Hydroxymethylation and polycondensation reactions in urea-formaldehyde resin synthesisChristjanson, Peep; Pehk, Tõnis; Siimer, KadriJournal of applied polymer science2006 / p. 1673-1680 : ill https://www.researchgate.net/publication/230275426_Hydroxymethylation_and_polycondensation_reactions_in_urea-formaldehyde_resin_synthesis