Urea-Aldehyde Condensates With pH-Controlled HWIN-Free Polymerization

The patent changes the pH parameter from acidic (conventional) to basic conditions (pH 8-10) during the condensation reaction. This parameter change prevents HWIN formation while maintaining efficient polymerization, resolving the contradiction between reaction efficiency and nitrogen release consistency. The basic conditions allow the reaction to proceed effectively without forming the harmful insoluble byproducts that occur under acidic conditions.

The patent employs a two-stage temperature control strategy: first stage at 25-40°C during base-catalyzed condensation to limit polymerization degree and maintain water solubility, then second stage at 50-70°C during acid-catalyzed polymerization to achieve desired molecular weight. This temporal separation of temperature conditions resolves the contradiction by allowing efficient reaction progression without excessive polymerization that would reduce water solubility.

The patent uses a composite aldehyde system combining formaldehyde (C1) with a higher aldehyde (C2-C4). This composite approach provides superior control over the condensation reaction and degree of polymerization compared to single aldehydes, preventing HWIN formation. The different reactivity of the two aldehydes allows staged reaction control: formaldehyde reacts first under basic conditions, then the higher aldehyde participates during acidification, achieving precise polymerization control while maintaining process simplicity.

Instead of stopping the reaction by increasing pH to 7-8 (conventional approach), the patent inverts the approach by maintaining basic pH 8-10 throughout the condensation reaction and then adding acid to reach neutral pH. This inverted sequence prevents HWIN formation by ensuring the condensation occurs under basic conditions where HWIN does not form, while still achieving reaction completion and polymerization control. The harmful byproduct is eliminated while maintaining effective reaction control.