High-ortho novolacs

High-ortho novolacs (Fig. 7.8) are sometimes more desirable since they cure more rapidly with HMTA. A number of oxides, hydroxides, or organic salts of electropositive metals increase the reactivity of the ortho position during... 

Figure 7.9 Proposed chelate structures in the synthesis of high ortho novolac oligomers.

Figure 7.10 Intramolecular hydrogen bonding of high ortho novolacs.

High-ortho novolac resins, 379-381 High-performance liquid chromatography, 162... 

High molecular weight synthetic alkylated aromatic feedstocks, 23 533 High nuclearity carbonyl clusters, 16 64-66 High nuclearity metal carbonyl synthesis, 16 66-69 from salts, 16 68 from smaller carbonyls, 16 68-69 High ortho novolacs... 

These are commonly termed high ortho Novolacs. Zinc acetate is the most commonly used catalyst. The initial reaction is proposed to occur through chelation of phenol and formaldehyde through the metal acetate (Scheme... 

The Phenolic Resins Modified with Titanium are Synthesized from a High Ortho Novolac Resin and Tetraisopropyl Titanate. The Phenolic Resin Modified with both Titanium and Silicon is Prepared from 2 Weight Percent Titanium Containing Phenolic Resin and Diphenylsilanediol. (Data from Ref.[l 80])... 

High orthonovolac resins have been reported to be prepared by reacting phenol and formaldehyde in the presence of a divalent electropositive metal oxide, hydroxide, or organic salt based on sulfonates, fluoroborates, or acids selected from sulfonic or fluoroboric acid or mixtures [43]. This is in contrast to the conventional novolac resins prepared with strong acids (sulfuric acid, hydrochloric acid, or oxalic acid) and have a preponderance of para/para and ortho/para methylene bridges. The high ortho novolacs have mostly ortho/ortho methylene bridges such as ... 

The main advantages of the high ortho novolac resins is that they have a greater speed of curing with hexaethylenetetramine. The newer catalysts were reported to give 75-100 7o ortho vs. 50-75%, which was achieved by earlier-reported catalysts. 

Novolac resins, 378-398 high-ortho, 379-381 synthesis of, 378-379 Novolacs... 

In other systems, such as in some Friedel-Crafts alkylations, ortho-substitution is desirable. For example, extensive alkylation at both the ortho-and para-positions of phenol with formaldehyde in the presence of an acid catalyst yields highly branched novolac phenolic resin prepolymers [Eq. (26)]. 

High ortho-ortho linked Novolac resins. 1461... 

Another way to synthesize novolacs is under weak acidic conditions. Typical reaction conditions are a pH-range between 4 and 7 and the use of bivalent metal salts (e.g. Ca, Zn, Mg, Pb, Co, Cu, Ni) [56,57]. These conditions are highly selective for ortho,ortho -novolacs that are of increasing interest These compounds possess only a vacant para position for further reactions. Such materials have increased importance as molding compounds and foundry resins because ortho-linked novolacs can only react at the para position and they possess a hyperacidity [58]. The hyperacidity can be easily explained by the formation of intramolecular hydrogen bondings that stabilize the phenoxy anion. Complete methylene bridging at the ortho position of phenolic compounds can lead to calixarenes. 

Titanium modified phenolic resins are synthesized by reaction of high-ortho-content novolacs with either tetraisopropyl titanate or titanium tetrachloride. The modified phenolic resins contain between 2 and 13 percent of titanium. Those resins with a high titanium content (approximately 13 percent) are insoluble in organic solvents like alcohols, 2-propanone or benzene. Titanium modified phenolic resins with low contents of titanium (about 2-3 percent) are completely soluble in these solvents [180]. In addition, the reaction of the titanium modified phenolic resin with diphenylsilanediol gives modified... 

Octopus-Pot Model. Honda et al 32) proposed that the high ortho-ortho structure of novolac allows multiple phenols to bind to the DNQ carbonyl, thus, blocking developer diffusion into the resist. The lipophilic backside of the polymer forms a hydrophobic pot while the DNQ PAC rests atop the pot resembling an octopus (Figure 5). The hydrogen bonding of the novolac to the DNQ carbonyl was observed by infrared spectroscopy. In terms of percolation theory, the active sites of the polymer are blocked, which effectively lowers the percolation parameter, p. 

The acidity of the reaction medium appears to be the most important factor governing the reactions between phenol and formaldehyde. The rate of the phenol-formaldehyde reaction at pH 1 to pH 4 is proportional to the hydrogen ion concentration, but above pH 5 it is proportional to the hydroxyl ion concentration, indicating a change in reaction mechanism. Four types of polymers can be obtained novolacs, high ortho-ortho novolacs, resoles, and high ortho-ortho resoles. 

High ortho-ortho novolacs are produced under weakly acidic conditions, by the use of specific catalysts, usually metal ion carboxylates. The first such resins were prepared by Bender and Farnham, using oxides of Zn, Mg, and A1 within the pH range of 4 to 7. Fraser et al used a broad range of salts of the divalent metals. Both groups of workers used a large excess of phenol, which was later removed by distillation. The use of acetates, lactates, formates, and benzoates was claimed to improve the solubility and activity of these catalysts, including rare earth acetates. ... 

More recently, Culbertson has employed anhydrous reaction condi-tions, first disclosed by Robins, to produce high ortho-ortho novolacs at relatively low reaction temperatures and low phenol/formaldehyde ratios. 

Table I. Reaction Conditions for High Ortho-Ortho Novolacs...

Pizzi has classified such resins as ortho-ortho novolacs, indicating that they also contain dibenzylic ether structures and may also contain methylol groups, if the reaction is performed at low temperatures. It is suggested, however, that they be considered as high ortho-ortho resoles, since they contain more formaldehyde than phenol (on a molar basis) and they can be cured at elevated temperatures, especially in the presence of acidic or basic catalysts. 

Modifications of novolacs has to take place at the phenolic hydroxyl. Dannels and Shepard report that novolacs of high ortho-ortho substitution can be esterified with relatively large amounts of inorganic acid to yield soluble, fusible products. Regular novolacs under the same conditions yield crosslinked insoluble, infusible polymers, undergoing intermolecular esterification. Cyclic esters from ortho-ortho novolacs are described by Prochaska to form cyclic carbonates at low temperatures, which resinify at elevated temperatures.Structure 30 is typical of the type of products obtained from these reactions. 

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