PET Polymer Chemistry and Synthesis
category
PET (polyethylene terephthalate) is synthesised by polycondensation of terephthalic acid (TPA) or dimethyl terephthalate (DMT) with ethylene glycol (EG), producing a linear semicrystalline thermoplastic polyester with repeat unit –[OC–C₆H₄–CO–O–CH₂CH₂–O]–. Number-average molecular weight for fibre-grade PET is typically 15,000–20,000 g/mol with intrinsic viscosity 0.60–0.68 dL/g.
Role
Understanding PET chemistry is essential for controlling fibre properties, optimising polymerisation conditions, and designing copolymers with modified performance. It underpins all downstream processing and functional finishing knowledge.
Subtopics
- Esterification and Transesterification TPA route: direct esterification of TPA with EG at 240–260°C produces bis(2-hydroxyethyl) terephthal…
- Polycondensation Kinetics and Thermodynamics Polycondensation of BHET at 270–285°C under high vacuum (<1 mmHg) with antimony trioxide catalyst re…
- Molecular Weight and Intrinsic Viscosity Intrinsic viscosity (IV) of PET, measured in phenol/tetrachloroethane (60:40) at 25°C, correlates wi…
- Copolymerisation for Modified Properties Incorporation of co-monomers modifies PET crystallinity and dyeability: isophthalic acid (IPA) reduc…
- Catalyst Systems in PET Synthesis Antimony trioxide (Sb₂O₃) is the dominant polycondensation catalyst (200–300 ppm Sb). Alternatives: …
- Solid-State Polymerisation (SSP) SSP increases IV of PET chips from 0.60 to 0.80–0.95 dL/g by heating crystallised chips at 200–230°C…
- End-Group Analysis and Chain Termination PET chains terminate with hydroxyl (-OH) and carboxyl (-COOH) end groups. COOH end groups are measur…
- Thermal and Thermooxidative Degradation PET undergoes thermal degradation above 290°C via β-scission (chain scission generating vinyl ester …
- Recycled PET Chemistry (rPET) Chemical recycling of PET includes glycolysis (EG depolymerisation to BHET oligomers at 190–220°C), …
- Bio-Based and Biodegradable Polyesters Bio-PET uses bio-based monoethylene glycol (from bioethanol, 30% bio-content) with petrochemical TPA…