Epoxy resin molecular weight

Cross-linking with aminoplasts and phenoplasts constitutes an important class of hardeners for high molecular-weight epoxy resins that require elevated temperature cures (see Amino resins). 

The DP is dependent on the ratio of reactants. Generally an excess of the epichlorohydrin is used to produce cyclic ether end groups. Epoxies are formed from the reaction of diamines with low molecular weight epoxy resins that retain their cyclic ether end groups. Figure 4.9 shows the formation of this process. These materials are often sold as two-part, or two-pot, epoxy adhesives. Most use-at-home epoxy packages contain a part A of epoxy resin and a part B of hardener (typically a diamine). These two are mixed as directed and applied. They dry fast, so they can be handled in 5 10 min. Full strength occurs after 5 7 days. 

Different kinds of carbon-intense fibers are used, the most common being carbon and graphite fibers, and carbon black. As is the case with fibrous glass, surface voids are present. Carbon-intense fibers are often surface-treated with agents such as low molecular weight epoxy resins. Such surface treatments also aim at increasing the fiber-matrix adhesion. 

The overall procedure was similar for each sample (high molecular weight polystyrene, low molecular weight epoxy resin) and is outlined in Table I. 

Figure 8. GPC analysis of low molecular weight epoxy resin.

As previously stated, to increase the cross-link density, multifunctional resins are mixed with these high molecular weight linear resins. An alternative to that approach is to add a multifunctional resin to the advancement process, thus synthesizing branched high molecular weight epoxy resins. 

Bisphenol A diglycidyl ether is a contact allergen among people who have worked with low-molecular-weight epoxy resins (lARC, 1989). 

Diglycidyl ether of bisphenol 25 g, 73 mmol A (low molecular weight epoxy resins epoxy value ca. 

To a round-bottomed flask (250 ml) equipped with a long-necked adapter, reflux condenser, and a magnetic stirrer bar, add low molecular weight epoxy resin (25 g, 73 mmol), bisphenol-A (11 g, 48 mmol) and 2-methylimidazole (19 mg, 0.24 mmol). 

The primary reactive diluents are monoepoxy low-molecular-weight epoxy resins. These may be used at rather high concentration with little effect on cured properties. Often they are employed to make selective improvements on certain properties such as adhesion, thermal cycling resistance, and impact strength. Some lower-viscosity commercial epoxy resins are already reduced with these diluents. 

Solid epoxy adhesives generally rely on high-molecular-weight epoxy resin for the solid appearance of the uncured adhesive. This epoxy resin is generally formulated with either ... 

Ultrahigh-molecular-weight epoxy resins can be used directly as a thermoplastic adhesive. The hydroxyl groups and good wetting characteristics provide for good adhesion to many surfaces. These adhesives are prepared in film form by solvent casting or extrusion. 

Table 13.6 shows the characteristics and properties of supported and nonsupported high-molecular-weight epoxy resins cast from solvent solution. A crosslinked and uncrosslinked formulation using the same high-molecular-weight epoxy is shown for comparison. 

The higher-molecular-weight epoxy resins can be produced commercially either through the direct reaction of bisphenol A, NaOH, and epichlorohydrin or by chain extension of the DGEBA with bisphenol A. For resins with n > 2, the number of secondary hydroxyls exceeds the number of oxirane groups. They are often used as the reactive site for coatings. 

Another explanation of the increase in the major glass transition 126) of SIN s relates to the retention of low molecular weight polymer of one component by the other phase. In this case low molecular weight fractions of the epoxy may be trapped in the rubber. When the epoxy is at its gel point, there is still much low molecular weight epoxy resin that has not reacted. At the point when the n-butyl acrylate is still mostly... 

Epoxy-phenoUc High molecular weight epoxy resins cross-linked with phenolic resole resins Good Very good Most widely used system Universal gold lacquer for three piece cans Shallow drawn cans... 

Epoxy-amino and epoxyacrylate High molecular weight epoxy resins cross-linked with amino or acrylate resins Water reducible for reduced environmental impact Good Limited Universal lacquer for beer and beverage cans (water reducible) Side seam stripes Some food systems... 

Organosol PVC dispersed in an appropriate varnish and conventionally stabilised with a low molecular weight epoxy, resin or epoxidised bean/seed oils Very good Very good Drawn cans Easy-open ends Closures Often used over epoxy-phenolic basecoat... 

Thermoset polyester Polyester resins cross-linked with amino or phenolic resins May contain lower molecular weight epoxy resin Very good Pack dependent May not be suitable for very acidic and aggressive foods... 

The changes of molecular dynamics from the starting material of low-molecular-weight epoxy resins to the fully polymerized state during polymerization reaction are well brought out by the large number of experimental studies of the evolution of the primary and secondary relaxations over the past... 

Water-Borne Coatings Prepared from High Molecular Weight Epoxy Resins... 

As with polybasic carboxylic acids, phenols have not achieved significant importance as curing agents however, the reaction of phenols with epoxides is technologically important. For example, the reaction of blsphenols with the diglycidyl ethers of the bisphenol is used conimercially to prepare higher molecular weight epoxy resins (12). 

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