Randy Woelfel resigned as CEO of Canada's Nova Chemicals on May 1. His departure was announced shortly before the company's first-quarter earnings conference call.

In a statement the Canadian chemical producer said its board of directors and chief executive had been unable to agree on mutually satisfactory contract renewal terms and that the resignation was not due to differences of opinion about Nova's overall business strategy.

Todd Karran, the company's chief financial officer, has been appointed acting CEO to serve until a permanent chief executive has been found. Woelfel had headed Nova since 2009.