Phenol formaldehyde novolak

Since the days of Bakeland many varieties and applications of phenol-formaldehyde resins have been found (1). In this paper we are concerned only with recent applications of functionally substituted phenol-formaldehyde-Novolak resins as applied to lithographic uses for micro-image fabrication. 

Bulky AlkyllAryl Substituted Phenol-Formaldehyde Novolak Resins. Low molecular weight cresol-formaldehyde Novolak resins tend to have high solubility rates in alkaline developers. To increase developer resistance, Novolak resins containing a hydrophobic chain incorporated on a portion of the phenol group were synthesized, as shown below (17). As the number of alkyl... 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Many halogen-substituted cresol/phenol-formaldehyde Novolak resins were prepared and tested for their electron beam sensitivity when mixed together with a photoactive compound. The following halogen-substituted phenols and cresols were used as starting materials o-, m-, p-chlorophenols o-,... 

Figure 14. Dynamic properties of a phenol-formaldehyde novolak cross-linked with various amounts of hexamethylenetetramine by heating for one hour at 175 C,...

Synonyms Novolak resin PF Phenol-formaldehyde (novolak) resin ... 

More important polymers of furfural are based on its ability to react with phenols to form thermosetting resins. The most common resins of this kind are of the novolak type made by reaction of a slight molar excess of phenol with furfural in the presence of an alkaline catalyst (cf. Chapter 12). Usually, blends of phenol-furfural novolaks and phenol-formaldehyde novolaks are used in the production of moulding powders with enhanced flow properties. 

Wei et al. (2002) have dip coated phenol-formaldehyde novolak resin containing a small amount of hexamethylene tetramine onto the surface of green tubular supports of fine phenol-formaldehyde novalac resin particles. During pyrolysis, the hexamethylamine has mobility that reduces the creation of large pores in the surface during pyrolysis. Because the selective layer and support have similar composition, there is also less stress during pyrolysis from shrinkage. The supported membranes were pyrolyzed at 900°C. The concentration of the solution used for the selective layer and the thickness had a considerable effect on the separation performance. 

In terms of volume used, the most popular photoresist type has been a physical combination of a phenol-formaldehyde novolak resin with a diazoqninone. The novolak (molecular weight of about 500-2000) does not dissolve in dilnte alkali when 20%-50% of a diazoketone is present in the dry film. However, UV light converts the alkali-insoluble diazoquinone into the hydrophilic carboxylate form via the Wolff rearrangement (Figure 13.9). Without the diazoquinone dissolution inhibitor in the exposed areas, the novolak now dissolves in dilute alkali. 

---