If you're just milling a slot in the acrylic, try a bit of taper.
Very smooth surfaces help too.

If it works have your tool grinder modify an appropriate end
mill so you can bang out the slots.

Another ploy is to make the mold in pieces, fastened together
for the pour.

Teflon molds? Not much sticks to that stuff...Pricey, though.

 Jack
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