Novolac-based epoxy resins

A biphenyl diglycidyl ether based epoxy resin was crosslinked with aminecuring agents (d -diaminodiphenylmethane and aniline novolac) and phenolcuring agents (phenol novolac and catechol novolac), and the thermomechanical... 

Epoxy novolac resins also differ from standard DGEBA-based epoxy resins in their multifunctionality, which is about 2.5 to 6.0. The multiplicity of epoxy groups allows these resins to achieve increased crosslink density. The commercial epoxy novolac resins (e.g., DER 438, Dow Plastics, and EPON 164, Resolution Performance Products LLC) are semisolid to solid resins with EEW in the range of 170 to 230. Recently low-viscosity epoxy novolac resins have been produced (18,000 to 28,000 cP) to provide easy processing however, these generally have lower epoxy content. 

A general-purpose two-component adhesive that will provide high tensile shear strength up to 150°C is described in Table 12.11. The base epoxy resin in this formulation is a mixture of an epoxy novolac and a liquid DGEBA epoxy resin. 

Bisphenol F based epoxy resins. Instead of reacting bisphenol A with epichlorohydrin to form a liquid resin, a similar reaction can be conducted with bisphenol F (Figure 2.2). Bisphenol F is composed of a mixture of isomers - ortho-ortho, ortho-para and para-para linkages -whereas bisphenol A is composed mainly of para-para linkages. If n is less than about 0.2, the resins are called bisphenol F epoxides. If n is higher they are referred to as epoxy phenol novolac (EPN) resins (Helfad, 1996). 

Pure meto-cresol has been used for manufacture of synthetic musk— musk ambrette, used as a fixative to perfumes, for manufacture of synthetic Thymol and Menthol amd also leather preservative p-chloro-meto-cresol, synthetic pyre-throids, and lastly for manufacture of 2,3,6-trimethylphe-nol—an intermediate for vitamin E. o-Cresol has been used for manufacture of Coumarin and some derivatives which are employed in perfumery as fixative. o-Cresol has also been used for making Novolac and epoxy resins and also for the herbicides based on di-nitro-oAt/io-cresol, etc. In sum, individual cresols have been very successfully converted to important intermediates in the organic chemical synthesis. It is expected that further development work will lead to synthesis of many more organic chemicals of vital importance. While new chemicals using individual cresols are in the pipeline... 

In order to provide the required flame retardancy to the molding compound, an encapsulated formulation usually contains brominated resins and antimony oxide. The brominated resins used in the encapsulated formulation are mainly tetrabromobisphenol A (TBBA) based epoxy resin or brominated epoxy novolac. These bromine-containing additives were reported to cause bond degradation at high temperature through accelerated void formation in the gold-aluminum intermetallic phases (1-4). 

Chem. Deserp. One-part, water-based epoxy resin with conosion inhibitors Bisphenol /Vepichlorohydrin epoxy (< 10%), bisphenol A novolac epoxy resin (< 10%), ethanol (2-10%), propylene glycol (5-15%), carbo) zircoaluminate sol n. (< 5%), etc. 

Epoxy-novolac resin n. A two-step resin made by reacting epichlorohydrin with a phenol-formaldehyde condensate. Such resins are also known as thermoplastic, B-stage phenohc resins that are in a state of partial cure. Whereas bisphenol-based epoxy resins contain up to two epoxy groups per molecule, the epoxy novolacs may have seven or more such groups, producing more tightly crossHnked structures in the cured resins. Thus they are stronger and superior in other properties. 

Epoxy novolac resins are normally used as modifiers for Bisphenol A based epoxy resins in adhesives. When used alone, the epoxy novolac resins tend to yield adhesives which are too brittle for most applications. 

Eor more demanding uses at higher temperatures, for example, in aircraft and aerospace and certain electrical and electronic appHcations, multifunctional epoxy resin systems based on epoxy novolac resins and the tetraglycidyl amine of methylenedianiline are used. The tetraglycidyl amine of methylenedianiline is currently the epoxy resin most often used in advance composites. Tetraglycidyl methylenedianiline [28768-32-3] (TGALDA) cured with diamino diphenyl sulfone [80-08-0] (DDS) was the first system to meet the performance requirements of the aerospace industry and is still used extensively. 

