Large Russian corporations frequently employ former high-ranking European politicians to utilise their ties and influence.
Ex-German chancellor Gerhard Schroeder is the chairman of the shareholders' committee at Nord Stream's operating company, while Russian energy giant Rosneft earlier this year appointed former Austrian foreign minister Karin Kneissl to its board.
The Kremlin has said that Fillon, who served as premier under Nicolas Sarkozy from 2007-2012, has had "rather good relations" with President Vladimir Putin.
Privately owned Sibur is the largest petrochemicals producer in eastern Europe. It has long planned an initial public offering.
Its largest shareholders are Leonid Mikhelson, the head of, and a major stakeholder in, Russia's largest liquefied natural gas producer Novatek, and businessman Gennady Timchenko, a close ally of Putin.
(Reporting by Vladimir Soldatkin; Editing by Kirsten Donovan)
