How hot does popcorn need to be before it pops?
Some kernels would pop, but generally speaking it would not work very well at all. A popcorn kernel pops because of the water trapped inside -- it is heated rapidly on the stove, and its expansion is rapid enough to produce explosive force. The oven would cause the water inside the kernels to heat more slowly. The shell of unpopped corn is not perfectly enclosed, so slow heating would allow the water vapor to harmlessly escape.