Epoxy high functionality

Many types of epoxy resins can be used in adhesive formulations. These are characterized in Table 4.1. The most commonly used type is the resin-based diglycidyl ether of bisphenol A (DGEB A). Epoxy novolac, flexible epoxy, high-functionality, and fihu-forming epoxy resins are also used in specialty applications. 

Subsequent epoxidation with epichl orohydrin yields the highly functional epoxy novolak. The product can range from a high viscosity Hquid of n = 0.2 to a soHd of n value greater than 3. 

Thus, the cured epoxy resin is a highly functional material whose final chemical, physical, and electrical properties dictate the ultimate utility of that material. 

A majority of the world s epoxy resin market consists of the DGEBA type. The liquid DGEBA resins are typically used where low viscosity, high reactivity, and high crosslink density are required. The low viscosity allows them to be conveniently and easily compounded with fdlers and other additives. The relatively high functionality allows them to... 

Diglycidyl ether of resorcinol-based epoxy resins provide the highest functionality in an aromatic diepoxide. It is one of the most fluid of epoxy resins, with a viscosity of 300 to 500 cP at 25°C. Because of its high functionality, it is a very reactive resin and cures more rapidly than DGEBA epoxies with most conventional curing agents. 

A comparison of Figs. 11 and 12 also serves to highlight the effect of functionality on cure and properties. The system of Fig. 11 is a trifunctional epoxy cured with a tetrafunctional aromatic amine, whereas the system of Fig. 12 is a difunctional epoxy cured with the same amine. As expected, the more highly functional system has the higher Tg, and shorter times to gelation the times to vitrification are also shorter. The difference in these transformation times arises from two factors ... 

On the other hand, the glassy-state modulus was retained in all epoxy systems. The Tg improvement was caused by the promotion of the diffusion-controlled epoxy-amine reaction, hence, this promotion worked better in a network with a higher AT. Moreover, the addition of a small amount of POSS-triol ensured the consistency of the thermomechanical properties of epoxy networks with a high degree of steric constraints (high functionality of epoxy monomer), as evidenced by several parallel experiments. Because the addition of such a small amount of POSS-triol did not increase the viscosity of... 

Other phenol derivatives that are used to form the backbone of an epoxy resin include bisphenol E, bisphenol F, resorcinol, brominated bisphenols, and more highly functionalized molecules such as tetrakisphenylolethane. Alcohols, amines, and carboxylic acids may be combined with epichlorohydrin to give a range of diglycidyl ether based epoxy resins. Non-aromatic, commercially available epoxides are produced by peracid epoxidation of alkenes and dienes, such as vinyl cyclohexene and esters of cyclohexane carboxylic acids [23]. The chemical formulas for two common uncured polymers are shown below ... 

Similarly, non-racemic 2,3-epoxyaldehyde 38 displays a preference for Felkin-Anh addition with the bis-stannylated 39 yielding the highly functionalized epoxy-alcohol 40 (Scheme 5.2.9).i ... 

Three stereoisomeric inositols were prepared from the highly functionalized derivative 215 which can be derived from 214 in one step by the reaction with KMn04 (Scheme 4-13).82 Treatment of 215 with AI2O3 in an aqueous medium afforded stereoselectively the ketoalcohol 216 in 85% yield, which was converted efficiently to allo-inositol (217) essentially as a single product. The epoxy diol 215 was converted under basic conditions to D-chiro-inositol (125) with more than 95% selectivity by attack of the hydroxide ion on one side of the epoxide carbon atom while its treatment under acidic conditions furnished neo-inositol (219) as a minor product along with 125 (3 7) resulting from the attack of H2O from the other side. 

Heat distortion temperature (HDT) or deflection temperature (DT) is a measure of the tendency of cured product to soften when heated. It is a feature of the inherent thermo-plasticity in cured epoxy compounds as a result of the relatively low cross-linking density, and may be any value from below 50°C to about 250°C, depending on formulation and cure cycle. Resins and hardeners of high functionality tend to have higher HDT. Postcuring at elevated temperature can increase HDT significantly. 

Becker, O., Cheng, Y.-B., Varley, R. J., and Simon, G. R, Layered silicate nanocomposites based on various high functionality epoxy resins the influence of cure temperature on morphology, mechanical properties and free volume, Macmmolecules, 36,1616-1625 (2003). 

Chem. Descrip. Aromatic urethane acrylate oli mer Uses Urethane-acrylic tor abrasion-resist, coatings Features Low vise. cost-effective altemative to highly functional urethane acrylates with nearly same wear and abrasion resist, props. better abrasion and yellowing resist, than rrxrst epoxy acrylates Properties APHA40 color dens. 10.5 Ib/gal vise. 1200 cps (60 C) tens, str. 2700 psi elong. 2%... 

Genski and Taylor have employed sucx essfully epoxy-activated alkene 191 for coupling with paraformaldehyde in the presence of EtsAl/BusP to provide the MBH adduct 192, a highly functionalized molecule (containing epoxide and protected alcohol moieties in addition to the p-substituted enone), and transformed the adduct into the bioactive natural product ( )-c/)i-epoxydon (193) (Scheme 2.98). 

Another class of epoxy resins is the novolacs, particularly the epoxy cresols and the epoxy phenol novolacs. These are produced by reacting a novolac resin, usually formed by the reaction of o-aesol or phenol and formaldehyde with epichlorohydrin. These highly functional materials are particularly recommended for transfer molding powders, electrical laminates, and parts in which superior thermal properties, high resistance to solvents and chemicals, and high reactivity with hardeners are needed. 

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