Novolac type resins

Novolac (Resin). The raw materials used for novolac-type resins are phenols and aldehydes just as for resol-type resins. These materials... 

Studies of novolac-type resins (phenolic polyethylene oxide blends) show by C NMR that a blend of 30 70 composition leads to a ca 2 ppm high freqnency shift compared to a pure phenolic resin. This is ascribed by the anthors to increased hydrogen bonding . 

A more complicated system exists if a two nucleus phenolic compound is used for the synthesis of phenolics. In 4,4 -(l-methylethylidene)bisphenol, the para positions of the phenolic nuclei are substituted. Therefore, methanal can only react with the ortho positions relative to the hydroxy group. A uncatalyzed reaction of methanal with 4,4 -(l-methylethylidene)bisphenol gives novolac type resins (equation 41). 

Phenolic resins such as resol-type resins generate water and formaldehyde during curing as by-products of condensation reactions. Hexamethylenetetramine (HMTA) can be used as a source of formaldehyde for curing novolac-type resins, producing formaldehyde and ammonia as by-products. During curing. 

The substitution of HMTA, normally used to cure novolac-type resins, with epoxies has reduced void content. To retain the fire-retardant properties of phenolics, a network was formed with a higher phenol than epoxy content. 

The conformational properties of Novolac type resins prepared from p-cresol have been studied. The limited conformational flexibility of 4-phenylene polyamides and 4-phenylene polyesters causes them to have large persistent lengths. The existence of minima in the torsion potentials on each side of the planar conformation together with minor differences between the bond angles at... 

One of the most commonly used groups of epoxide resins is that comprised of the diglycidyl ethers, and these are made by reacting epichlorohydrin with a bisphenol such as bisphenol A. The preparation of the diglycidyl ether of bisphenol A has already been illustrated, but many other glycidyl ether type epoxides are of considerable importance. The preparation of an epoxide novolac type resin is shown below ... 

Fig. 5-1. Phenol-formaldehyde polymers, (a) Character of resole -type resins normally produced with excess formaldehyde under alkaline conditions, (b) "Novolac -type resins normally made with excess phenol under acidic conditions.

Most processors of fiber-reinforced composites choose a phenol formaldehyde (phenoHc) resin because these resins are inherently fire retardant, are highly heat resistant, and are very low in cost. When exposed to flames they give off very Htde smoke and that smoke is of low immediate toxicity. PhenoHc resins (qv) are often not chosen, however, because the resole types have limited shelf stabiHty, both resole and novolac types release volatiles during their condensation cure, formaldehyde [50-00-0] emissions are possible during both handling and cure, and the polymers formed are brittle compared with other thermosetting resins. 

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. 

An alternative copolymerization is illustrated by the method of Blasius. In this preparation, a phenol-formaldehyde (novolac) type system is formed. Monobenzo-18-crown-6, for example, is treated with a phenol (or alkylated aromatic like xylene) and formaldehyde in the presence of acid. As expected for this type of reaction, a highly crosslinked resin results. The method is illustrated in Eq. (6.23). It should also be noted that the additional aromatic can be left out and a crown-formaldehyde copolymer can be prepared in analogy to (6.22). ... 

A similar strategy consists in the liquefaction of biomass with phenol under acidic conditions to obtain phenolic monomers. The type of monomers obtained vary greatly (Lin et al, 2001). These monomers can be reticulated with the help of temperature and formaldehyde to obtain novolac- or resol-type resins. 

Shih et al. [60] studied the modification of a novolac-type epoxy resin with PDMS to overcome brittleness and poor impact resistance. This kind of resin is typically cured via their epoxy functions. The authors also introduced isocyanate monofunctionalized PDMS. Hence, the common treatment with MDA (4,4 -methylene dianiline) not only cured the resin on the one hand, but also made it possible to form the branched copolymer. Mechanical and thermal analyses showed that an optimum in isocyanate-terminated PDMS content was required to reach good thermal and physical properties and low moisture absorption. 

A novolac-type of resin has been prepared from the condensation product of an-isole with formaldehyde. Anisole has been condensed with an equimolecular amount of formaldehyde in the presence of sulfuric add and the product sulfonated at g 120 "C with sulfuric add. The sulfonated product has been made insoluble by treatment with formaldehyde or by heating at 140°-145 °C, and the resin prepared in this way has a superior resistance to the action of oxidizing agents such as IN nitric acid and O.IN potassium permanganate. 

The reactivity of the molding resin powder was determined by measuring the degree of reaction of the powder and o-cresol novolac type epoxy resin. The molding resin powder and the epoxy resin were mixed in a 100/5 weight ratio in acetone, dried for a day and heated at 170°C. 

The commercial importance of phenol-formaldehyde resins has resulted in extensive studies of these systems, with the aim of identifying the reaction mechanisms and intermediates that occur during subsequent polymerization reactions. However, the complexity of Novolac-type systems has made a detailed understanding of the subsequent chemical processes and their relationship to the physical properties of the final polymerized product difficult. Thus, it is necessary to simplify the system in order to more readily unravel this complexity. Model compounds are frequently used to understand complicated chemical systems and their application to phenol-formaldehyde systems has been well documented . ... 

Carboxylic acid and anhydride curing agents are used to a lesser extent in aerospace applications as compared to the amines which have mechanical properties and cure conditions that can be tailored to a wider variety of specific applications. Anhydrides tend to be somewhat brittle but offer useful service as high as 250 °C with novolac-type epoxy resins. In addition, the aliphatic dicarboxylic acid anhydrides give tough and sometimes flexible properties which are useful in encapsulation applications. 

Both resole and novolac types of phenolic resin are used in aerospace applications. The resoles are generally made by using alkaline catalysts and an excess of formaldehyde. The resole structure is highly complex and involves both methylene and dimethyl ether bridges between the phenolic moieties. During cure both water and formaldehyde are evolved. 

By reaction of phosphorylated materials with aldehydes, amines or with isocyanates highly thermally stable products have been then produced. TGA studies have indicated their superior properties compared to conventional cardanol/formaldehyde resins of the novolac type. It was also found that a phosphorylated CNSL polymer had improved adhesive properties when compared with conventional CNSUformaldehyde resins (ref.248) and certain compounded products had wear, fade and frictional properties comparable to those of conventional PhOH/formaldehyde/copolymer brake Hnings (ref.249). The phosphorylated product from CNSL and its bromination derivative possessed good fire-retardant characteristics (ref. 250). Phosphorus derivatives of cardanol and of 3-pentadecylphenol have been studied by reaction with phosphorus oxychloride and its thio analogue (ref. 251). 

Novolac type phenol formaldehyde resins are generally used as binders in these applications. This mechanism is shown in the scheme ... 

MAJOR RESIN TYPES DGEBA (diglycidyl ether of bisphenol A), novolacs, peracid resins, hydantoin resins, etc. 

Another miscible semicrystalline polymer/amorphous polymer blend SMP is a polyethylene oxide (PEO)/novolac-type phenolic resin blend [24]. The blend was found to be completely miscible in the amorphous phase when the phenolic content is up to 30 wt%, and the crystalline melting temperature (T,f) of the PEO phase working as a transition temperature can be tuned. 

Kar Karger-Kocsis, J., Gryshchuk, O. Morphology and fracture properties of modified bisphenol A and Novolac type vinyl ester resins. J. Appl. Polym. Sci. 100 (2006) 4012-4022. 

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