AbstractSeveral preparations of water‐soluble sulfonated amino‐formaldehyde resins were prepared under different reaction conditions. The stability of these solutions was studied after accelerated aging at 60°C for 2 weeks. Viscosity and pH changes were monitored with storage time. The results showed that our four‐step reaction procedure more stable products than the three‐step reaction procedure. The four steps of reaction are: hydroxymethylation, sulfonation, low‐pH condensation, and high‐pH rearrangement. The three‐step process discussed in the literature combines hydroxymethylation and sulfonation as one step followed by low‐pH condensation and high‐pH rearrangement. It was found that the more stable products of the four‐step process are affected slightly by the F/M molar ratio and the concentration of reactants in contrast with the three‐step process in which these variables affect stability drastically. In general, the pH, temperature, and time of reaction of the fourth step are the main controlling factors for product stability. An attempt was made to explain the stability behavior of these solutions in terms of their molecular weig
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