Delaware-based DuPont (E.I.) De Nemours&Co. announced that it has signed a definitive agreement with The Dow Chemical Co. under which both companies will combine in an all-stock merger. We are placing our ratings, including our 'A-' corporate credit rating, on DuPont on CreditWatch with negative implications. We will resolve the CreditWatch placement when further information is available or when the transaction closes, which we expect will occur in the second half of 2016. NEW YORK (Standard&Poor's) Dec. 11, 2015--Standard&Poor's Ratings Services said today it placed its 'A-' corporate credit rating on DuPont on CreditWatch with negative implications, indicating we could lower the ratings once we complete our review. We also placed our issue-level ratings