Polyurethanes (PU), the polymerization product of polyisocyanates and polyols (polyester or polyether polyols), are made using two basically different technologies. In the “one shot” method, polyisocyanate, polyol, additives and chain extenders are simply mixed in a mixing head and applied.
In the pre-polymer system there are two separate reaction steps. The first step is the reaction of one equivalent of polyol with up to two equivalents of isocyanate to yield an isocyanate-terminated pre-polymer. The final polyurethane is then formed by the reaction of the pre-polymer with a small bifunctional molecule containing active hydrogens - the so-called chain extender or curing agent. The chain extender links the pre-polymer molecules together and hence increases their molecular weight to form a complete polymer network.
The chain extender has a direct influence on the distribution of both hard and soft segments in the polyurethane polymer. The degree of crystallinity and crosslinking are also affected, depending on the structure of the chain extender and whether it is amino- or hydroxyl-functional.
DYTEK® A amine (MPMD), DYTEK® EP diamine (DAMP) and DYTEK® DCH-99 amine are used as chain extenders in a wide range of PU systems including coatings, adhesives, and elastomers. These specialty amines can help you to formulate new and innovative systems.
Another application of INVISTA DYTEK® amines is their use as isocyanate precursors. DYTEK® HMD (Hexamethylenediamine) is widely used in this application, particularly for the formulation of coatings, while DYTEK® A amine expands the availability of unique isocyanate monomers and imparts unique properties to elastomers and sealants.