Method of preparing cyclodextrin-coated surfaces

DETAILED DESCRIPTION OF THE INVENTION The invention herein is based on several key discoveries.
One is that in the reaction of cyclodextrins with polyisocyanates, especially diisocyanates, the solubility characteristics of the reaction product varies with the molar ratio of diisocyanate to cyclodextrin.
In particular, at low values of this ratio the crosslinked product is soluble in both water and the dipolar aprotic solvent in which the homogeneous reaction is conducted.
As this ratio increases, i.
e.
, as the product becomes more highly crosslinked, the product becomes insoluble in water while maintaining its solubility in certain dipolar aprotic solvents.
With still further increases in the ratio the product becomes insoluble in both water as well as the dipolar aprotic solvents.
But it is important to note that there is a window, often a narrow one, where the crosslinked cyclodextrin is insoluble in water but soluble in the organic solvent used.
For the purposes of this invention, a suitable polyisocyanate crosslinked cyclodextrin resin has a water solubility at 25.
degree.
C.
of less than 200 ppm, but has a solubility at 25.
degree.
C.
in a dipolar aprotic solvent of at least 0.
1 weight percent.
The second important observation is that the crosslinked cyclodextrin formed in the aforementioned "window" adheres readily to virtually any surface, thereby providing a thin film of uniform thickness of a cyclodextrin containing polymer.
A consequence of this is that such a polyisocyanate crosslinked cyclodextrin resin may be deposited on any surface and may be almost literally painted onto the surface.
Consequently such a coated surface is easy to prepare with a uniform film thickness.
The coatings have good adhesive qualities and chemisorption is unnecessary for its binding.
Such coated surfaces have several distinct advantages over discrete particles of the resins themselves.
One advantage is the simplicity of the composition and its preparation, both of which lead to substantial reduction in cost and time of preparation