1. G.R. Petrella, Blowing reaction catalyst composition that provides cell opening of the resulting polyurethane foam, U.S. Patent 5,039,713 (1991), available from http://www.freepatentsonline.com/5039713.html.
2. D.C. Krueger, L.D. Christman, H.A. Rothacker, B.T. Lee, Rigid polyurethane foams containing lithium salts for energy absorbing applications, U.S. Patent 5,258,416 (1993), available from http://www.freepatentsonline.com/5258416.html.
3. Y. Tamano, M. Ishida, S. Okuzono, Amine catalyst for producing polyurethane and process for producing polyurethane, U.S. Patent 5,374,666 (1994), available from http://patft.uspto.gov/.
4. H. Seyanagi, I. Kaoru, K. Ogawa, T. Masui, K. Ono, Process for producing polyurethane foam, U.S. Patent 7,098,255 (2006), available from http://patft.uspto.gov/.
5. C. Beck, J. Wagner, H. Ehbing, Polyurethane foam, U.S. Pat. 20050043425 (2005), available from http://www.freepatentsonline.com/20050043425.html.