Chemical giant DuPont Co on Wednesday offered to buy all the shares of its Canadian unit that it doesn't already own for C$1.4 billion as part of its plan to separate its textiles and interiors business. The Delaware-based company, which currently owns 76 per cent of DuPont Canada Inc, said in a statement is offering C$21 in cash for each Class A common share not owned by DuPont or its affiliates.