The semicrystalline precipitation phenomenon of the thiourea/formaldehyde polycondensation was described for the first time. Quantitative analysis revealed that the thiourea/formaldehyde polycondensation proceeded approximately in accordance with the linear alternate copolymerization. The FT-IR absorption peaks of N—H appeared at 3311 and 1541 cm^－1, which were strong in all samples. The absorption of C＝S stretching vibrations were obvious at 1137 cm^－1 in the samples synthesized using excessive amount of thiourea and that of the C—O—C stretching vibration was distinct at 1008 cm^－1 in the samples prepared under the reaction conditions of enough amount of formaldehyde. XRD and NMR analyses showed that a type of semicrystalline structure existed in the precipitate. However, ether-based polymeric structure was uncrystallizable due to existence of the complex intermolecular hydrogen bonding interaction. The scanning electron microscopy images showed that the precipitate was layered semi-crystallite, except the samples prepared from high proportion of formaldehyde exhibiting spherical particles made of the small cross-linked layered chips.

Key words: thiourea-formaldehyde resin, precipitation phenomenon, linear molecule, hydrogen bonding, layered semicrystallization