Resol-Type Foam Chemistry

Resol-Type Foam Chemistry. Resol is obtained as a result of the reaction between phenols (P) and formaldehyde (F) in the presence of basic catalyst. Generally, the reaction is made at a temperature below 

As described above, formaldehyde exists as trimethylene glycol in aqueous solution. Phenol reacts quickly with the alkali-hydroxyl group and produces resonance structural phenoxide ion, and trimethylene glycol is added to the O and P positions in the phenoxide ion. This quinoid-transition-state is stabilized by the movement of proton. The monomethylene-derivative produced in this way reacts further with formaldehyde and produces two types of dimethylol derivative and one type of trimethyl derivative. These reactions are expressed as second-order reactions  

The methyl derivative thus produced forms a multi-nucleus structure by the dehydration condensation. Generally, the numbers of benzene nuclei contained in resol for making phenolic foam are less than 10. The addition and condensation reactions used in synthesizing resol, and the reaction during foaming and curing are summarized as follows  

In manufacturing phenolic foams, a blowing agent such as R-113 (trichlorotrifluoroethane) is evaporated by using an exothermic reaction (Equation 7), and the blowing agent is included in the polymer. The reaction involved in forming the benzylic ether-type foam is shown below. Similarly, this foam will finally form a network polymer as do resol-type foams. 

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