* Dow Chemical to spin off unit, merge it with Olin

* Q4 GDP at 2.2 pct, but corporate profits fall

* Fed Chair Janet Yellen to speak shortly before the closing bell

* Futures off: Dow 40 pts, S&P 3 pts, Nasdaq 8 pts (Updates prices, adds GDP data, comment)

By Rodrigo Campos

NEW YORK, March 27 (Reuters) – U.S. stocks were set to dip at the open on Friday, setting indexes up for a full week of daily declines, as the dollar index added to the previous session’s rebound ahead of a speech by Federal Reserve Chair Janet Yellen.

Yellen will speak on monetary policy at 3:45 p.m. EDT (1945 GMT) in San Francisco, and traders will keep an ear out for clues on the timing of the start of the tightening path at the Fed.

Equities have traded in lockstep with the U.S. currency of late ahead of the start of earnings season, as traders gauge how much the greenback’s strength will hurt corporations’ bottom lines.

“Yellen will be the big news of the day, certainly, so I don’t expect a lot of movement before that,” said Peter Jankovskis, co-chief investment officer at OakBrook Investments LLC in Lisle, Illinois.

“We’ll see how people interpret what she has to say.”

S&P 500 e-mini futures were down 3 points and fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract, indicated a slightly lower open. Dow Jones industrial average e-mini futures fell 40 points and Nasdaq 100 e-mini futures lost 8 points.

The final reading on gross domestic product for the last quarter of 2014 came in unchanged from the previous forecast, at a 2.2 percent rate of expansion. After-tax corporate profits fell at a 1.6 percent rate in the fourth quarter as a strong dollar dented the earnings of multinationals.

The University of Michigan final March consumer sentiment reading is due at 10 a.m. EDT (1400 GMT).

Dow Chemical shares jumped near 4 percent in premarket trading after it announced the spinoff of part of a unit that will then merge with Olin Corp. Olin shares soared 25 percent in light trading.

BlackBerry posted a fiscal fourth-quarter profit, its turnaround efforts beginning to gain traction. BlackBerry shares were up 5.6 percent in volatile premarket trading.

(Reporting by Rodrigo Campos; Editing by Chizu Nomiyama and Nick Zieminski)