Syntactic polyurethane elastomers for use in subsea pipeline insulation

A process for producing a substrate having an applied syntactic polyurethane elastomer, comprising the steps of

• a) forming a first section of syntactic polyurethane elastomer on at least a portion of the substrate by (i) applying a first reaction mixture containing one or more polyether polyols including at least one polymer polyol having a continuous phase of a liquid polyether polyol having a hydroxyl equivalent weight of at least 800 and dispersed polymer particles, the dispersed polymer particles constituting 1 to 50 wt. % of the combined weight of the particles and all polyether polyol(s) in the reaction mixture, 5 to 50 weight percent of microspheres based on the total weight of the reaction mixture, 1 to 30 parts by weight of a hydroxyl-terminated chain extender per 100 parts by weight of the polyether polyol(s), an aromatic polyisocyanate in amount to provide an isocyanate index of 80 to 130, 0.10 to 0.25 wt. % based on the combined weight of all components of the reaction mixture except the aromatic polyisocyanate of a β-diketone compound, and a zinc carboxylate catalyst to at least a portion of the substrate, wherein the first reaction mixture is devoid of mercury compounds, and (ii) partially curing the first reaction mixture to maintain its shape to form the first section of syntactic polyurethane elastomer, and then
• b) forming a second section of syntactic polyurethane elastomer on at least a portion of the substrate by (i) applying a second reaction mixture containing one or more polyether polyols including at least one polymer polyol having a continuous phase of a liquid polyether polyol having a hydroxyl equivalent weight of at least 800 and dispersed polymer particles, the dispersed polymer particles constituting 1 to 50 wt. % of the combined the weight of particles and all polyether polyol(s) in the reaction mixture, 5 to 50 weight percent of microspheres based on the total weight of the reaction mixture, 1 to 30 parts by weight of a hydroxyl-terminated chain extender per 100 parts by weight of the polyether polyol(s), an aromatic polyisocyanate in amount to provide an isocyanate index of 80 to 130, 0.10 to 0.25 wt. % based on the combined weight of all components of the reaction mixture except the aromatic polyisocyanate of a β-diketone compound, and a zinc carboxylate catalyst to at least a portion of the substrate and in contact with the first section of syntactic polyurethane elastomer to form at least one bondline between the first section of syntactic polyurethane elastomer and the second reaction mixture, wherein the second reaction mixture is devoid of mercury compounds, and (ii) at least partially curing the second reaction mixture to form the second section of syntactic polyurethane elastomer adherent to the first section of syntactic polyurethane elastomer, wherein the bondline has a bond strength of at least 8.0 MPa, as measured according to ASTM D638.