Is it ok to use plastic containers to bake in an electric oven?
Here is a list of common plastics found in kitchen containers. You will find this information on the bottom of the container, in a triangle with a number inside.

While some plastics used in microwavable applications appear to have a high melting point, PET for instance melts at 510ºF, please remember that the material will soften, weaken and otherwise degrade long before actually melting into liquid. Other plastics labeled microwave safe, like HDPE, melts at a mere 265ºF! While microwave safe plastics may have a relatively high short term temperature resistance, sustained temperature tolerance, as in leaving it in an oven for baking, is much lower.

Silicone bakeware, by contrast, has a melting point of 935ºF, but is only rated for use at sustained temperatures no greater than 675ºF. Above that point, and the material will soften, warp and degrade. Thermoplastics have a much lower melting point, and it can be expected that their sustained temperature resistance is likewise much lower, to the point where using them as bakeware is unadvisable.