Viscosity epoxide resins

Cycloaliphatic Epoxy Resins. This family of aUphatic, low viscosity epoxy resins consists of two principal varieties, cycloolefins epoxidized with peracetic acid and diglycidyl esters of cycHc dicarboxyhc acids. 

The epoxidation is generally conducted in two steps (/) the polyol is added to epichlorohydrin in the presence of a Lewis acid catalyst (stannic chloride, boron triduoride) to produce the chlorohydrin intermediate, and (2) the intermediate is dehydrohalogenated with sodium hydroxide to yield the aliphatic glycidyl ether. A prominent side-reaction is the conversion of aliphatic hydroxyl groups (formed by the initial reaction) into chloromethyl groups by epichlorohydrin. The aliphatic glycidyl ether resins are used as flexibilizers for aromatic resins and as reactive diluents to reduce viscosities in resin systems. 

For a number of purposes the unmodified epoxide resins may be considered to have certain disadvantages. These disadvantages include high viscosity, high cost and too great a rigidity for specific applications. The resins are therefore often modified by incorporation of diluents, fillers, and flexibilisers and sometimes, particularly for surface coating applications, blended with other resins. 

Epoxide Resin with Hardener and Epo-Kwick mixed at 5 parts resin to 1 part hardener, by weight, for n = 1.565 or Epo-Thin, a low viscosity resin mixed at 10 parts resin to 3.6 parts hardener ... 

Diluents are added to epoxide resins primarily to lower viscosity and thus to improve handling characteristics. They also modify the cured properties of the resin. Diluents can be divided into two classes (a) the reactive diluents and (b) the non-reactive diluents. 

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. 

For many uses of epoxide resin systems, a low viscosity product is required and the role of the diluent is usually to reduce the viscosity of the formulated compound. Diluents can also be used to tailor other characteristics of the epoxide, such as the chemical resistance, electrical properties, thermal expansion coefficient and glass transition temperature. They may be conveniently divided into two groups, the reactive diluents and the non-reactive diluents. 

Epoxy vinyl ester, phenolic, methacrylate, styrene-divinylbenzene, cyanafe ester, and dicyclopentadiene (DCPD) resins have been made in Pittman s laboratory in which various POSS macromers have been chemically incorporated. For example, a low-viscosity aliphatic epoxide resin was blended with macromer 32 (Fig. 15) and aliphatic triamine curing agents, and these blends were cured in five stages to both 120°C and 150°C. The incorporation of 5 and 25 wt % of 32 into these epoxy resins gave an increase in the storage modulus versus that of the neat epoxy. " The... 

Polyesters. Polyester is used in embedding resins for electronic components because of its low cost compared to siUcones and epoxides. Polyesters (qv) are condensation products of dicarboxyhc acids and dihydroxy alcohols the reaction provides a wide range of viscosities for polyesters. 

The pure diglycidyl ether of bisphenol A [1675-54-3] DGEBA is a crystalline soHd (mp 43°C) with a weight per epoxide (WPE) = 170. The typical commercial unmodified Hquid resins are viscous Hquids with viscosities of 11—16 Pa-s (110—160 P) at 25°C, and an epoxy equivalent weight of ca 188. 

Resin Average Mol. Wr. Epoxide equivalent Viscosity cP at 25 C Melting point °C (Durrans)... 

When cured with room temperature curing system these resins have similar thermal stability to ordinary bis-phenol A type epoxides. However, when they are cured with high-temperature hardeners such as methyl nadic anhydride both thermal degradation stability and heat deflection temperatures are considerably improved. Chemical resistance is also markedly improved. Perhaps the most serious limitation of these materials is their high viscosity. 

The polysulphides used are relatively mobile liquids with viscosities of about 10 poise and are thus useful as reactive diluents. They may be employed in any ratio with epoxide and produets will range from soft rubbers, where only polysulphides are employed, to hard resins using only epoxide. 

Laminates have been prepared for the manufacture of chemical plant. They have better heat and chemical resistance than the polyester- epoxide- phenolic- or aminoplastic-based laminates but because of the low viscosity of the resins were not easy to handle. Because they were also somewhat brittle, furan-based laminates have been limited in their applications. 

Another resin application based on the same hyperbranched polyester structure described herein is low-VOC alkyds, which have very low viscosity and high reactivity compared to conventional high-solid alkyds. Other resin structures are unsaturated polyesters, polyurethane dispersions, and epoxides. ... 

An homologous series of epoxy resins with constant epoxide equivalent weight and increasing branch concentration displayed increased melt viscosity and weight average molecular weight. 

Other products that may be epoxidized in this way include dihydric and trihydric phenols, aliphatic polyols such as glycerol, and simple alcohols such as butanol or alyl alcohol. These products, especially the monofunctional glycidyl ethers, are used at relatively low percentages to reduce the viscosity of formulations containing DGEBA resins. In this way, they act as reactive diluents. 

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