Resole polycondensation

Altshluser et al. has investigated macrocyclic polymers, which were obtained by the catalytic resol polycondensation of calix[4]resorcinarene derivatives with formaldehyde (Fig. 13) [11]. 

Processing of phenol-aldehyde oligomers into various articles is based on a polycondensation reaction which leads to solidification of the material at temperatures below 200°C and pressures exceeding 10 MPa. The process is accompanied by volatile product formation. However, phenol-formaldehyde resins of the resol type can be cast without additional pressure and heat. The raw molding reactants contain different organic and mineral fillers and other additives in addition to the basic resin. 

Due to the presence of reactive CH2OH groups, resol oligomers may be converted into highly crosslinked products without the addition of hardeners. Heat curing is conducted at T 130 200°C. The polycondensation mechanisms are complex and different bridges are possible CH2-0-CH2-and CH2. The latter is thermodynamically the most stable. Therefore the methylene bridges are the prevalent crosslinks in cured resols. 

Binders are at the heart of mineral and glass wool [1]. The best binders are based on resole resins prepared by the polycondensation reaction of phenol with formaldehyde in the presence of a basic catalyst [2]. To such resoles, urea is added to improve fire resistance and scavenge free formaldehyde. 

Resol resins, having very reactive methylol groups (obtained by the condensation of phenol with formaldehyde in basic media), are rarely used as starters for rigid polyether polyols. One reason is the impossibility of melting these resins at the propoxylation temperature, because upon heating they rapidly polycondensate and crosslink. An interesting representative of this group of resin is trimethylol phenol (reaction 15.26). 

A thermosetting resin containing approximately 40% of cardanol by weight has been synthesized by adding an epoxy monomer and an acid-based catalyst to a resole compound (Maffezzoli et al., 2004). This last was manufactured through a polycondensation reaction between cardanol and formaldehyde in the presence of a basic catalyst. The formulation characterized by adequate properties and curing temperatures was reinforced with natural fibers (i.e. short ramie, flax, hemp fibers and a jute fabric) to obtain samples which were then tested both in tensile and in flexural configurations. 

The overall mechanism of such a polycondensation is independent of the type of amine used. The first step is similar to that previously described for the formation of resols ... 

Resols are prepolymers obtained in basic medium in the presence of an excess of formaldehyde. They consist primarily of methylolphenols as well as di-, tri-, and tetraphenolic compounds resulting from the polycondensation of phenol with... 

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