1. J.K. Smid et al., Eur. patent 0102,118, 1982.
2. J.K. Smid et al., Eur. patent 0219,893, 1985.
3. Sakamoto et al., United States patent 5919,749A, 1999.
4. H. Fuzuki, K. Isobe, J. Smiel, Proceedings of 4th world surfactants Congress (I), Barcelona, 1996, pp. 227–237.