Polyurethane is a class of polymers containing ammonia ester type repeating structural units in the macromolecular chain, the full name of polyurethane, referred to as PU or PUR. PU is a product of the reaction of polyisocyanate with polyether or polyvinegar polyols at a fixed ratio, usually referring to a class of polymers containing specific groups. Because of the different types and compositions of the two synthetic monomers, they can be divided into linear thermoplastic PU and thermosetting PU. PU can be divided into two categories of elastomer and foam, which has been dominated by foam, and the current development rate of elastomer is very rapid, and its use is more and more widely.
Polyurethane is mainly composed of isocyanates and polyols.
The main varieties of isocyanate are: toluene diisocyanate, which can be used for soft to hard foam products. Diphenylmethane diisocyanate, used in semi-hard and rigid foam products. Polymethylene p-phenyl polyisocyanate can be used for thermosetting rigid foam, mixing and casting PU products.
Polyols - : Generally do not refer to the direct use of polyols, but use oligomers containing hydroxyl groups at the end, which are divided into polyether polyols and polyester polyols. Polyether polyols are formed by ring-opening polymerization of polyols, polyamines or other organic compounds containing active hydrogen with oxidized olefin. Polyether polyols have the advantages of low viscosity and high elasticity, and are often used in soft PU. Polyester polyol is formed by polycondensation reaction of organic polyacid and polyol, linear polyester polyol synthesized by dibasic acid and dibasic alcohol is mainly used for soft PU, branched polyvinegar polyol synthesized by dibasic acid and ternary alcohol is mainly used for hard PU. The viscosity of polyester polyol is large, not as widely used as polyether type, often used in insulation, oil resistance, heat resistance, dimensional stability and high mechanical properties of PU products.
Additives are mainly divided into catalysts, foaming machines, foam stabilizers and crosslinkers. The catalytic action is to accelerate the polymerization reaction, there are two types of amines and tin. Foaming agents are used for foaming products. Foam stabilizer used for foam products, commonly water-soluble polyether siloxane. Glycerol, trimethylol propane and pentaerythritol were commonly used as crosslinking agents and chain extenders.