A copolymer of 2-acrylamido-2methyl propane sulfonate and acrylamide. AMPS polymers are highly water-soluble anionic additives designed for high-salinity and high-temperature water-mud applications. (Alkyl-substituted acrylamide can be used instead of ordinary acrylamide, which lessens its vulnerability to hydrolysis at high temperature and high pH. ) Polymers from 0. 75 to 1. 5 MM molecular weight are suggested for fluid-loss control in these difficult muds.

Reference:
Perricone AC, Enright DP and Lucas JM: "Vinyl Sulfonate Copolymers for High-Temperature Filtration Control of Water-Base Muds," SPE Drilling Engineering 1, no. 5 (October 1986): 358-364.