Phenol-formaldehyde resins Infusible

In contrast to the linear thermoplastic polymers, which are soluble and fusible, the cross-linked network polymers are insoluble and infusible. They are formed from polymerizing systems containing monomers or prepolymers with a functionality of three or more. A good example is the phenol-formaldehyde resin systems. The cross-linking reaction takes place in the bond under applied pressure and heat, and the whole adhesive bond might consist of only one super giant molecule. Such resins are, therefore, called thermosetting resins. 

C-Stage resin. (resite). The fully cross-linked phenol-formaldehyde resin, which is infusible and insoluble in all solvents. 

Matsumoto and coworkers incorporated poly(A -(hydroxyphenyl)maleimides) into composite materials with phenol-formaldehyde resins. Poly(iV-(4-hydroxyphenyl)malei-mide) has been shown to form miscible blends with phenolic resins and, after crosslinking, produces composites with good thermal and chemical stability. The hardening or crosslinking agent most commonly used is hexamethylenetetramine (HMTA), to form an insolnble and infusible three-dimensional polymeric network (Scheme 29). 

The formation of crosslinked networks has been the basis for polymer technology since the development of phenol-formaldehyde resins by Baekeland in 1910. The changes to the rheology of the phenolic system, as it develops from a liquid to a rubber and then to a glass, arise from the formation of a three-dimensional network as the step-growth chemical reactions occur. Water is evolved and the end product is a solid infusible mass. 

Resite n. A phenol-formaldehyde resin in the final state of the curing process. In this stage it is insoluble in alcohol and acetone, and infusible. Alternate term for C-stage. See C-stage also called resitol and resol. 

Both one and two stage polymers are used individually or in combination in applications. The final insoluble and infusible phenol-formaldehyde resins are called Bakelite [1]. Phenol-formaldehyde resins are good electrical insnlators, they are resistant to heat and chemical attack. However, they are brittle and their mechanical properties are not too good. 

Baekeland himself mixed natural rubber with a phenol-formaldehyde resin at an intermediate stage of condensation. Catalysts made the resin infusible on vulcanization of the rubber. Other very early products of rubber blended with phenol and formaldehyde or other aldehydes were described by McGavack, " ° Aylsworth, Frood, and exhaustively reviewed by Ellis (Reference 111, Chapter 20). 

Some commercially important cross-linked polymers go virtually without names. These are heavily and randomly cross-linked polymers which are insoluble and infusible and therefore widely used in the manufacture of such molded items as automobile and household appliance parts. These materials are called resins and, at best, are named by specifying the monomers which go into their production. Often even this information is sketchy. Examples of this situation are provided by phenol-formaldehyde and urea-formaldehyde resins, for which typical structures are given by structures [IV] and [V], respectively ... 

The cationic polymerization of cardanol under acidic conditions has been referred to earlier [170,171], NMR studies [16] indicated a carbonium ion initiated mechanism for oligomerization. PCP was found to be highly reactive with aldehydes, amines, and isocyates. Highly insoluble and infusible thermoset products could be obtained. Hexamine-cured PCP showed much superior thermal stability (Fig. 12) at temperatures above 500°C to that of the unmodified cardanol-formaldehyde resins. However, it was definitely inferior to phenolic resins at all temperatures. The difference in thermal stability between phenolic and PCP resins could be understood from the presence of the libile hydrocarbon segment in PCP. 

Baekeland found that a relatively stable resole prepolymer could be obtained by the controlled condensation of phenol and formaldehyde under alkaline conditions. These linear polymers of phenol-formaldehyde (PF) may be converted to infusible cross-linked polymers called resites by heating or by the addition of mineral acids. As shown in structure 4.80, the initial products obtained when formaldehyde is condensed with phenol are hydroxybenzyl alcohols. The linear resole polymer is called an A-stage resin, and the cross-linked resite is called a C-stage resin. 

PHENOL-FURFURAL RESIN, A phenolic resin that has a somewhat sharper transition than phenol-formaldehyde from the soft, thermoplastic stage to the cured, infusible state and can be fabricated by injection molding since it has little tendency to harden before curing conditions are reached. 

