Aliphatic polyurethane optical endpoint detection windows and CMP polishing pads containing them

A chemical mechanical (CMP) polishing pad for polishing a substrate chosen from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate, the CMP polishing pad comprising one or more endpoint detection windows, the one or more endpoint detection windows being a polyurethane, the polyurethane has a UV cut-off at a wavelength of 325 nm or lower, and is a product of a reaction mixture of (A) from 30 to 56 wt. % of one or more cycloaliphatic diisocyanates or polyisocyanates with (B) from 43 to 69.9999 wt. % of a polyol mixture of (i) a polymeric diol having an average molecular weight of from 500 to 1,500 and (ii) a triol having an average molecular weight of from 120 to 320 in a weight ratio of (B)(i) polymeric diol to (B)(ii) triol ranging from 1.6:1 to 5.2:1, and (C) a catalyst chosen from a tin containing catalyst in the amount of from 0.00001 to 0.1 wt. % or an aliphatic amine catalyst in the amount of from 0.01 to 1 wt. %, all weight percent's based on the total solids weight of the reaction mixture, for reacting the reaction mixture of (A) and (B).