The deal to combine two of the biggest and oldest U.S. chemical producers is a prelude to an eventual split-up of the combined company into three discrete businesses, Dow and DuPont said on Friday. Excluding preferred shares, existing shareholders of Dow and DuPont will each own about 50 percent of the combined company, to be called DowDuPont. DuPont Chief Executive Ed Breen will be CEO of the new company, and Dow Chemical CEO Andrew Liveris will be executive chairman.