Well, the Fuji FP100C originally mentioned is a colour peel apart film. Substituting the Polaroid Positive/Negative B/W film would give very different results. I understand what the OP wants to achieve, though it is not an easy manipulation, even using films that Polaroid recommends for that.
Getting a transparency from any Polaroid film is something very different. It was possible with the old SX-70 TimeZero instant film. That method involved cutting the edges of the print soon after processing, then carefully washing and rubbing away the backing chemicals. The result was sort of a transparency, though with obvious rub marks and degradation . . . sometimes cool looking stuff, but not a perfect transparency. Supposedly the 600 Instant films can undergo the same manipulation and sort of work, though the chemicals adhere better; the result is more deteriorated and degradation look to the final transparency.
In silkscreening for making T-Shirt printing, there is a reducing agent. That sort of chemical might work for making paper negatives, but I have never tried something like that. It is probably the only chemical I could think of that might work, though I would not want to attempt it (I don't really like this chemical).
Ciao!
Gordon Moat
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