Chemical mechanical polishing pad with endpoint detection window

A chemical mechanical polishing pad, comprising:

• a polishing layer having a polishing surface;
• and,
• an endpoint detection window;
• wherein the endpoint detection window comprises a reaction product of ingredients, comprising:
• (i) an isocyanate terminated urethane prepolymer having 5.5 to 9.5 wt % unreacted NCO groups, wherein the isocyanate terminated urethane prepolymer is a reaction product of ingredients comprising:
• (a) an aromatic polyfunctional isocyanate, wherein the aromatic polyfunctional isocyanate is selected from the group consisting of 2,4-toluene diisocyanate;
• 2,6-toluene diisocyanate;
• 4,4′-diphenylmethane diisocyanate;
• naphthalene-1,5-diisocyanate;
• tolidine diisocyanate;
• para-phenylene diisocyanate;
• xylylene diisocyanate;
• and mixtures thereof;
• and,
• (b) a prepolymer polyol, wherein the prepolymer polyol is selected from the group consisting of polyether polyols;
• polycarbonate polyols;
• polyester polyols;
• polycaprolactone polyols;
• mixtures thereof;
• and, mixtures thereof with one or more low molecular weight polyols selected from the group consisting of ethylene glycol;
• 1,2-propylene glycol;
• 1,3-propylene glycol;
• 1,2-butanediol;
• 1,3-butanediol;
• 2-methyl-1,3-propanediol;
• 1,4-butanediol;
• neopentyl glycol;
• 1,5-pentanediol;
• 3-methyl-1,5-pentanediol;
• 1,6-hexanediol;
• diethylene glycol;
• dipropylene glycol;
• and, tripropylene glycol;
• and,
• (ii) a curative system, comprising:
• 0 to 70 wt % of a difunctional curative;
• and,
• 30 to 100 wt % of an amine initiated polyol curative having two to four nitrogen atoms per molecule and an average of three to six hydroxyl groups per molecule;
• wherein the curative system contains <1 wt % of a high molecular weight polyol curative having a number average molecular weight, MN, of 2,000 to 100,000 and an average of 3 to 10 hydroxyl groups per molecule;
• and,
• wherein the endpoint detection window exhibits a double pass transmission at 400 nm, DPT400, of 25 to 100%;
• wherein the endpoint detection window exhibits a double pass transmission at 800 nm, DPT800, of 40 to 100%, and, wherein the endpoint detection window also exhibits a double pass transmission delta between 800 nm and 400 nm, ΔDPT800-400, of <30%.