Thermoset polyurethane synthesis

By inclusion of a limited amount of water or alcohol in the synthesis, oligomers of this type can be made with controlled hydroxyl content. Such products are exemplified by Akzo Nobel s Fyrol 51 or Fyrol 58 flame retardants which are useful as reactive oligomers in thermosets. In resin-treated automotive air filters this type of product is chemically linked into the resin and resists leaching by water when the filters are cleaned. Fyrol 51 has also found utility in making flame-retarded polyurethanes and textile flnishes. 

Unsaturated low molecular weight (M between 1000 and 10000), often branched, used as macromonomers for synthesis of thermosets (polyester resins), or thermosetting materials by themselves (alkyd resins). They are prepared from several monomers, namely phthalic and maleic anhydrides, adipic acid, iso-phthalic acid, natural fatty acids or triglycerides, and a great variety of multifunctional alcohols. In a few special cases, they may be saturated and/or linear for use as macromonomers in the production of polyurethanes or other polymers. 

PUs can be both thermoplastic and thermosetting materials composed by HS and SS. Thermoplastic polyurethanes (TPU) are formed by linear polymer chains with functionality equal to two. This means that the SS, the polyol, is a diol and the HS, the isocyanate, is a diisocyanate. The thermodynamic incompatibility between the hard and the SSs as well as the NCO OH ratio, the synthesis procedure, etc. can generate a phase separation into the TPU. On the other hand, the thermosetting PUs are formed by polyols and/or isocyanates with functionalities higher than 2, with a NCO OH ratio higher than 1 or are obtained by using cross-linker agents. 

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