<P> Polyesters as thermoplastics may change shape after the application of heat . While combustible at high temperatures, polyesters tend to shrink away from flames and self - extinguish upon ignition . Polyester fibers have high tenacity and E-modulus as well as low water absorption and minimal shrinkage in comparison with other industrial fibers . </P> <P> Unsaturated polyesters (UPR) are thermosetting resins . They are used in the liquid state as casting materials, in sheet molding compounds, as fiberglass laminating resins and in non-metallic auto - body fillers . They are also used as the thermoset polymer matrix in pre-pregs . Fiberglass - reinforced unsaturated polyesters find wide application in bodies of yachts and as body parts of cars . </P> <P> According to the composition of their main chain, polyesters can be: </P> <Table> <Tr> <Th> Main chain composition </Th> <Th> Type </Th> <Th_colspan="2"> Examples of </Th> </Tr> <Tr> <Th> Polyesters </Th> <Th> Manufacturing methods </Th> </Tr> <Tr> <Td> Aliphatic </Td> <Td> Homopolymer </Td> <Td> Polyglycolide or polyglycolic acid (PGA) </Td> <Td> Polycondensation of glycolic acid </Td> </Tr> <Tr> <Td> Polylactic acid (PLA) </Td> <Td> Ring - opening polymerization of lactide </Td> </Tr> <Tr> <Td> Polycaprolactone (PCL) </Td> <Td> Ring - opening polymerization of caprolactone </Td> </Tr> <Tr> <Td> Polyhydroxyalkanoate (PHA) </Td> <Td> </Td> </Tr> <Tr> <Td> Polyhydroxybutyrate (PHB) </Td> <Td> </Td> </Tr> <Tr> <Td> Copolymer </Td> <Td> Polyethylene adipate (PEA) </Td> <Td> </Td> </Tr> <Tr> <Td> Polybutylene succinate (PBS) </Td> <Td> Polycondensation of succinic acid with 1, 4 - butanediol </Td> </Tr> <Tr> <Td> Poly (3 - hydroxybutyrate - co-3 - hydroxyvalerate) (PHBV) </Td> <Td> Copolymerization of 3 - hydroxybutanoic acid and 3 - hydroxypentanoic acid, butyrolactone, and valerolactone (oligomeric aluminoxane as a catalyst) </Td> </Tr> <Tr> <Td> Semi-aromatic </Td> <Td> Copolymer </Td> <Td> Polyethylene terephthalate (PET) </Td> <Td> Polycondensation of terephthalic acid with ethylene glycol </Td> </Tr> <Tr> <Td> Polybutylene terephthalate (PBT) </Td> <Td> Polycondensation of terephthalic acid with 1, 4 - butanediol </Td> </Tr> <Tr> <Td> Polytrimethylene terephthalate (PTT) </Td> <Td> Polycondensation of terephthalic acid with 1, 3 - propanediol </Td> </Tr> <Tr> <Td> Polyethylene naphthalate (PEN) </Td> <Td> Polycondensation of at least one naphthalene dicarboxylic acid with ethylene glycol </Td> </Tr> <Tr> <Td> Aromatic </Td> <Td> Copolymer </Td> <Td> Vectran </Td> <Td> Polycondensation of 4 - hydroxybenzoic acid and 6 - hydroxynaphthalene - 2 - carboxylic acid </Td> </Tr> </Table>

Where does polyester come from and how is it made