Original: Polyurethane polymers are formed through step-growth polymerization by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a catalyst.
Simplified: Polyurethane polymers are formed through step-growth polymerization. In this process, a monomer containing at least two isocyanate functional groups reacts with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a catalyst.