Cold flow of glassy polymers. III. Temperature dependence of yield elongation in BPA polycarbonate

A definition of “free” or maximum unoccupied volume, f = 1 — da/dc, is presented where da and da are the densities of the amorphous and ideally crystalline phases of a glassy amorphous polymer. This definition was combined with the well-known hypothesis that drawing a glassy polymer introduces free volume. With the further postulate that the maximum unoccupied volume in a polymer drawn to the yield point at a temperature T is the same as in a polymer at a temperature T, just where the yield disappears, we were able to calculate elongations at yield of BPA polycarbonate from — 50 to 150[ddot]C, and for polyethylene terephthalate at 20[ddot]C, which agreed reasonably well with experiment.