An Introduction to PU chemistry

The name ‘Polyurethanes’ applies to a large number of polymers. These are big chain-like molecules with a high relative molecular weight. They are synthesised by polyfunctional isocyanates and reactive polyols in the presence of suitable catalysts and additives.
PU production used to be based on polyester polyols, but the introduction of polyether polyols resulted in economical production of flexible foams (mainly for furniture and bedding) and huge growth within the industry.
With the introduction of rigid PU foams, the insulation market opened a wealth of new opportunities.
Polyester and polyether polyols are used nowadays in rigid foams. We speak about PIR and PUR foams.
In PIR foams (Polyisocyanurate),  the proportion of MDI is higher than for PUR and instead of a polyether polyol a polyester derived polyol is used in the reaction. Catalysts and additives used in PIR formulations also differ from those used in PUR formulations. PIR closed-cell foams are mostly used as rigid thermal insulation foam where superior thermal and fire resistance properties are requested. The typical thermal conductivity value of PIR is 0.023 W/mK.
Today polyurethanes are recognised as extremely versatile materials and are widely used in lots of industries and applications.
With an extensive choice of polyols, isocyanates, chain extenders, blowing agents, additives etc., PU offers many different properties with varying stiffness, hardness and densities.
Polyurethane can be formulated into many different types of products:
  • Flexible foam
  • Rigid foam
  • CASE (Coating, Adhesive, Sealant, Elastomer)
  • Binder
  • RIM (Reaction Injection Moulding)
Future trends show that continuing research and development within the polyurethane industry will provide new capabilities, solutions and products for new applications.
Click on the tabs above for more information on the chemistry of MDI and TDI, key components used in the production of polyurethane.
See how PU is made.