Phenol-formaldehyde condensations

Fig. 13. Polymerization chemistry of phenol—formaldehyde condensation synthesis of novolac resia. The phenol monomer(s) are used ia stoichiometric excess to avoid geUation, although branching iavariably occurs due to the multiple reactive sites on the aromatic ring.

Reaction rates are at a minimum at pH 3, and, unlike with the phenol-formaldehyde condensates, which have a minimum at pH 7, setting can occur under neutral conditions. 

A process for separating crude oil emulsions of the water-in-oil type based on certain ethylene oxide-propylene oxide block pol5miers and certain poly-glycidol ethers of phenol-formaldehyde-condensation products has been described [1026-1028]. 

Diglycidyl ether of bisphenol A (DGEBA, MW 340 Da) and 4,4 -dihydroxy-diphenylmethane (DHDPM, MW 200 Da) were analysed by SEC-MALS [784]. DGEBA and DHDPM are the basic oligomers of epoxy resins and phenol-formaldehyde condensates, respectively, which are widely used in the electronic and automotive industries. Excellent reproducibility ( 1 %) and good accuracy (better than 10%) were observed. SEC has also been used for the determination of mineral oil in extended elastomers [785] and in PS [178]. With heptane containing 0.05% isopropanol as the mobile phase, mineral oil is completely unretained and elutes before the solvent via SEC all other components in a PS extract are retained on silica and elute after the solvent peak. 

Bayer, A. 1878. Phenol-formaldehyde condensates. Ber. Bunsenges. Phys. Chem., 5 280, 1094. Brunelle, D.J. and Korn, M. 2005. Advances in Polycarbonates. Oxford University Press, New York. Carothers, W.H. 1929. An introduction to the general theory of condensation polymers. J. Amer. Chem. Soc., 51 2548. 

Trade (and/or brand) names and abbreviations are often used to describe a particular material or a group of materials. They may be used to identify the product of a manufacturer, processor, or fabricator, and may be associated with a particular product or with a material or modified material, or a material grouping. Trade names are used to describe specific groups of materials that are produced by a specific company or under license of that company. Bakelite is the trade name given for the phenol-formaldehyde condensation developed by Baekeland. A sweater whose material is described as containing Orion contains polyacrylonitrile fibers that are protected under the Orion trademark and produced or licensed to be produced by the holder of the Orion trademark. Carina, Cobex, Dacovin,... 

Acid-Catalyzed Phenol-Formaldehyde Condensation (Novolaks)... 

Phenolic There are various kinds of phenolic resins. The ones that are produced from phenol-formaldehyde condensation are veiy weak acid exchangers, where the phenolic -OH groups are the fixed-ionic groups. The formaldehyde content decides the extent of cross-linking in the resin. On the other hand, phenolsulfonic acid resins contain both strong acid -S03H and weak acid -OH groups. 

Research Focus Method for minimizing the formation of phenol-formaldehyde tetramers in phenol-formaldehyde condensation reactions. 

Resorcinol/phenol-formaldehyde condensation products prepared by Durairaj et al. (3) using zinc acetate as the reaction catalyst contained 2% / -//-phenolic, 16% -p -phenolic, 64% o-o -phenolic-4-4 -resorcinolic, 16% 2-4 -resorcinolic, and 2% 2-2 -resorcinolic methylene bridges. 

Macrocyclic phenol-formaldehyde condensation products have been termed calixarenes509 and are capable of providing a cavity for complexation (132). Rb+ was shown to be a good templating device during synthesis and this hinted at complex formation. Transport experiments have shown calixarenes-[4], -[6] and -[8] to be selective for Cs+ using MN03 no transport was detected but with MOH it occurred. 18-Crown-6 behaved in a contrary fashion ... 

Branched phenol-formaldehyde condensates can be formed on a series of polyamides by heating the phenolic solution of the reactants up to 180° C in the presence of p-toluene sulfonic acid, with or without the addition of another solvent such as xylene, dimethyl sulfoxide or dimethyl formamide (7). 

Calixarenes (12), from the Greek meaning chalice and arene (incorporation of aromatic rings), are macrocyclic phenol-formaldehyde condensation products. 

A number of early homogeneous membranes were made by simple condensation reactions of suitable monomers, such as phenol-formaldehyde condensation reactions of the type ... 

Plots of (absorbance)-1 versus time were linear for greater than 90% of the reaction for each system studied. These observations may be interpreted in terms of the reaction obeying second-order kinetics where the reactants are equimolar (40). Second-order or more complex kinetics are typical of phenol-formaldehyde condensations under alkaline conditions (7). 