Novolac epoxy resins are produced by reaction of novolac, a phenolformaldehyde resin, with epichlorohyrin and a base. ... 

Synthesis Epoxy resins consisting ofglycidyl ether, ester and amines are generally prepared by the condensation reaction between diol, dibasic acid or amine and epichlorohydrin in the presence of sodium hydroxide with the elimination of hydrochloric acid. The commercially available epoxy resins are, however, made by the reaction of epichlorohydrin and bisphenol-A. Cashew nut shell liquid (CNSL)-based novolac epoxy resins have also been reported [342]. 

Agrawal, J.P., Dev, S.S., Gholap, D.H., Satpute, R.S., Tapaswi, M.A., and Nigde, B.N. (1986) Improvement of Low and High Temperatures Characteristics of Novolac Epoxy Resin Used for Inhibition of HTPB Based Composite Propellants. ERDL Report No. 8/86. 

In addition to the DGEB A resins, there are several other types of epoxy resins of commercial significance. The most common of these are epoxy novolacs, glycidyl ether of tetraphe-nolethane, bisphenol F-based resins, and aliphatic and cycloaliphatic resins. 

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. 

For maximum heat resistance, pyromellitic dianhydride is often used. The composition and properties of metal-to-metal adhesives based on a combination of epoxy novolac and a bisphenol A epoxy resin have been described in Sec. 12.5.1. Depending on the cure temperature and the choice of amine curing agent, strength as high as 3000 psi at room temperature and over 1000 psi in the range of-55 to + 150°C is possible. 

Epoxy resins based on glycidylation of bisphenols, cresol and phenol novolacs, polycarboxylic acids, polyols, amines, and aminophenols have been long known. Epoxidized linear and cyclic olefins have also been used as specialty epoxy resins. More recently, glycidylated heterocycles have been introduced, initially as specialty resins promising improved resistance to weathering. One heterocycle in particular, the hydantoin ring, has become of particular interest as an epoxy substrate (J ). 

Ho et al (1996) examined polyol or polysiloxane thermoplastic polyurethanes (TPUs) as modifiers in cresol-formaldehye novolac epoxy resins cured with phenolic novolac resin for computer-chip encapsulation. A stable sea-island dispersion of TPU particles was achieved by the epoxy ring-opening with isocyanate groups of the urethane prepolymer to form an oxazolidone. The flexural modulus was reduced by addition of TPU and also the Tg was increased due to the rigid oxazolidone structure. Mayadunne et al (1999) extended this work to a series of phenol- and naphthol-based aralkyl epoxy resins. 

Solid epoxy resins based on bisphenol A can be categorized as effectively non-toxic they are not irritating and scarcely sensitizing. The same is true for the novolac epoxy resins although their liquid forms can have a sensitizing effect. 

Although DGEBA resins provide the backbone of most epoxy formulations, they may be blended with other types to achieve modifications. Epoxy novolacs, having higher functionality, increase the cross-linking density, which improves heat resistance but decreases impact resistance. Incorporation of epoxidized oils increases flexibility at the expense of heat and chemical resistance. Low-viscosity polyfunctional epoxies based on polyols or polyhydric phenols reduce viscosity and can increase functionality without impairing cured properties. Monofunctional reactive diluents will also decrease viscosity and form part of the polymer backbone, to impart a measure of flexibility without the possibility of migration. Properties of commercially available epoxy resins and diluents from various suppliers are listed in Table 1. 

Compounds are available formulated on epoxy novolac-based resins and bisphenol epoxies. The latest bisphenol-A compounds offer high mechanical properties at a cost saving, in comparison with novolacs. Especially at glass contents of over 35 wt%, VE SMC offers advantages over isopolyester SMC. Under stress, SMC/BMC parts with low glass content show initiation at a higher elongation (2.2%) than equivalent... 

Chem. Descrip. Bisphenol F-based epoxy novolac resin Uses Epoxy for high-solids and solv.-free industrial maintenance coatings, chem.-resist. flooring, groufs, and high-temp, adhesives and laminates inc. crosslink dens, and chem. resist, of ambient cured systems Properties Gardner 1 iiq. sp.gr, 1.19 dens. 9.9 Ih/gal vise. 16,000cps EEW 175 100% solids Epotuf 91-263 [Reichhold]... 

---