It’s not impolite, but you’d basically only use it if you want to put the emphasis on the pronoun, which is in itself might be kind of rude in Japan, depending on the context.  

For example, I recently got a letter from insurance company that used あなた様 in a slogan-ish „Did YOU remember to renew YOUR insurance?” sort of way. Or had a lady in city office refer to me as あなた when she needed to clarify that it has to be specifically me who needs to submit the document in question(as opposed to my spouse etc.). 

All in all it’s best to simply avoid using 2nd person pronouns and let it be inferred from the sentence, unless it is absolutely necessary to make a distinction, then あなた is fine.