Epoxy resin systems Difunctional

In a heat-cured epoxy resin system, the hydroxyls generally react with either epoxy or acid groups. Hence, heat-cured diepoxies can be regarded as being potentially tetrafunc-tional, rather than difunctional. Conventional diepoxy resins, therefore, yield much more highly crosslinked structures with higher heat and chemical resistance after heat cure than after room temperature cure. 

Epoxy resin ceiling temperatures depend crucially on both the epoxy resin and the hardener. The difunctional DGEBA (diglycidyl ether of bisphenol A) epoxy resin system is the most common, producing high heat distortion... 

The epoxy resin can be defined as any molecule that contains two or more alpha-epoxy groups which can be reacted to form a thermoset system. An example of a difunctional epoxy resin is diglycidyl ether of Bisphenol-A (DGEBA) which is formed... 

F. 4. TTT cure diagram temperature of cure vs. time to the isoviscous event, gelation and vitrification, including TBA and gel fraction data , isoviscous (TBA) O, gelation (TBA) A, vitrification (TBA) , gelation (gel fraction). The system studied was a difunctional epoxy resin, Epon 828 (DGEBA, Shell Chemical Co.), cured with a tetrafimctional aliphatic amine, PACM-20. (bis(p-aminocyclohexyl)methane, DuPont]... 

Fig. 7. T, vs. temperature of cure for dinerent times of cure. The solid lines are the best straight line fits to experimental data (symbols) the dashed lines are the extrapolations to T, to obtain the temperature of cure to reach full cure for the given time. The T, line is also included. The system studied was a difunctional epoxy resin, DER331 (DGEBA, Dow Chemical Co.), cured with TMAB (see Fig. 3 caption). (Peng, X., GiUham, J. K., Ref. )...

OSaJin Jin, F.-L., Park, S.-J. Fracture toughness of difunctional epoxy resin/thermally latent initiator system modified with polyesters. J. Industrial Eng. Chem. 14 (2008) 564—567. 

The compositions of materials photocrosslinkable by cationic mechanism consist of mixtures of various vinyl ethers, or epoxides, or both. Difunctional cycloaliphatic epoxides have been used extensively in some UV curable systems, often as diluents for the various epoxy resins described in Chapter 6. Use of various divinyl ethers is also extensive. Because some cationic photoinitiators also generate free radicals, some compositions may contain mixtures of both types of materials, those that cure by cationic and those that cure by free-radical mechanisms. 

Standard Epoxies. Two resin systems are used to make GF laminate difunctional and tetrafnnctional. These systems are distinguished by the nature of the epoxy cross-linking. In a difnnctional system, the epoxide molecule has two cross-Unking sites, and the cured epoxy contains long linear molecular chains. Pure difnnctional laminates have excellent physical properties, and for many years were the mainstay of the industry. They have aTg of 120°C, which is adequate for most use environments, but is low for some apphcations and too low for LFA. 

Most of the BPA-based epoxy resins are quite rigid and are based on petrochemicals. A quite different type of flexible epoxy resin is based on cardanol, derived from cashew nut shell liquid. Mono-, di- and multifunctional derivatives are possible. Mono- and difunctional low viscosity derivatives are used as modifiers and diluents, while complex di- and multifunctional epoxies are used in two-component ambient cure epoxy systems. They give the cross-linked matrix excellent flexibility, toughness and impact resistance. They possess very good water, chemical and corrosion resistance. 

The multiepoxy functionality of the epoxy novolaks (2.2 to >5 epoxy groups per molecule) (3) produce more tightly cross-linked cured systems having improved elevated temperature performance and chemical resistance than the difunctional bisphenol A-based resins. 

---