1. H. Aoyama, US Patent 5 516 951, 1996
2. W.M. Lamberts, Proc. Polyurethanes World Congress, 24–26 September, 1991, pp. 734–739
3. N. Lui, A. Marhold, D. Bielefeldt, US Patent 5 523 497, 1996
4. N. Lui, A. Marhold, D. Bielefeldt, US Patent 5 315 047, 1994
5. E. Seki, H. Aoyama, T. Nakada, S. Koyama, US Patent 5 364 991, 1994