线型脲醛树脂的半结晶模板化作用

酸性条件下硅溶胶体系中尿素和甲醛聚合反应会产生脲醛树脂-氧化硅杂化沉淀. 沉淀的质量随有机组分比例的增加而增加, 当尿素和甲醛物质的量比≥1.0时生成沉淀的量为恒定最大值. 红外分析表明杂化材料在3348, 1635, 1572和784 cm^－1处产生了可被归结为线型结构(—NHCONHCH₂]_n—)的特征吸收. XRD分析表明这种线型分子可形成氢键(C＝O…H—N)导向型的半结晶. 微分热重和XRD结果证明结晶物种在290 ℃完全分解. SEM表征显示半结晶杂化沉淀以三维网络结构为特征, 具有层状结晶的各向异性, 其初级粒子即使在室温下干燥也容易开裂. 随着反应时间的延长、酸性的增加或无机组分量的相对增加杂化粒子变得更加致密. 液氮吸附结果证明沉淀焙烧后所得氧化硅材料的结构具有层状孔结构性质, 其比表面积、孔尺寸和孔体积可以达到510 m²/g, 14.3 nm和1.68 cm³/g. 改变反应体系的酸性和反应组分配比等条件可以方便地控制杂化材料的结构.

Templating Effect of Semicrystalline Urea-Formaldehyde Resin with Linear Molecular Structure

Polymer-silica hybrid precipitate could be observed in urea and formaldehyde condensation reaction in silica sol-gel. The amount of the precipitate increased with that of the organic component used in the reaction and achieved its maximum when the urea to formaldehyde molar ratio was above the value of 1.0. The IR absorption of the precipitate at ca. 3348, 1572, 1635 and 784 cm^－1 could be attributed to the characteristics of a linear structure —HNCONHCH₂—. XRD pattern of the precipitate was correlated with the semicrystallization of the linear structure via hydrogen bond interaction (C＝O…H—N). Decomposition of the crystal species occurred around 290 ℃ according to DTGA and XRD analyses. SEM results show that the hybrid particles have a three-dimensional network structure, which tended to crack even under the room temperature drying conditions. With increasing the reaction time, acidity or content of the inorganic component, the hybrid particles became more compact. BET results demonstrate that the calcined samples have a lamellar structure. A large pore size of 14.3 nm, a pore volume of 1.68 cm³/g, and a BET surface area of 536 m²/g were obtained under the highest acidity reaction conditions. Meanwhile the structural characteristics of the silica or hybrids could be controlled by the acidity and molar ratio of the reactants.