Novolac resins epoxide

The epoxy novolac resins are synthesized by reaction of phenolic or cresol novolacs with epichlorohydrin in the same fashion as the bisphenol A resins. The number of epoxy groups per molecule is dependent on the number of hydroxyls in the phenol novolac molecule and to the extent to which they are reacted. Complete epoxidation can be accomplished, but this will lead to steric factors, which could limit the useful size of the cured polymer. Thus, selective epoxidation is often practiced.9... 

Alternatively, a Novolac resin can be used in place of the bisphenol A or F and this gives rise to an epoxy resin with a higher functionahty in terms of epoxide gronps per molecules, such as formula D. Thus, whilst the bisphenol resins have a maximnm of two epoxides per molecule (theoretical maximum, the actual value is slightly less), the Novolac can have up to about 10, the average chain length of commercial Novolacs. 

Chem. Descrip. Epoxidized bisphenol A novolac resin aq. disp. 

Three types of alternative epoxy resin are worth a special mention. First is the epoxy novolac resin, which contains more than two epoxide rings. Such a resin is made from a phenolic novolac (see p. 157) and epichlorhydrin and usually contains three to four epoxy rings per molecule ... 

Different compounds such as epoxides and allyl chloride are used in this important modification of phenolic resins. Epoxides are one key component for phenolic resin modification by an etherification reaction. Technological important reactions are the conversion of novolacs into epoxy novolacs and the ctosslinking of phenolics with epoxy resins. Recently, hydroxymethyl-group-containing phenolics have been converted into epoxides. 

The epoxy novolac resin was prepared by two step reactions. The first step was involved in the formation of novolac resin through chemical reaction between phenol and formaldehyde in acid environment. In the second step, the epoxidation of previously prepared novolac resin was carried out by reacting epichlorohydrin with a novolac resin in a specific molar ratio. The detail of the synthesis of novolac resin and its epoxidation was described in our previous report [19,20]. The typical properties of the synthesized ENR are given in Table 16.2. 

The neat novolac resins are also the precursors in the manufacture of a range of (see Epoxide adhesives), such as epoxy phenol novolacs and epoxy cresol novolacs spoxy resins. 

Epoxy NovolaC Resins. Epoxy novolacs are multifunctional epoxies based on phenolic formaldehyde novolacs. Both epoxy phenol novolac resins (EPN) and epoxy cresol novolac resins (ECN) have attained commercial importance (53). The former is made by epoxidation of the phenol-formaldehyde condensates (novolacs) obtained from acid-catalyzed condensation of phenol and formaldehyde (see Phenolic Resins). This produces random ortho- and para-methylene bridges. 

Figure 54 IR spectra of (a) phenol Novolac-type epoxide, (b) Ciba-Geigy s tetrafunctional epoxy resin, (c) alicyclic epoxide, and (d) polyglycol epoxide.

DOW Chemical Company provided the commercial availability of epoxidized phenol novolac resins in the late 1950 s (6). 

The first example in Table 2.5 was made from a partly epoxidized butadiene resin by reaction with dimethylamine followed by acrylic acid. The second example was again a reaction product of polybutadiene with maleic acid, followed by treatment with N,N-dimethylaminopropyl-amine. This polyamine was mixed with a novolac resin containing sites of unsaturation, an example of which is shown in Fig. 2.10. 

Novolac resins are broadly used in electronics because their functionality higher than two increases the crossimkmg density and yields cured resins exhibiting enhanced chemical and physical properties. Mixtures of epoxy resins and phenol novolacs 61 are excellent structural adhesives in the aerospace industry. However, the phenolic hydroxyl groups are not very reachve at moderate temperatures and most systems include catalysts or accelerators. Classical adhesive compositions are prepared by mixing a solid epoxy resin, t5rpicahy an epoxidized phenol novolac resin (60 parts), a phenol novolac resin (40 parts), a solvent such as 2-butoxyethanol or butylcehosolve acetate, an imidazole catalyst, and silver flakes. 

The composition of an epoxide moulding material will greatly depend on the specific application, and this has been discussed at length. ". The resin may be of the epoxide novolac type and there will also be present hardeners, fillers (such as silica), a silane coupling agent, pigment, flame retardant and a wax release agent. 

Epoxidized soyabean or linseed oils Plasticizers for novolac epoxy resins. Also prevent auto-catalytic decomposition of NG during storage... 

The number of epoxide groups per molecule and the rigidity of the molecular structure are factors that affect the hot strength of the epoxy adhesive. Thus, epoxy novolac and gly-cidyl ethers of tetraphenolethane have become important resins for incorporating into high-temperature epoxy adhesives because of their multifunctionality. 

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). 

The epoxy-cresol—novolaks resins are prepared by glyci-dylation of o-cresol-formaldehyde condensates in the same manner as phenol-novolak resins, o-cresol-formaldehyde condensates are prepared under acidic conditions with HCHO-o-cresol ratios of less than unity. The o-cresol novolacs of commercial significance possesses degrees of polymerization, n, of 1.7-4.4 and the epoxide functionality of the resultant glycidylated resins varies from 2.7 to 5.4. Softening points (Durrain s) of the products are 35-99°C [31]. 

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