Bifunctional monomers are molecules that have two functional groups capable of participating in polymerization. These functional groups can react with other monomers to form linkages and build a polymer chain. Examples include diols (containing two hydroxyl groups), diamines (containing two amine groups), and dicarboxylic acids (containing two carboxyl groups). Bifunctional monomers are essential for step-growth polymerization.

双官能单体是具有两个能够参与聚合的官能团的分子。这些官能团可以与其他单体反应形成键并构建聚合物链。例子包括二醇（含有两个羟基）、二胺（含有两个胺基）和二羧酸（含有两个羧基）。双官能单体对于逐步增长聚合至关重要。