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.The polyurethanes are made by reactinga) 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; withb) (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.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.