Polypropylene is considered quite stable under heating. More troubling is that there will be plasticizers, such as bisphenol-a, used in the manufacture of the product
A research group at McPherson college used mass spectrometry across a wide variety of polypropylene containers and found that there is no danger posed by microwaving polypropylene that contains food. If you want to lower your risk as far as possible, always microwave food in glass or plastics with an explicit "microwave safe" label. However, the evidence is overwhelming that polypropylene food container poses no health risk in the microwave.