Think of Pavlov's dogs...

Your weekend rides = fun and your commute = not so fun(?)

You've come to associate that "not so fun" feeling with riding your road bike correct? If that so, it's not so far fetched. Will buying a completely separate bike for commuting help change this association? Maybe. Datajunkie has a good point, "You're going about it wrong". Rethink your commute, make it fun. It may help with your recreational rides