US chemical giant DuPont plans to buy back up to $4 billion of its shares using the dividend expected from the spinoff of its Performance Chemicals division, which will trade in future as Chemours.

The new buyback, which will take over 12-18 months following the spin off, comes on top of an existing $5 billion program, the company said. DuPont has already bought back $2 billion of stock.

Under pressure from activist investor Nelson Peltz, who is calling for a breakup of DuPont to achieve savings of $4 billion, the Delaware-based group also widened its cost-reduction target by $300 million to at least $1.3 billion, which it expects to achieve by 2017.

DuPont has repeatedly highlighted the benefits of keeping its units together.

In last year's fourth-quarter, group operating profit of $4.01 per share was at the lower end of management's forecast of $4.00-4.10 per share, disappointing analysts. CEO Ellen Kulllman blamed the weaker performance in part on the strengthening dollar.

For 2015, Kullman has forecast earnings of $4 to $4.20 per share, which is below analysts' projections. Chief Financial Officer Nick Fanandakis said a weaker euro, reduced corn planting and lower prices for some chemicals would "more than offset growth in other segments" in the first quarter.