I don't know of any specific films prior to Pillow Talk that used split screen, but I feel like I've seen something older than that... As for articles on the subject, there was a flurry of interest in the mid-60s after the New York World's Fair films and popular use like "The Thomas Crown Affair". I'm sure there has also been much written about DePalma's use of split-screen effect.
There is also a relatively obscure (and not very good) film called "Wicked Wicked" released by MGM in the early 70s shot entirely in Split Screen (They called it "Duo-Vision"). It's a slasher movie, with one half of the screen given over entirely to the killer's point of view..... It's probably worth a look.
Robert Hunt

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