Politereftalato

Politereftalato is a class of thermoplastic polyesters derived from terephthalic acid and glycols. The most economically significant member is polyethyleneterephthalate (PET), produced by condensation of terephthalic acid or dimethyl terephthalate with ethylene glycol. Other related polymers in this family include polybutylene terephthalate (PBT) and glycol-modified PET (PETG). The repeating unit in these polymers consists of terephthalate residues linked by ester bonds to diol segments.

Synthesis of politereftalati typically involves a polycondensation process. This can proceed via esterification of terephthalic acid with a glycol or via transesterification of dimethyl terephthalate with a glycol, followed by polycondensation under reduced pressure to achieve high molecular weight. Catalysts and controlled removal of water or methanol drive the reaction toward polymer formation.

Properties of politereftalati include thermoplastic behavior, with the ability to soften and flow when heated and harden upon cooling. They can be semi-crystalline or amorphous, influencing transparency and barrier properties. PET, for example, offers good mechanical strength, chemical resistance, and gas barrier performance, with a glass transition temperature in the range of about 70–80°C and a melting point around 250°C. Crystallinity and orientation impact transparency, stiffness, and permeability. Densities are typically around 1.3–1.4 g/cm3.

Applications are diverse and include textile fibers, beverage bottles, food packaging films, and engineering resins for automotive and electronic parts. PETG variants are valued for clarity and impact resistance.

Recycling and sustainability efforts focus on mechanical recycling to create new resins or fibers and on chemical recycling to recover monomers. Safety profiles are generally favorable for food contact applications when properly manufactured and regulated.