Polyester
Polyesters are polymers containing ester groups - [ -CO- O-] - in its main chain. Although polyester also occur in nature, but today is meant by polyester rather a large family of synthetic polymers (plastics ), to which the polycarbonates much used ( PC) and especially the technically important thermoplastic polyethylene terephthalate ( PET) belong.
A particular form of processing of polyethylene terephthalate is the biaxially oriented polyester film as. Another form is the thermosetting unsaturated polyester resin (UP), which is used as an inexpensive matrix resin in the field fiber composite plastics. In addition, aromatic polyesters can be arranged to liquid-crystalline polymer chains, resulting in the property profile of a high- performance plastic.
The first synthetic polyester Glycerinphthalat was used in World War I as an impregnant. Natural polyesters are known since about 1830.
Applications
- Fibers (including microfibres ) for Textiles and Nonwovens
- PET bottles (these were initially not for alcoholic beverages available, since the polyester dissolved in it)
- Films, for example copyable film for overhead projectors, base material for flexible printed circuit boards, dielectric for capacitors
- Movies (next to cellulose triacetate polyester is the most important base material )
- Tennis Strings
- Fiber composites
- Than polyester resins in paints
- Polyester polyols are used as a raw material in the reaction of isocyanates to form polyurethanes.
Abbreviations
- PES or PE polyester ( group name)
- PBT polybutylene terephthalate, a terephthalic acid derivative of the
- PET polyethylene terephthalate, a derivative of terephthalic acid
- PTT polytrimethyleneterephthalate
- PEN polyethylene
- PC polycarbonate, a derivative of carbonic acid
- UP unsaturated polyester resin
Synthesis
The polyesters synthesized by a polycondensation reaction or by ring-opening polymerization.
Azeotropic esterification
The azeotropic esterification is a classical (laboratory ) method in which an alcohol and a carboxylic acid react to form a carboxylic acid ester. To represent a polymer, the water formed during the reaction must be continuously removed by azeotropic distillation in order to shift the chemical equilibrium to the ester side.
Alcoholic transesterification
Transesterification with the alcohol is a diol in the melt on the contact catalyst is reacted with a dicarboxylic acid ester. With this method, the bulk plastics polybutylene terephthalate ( PBT) and polyethylene terephthalate (PET ) are produced.
Hydrochloric acid method
The acid is present as an acid chloride, the polycondensation takes place as the elimination of hydrochloric acid ( HCl), in place of water (H2O). This acylation can in solvents take place as interphase or as a melt reaction.
Acetatmethode (transesterification)
At this appropriate only for phenolic hydroxy method measures the free acid reacts with the already esterified with acetic alcohol component. When condensation occurs again free acetic acid, which is not as easy to remove as water or hydrochloric acid, causing the pH decreases, and there are often acidic side reactions.
Ring-Opening Polymerization
In the ring-opening polymerization of aliphatic polyesters can be prepared from lactones via anionic, cationic or organometallic catalysis without condensation reaction under very mild conditions.
Dyeing of polyester fibers
Since polyester fibers are largely non-polar, they are dyed by disperse dyeing. Here, a suspension is prepared, in which the fiber is dipped. The dye diffuses into the fibers and stays there also after drying. However, the color stability is, in such a color is not too high, but can be the so-called high temperature process ( HT process, temperature of ≥ 130 ° C) can be improved.
Trade names
Substances or artificial skins made of polyester are marketed under various trade names:
- Polarguard
- Thermolite
- Trevira
- Dacron
- Diols
- Vestan
- Grisuten