Полиэстерлер: түрлері, қасиеттері және қолданылуы

Category of polymers, in which the monomers are joined together by ester links
the 1981 motion picture
Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include naturally occurring chemicals, such as in plants and insects, as well as synthetics such as polybutyrate. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Synthetic polyesters are used extensively in clothing. Polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties. Cotton polyester blends can be strong, wrinkle and tear resistant, and reduce shrinking. Synthetic fibers using polyester have high water, wind, and environmental resistance compared to plant derived fibers. They are less fire resistant and can melt when ignited. Liquid crystalline polyesters are among the first industrially used liquid crystal polymers. They are used for their mechanical properties and heat resistance. These traits are also important in their application as an abradable seal in jet engines.

Polyesters are one of the most economically important classes of polymers, driven especially by PET, which is counted among the commodity plastics; in 2019 around 30.5 million metric tons were produced worldwide. earning them the nickname "polyester bees".

Thermally stable polymers, which generally have a high proportion of aromatic structures, are also called high performance plastics. This application oriented classification compares such polymers with engineering plastics and commodity plastics. The continuous service temperature of high performance plastics is generally stated as being higher than 150 °C, whereas engineering plastics (such as polyamide or polycarbonate) are often defined as thermoplastics that retain their properties above 100 °C.⁠ Commodity plastics (such as polyethylene or polypropylene) have in this respect even greater limitations, but they are manufactured in great amounts at low cost. Poly(ester imides) contain an aromatic imide group in the repeat unit, the imide based polymers have a high proportion of aromatic structures in the main chain and belong to the class of thermally stable polymers. Such polymers contain structures that impart high melting temperatures, resistance to oxidative degradation and stability to radiation and chemical reagents. Among the thermally stable polymers with commercial relevance are polyimides, polysulfones, polyetherketones, and polybenzimidazoles. Of these, polyimides are most widely applied. The polymers' structures result also in poor processing characteristics, in particular a high melting point and low solubility. The named properties are in particular based on a high percentage of aromatic carbons in the polymer backbone which produces a certain stiffness.⁠ Approaches for an improvement of processability include the incorporation of flexible spacers into the backbone, the attachment of stable pendent groups or the incorporation of non symmetrical structures. Polyesters are also used to make bottles, films, tarpaulin, sails (Dacron), canoes, liquid crystal displays, holograms, filters, dielectric film for capacitors, film insulation for wire and insulating tapes. Polyesters are widely used as a finish on high quality wood products such as guitars, pianos, and vehicle/yacht interiors. Thixotropic properties of spray applicable polyesters make them ideal for use on open grain timbers, as they can quickly fill wood grain, with a high build film thickness per coat. It can be used for fashionable dresses, but it is most admired for its ability to resist wrinkling and shrinking while washing the product. Its toughness makes it a frequent choice for children's wear. Polyester is often blended with other fibres like cotton to get the desirable properties of both materials. Cured polyesters can be sanded and polished to a high gloss, durable finish.

Aliphatic polyesters can be assembled from lactones under very mild conditions, catalyzed anionically, cationically, metallorganically or enzyme based. A number of catalytic methods for the copolymerization of epoxides with cyclic anhydrides have also recently been shown to provide a wide array of functionalized polyesters, both saturated and unsaturated. Ring opening polymerization of lactones and lactides is also applied on the industrial scale.

Numerous other reactions have been reported for the synthesis of selected polyesters, but are limited to laboratory scale syntheses using specific conditions, for example using dicarboxylic acid salts and dialkyl halides or reactions between bisketenes and diols. Instead of acyl chlorides, so called activating agents can be used, such as 1,1' carbonyldiimidazole, dicyclohexylcarbodiimide, or trifluoroacetic anhydride. The polycondensation proceeds via the in situ conversion of the carboxylic acid into a more reactive intermediate while the activating agents are consumed. The reaction proceeds, for example, via an intermediate N acylimidazole which reacts with catalytically acting sodium alkoxide: into two main categories: a) equilibrium polyesterifications (mainly alcohol acid reaction, alcohol–ester and acid–ester interchange reactions, carried out in bulk at high temperatures), and b) non equilibrium polyesterifications, using highly reactive monomers (for example acid chlorides or activated carboxylic acids, mostly carried out at lower temperatures in solution). The acid alcohol based polyesterification is one example of an equilibrium reaction. The ratio between the polymer forming ester group ( C(O)O ) and the condensation product water (H2O) against the acid based ( C(O)OH) and alcohol based ( OH) monomers is described by the equilibrium constant KC. The equilibrium constant of the acid alcohol based polyesterification is typically KC ≤ 10, what is not high enough to obtain high molecular weight polymers (DPn ≥ 100), as the number average degree of polymerization (DPn) can be calculated from the equilibrium constant KC. In equilibrium reactions, it is therefore necessary to remove the condensation product continuously and efficiently from the reaction medium in order to drive the equilibrium towards polymer. 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).

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.

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.

Ahmed Shafik was a sexologist who won a Ig Nobel Prize on his research regarding how polyester can affect the fertility of rats, dogs, and men. Bisphenol A which is a endocrine disrupting chemical may be used in the synthesis of polyester.

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 recyclable polymers, polyester PET is one of the most recycled plastics. The ester bond present in polyesters is susceptible to hydrolysis (acidic or basic conditions), methanolysis and glycolysis which makes this class of polymers suitable for chemical recycling. Enzymatic/biological recycling of PET can be carried out using different enzymes like PETase, cutinase, esterase, lipase, etc. PETase has been also reported for enzymatic degradation of other synthetic polyesters (PBT, PHT, Akestra™, etc.) which contains similar aromatic ester bond as that of PET.