Plastics whose molecules contain sulfone groups (–SO₂–) in the main chain, as well as a variety of additional constituents such as ether or isopropylidene groups. Polysulfones based on aromatic backbones constitute a useful class of engineering plastics, owing to their high strength, stiffness, and toughness together with high thermal and oxidative stability, low creep, transparency, and the ability to be processed by standard techniques for thermoplastics. Aliphatic polysulfones are less stable to thermal degradation or hydrolysis, so they are not of commercial interest.