DOVER, Del. — Dow Chemical and DuPont will attempt to merge in an all-stock deal that would create a colossal chemical producer worth $130 billion, before splitting into three separate companies. The deal announced Friday is being billed a merger of equals, to be called DowDuPont. The plan is to then split DowDuPont into three companies, one focused materials, one on agriculture and the last on specialty products. Dow CEO Andrew Liveris will become executive chairman of the newly formed DowDuPont board of directors.