Methylol polyamide resins

Such a dependence was also observed in [23], where the decrease in the absorption of formaldehyde by the polyamide resin was partially explained by an increase in the number of cross-links in the sample on account of the interaction of methylol derivatives. 

A study of the infrared spectra of hardened methylol-polyamide [26] showed that the appearance of three-dimensional structures in such resins is related to the formation of methylene bridges. 

The fluid dimer polyamides and fatty amido amines also react with phenolic resins (23). These reactions are significantly different from those of epoxy resins. With the heat-reactive phenolic resins, the aminopolyamide portions react with methylol groups. A carbon-nitrogen bond or cross-link is formed and a volatile byproduct, water, is produced. This reaction requires external heat to remove water. At temperatures near 150 °C the reaction proceeds smoothly. Since curing at elevated temperatures is required, the pot life or shelf life at room temperature is relatively long. The liquid dimer polyamide and fatty amido amines also react with alpha, beta unsaturated acids and esters (29) and with polyesters (30). The unsaturated esters reduce viscosity, lengthen useful pot life, and reduce heat of reaction. Thus, they are useful diluents when low viscosity is desired. 

Products of polymerized vegetable oil acids and polyamines, which are highly branched liquid polyamides, are mixed with phenolic resins to produce a thermosetting composition with a wide range of properties. Cure usually is accomplished in 60 min at 300°F. The reaction involves the condensation between methylol groups and amine groups. 

Even at the early stages of absorption of formaldehyde, no methylol derivatives could be detected in these resins. This is apparently due to the rapid formation of methylene bonds in the resins. In polyamide 68, methylol derivatives were detected (up to 3% of the weight of the polymer 15 min after the beginning of the experiment) at all stages of the absorption of formaldehyde. The content of methylol groups was determined polar igraphically. It corresponded to the amount of free polyformaldehyde liberated in the decomposition of methylol groups in alkaline medium [27]. However, even at the maximum absorption of formaldehyde, polyamide 68 remains entirely soluble in tricresol imder these conditions. 

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