* Dow Chemical to spin off unit, merge it with Olin
* Fed Chair Janet Yellen to speak shortly before the closing bell
* Futures off: Dow 23 pts, S&P 2 pts, Nasdaq 4 pts
NEW YORK, March 27 (Reuters) - U.S. stock index futures dipped 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 from Federal Reserve Chair Janet Yellen.
* Yellen will speak on monetary policy at the San Francisco Fed at 3:45 p.m. EDT (1945 GMT).
* Equities have traded in lock step 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.
* Dow Chemical shares jumped near 8 percent in premarket trading after it announced the spinoff of part of a unit which will then merge with Olin Corp. Olin shares gained 4.8 percent in light trading.
* The final reading on gross domestic product for the last quarter of 2014 is expected at 8:30 a.m. EDT (1230 GMT), with the headline number expected to rise to 2.4 percent from 2.2 percent. The University of Michigan final March consumer sentiment reading is due at 10 a.m. (1400 GMT).
* BlackBerry posted a fiscal fourth-quarter profit, its turnaround efforts beginning to gain traction. Shares edged up before being halted prior to the earnings announcement. BlackBerry shares were down 2 percent in premarket trading.
Futures snapshot at 7:25 a.m. (1125 GMT):
* S&P 500 e-minis were down 2 points, or 0.1 percent, with 127,084 contracts changing hands.
* Nasdaq 100 e-minis were down 3.75 points, or 0.09 percent, in volume of 22,732 contracts.
* Dow e-minis were down 23 points, or 0.13 percent, with 25,047 contracts changing hands. (Reporting by Rodrigo Campos; Editing by Chizu Nomiyama)