DowDuPont Inc (DWDP.N) chief Andrew Liveris will step down on April 1, making good on an earlier promise to retire as the company named existing managers to head its materials science unit when it is spun off as Dow next year.

Liveris, a 40-year industry veteran, is exiting after piloting the merger of the United States' two largest chemical producers - Dupont and Dow - in a US$130 billion deal last year. That paved the way for the new firm to be divided into three separate businesses.

The materials science unit, which accounts for most legacy Dow businesses and will retain the Dow brand, produces chemicals that go into making everything from cosmetics to packaging material to brake fluids.

It will be headed by the division's current chief operating officer Jim Fitterling and his chief financial officerHoward Ungerleider, both Dow veterans who have worked extensively on the merger.

The company has not announced who will lead the two other units, a specialty plastics and polymers business which will carry the DuPont name, and agriculture-focussed Corteva Agriscience.

"The plans announced today (are) the result of many years of working on a succession pipeline," Liveris told Reuters, adding that he made up his mind to leave during the Christmas holidays.

"Jim and Howard have been valued members of Dow's and my most senior leadership team and have each played a pivotal role in developing and executing Dow's market-driven strategy."

63-year-old Liveris spent more than forty years at Dow Chemical - more than a decade of those as CEO - before taking over as executive chairman at the joint company.

He will stay on as director until July 1, after which he will retire, in line with an initial announcement two years ago.

Liveris did not say what he plans to do after retirement but said it could be something in the "intersection of business and policy."

He was named head of President Trump's Manufacturing Council before its dissolution last year. Before that, Liveris had served as co-chair of President Obama's Advanced Manufacturing Partnership steering committee.

DowDuPont shares were trading at US$72.40 Monday morning, little changed from Friday.