Highly Branched Polyurea-Enhanced Urea-Formaldehyde Resin

Highly branched polyurea (HBPU) was synthesized through polycondensations between urea and tris(2-aminoethyl)amine (TAEA) with no solvents and catalysts used. Characterizations were performed by employing electrospray ionization–mass spectroscopy (ESI–MS), gel permeation chromatography (GPC), and 13C NMR analytical techniques. The GPC results showed that the HBPU polymers with molecular weights (Mn) above 160,000 are formed. The 13C NMR analysis indicated that the branches of the polymers are basically urea-terminated when the U/TAEA molar ratio is controlled to be 3.0. The HBPU was then used to modify the traditional low-molar-ratio urea-formaldehyde (UF) resin by adding HBPU at the final alkaline reaction stage during UF synthesis. ESI–MS analysis indicated that both hydroxymethylation of HBPU polymers and co-condensations between HBPU polymers and UF components occurred. Differential scanning calorimetry analysis suggested that the HBPU can accelerate cure of UF resin. In bonding performance tests, the modified resins exhibited much better water resistance than the unmodified resin. Moreover, much lower formaldehyde emission level is also an advantage of the modified resins. Based on the results of this work, it was concluded that the polymers with highly branched structure, high molecular weights, high functionality, and urea-like reactivity can be promising modifiers of UF resin.