Hey,
You cannot do B.A from polytechnic college. Polytechnic colleges only offer engineering courses or technical courses. For these courses, a candidate must have completed 10th standard with minimum required score.
Also, you won't be a graduate after diploma, you will be a junior engineer. For becoming a graduate in engineering, you will have to do B.Tech or B.E after diploma.
You can do B.A only after completion of 12th or equivalent examination from Universities offering Arts.

Hope this helps!

Yes, you can do B.A. after completion of your polytechnic degree. But you will just waste your time. When you are doing diploma in engineering, you can get lateral entry to regular B.Tech course and you can complete your graduation. If you complete your graduation degree, you will be able to get placed in top companies.