| 摘要 |
PROBLEM TO BE SOLVED: To obtain a copolymer usable in a wider temperature range compared to the conventional technique and suited for use in drilling mud. SOLUTION: A water soluble copolymer is constituted with (A) 5-95 wt.% divalent structural unit derived from acrylamidopropenylmethylenesulfonic acid or its salt, (B) 1-45 wt.% divalent structural unit derived from an open chain N-vinylamide, (C) 1-45 wt.% divalent structural unit derived from a cyclic N- vinyl substituted amide, and optionally, (D) 0-50 wt.% additional another comonomer selected from the group consisting of acrylamide, acrylic acid and acrylonitrile (provided that the sum of components (A) to (C) and, if necessary, component (D) is 100 wt.%).
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