Epoxies commercial epoxy resins

Fig. 1. Structures of commercial epoxy resins (a) phenolic novolac epoxy resin, (b) glycidated polybasic acid, (c) glycidated polyamine (A,A,A, A -tetraglycidyl-4,4 -diaminodiphenylmethane [28768-32-3] (TGMDA)), and (d) glycidated bisphenol A.

The syntheses of commercial epoxy resins that are commonly used in many applications were discussed in Chap. 2. Additional information is provided in this chapter with regard to the physical and chemical properties of certain epoxy resins relative to their use in adhesive systems. 

VLB for paint-related polymer solutions including commercial epoxy resins " ... 

Some typical results are shown in Figure 16.2 (LLE for PS/acetone), Table 16.4 (infinite dilution activity coefficient for PBMA solutions in a variety of solvents). Tables 16.5 and 16.6 (activity coefficients of low- and heavy-molecular-weight alkanes in asymmetric athermal-alkane solutions). Table 16.7 (VLB for ternary polymer-solvent solutions). Figure 16.6 (VLB calculations for systems containing the commercial epoxy resin Araldit), and Table 16.8 (comparison of LLE results from various thermodynamic models). 

The uncatalyzed reaction of acid anhydrides with epoxides is slow even at 200 C however, with either acidic or basic catalysts the reaction proceeds readily with the formation of ester linkages. The reaction of acid anhydrides with conventional commercial epoxy resins is probably initiated by water or hydroxyl and carboxyl compounds present in the mixture. The following sequence is illustrative of initiation by a hydroxyl-containing material ... 

Thus, the direct reaction between epoxide and anhydride has been found to be very slow, and the anhydride ring must first be opened before reaction can occur. Ring opening can result from reaction with hydroxyl groups present in commercial epoxy resins addition of basic catalysts, such as tertiary amines and carboxylate ions or addition of Lewis acids (not discussed here). Ring opening by... 

Copolymerization of TXN with epoxides, particularly with diepoxides, was also used for the preparation of polyTXN with increased stiffness. Thus, terpolymerization of TXN, DXL and diepoxides (0.1-0.25% mol) (commercial epoxy resins) gives polymers with considerably higher moduli than conventional TXN-DXL copolymers 146). For example, the addition of 0.25 % mol Epidian 5 resin (a Polish product) leads to an increase in the modulus from 2300 MN/m2 to 2880 MN/m2. These products have been proposed as components in mixtures with conventional TXN-DXL copolymers. 

FIGURE 28-28 Applications of size-exclusion chromatography, (a) Separation of fatty acids. Column polystyrene based, 7.5 x 600 nm, with exclusion limit of t x t0 Mobile phase telrahydrofuran. Flow rale 1.2 mL/min. Deteclor refractive index, (b) Analysis of a commercial epoxy resin n - number of monomeric units in the polymer). Column porous silica 6.2 > 250 mm. Mobile phase letrahydrofuran, Flow rate t.3 mL/min. Deteclor UV absorption. (Courtesy of BTR Separations.)... 

The polymers offer further the advantages of dimensional and thermal stability, mechanical strength, and chemical resistance. It was therefore very Interesting to develop new photolnltlatlng systems that were able to make these epoxides available for Imaging technology. Epoxides or epoxy derivatives refer here to the 1.2-alkylene oxides shown below, whether they are monomers, prepolymers, or commercial epoxy resins. 

Macro-diisocyanates based on the reaction of an excess of 2,4-toluene diisocyanate with different poly(dimethylsiloxane)diols of different lengths have been prepared by Nikolaev et al. [71]. These macro-diisocyanates were reacted with 2 in stoichiometric proportions and the resulting adduct (22) was cured with a commercial epoxy resin in the presence of what was termed poly(ethylene)-poly(amine) at room temp-cerature, 80, and 100°C. The mechanical and thermal properties of steel-to-steel assemblies joined by these adhesives were better than those obtained using more common binders. 

Four commercial epoxy resins were investigated, which are described in Table I. For research purposes, four special resin systems were used with well-defined, but different cross-linkings. The average chain length, 5, between two cross-links... 

The earliest developed commercial epoxy resins were diglycidyl ethers of 4,4 -isopropylidine-diphenol (Bisphenol A) formed by reacting epichlorohydrin with the diphenol. The reaction sequences involve formations of alkoxide ions, followed by nucleophilic additions to the least hindered carbons... 

Epoxidised canola oil and sunflower oil with a high oleic acid content (74% and 86%, respectively), canola oil with standard oleic acid content (64%) and soybean oil with low oleic acid content (22%), are blended with a commercial epoxy resin and used as the matrix in the preparation of composites which use E-glass as the structural fibre. The resultant products showed that the level of unsaturation and the amount of bio-based epoxy resin in the matrix directly affect the mechanical properties of anhydride-cured composites. 

Epoxy-amine systems follow an addition step-growth polymerisation mechanism. The two principal reactions of primary and secondary amines with epoxy oligomers are shown in Reaction scheme 1 [30]. These reactions are catalysed by acids, phenols and alcohols (e.g. impurities in commercial epoxy resins). The presence of water causes a tremendous acceleration, but does not alter the network structure. The hydroxyl groups formed by the amine-epoxy addition steps are also active catalysts, so that the curing reaction usually shows an accelerating effect in its early stage (autocatalysis). 

PPE was also blended with some commercial epoxy resins (Chao et al. 1993) to improve the dielectric properties (lower the dielectric constant), toughness, and moisture resistance of the cured thermoset. These formulations with fiberglass reinforcements were used for the printed circuit boards and other electronic applications. In one formulation of epoxy resin (Epon 825, Shell) cured with aluminum alkoxide, incorporation of 30 % PPE increased the tensile elongation at break for the epoxy thermoset from <2 % to 17 %. The HOT was increased from 60 °C to 195 °C. The dissolution of PPE in the epoxy raised its viscosity from 0.2 to 400 Pa.s. (Anonymous 1991). 

The main constituent of most commercial epoxy resins prior to curing, DGEBA is formed by the reaction of excess epichloro-hydrin with bisphenol A in the presence of aqueous sodium hydroxide. 

In almost all commercial epoxy resin/anhydride formulations, some form of accelerator is used. Tertiary amines are more conventionally used accelerators. These may be benzyldimethylamine (BDMA) and tris (dimethylaminomethyl)-phenol (DMP-30). Optimum amounts of tertiary amine accelerators in terms of cured properties fall iu the 1 to 5 phr rauge. 

Fig. 11. An example of the Gillham-Enns diagram generated by the author on a commercial epoxy resin system. The lines of gelation and vitrification are marked.

Commercially, epoxy resins are predominantly cured with coreactive curing agents. Following are important classes of epoxy coreactive curing agents. 

The processing behavior (mainly viscosity and substrate wetting) and other properties of an epoxy system can be modified by diluents, fillers, toughening agents, thixotropic agents, etc. Most commercial epoxy resin systems contain modifying agents. 

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