Applications of Small Molecule Polyfunctional Compounds

Among the small molecule polyfunctional compounds used in polyurethane materials, diols, polyols, alkanolamines, and diamines are versatile raw materials: diols, polyols, and alkanolamines can be used as chain extenders or crosslinking agents (curing agents); diols and a small amount of polyols can be used to synthesize polyester polyols; some diols, polyols, and alkanolamines can be used as initiators for the synthesis of polyethers; and some special diamines are also raw materials for the manufacture of diisocyanates. Dicarboxylic acids are generally used to manufacture polyester polyols.

Chain Extenders and Crosslinking Agents

In polyurethane material formulations, chain extenders or crosslinking agents are commonly used additives. Chain extenders refer to compounds containing two functional groups, such as diols, diamines, and ethanolamines, which form linear polymers through chain extension reactions; in the polyurethane industry, crosslinking agents generally refer to trifunctional and tetrafunctional compounds such as triols and tetraols, which cause polyurethanes to form a crosslinked network structure.

Chain extenders and crosslinking agents are used in various types of polyurethane materials, including cast non-foamed polyurethane elastomers, microporous polyurethane elastomers, RIM polyurethanes, thermoplastic polyurethane elastomers, polyurethane coatings, adhesives, high-resilience foams, and semi-rigid foams.

Chain extenders and crosslinking agents are small molecules that contribute to the hard segment content in polyurethane molecules. Under the premise of sufficient curing, the more chain extender is used, the more diisocyanate is needed, resulting in a higher hard segment content in the polyurethane, thus obtaining materials with high strength and higher hardness.

Chain extenders and crosslinking agents can be used in the one-step synthesis of polyurethanes (including prepolymers). Diamines, diols, or polyols used to cure prepolymers are also called curing agents.

Water is a special chain extender and curing agent; both hydrogen atoms of the water molecule react with isocyanate groups, acting as a difunctional chain extender. Moisture-curing polyurethane adhesives and coatings utilize moisture in the air for the curing reaction. Oligomeric polyols react with diisocyanates to form (hydroxyl-terminated or polyisocyanate-terminated) prepolymers or polyurethane elastomers. Because a small amount of diisocyanate is used, it is sometimes referred to as a chain extender or curing agent. Triisocyanates are commonly used as crosslinking agents or curing agents in two-component polyurethane coatings and polyurethane adhesives.

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