酚醛树脂Bakelite

苯酚羟基使邻位和对位活化，甲醛在这些位置发生亲电取代生成羟甲基酚，羟甲基再与另一苯酚缩合形成亚甲基桥（–CH₂–）或醚键。酸催化、苯酚过量时得到线型可熔的热塑性酚醛树脂（novolac），需加六亚甲基四胺固化；碱催化、甲醛过量时得到含大量羟甲基的甲阶树脂（resol），加热即可自行交联。每个苯酚有三个活性位置，因此能形成三维网络。

The phenol OH activates the ortho and para positions, where formaldehyde substitutes electrophilically to give hydroxymethylphenols, which condense with more phenol to form methylene (–CH₂–) or ether bridges. With acid and excess phenol the product is a linear, fusible novolac that needs hexamethylenetetramine to cure; with base and excess formaldehyde it is a resol rich in hydroxymethyl groups that crosslinks on heating alone. With three reactive positions per phenol, a three-dimensional network forms.

1872 年拜尔已观察到苯酚与醛反应生成树脂状物质，但未能利用。比利时裔美国化学家利奥·贝克兰在加压加热条件下控制反应，于 1907 年申请专利、1909 年公布，命名为 Bakelite，开启了塑料时代。电木被用于电话机、收音机外壳、电器插座和台球等。

In 1872 Baeyer saw phenol and aldehydes form resinous masses but found no use for them. The Belgian-born American chemist Leo Baekeland controlled the reaction under heat and pressure, filed his patent in 1907 and announced it in 1909, naming it Bakelite and opening the age of plastics. It went into telephones, radio cabinets, electrical sockets and billiard balls.

现在酚醛树脂主要用于胶合板和刨花板胶黏剂、刹车片和砂轮的黏结剂、电器绝缘件、耐火保温泡沫以及航天器的烧蚀防热材料。缺点是颜色深（棕黑色）、较脆，且残留游离甲醛需控制。

Today phenolics are used mainly as adhesives for plywood and particleboard, binders for brake pads and grinding wheels, electrical insulating parts, fire-resistant foams and ablative heat shields for spacecraft. Drawbacks are a dark brown colour, brittleness and the need to control residual free formaldehyde.