Mechanism of thermal degradation of urea-formaldehyde polycondensates

The thermal degradation to 500°C of urea-formaldehyde polycondensate occurs in four successive steps. In each step, partial volatilisation takes place while the polymer undergoes chemical modification to give progressively more stable structures. Below 200°C methylene ether bridges are transformed into methylene bridges and branching and crosslinking reactions occur with maximum rates at 125°C and 165°C, respectively. Above 200°C radicals formed by chain scission induce the formation of cyclic structures in the polymer which undergoes extensive fragmentation above 300°C. Water, formaldehyde, carbon monoxide and dioxide, methane, ammonia, monomethylamine and trimethylamine are the gaseous products evolved. By combining data on the chemical modifications and gases evolved in each step, reaction mechanisms are proposed.