Recent Developments in Polyurethane Coatings Using Reactive Halogen-Free Flame Retardant Oligomeric Phosphonate Compounds

摘要

Polyurethane (PU) coatings have an established place in the coating industry. In some applications, they dominate the market because they combine outstanding resistance to solvents and chemicals with good weather stability. Oligomeric phosphonates form a class of environmentally friendly flame-retardant additives. They are soluble in most oxygenated solvents and halogenated solvents but show poor solubility in hydrocarbon solvents. These phosphonate oligomers are difunctional and have phenolic hydroxyl groups available to participate in the reaction with isocyanates. This paper reports on the effect of various metal catalysts on the reaction between the phosphonate oligomer and isocyanate and between a mixture of the oligomer and a polyol and isocyanate in dimethyl formamide (DMF). The results show that bismuth carboxylate and dimethyltin mercaptide are effective catalysts for the phosphonate oligomers. As part of the polyurethane backbone, the phosphonate oligomers will not leach out of the coating during the product life cycle.