A director may or may not have executive powers
A chairman would although is unlikely to be coercive about it
A director may or may not sit on the board
A chairman would
A director is more likely to be hands on
A chairman will spend his time into strategy, lobbying, networking, golf, that kind of thing
The chairman would round up, direct and facilitate his board of directors
Unless he is an Alan Sugar who completely disproves all of my points above, but then he is a glorified barrowboy so what do you expect (JOKE!!)