When a polyaddition reaction occurs between a diisocyanate and one or more diols in a specific way, it produces TPU. The three basic raw materials required to produce a TPU are:
A polyol or long-chain diol
A chain extender or short-chain diol
A diisocyanate
It is a linear segmented block copolymer composed of soft and hard segments.
Soft Segment (polyether or polyester): It is built out of a polyol and an isocyanate. Provides flexibility and the elastomeric character of a TPU.
Hard Segment (aromatic or aliphatic): It is constructed from a chain extender and isocyanate. This gives TPU its toughness and physical performance properties.
Aromatic TPUs - based on isocyanates such as MDI
Aliphatic TPUs - based on isocyanates like H12 MDI, HDI, and IPDI
Molecular Structure of Thermoplastic Polyurethanes