(Adds details from interview and background)
ZURICH, Sept 1 (Reuters) - Huntsman Chief Executive Peter Huntsman said shareholders in Clariant and his own company "almost without exception" support their planned merger after learning the rationale for the $20 billion deal, according to an interview published in Swiss newspaper Finanz und Wirtschaft.
"I have met with more Clariant shareholders than Huntsman shareholders since the transaction was announced earlier this year, and I do not have the impression Clariant shareholders oppose the deal," Huntsman, a son of the founder, said in the interview published on Friday.
Investors including Corvex's Keith Meister who own 10 percent of Swiss-listed Clariant shares oppose the combination of the chemicals groups and are seeking to convince shareholders to reject the merger.
Clariant has hired Goldman Sachs to help it keep the deal on track.
Shareholders at Huntsman and Clariant have to vote on the deal, with Clariant requiring 66 percent support for the transaction to go through and Huntsman a 50 percent majority.
In the Finanz und Wirtschaft interview, Huntsman predicted the merged company's earnings before interest, taxes, depreciation and amortisation (EBITDA) will hit 20 percent of annual sales in five years -- both have about 15 percent margins now -- with cashflow reaching more than 50 percent of EBITDA.
After the merger, HuntsmanClariant can grow at least twice as fast as global gross domestic product, he said, with the merged company rated at investment grade in less than five years.
Huntsman has a long-term rating of "BB" from Standard & Poor's, while Clariant has a "BBB-" rating. (Reporting by John Miller; Editing by Michael Shields)