What polymer can be dissolved in ethanol and is insoluble in water?
As a preface, I'm not sure what the exact solubility levels are, so this answer is qualitative.  Hopefully someone else can improve upon it or suggest something better, but for now:



Poly(1,2butylene glycol) (PBG) of moderate molar mass (Mn ~1000) is soluble in ethanol but sparingly soluble in water. Most solids will wind up being soluble in water if they're soluble in ethanol, owing to the two solvents' similar intermollecular forces but water's smaller size and greater overall solvent strength. This said, materials with the ethyleneoxy- repeating unit like Polyethyleneglycol (PEG), Poly(1,2butylene glycol) (PBG), or crown ethers have enhanced solubility in ethanol due to ethanol's ability to line up along the backbone of the polymer. Meanwhile, the ethyl pendant group hanging off the backbone of Poly(1,2butylene glycol) strongly decreases water solubility. The end of the ethyl group is far enough away from the oxygen that it's completely non-polar and the shape winds up causing something called clathrate formation in the water. 

This polymer is mostly used as a Solgel or a coating. It could also be used for chelating some metal salts in solution. However, it would make a rather terrible structural polymer.