CMP pad having polishing layer of low specific gravity

A polishing pad for chemical mechanical polishing comprising:

• a polishing layer that comprises a polyurethane matrix that is the reaction product of an isocyanate terminated oligomer or polymer, with a curative blend comprising a mono-aromatic polyamine curative wherein the mono-aromatic polyamine curative comprises dimethylthiotoulenediamine, monomethylthiotoulenediamine, or both and a polyamine curative having two or more aromatic rings wherein the polyamine curative having two or more aromatic rings comprises 4,4′-methylene-bis-o-chloroaniline, 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) or both and the molar ratio of the polyamine curative having two or more aromatic rings to the mono-aromatic polyamine curative is 25:75 to 75:25, wherein the polyurethane matrix has polyurea-polyurethane hard segment domains and soft segment domains wherein pores are present in the polyurethane matrix, such pores being formed by expansion of pre-expanded fluid filled polymeric microspheres such expansion occurring during reaction of the isocyanate terminated oligomer or polymer with the mono-aromatic amine curative and the polyamine curative, wherein the pores have a unimodal size distribution and wherein the polishing layer has a specific gravity of less than 0.70 g/cm3.