Novolaks, linear resins

In the case of phenoHcs, it is possible to make linear thermoplastic polymers called novolaks, but this is done by reaction of less than one mole of formaldehyde with one mole of phenol the resulting resin has a large excess of free phenol. Usually in appHcation hexamethylene tetramine (HEXA) is added to the novolak. When heated, the HEXA breaks down into ammonia and formaldehyde and enters the reaction to form a light degree of cross-links in the final product. 

Crosslinking in phenol-formaldehyde resins is carried out on essentially linear prepolymers which have been formed by having one of the components in sufficient excess to minimise crosslinking during the initial step. These prepolymers may be one of two kinds the so-called resoles or the so-called novolaks. 

Dry Etch Resistance. Polyvinylnaphthalene and its derivatives were reported to be highly resistant to dry etching ( 9 ). Under Ar ion milling or CCl sputter etching conditions, etch rates for poly(2-vinylnaphthalene) were found to be about two-thirds of those for polystyrene or novolak resin resists. To find relationships between etch resistance and chemical structure, etch rate measurements for various metal-free polymers were made under Ar or C>2 ion beam incidence. It was found that the etch rate under ion bombardment depends linearly on N/(Nc -N0), where N denotes the total number of atoms in a monomer unit, Nc and N0 are the number of carbon atoms and the number of oxygen atoms in a monomer unit, respectively ( ). The dependence on "N/(NC-N0) factor" indicates that... 

If a linear and essentially non-cross-linking prepolymer is prepared from phenol and formaldehyde, it can be coreacted with a nonlinear and cross-linking prepolymer to form a resin. The latter resin will have some initially semithermoplastic or dry flow character but will be primarily thermosetting. The product is an alkaline novolak-resol copolymer. 

The curing reaction of a DICY-based epoxy resin was characterized by DSC. The epoxy resin was composed of a mixture of brominated bisphenol-A diglycidyl ether and of epoxidized cresol novolak with dicyandiamide (DICY) as hardener and tetramethyl butane diamine (TMBDA) as catalyst. The optimum ratio of epoxy/ DICY in terms of the glass transiticii temperature (Tg) was determined to be about 8 1. It could be shown that the heat of reaction (AH) at B-stage is strongly dependent on the amount of unreacted DICY. It was observed that for the optimum formulation, Tg increased linearly with conversion Cor AH) up to 95% conversion. 

Calixarenes, coined by C. D. Gutsche, are the cyclic oligomers produced by condensation of phenols and formaldehyde (1). In other words, they are cyclic phenol resins, but their physical and chemical properties are much different from those of linear phenol resins. Many of the calixarenes are crystalline and generally have poor solubilities in either water or in organic solvents. Their melting points are generally high, while ordinary phenol resins, novolaks, soften below 150°C. 

---