What is polymer chemistry



A polymer [polyˈmeːr] (ancient Greek πολύpolý "much"; μέροςméros, "Part") is a chemical compound that consists of chain or branched molecules (macromolecules) that consist of the same or similar units (the so-called monomers). The adjective polymer means accordingly made up of many equal parts. Although this term usually describes covalently bound substances, which are also referred to as macromolecules, it is often advantageous to include salts and metals in the definition. Again, all of the stuff is here from many identical particles, the formula units.

Definition (within the meaning of the Chemicals Act)

A polymer is a substance whose molecules consist of linked monomer units.

This substance is then considered a polymer

  • when a simple majority by weight of molecules with at least three monomer units is included
  • which are linked to a further monomer unit or another reactant
  • and have entered into a bond by means of an atomic bond (covalent / electron pair bond).

A substance is also considered a polymer if different

  • contains less than a simple majority by weight of molecules
  • which are in a certain molar mass range
  • wherein the deviations in the molar mass are essentially due to the differences in the number of monomer units.

For the purposes of this definition, a monomer unit is the bound form of a monomer in a polymer.

Alternative definition

Polymers are “Substances whose molecular weights are in an integer ratio to one another with the same percentage atomic composition and also have the same internal structure. The same internal structure is distributed over the entire macromolecule. The definition of a polymer also includes the property that a polymer molecule made up of n units cannot be distinguished from a polymer molecule made up of n-1 or n + 1 basic building blocks.[1] This also includes inorganic macromolecules, e.g. B. from elements such as sulfur, or anorg. Compounds [-A ^ - - B ^ + -A ^ - - B ^ + -]. These can be from B, Si, Al, Ti, Ge, P, As with S or O2 are formed. Silicones (polysiloxanes) are also included here.

Classification

Polymers can be classified according to the number of basic monomers. However, it is important that at least one monomeric substance builds the chain.

  • Homopolymer: In the simplest case, the polymer consists of only one type of monomer, e.g. B. PE, PP, PVC and PA6.
  • Copolymers are made up of various monomers, such as B. polyesters, polyurethanes and some polyamides (PA 66).

A distinction is also made between organic and inorganic polymers. The organic polymers can be further subdivided into

  • Biopolymers or natural polymers: they are the basic building blocks of living organisms.
  • chemically modified polymers arise from the further processing of biopolymers, e.g. B. nitrocellulose, celluloid or starch derivatives
  • synthetic polymers: Synthetic polymers that are manufactured industrially or on a laboratory scale by polymerization processes include polyethylene, polystyrene, polyvinyl chloride, etc.

Other polymers:

Polymer chemistry

The chain formation, i.e. the connection of individual monomers, takes place through polyreactions (such as, for example, polymerization, polycondensation or polyaddition). The monomers combine to form polymers.

Polymers made from differently built monomers are called heteropolymers or copolymers.

Most plastics are polymers in which the carbon is responsible for the molecular chain formation.

A distinction is made between isotactic polymers in which all substituents of a polymer chain have the same stereoelectronic conformation, such as e.g. B. isotactic polystyrene with configuration R-R-R-R-R-… or S-S-S-S-S-… In atactic polymers the substituents are randomly ordered (a kind of racemate). Polymers whose substituents consist alternately of R and S are called syndiotactic.

Examples

  • Synthetic carbon-based polymers:
  • Synthetic polymers on a different basis:
    • The silicon is also able to form stable bonds with itself. This creates silicones.
  • Biopolymers:

Ecological considerations

Health risks are practically never caused by the polymer itself.

One example of this is PVC: the toxic and highly corrosive gas hydrogen chloride is only produced when it is burned, and it dissolves in water to form hydrochloric acid (hydrochloric acid). In addition, large quantities of polychlorinated dibenzodioxins and furans are produced in smoldering fires. The polymer PVC itself is food-safe and, due to its excellent gas-tightness, is used in medicine, for example for blood products.

Additional problems can arise from additives that are found in virtually every plastic article, such as B. Plasticizers. These are mainly used with PVC.

Polymer physics

According to their physical properties, the polymers are divided into:

  1. The thermoplastics,
  2. the elastomers and
  3. the thermosets.

In the case of thermoplastics, a distinction is made between (partially) crystalline and amorphous thermoplastics. Polymers are theoretically inter alia. described by the Freely Jointed Chain Model or the Wormlike Chain Model.

Polymer electronics

(see main article organic electronics)

Here conductive (electrically active) polymers are used to build up polytronic applications. In contrast to molecular electronics, the information is not processed in individual molecules, but in differently doped volumes.

Such electronic applications are for example:

Another application is that processing of polymers with the help of electronics in electrospinning.

swell

  1. Kunz: Polymerization technology. P. 11.

literature

  • Lechner, Gehrke, Nordmeier: Macromolecular Chemistry. 3. Edition. Birkhäuser, Basel 2003, ISBN 3-7643-6952-3.

Categories: Soft Matter | Plastic | Macromolecular Chemistry