Resole-type prepolymers

The functionality may vary with reaction conditions. For example, in base-catalyzed copolymerization of phenol and formaldehyde, both monomers are bifunctional at ambient temperature, but phenol becomes trifunctional if the temperature is raised sufficiently. Copolymerization at ambient temperature can produce essentially linear, liquid, resole-type "prepolymers" of low molecular weight. Upon acidification and heat-curing, methylene and ether crosslinks formed by the now trifunctional phenol units transform the polymer into an insoluble resin [7] (see next page). The original Bakelite was such a "thermosetting" product. 

Synthesis of Resole Type Prepolymers 1. Catalysts for the Synthesis of Resoles... 

When phenol reacts with a larger than stoichiometric amount of methanal at pH values numerically larger than 5, hydroxymethyl phenols form which can subsequently react by forming methylene or ether linkages between the aromatic units. These are resole type prepolymers that are called resole in the following text. This reaction is shown in equation 13 and was first reported by Lederer and Manasse in 1894 [68]. The first step of this reaction at a pH>5 is the formation of mono-, bis- andtris-hydroxymethylated phenol [68,69], as... 

What are the reaction conditions for preparation of novolac or resole type prepolymers ... 

Such a resin of the alkaline novolak-resol type can be prepared by coreacting a prepolymer, prepared by reacting formaldehyde and phenol in the molar ratio of 2.6 1.0, and a prepolymer obtained by reacting formaldehyde and phenol in the molar ratio of 1 1. The two prepolymers are then mixed in 50 50 proportions by mass and coreacted. 

Since the cross-linked polymer of phenol-formaldehyde reaction is insoluble and infusible, it is necessary for commercial applications to produce first a tractable and fusible low-molecular-weight prepolymer which may, when desired, be transformed into the cross-linked polymer [14,44,45]. The initial phenol-formaldehyde products (prepolymers) may be of two types resols and novolacs. 

The PF prepolymers may be of two types, the novolaks and resols. The novolaks are prepared from excess phenol and formaldehyde (in the molar ratio 5 4) under acidic conditions. The monomers react slowly to form o- and p-methylol phenols (Reaction 1), which then condense rapidly with further phenol to give dihydroxyl diphenyl methane types (Reaction 2) ... 

There are two types of phenol-formaldehyde resin. Those prepared using an excess of formaldehyde with base catalysis are known as resoles. The resole prepolymers possess many unreacted methylol groups that upon further heating react to produce the network structure. 

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