| abstract |
The present invention teaches a new process to produce novel, hard, optically clear, impact-resistant polyurethane polymers that are characterized by excellent thermo mechanical properties and chemical resistance, and the polymers made as a result of such a process. n The polyurethanes are made by reacting n a) a prepolymer made by reacting a polyisocyanate with a primary amine-terminated polyether with an amine functionality of about 2 and a molecular weight of >1000, and in which the free —NCO content of the resulting prepolymer is >18% by weight; with n b) (i) a polyol having an average hydroxyl functionality greater than or equal to 2 and an average hydroxyl equivalent weight of from about 300 to about 1,000, and (ii) a curing agent that has isocyanate reactive groups, a functionality of 2 to 3 and a molecular weight of <400. n More preferably the prepolymer is made by reacting a cycloaliphatic polyisocyanate with a primary amine-terminated polyether diamine of 2000 to about 2500 molecular weight, the polyol is either a polyester polyol triol with a molecular weight of between about 540 and 900, or a polyether glycol with a molecular weight of between about 650 and 2000, or a polyester polyol diol with a molecular weight of up to 2,000, and the curing agent is either dianhydrohexitol, an aromatic diamine, an aromatic ring containing diol or a cyclohexanedimethanol. |