The majority of plastics can withstand microwave radiation and won’t break down nor melt. If you are buying commercial products, you might be able to find “microwave safe” symbols on them, which I think look like three squigly lines. Essentially, if you’re buying plastics that look like they were designed for storing food, then they are microwave safe.
Generally, for a plastic to be safe in a microwave it can’t react with the food, leach out components in the food, or decompose. A lot of storage containers such as plastic butter containers, sour cream containers, etc., can either melt or decompose. This also includes water bottles- don’t reheat water bottles if you want to be safe. Also, plastic bags from the grocery store should not be placed in the microwave.