There are no polar bears in Antarctica because polar bears live in the North Pole, or the Arctic. Some people have suggested moving polar bears to Antarctica because they are currently listed as "vulnerable" by the ICUN, and with rising temperatures in the North Pole, the polar bear is on its way to becoming endangered.
However, it would not benefit the native species to move polar bear populations to Antarctica. Most of the time when non-native species are introduced to a new ecosystem, they destroy the ecosystem and disrupt the natural biodiversity present there. For now, the polar bears will stay in their native Arctic lands and the penguins will stay in Antarctica.