Team:TU Darmstadt/Protocols/Synthesis of polyethylene terephthalate in presence of sulfuric acid

Synthesis of polyethylene terephthalate in presence of sulfuric acid

Theory

To gain information about different methods of synthesis for polyethylene terephthalate (PET) and the effect on physical and surface propieties, three experiments are done. The resulting oligo- and polymer is melted, cooled in liquid nitrogen and investigated with AFM. As the synthesis of polyethylene theephthalate is a reversible polykondensation of ethylene glycol and diemthyl terephthalate the developing methanol has to be removed from the reaction by destillation. Concentrated sulfuric acid is used as a catalyst.

Preparation

Conversion to polyethylene terephthalate 1

For the preparation of polyethylene terephthalate 2.73 g (14.05 mmol) of dimethylterephthalate were added to 43.68 mL (781.13 mmol) of ethylene glycol. After the addition of 2-3 drops of concentrated sulfuric acid the solution was heated under reflux at 65 °C for 20 min. After destillation of the Methanol, the resulting yellow solution was cooled for 48 hours at 5 °C and filtered. White crystals were precipitated, they were washed with cold hexane and then with a little cold water. The dried crystals are melted at 80 °C and poured on a flat metal plate. Which was immediately cooled to -195 °C. The resulting solid was investigated by atomic force microscopy.

Conversion to polyethylene terephthalate 2

For the preparation of polyethylene terephthalate 2.643 g (13.59 mmol) of dimethylterephthalate were added to 0.76 mL (13.59 mmol) of ethylene glycol in 50 mL DMSO. After the addition of 2-3 drops of concentrated sulfuric acid the solution was heated under reflux at 65 °C for 20 min. After destillation of the Methanol, the resulting yellow solution was cooled for 48 hours at 5 °C and filtered. White crystals were precipitated, they were washed with cold hexane and then with a little cold water. The dried crystals are melted at 120 °C and poured on a flat metal plate. Which was immediately cooled to -195 °C. The resulting solid was investigated by atomic force microscopy.

Conversion to polyethylene terephthalate 3

For the preparation of polyethylene terephthalate 2.71 g (13.95 mmol) of dimethylterephthalate were added to 0.39 mL (0.69 mmol) of ethylene glycol in 50 mL DMSO. After the addition of 2-3 drops of concentrated sulfuric acid the solution was heated under reflux at 65 °C for 20 min. 0.39 mL (0.69 mmol) of ethylene glycol were added dropwise over 30 min. After destillation of the Methanol, the resulting yellow solution was cooled for 48 hours at 5 °C and filtered. White crystals were precipitated, they were washed with cold hexane and then with a little cold water. The dried crystals were melted at 170 °C. While reaching the temperature of 170 °C the crystals suplimated immediatly leading to a total loss of product.