Can anyone think of a natural polymer that is ethanol soluble and water insoluble?

Ethyl cellulose is not natural.

Hello. 

As stated by the previous answer, ethyl cellulose isn't a natural polymer though its synthesis involves cellulose (obviously). Are you asking the question because you want to find a natural alternative to ethyl cellulose?

I can think of some natural polymers that are water-insoluble. Gutta-percha, lignins, cellulose itself of course, shellac (in some pH ranges)... but a lot of these will be ethanol-insoluble. Shellac might  be an interesting choice, depending on what you want it for.

 

 

I've read that some types of cab [ cellulose acetate butyrate ] with a high level of butyryl can be soluble in alcohol. Not actually a natural resin but made with cellulose so it's pretty close. For actual natural resin ,Shellac of course is soluble in ethanol alcohol. I think some types of copal also are, they dissolve quicker than the shellac. Also the modified Rosin    Fumaric Resin [ not sure if you would consider it natural] it' seems pretty close to me, it is soluble in alcohol and dissolves super quick in my experience.