Gelatin has active cross linking sites that work with formalin or other hardeners. These are amine based. Other active sites which can be placed on polymers are -C=O CH2 C=O (this is hard to draw and explain). In any event, Poly Vinyl Alcohol by itself is difficult to harden and has no sites to peptize Silver Halide grains as they form.
Therefore, something else (Silane?) is helping Bill. I am curious as well.