A very limited amount of information deals with the efficiency of polycondensate antioxidants. It was reported [158] that the efficiency of linear phenol-formaldehyde condensates drops in systems containing more than three phenolic nuclei. Similarly, an optimum AO effect was observed with 4-methoxyphenol-formal-dehyde condensates having a molecular weight of 1000 as a maximum [160]. Both reported data [158, 160] deal more or less with the inherent chemical efficiency of stabilizers. The physical persistency was not particularly considered in this case. 

Other recent references to phenol—formaldehyde condensations include those of Yeddanapalli et al. [200, 201]. The complications of melamine/ formaldehyde and urea/formaldehyde reactions kinetics are analogous, and have been examined in two recent papers [202, 203]. 

Neither a historical review nor a complete story of this field of polymer making is presented here. Rather, this is a series of views of the chemistry and procedures, from which one may obtain some idea of the potential as well as of the limitations of the methods. The discussion includes only reactions which yield essentially linear polymers, bypassing polyurethane foams and phenol-formaldehyde condensates. 

As with condensation polymers many examples of biochemically formed vinyl addition polymers, such as the poly-cis-isoprene found in the sap of rubber trees, were known long before we were able to replicate these materials even in the laboratory. Our ability to initiate and control the preparation of vinylic polymers on a laboratory scale came in the early 1930s, substantially later than the commercialization of phenol-formaldehyde condensation polymers. Since then, however, starting with the synthesis of polyethylene, then poly(vi-nyl chloride) (PVC), synthetic rubbers and polystyrene, the scale of production of this class of polymer has outstripped the polycondensation class by more than an order of magnitude. Table 23.1 displays some representative production figures to illustrate this. 

Since the introduction of the first commercial thermoset, Bakelite, based on phenol formaldehyde condensation, a wide range of thermoset materials have been introduced. These are typically designed for specific properties related to their chemistry and processability. Some commercially important thermosets include phenolics, ureas, melamines, epoxy resins, unsaturated polyesters, silicones, rubbers, polyurethanes, acrylics, cyanates, polyimides, and benzocyclobutenes. ... 

In some exploratory experiments test conditions were selected for the phenol/ formaldehyde condensation. It was found that catalytic test experiments could best be carried out at a relatively high temperature, 180 C, to increase conversions generally a reaction time of 4Vi h was found suitable to compare materials with higher and lower deactivation rates. Application of 1,4-dioxane as a solvent did not improve the selectivity much, and therefore the experiments were carried out solvent free. Selectivities could be improved considerably when a higher phenol/formaldehyde-ratio was applied (see for example Figure 3) but, again to compare different catalysts, a molar ratio of 2/1 was considered most suitable in the catalytic test experiments. 

To overcome such problems, an alternative definition has been introduced. According to this definition, polymers whose main chains consist entirely of C-C bonds are classified as addition polymers, whereas those in which heteratoms (O, N, S, Si) are present in the polymer backbone are considered to be condensation polymers. A polymer which satisfies both the original definition (of Carothers) and the alternative definition or either of them, is classified as a condensation polymer. Phenol-formaldehyde condensation polymers, for example, satisfy the first definition but not the second. 

As just mentioned, strong or weak acidic ion exchangers contain sulfonic acid or carboxylic acid groups in the H or alkali metal salt form and consist of 1,4-divinylbenzene cross-linked polyst3Tene or poly(acrylic acid) as shown in formulae 7a and 7b. Another example is the sulfonated phenol-formaldehyde condensation polymer 8. The preparation of ion-exchange resins and the determination of their capacities are described in Section 5.4, Experiments 5-1 and 5-2. 

Preparation of Cation Exchanger 8 by Sulfonation of a Phenol-Formaldehyde Condensation Polymer (Section 5.1.1)... 

Sulfonation of the phenol-formaldehyde condensation polymer 40 g of the uncross-linked phenol-formaldehyde condensation polymer are gradually wanned to 140 °C in 120 g of 95% sulfuric acid in a 250 mL round-bottomed flask fitted with a reflux condenser. As soon as the resin has completely dissolved, the solution is cooled to room temperature, poured into an iron dish and 30 mL of 37% aqueous formaldehyde solution are stirred in with a spatula as quickly as possible. The metal dish is then placed in an oil bath at 110 °C and the resin allowed to harden for 2 h. The cooled product is washed with water, broken up with a hammer, and ground down to pieces of 1-3 mm size in a mortar. The particles are then washed with water until the washings are clear. 

---