* Buechner's takeover defense alienated some investors
* CEO's departure not seen igniting new PPG bid
* Analysts say board, not just Buechner, opposed merger
* Vanlancker has to deliver on performance promises (Adds analysts saying PPG unlikely to bid again soon)
AMSTERDAM, July 19 (Reuters) - The chief executive of Akzo Nobel, Ton Buechner, has stepped down for health reasons, leaving his successor to deliver the higher sales and margins promised when the Dutch paintmaker fended off a U.S. takeover attempt this year.
Chemicals division chief Thierry Vanlancker, 52, who joined in 2016, replaces Buechner, who repelled a 26.3 billion euro ($30.35 billion) bid by U.S. rival PPG Industries with promises to produce better investor returns alone.
A chunk of the Dutch firm's shareholders, including hedge fund Elliott Advisors, were open to a PPG buyout and frustrated by Buechner's defense.
PPG cannot swiftly launch a new bid after the change of CEO as Dutch market rules mean it must wait until November at the earliest. PPG may also be reluctant to try again as its bid was equally opposed by Akzo Chairman Antony Burgmans, who remains.
Akzo shares traded flat at 77.96 euros in mid-morning trade.
Vanlancker, a Belgian, now has to deliver the stronger sales growth and margin improvements that Buechner and Burgmans promised in their struggle to avoid a merger. Analysts say those targets will be tough to achieve.
In his resignation statement, Buechner said: "For me this was an extraordinarily difficult decision to make but my focus must now be on my health."
Burgmans declined to elaborate on details of Buechner's illness, saying he regretted "only that he has decided to step down."
Buechner "felt that if he continued to subject himself to the pressures of his office, that would endanger his health," Burgmans told reporters on a conference call.
Buechner told Akzo's board about his decision on Tuesday, Burgmans said.
Vanlancker was previously identified as the person who would take Buechner's job as part of emergency contingency planning.
In his current post, Vanlancker was expected to oversee the sale or initial public offering (IPO) of Akzo's specialty chemicals division. Vanlancker previously worked for Chemours, which was spun off from DuPont in 2015.
Buechner's surprise announcement means his tenure at Akzo Nobel has ended almost as it began.
In September 2012, a half year after he took the top job, Buechner stepped down on his doctor's advice, suffering from what the company described as "over-tiredness." He resumed work in December the same year.
Buechner's tenure was mostly regarded as successful.
"Buechner has been responsible for overseeing the successful transformation of the business, including portfolio reshaping ..., de-risking of the pension funds, cutting costs and driving efficiency gains that have raised both margins and returns," Morgan Stanley analyst wrote in a note.
But the firm faced a minor shareholder rebellion after it rejected talks with PPG, leading to a shareholder lawsuit still in progress seeking to have Burgmans ousted.
Faced with opposition from Akzo's board, many employees and Dutch politicians, PPG walked away from its bid for Akzo on June 1.
Baader Helvea analysts said changing the CEO was "neither an indication that a renewed PPG bid with a higher success chance might occur nor that the activist investors were successful."
Repeating a "sell" rating, they said Akzo Nobel's supervisory board was the main obstacle to a merger and said the company's operations have likely been suffering from higher raw material prices for key paint ingredients.
Akzo reports second quarter earnings July 25.
($1 = 0.8666 euros) (Reporting by Toby Sterling; Editing by Edmund Blair)