CMP polishing pad with window having transparency at low wavelengths and material useful in such window

A polishing pad useful in chemical mechanical polishing comprising

• a polishing portion having a top polishing surface and a polishing material,
• an opening through the polishing pad, and
• a transparent window within the opening in the polishing pad, the transparent window being secured to the polishing pad wherein the window comprises a polyurethane composition formed by reacting a polymeric polyol, a polyisocyanate, and a curing agent comprising three or more hydroxyl groups forming hard segments, the reacting being in the presence of a hard segment inhibitor for reducing size of hard segment domains wherein the hard segment inhibitor is a sulfate, sulfonate or phosphate ester of a polyalkylene oxide and wherein the polyurethane composition is an amorphous mixture of hard segments in a soft segments matrix and the polyurethane composition is free of carbon-carbon double bonds and wherein the transparent window has a Shore D Hardness no greater than 75.