SAO PAULO, May 6 (Reuters) - Abu Dhabi National Oil Company (ADNOC) has terminated talks to buy a controlling stake in Braskem, the Brazilian petrochemical producer said on Monday, driving its shares down almost 15%.

ADNOC presented a non-binding offer in November for the stake held by conglomerate Novonor in Braskem, with an implied price of 37.29 reais per share for an equity value of 10.5 billion reais ($2.1 billion).

However, ADNOC has now informed Novonor about its decision not to go forward with the negotiations, Braskem said in a securities filing.

Braskem's Sao Paulo-traded shares dropped 14.75% to their lowest level since February, the biggest faller on Brazil's benchmark Bovespa index, which was up 0.4%.

Novonor, formerly known as Odebrecht, holds a 38.3% controlling stake in the petrochemical firm, which it has long been looking to sell as part of a broader restructuring.

State-run oil giant Petrobras is also a major Braskem shareholder.

Brazil's Unipar Carbocloro and J&F were among other bidders for Braskem.

($1 = 5.0839 reais) (Reporting by Andre Romani; editing by Gabriel Araujo, Kirsten Donovan)