polyurethanes

Polyurethanes are a family of polymers formed by the reaction of di- or polyisocyanates with polyols, creating urethane linkages in the polymer backbone. The versatility of polyurethanes comes from the wide range of isocyanates and polyols that can be used, producing materials that are rigid or flexible, transparent or opaque, and with varying mechanical properties.

Commercial production primarily uses methylene diphenyl diisocyanate (MDI) or toluene diisocyanate (TDI) with polyols such as polyether or polyester polyols, often combined with chain extenders and blowing agents to form foams. The polymerization is a step-growth process, and materials may be prepared as prepolymers that are subsequently extended or cured to form the final network.

Polymers are widely categorized into rigid foams, flexible foams, elastomeric polyurethanes, coatings, adhesives, and sealants. Rigid foams are valued for thermal insulation and structural applications; flexible foams provide cushioning in furniture and bedding; elastomeric polyurethanes offer toughness and elasticity for components such as wheels, bushings, and seals; coatings, adhesives, and sealants provide surface protection, adhesion, and sealing performance. Formulations can also incorporate renewable polyols to reduce petroleum dependence.

Sustainability and safety considerations include the handling of isocyanates, which require proper ventilation and protective equipment. Environmental aspects cover blowing agents and waste streams, with recycling approaches ranging from mechanical recycling of foams to chemical recycling and energy recovery in some processes.