Abstract: An improved polyurethane is prepared by reacting a diol, an organic diisocyanate and a carboxylic acid with a critical selection of the amount of water in the reaction mixture. The polyurethane has improved adhesion, hydrophilicty and strength. The polymer has improved feel, and washability. Solutions of the polymer have low viscosity in aqueous solutions.

Abstract: A lens structure without spherical aberration, formed by a first (S) and second (S') curved surface of transparent material facing one towards the other, wherein the first surface (S) has a configuration chosen between a first and second sub-configuration, the first sub-configuration being obtained by applying the sine of the limit refraction angle (i') of the transparent material, the derived value being the focus location of the first configuration on a horizontal axis (XX'), and the second sub-configuration being obtained by applying the sine of the limit refraction angle (i') of the transparent material, the derived value being the focus location of the first configuration on a horizontal axis (XX'), and the second sub-configuration being obtained by applying the sine of the limit refraction angle (I') of the transparent material for vertex (v) positioning of the second configuration on the horizontal axis (XX').