I'm not exactly sure how the physics degree would help you as a chem e. Perhaps someone with more experience in the physics field would be able to answer that for you. But if you want to do research within physics then obviously getting a graduate degree in physics is the way to go. I am also interested in both paths and decided nuclear engineering was kind of a middleground that involved a little of both fields. In my opinion, you should try make a definite decision on what you want to do. If you want to work solely as a chemical engineer I don't see the physics degree helping very much and getting a graduate degree in it might be a waste of time if you end up working as a chem e in the end. However, as I stated before, this could be wrong and someone with more knowledge of physics careers might be able to offer better advice. Maybe someone knows of another field, other than nuclear e, that you will have to utilize everything from both a physics and chem e degree.