Thermoset A resin or plastic compound that in its final state is substantially infusible and insoluble. It cannot be repeatedly softened by heating and hardened by cooling. Examples of thermosets are epoxy, phenol-formaldehyde, some types of polyester, some types of... 

Synonyms Formaldehyde, phenol polymer Formaldehyde, polymer with paraformaldehyde and phenol Paraformaldehyde, formaldehyde, phenol polymer Paraformaldehyde, phenol polymer Phenol-formaldehyde copolymer Phenol, formaldehyde polymer Phenol, polymer with formaldehyde Phenol, polymer with paraformaldehyde Classification Thermosetting polymer Definition Reaction prod, of phenol with aq. 37-50% formaldehyde with basic catalyst chief class of phenolic resin Formula (CeHeO (CH20)x)x Properties Gray to bik., hard, infusible solid when cured resist, to moisture, soivs., heat to 200 C dimensionally stable good elec, resist. noncombustible... 

Commonly accepted practice restricts the term to plastics that serve engineering purposes and can be processed and reprocessed by injection and extmsion methods. This excludes the so-called specialty plastics, eg, fluorocarbon polymers and infusible film products such as Kapton and Updex polyimide film, and thermosets including phenoHcs, epoxies, urea—formaldehydes, and sdicones, some of which have been termed engineering plastics by other authors (4) (see Elastol rs, synthetic-fluorocarbon elastol rs Eluorine compounds, organic-tdtrafluoroethylenecopolyt rs with ethylene Phenolic resins Epoxy resins Amino resins and plastics). 

Of the various amino-resins that have been prepared, the urea-formaldehyde (U-F) resins are by far the most important commercially. Like the phenolic resins, they are, in the finished product, cross-linked (thermoset) insoluble, infusible materials. For application, a low molecular weight product or resin is first produced and this is then cross-linked only at the end of the fabrication process. 

A procedure based on condensation with phenol and paraform (used as formaldehyde source) was developed to convert spent UNEX solvent (CCD, PEG-400, Ph2-CMPO, and FS-13) into a solid infusible resin for disposal. The resulting material is insoluble in aqueous alkali and acidic solutions and organic solvents. Incorporation of FS-13 in the cross-linked polymer was confirmed by physicochemical methods. Resistance of the cured resin to high temperatures was proven by thermogravimetry... 

Attempts to make adhesive formulations by direct reaction of formaldehyde or its equivalent resulted in products that were excessively viscous, and the working time was too short for commercial application (57). It was concluded that formaldehyde, although readily reactive with the tannin molecule, provided much too short linkages to connect the bulky tannin molecules. This problem was circumvented by the preparation of a polymethylolphenol reagent that, when put in solution with the bark extract, formed a combination that was stable for several weeks at room temperature. When heated, the polymethylolphenol and bark extract reacted rapidly to form an infusible resin. Commercial trials were made to produce exterior-grade Douglas-fir plywood. Widespread use of the extracts for this purpose, however, was inhibited by a drop in the price of phenol below what the bark extracts could be manufactured for. (The best extract for adhesive purposes was an ammonia extract of hemlock bark converted to a sodium derivative prior to spray drying, a more costly extraction procedure than simple sodium hydroxide extraction of bark.)... 

Thermosetting phenolic resins form a separate class of polymers containing aromatic rings and aliphatic carbon groups in the polymeric network. These resins are formed from the reaction of phenol (or substituted phenols) with formaldehyde. The fully crosslinked macromolecule is insoluble and infusible. Other thermosetting resins are known in practice, some derived from the reaction of melamine or of urea with formaldehyde. Because these have a different chemical structure, containing nitrogen, they are included in a different class (see Section 15.3). 

The physical form of these products is dependent on their molecular weight and the amount of reacted formaldehyde. The initial reaction products, mixed methylols of phenol, are low viscosity liquids that are water soluble. This mixture can be separated into pure crystalline compounds. On further condensation, viscous reactive liquids are obtained, which are difficult to isolate in an anhydrous form. These products are soluble in alcohols and other polar solvents. Increasing the molecular weight further with only a slight excess of formaldehyde results in grindable, fusible, resinous solids that are soluble in polar solvents. Further polymerization decreases the solubility and increases the softening point until an infusible, insoluble gel is obtained. 

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