the bulk), promoted by the elevated temperatures. Equilibrium constants of magnitude KC ≥ 104 are achieved when using reactive reactants (acid chlorides or acid anhydrides) or activating agents like 1,1′-carbonyldiimidazole. Using these reactants, molecular weights required for technical applications can be achieved even without active removal of the condensation product. History In 1926, United States–based DuPont began research on large molecules and synthetic fibers. This early research, headed by Wallace Carothers, centered on what became nylon, which was one of the first synthetic fibers. Carothers was working for duPont at the time. Carothers' research was incomplete and had not advanced to investigating the polyester formed from mixing ethylene glycol and terephthalic acid. In 1928 polyester was patented in Britain by the International General Electric company. Carothers' project was revived by British scientists Whinfield and Dickson, who patented polyethylene terephthalate (PET) or PETE in 1941. Polyethylene terephthalate forms the basis for synthetic fibers like Dacron, Terylene and polyester. In 1946, duPont bought all legal rights from Imperial Chemical Industries (ICI). Biodegradation and environmental concerns The Futuro houses were made of fibreglass-reinforced polyester plastic; polyester-polyurethane, and poly(methyl methacrylate). One house was found to be degrading by cyanobacteria and Archaea. Cross-linking Unsaturated polyesters are thermosetting polymers. They are generally copolymers prepared by polymerizing one or more diols with saturated and unsaturated dicarboxylic acids (maleic acid, fumaric acid, etc.) or their anhydrides. The double bond of unsaturated polyesters reacts with a vinyl monomer, usually styrene, resulting in a 3-D cross-linked structure. This structure acts as a thermoset. The exothermic cross-linking reaction is initiated through a catalyst, usually an organic peroxide such as methyl ethyl ketone peroxide or benzoyl peroxide. Pollution of freshwater and seawater habitats A team at Plymouth University in the UK spent 12 months analysing what happened when a number of synthetic materials were washed at different temperatures in domestic washing machines, using different combinations of detergents, to quantify the microfibres shed. They found that an average washing load of 6 kg could release an estimated 137,951 fibres from polyester-cotton blend fabric, 496,030 fibres from polyester and 728,789 from acrylic. Those fibers add to the general microplastics pollution. Recycling Recycling of polymers has become very important as the production and use of plastic is continuously rising. Global plastic waste may almost triple by 2060 if this continues. Plastics can be recycled by various means like mechanical recycling, chemical recycling, etc. Among the