Unsaturated polyesters (UPR) are thermosetting resins. Liquid crystalline polyesters are among the first industrially used liquid crystal polymers. Products of these intermediates include polystyrene, unsaturated polyesters and ethylene-propylene terpolymers. Dicarboxylic acids are also used in the preparation of copolymers such as polyamides and polyesters. Succinic acid is a precursor to some polyesters and a component of some alkyd resins. Compared to aliphatic polyesters, Nylon 6 has poor biodegradability. Later Flory (1946) proposed an improved synthesis of aliphatic polyesters with diacid chloride. These substances were much more stable than the polyesters formed by using the glycols. PBT is closely related to other thermoplastic polyesters. Examples of thermoset polyesters include some of the Desmophen brand from Bayer. Polyesters as thermoplastics may change shape after the application of heat. They are stronger than polyesters and more resistant to impact than epoxies. A variety of biopolymers, such as polysaccharides, polyesters, and polyamides, are produced by microorganisms. It is used in many applications including PVC's and unsaturated polyesters. It is used in the synthesis of polyesters, paints, lubricants, and plasticizers.