硫脲甲醛聚合反应中的半结晶沉淀现象

首次报道了硫脲甲醛聚合反应中的半结晶沉淀现象.定量分析结果显示硫脲甲醛之间的聚合反应接近一种线性交替共聚反应过程.红外光谱的结果证明不同硫脲甲醛物质的量比反应条件下产物中始终存在较强的N—H特征振动吸收峰(v=3311cm-1,δ=1541cm-1).当甲醛用量较高和硫脲用量增加时分别在1008和1137cm-1处检测到较强的C—O—C和C=S伸缩振动吸收峰.结合XRD和核磁共振分析结果推测:硫脲甲醛聚合产物中存在着一种氢键导向型结晶结构;分子中含有醚键的聚合产物因具有复杂的氢键作用没有结晶性.扫描电镜分析显示较高硫脲用量反应条件下生成了层状半结晶碎片产物,而高甲醛比例条件得到的产物为细小的层状碎片交联聚集成的球形粒子.

Semicrystalline Precipitation Phenomenon in the Thiourea/Formaldehyde Polycondensation

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.