The synthesis of polyethylene terephthalate PET from terephthalic acid TPA and ethylene glycol EG involves a two-step reaction mechanism: esterification and polycondensation.1. Esterification: In this step, terephthalic acid reacts with ethylene glycol to form a monomer called bis 2-hydroxyethyl terephthalate BHET . This reaction is an esterification process where the carboxylic acid groups of TPA react with the hydroxyl groups of EG, releasing water as a byproduct.Reaction: TPA + 2 EG BHET + 2 H2O2. Polycondensation: In this step, the BHET monomers undergo a condensation reaction, where the hydroxyl groups of one BHET molecule react with the ester groups of another BHET molecule, forming a long polymer chain of PET and releasing ethylene glycol as a byproduct.Reaction: n BHET PET + n-1 EGThe reaction conditions, such as temperature and pressure, play a crucial role in determining the yield and properties of the resulting PET polymer.Temperature: The esterification and polycondensation reactions are typically carried out at elevated temperatures around 240-280C for esterification and 270-290C for polycondensation . Higher temperatures increase the reaction rate and promote the formation of longer polymer chains, resulting in a higher molecular weight PET. However, excessively high temperatures can lead to side reactions and degradation of the polymer.Pressure: The esterification reaction is usually performed at atmospheric pressure, while the polycondensation reaction is carried out under reduced pressure around 0.1-1.0 mmHg . The reduced pressure helps to remove the byproducts water and ethylene glycol from the reaction mixture, driving the equilibrium towards the formation of PET and increasing the yield. Additionally, the removal of byproducts prevents side reactions and the formation of low molecular weight oligomers, resulting in a higher molecular weight PET with better mechanical properties.In summary, controlling the reaction conditions, such as temperature and pressure, is crucial for optimizing the yield and properties of the synthesized PET polymer. Proper control of these conditions can result in a high molecular weight PET with desirable mechanical and thermal properties for various applications.