Polymer Characteristics, Classification, Material Examples And Types

The word polymers comes from the Greek poly , which means many, and mere , which means part. Polymers are compounds formed by macromolecules obtained through the union or combination of several small molecules called monomers.

Characteristic

  • Polymers are not homogeneous products. They contain a mixture of molecules of various molecular weights presenting what is called polymolecularity .
  • The polymers can have their chains without branches, taking zig-zag forms ( linear polymers ) or they can have branches called crosslinked polymers or three-dimensional polymers.
  • They are not attacked by acids , bases or atmospheric agents.
  • They withstand breakage and wear.
  • They have high electrical resistance.
  • They have low density, generally between 0.9 g/cm³ and 1.5 g/cm³.
  • They react variably when subjected to a certain temperature.
  • When in the solid state, they form  dipole -dipole interactions and hydrogen bonding,  along with Van der Walls forces , creating much greater resistance than is the case with shorter-chain molecules.
  • In solution, these interactions that occur between molecules of large molecular mass lead to a pronounced increase in viscosity , something that is not observed in micromolecules.
  • The evaporation of the solvent from these viscous solutions causes them to form films, while the solutions of those substances in the solid state that have low molecular mass form crystals.

Polymer Classification

Natural polymers

They are polymeric materials found in nature, which are not synthesized in industries. The human body is made up of various natural polymers, such as proteins and polysaccharides .

Natural rubber comes from latex, which is obtained from the sap of the rubber tree. Examples: cellulose: cellulose acetate and cellulose nitrate, Casein: galactite and ammonia: urea.

Synthetic polymers

They are the polymeric materials that are obtained through synthesizing reactions, in polymerization industries, through various raw materials from renewable or non-renewable sources.

The size of the macromolecules and their composition can be controlled to obtain an infinity of polymeric compounds and analyze the desired properties.

In turn, synthetic polymers are classified into three groups:

1) Addition polymers: formed by addition reactions of a large number of equal monomers, giving rise to a single molecule.

Examples: polyethylene, PVC (polyvinyl chloride), PTFE (polytetrafluoroethylene – Teflon), PS (polystyrene), PP (polypropylene), PAN (polyacrylonitrile or orlon), PVA (polyvinyl acetate), PMMA (polymethylmethacrylate or plexiglass) and the synthetic rubbers.

2) Condensation or elimination polymers: formed by condensation reactions between molecules of the same or different substances with the output of a small molecule, such as a water molecule.

Examples: Bakelite, nylon or polyamide, Kevlar, polyester (PET, Dacron or Terylene), silicones and polycarbonate.

3) Rearrangement polymers: in this case one or more monomers undergo rearrangement in their structures as the polymerization reaction occurs. An example is polyurethane.

Synthetic or artificial polymers are called plastics and in their manufacture heat and pressure are used to form them.

In addition to that, both natural and artificial polymers can be classified as thermoplastic (their format can be modified) and thermorigid or thermosetting (their three-dimensional structure is rigid with cross-links, so its format cannot be modified).

Nomenclature

According to IUPAC , the rule for naming polymers is to use the prefix poly-, followed by the structural unit that defines the polymer, written in parentheses. For example: Poly(thio-1,4-phenylene).

IUPAC standards are generally used to name polymers whose structure is complex, since they allow them to be identified without any ambiguity within the database of scientific articles.

However, they are not usually used for polymers that have a simpler structure or are in common use, since these polymers were invented before the first IUPAC rules were published in 1952, and therefore their names had already become popular. traditional.

Polymer Recycling

Some polymers, such as thermosets and rubbers, cannot be recycled directly, as there is no way to melt or depolymerize them.

In most of the times the recycling of thermoplastics is not economically viable due to its low price and low density. Only mass-consumed plastics such as PE and PET have good economic potential.

Another problem is the fact that recycled plastics are expensive as a second class material.

When they cannot be recycled, the alternative is to burn the plastics, transforming them into energy. However, those that present halogens such as PVC and PTFE , form toxic gases when burned. So that this does not happen, this material must be dehalogenized before burning.

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