1. U.S. Pat. 2 317 765 (1943) to W.F. Hester (Rohm & Haas Co.).
2. Belg. Pat. 617 407 (1962) to C.B. Lyon, J.W. Nemec and V.H. Unger (Rohm & Haas Co.).
3. Belg. Pat. 617 408 (1962) to J.W. Nemec, V.H. Unger and C.B. Lyon (Rohm & Haas Co.).
4. U.S. Pat. 3 379 610 (1968) to C.B. Lyon, J.W. Nemec and V.H. Unger (Rohm & Haas Co.).