| http://www.w3.org/ns/prov#value | - Rigid polyurethane foams used as core materials are prepared by employing a polyether, such as a polypropylene glycol reacted with a diisocyanate in the presence of water as a blowing agent, and a catalyst (amines, such as a polyethanol polyamine, like diethanol tetramine, and metal salts, such as tin compounds, like dialkyl tin), so that the water reacts with the diisocyanate to cause cross linki
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