether ketone chemistries. 

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