TYPES OF POLYMERS

 

MAIN TYPES OF POLYMERS

                                                    

-Amorphous and Crystalline Polymers:

If we could see the molecular chains of a polymer in a liquid state, we would see that they are completely elongated and relaxed and it is when they cool and solidify that these chains may or may not seek to accommodate themselves.

The resins that when solidifying do not seek an accommodation or in other words, solidify without an order are those that are known as amorphous (from the Greek "a" without and "morphos" form). It is this disorder that defines its physical properties. Amorphous resins are mostly transparent because light beams pass through the gaps left by the chains in their disorder.

Contrary to amorphous resins, crystalline resins have a good percentage of contraction, which represents certain considerations in their processing to achieve good dimensional stability and avoid problems such as shrinkage and deformation due to contraction.

Crystalline resins generally have good mechanical and thermal properties and have a defined melting point. Examples of crystalline resins are polyethylene (PE), polyoxymethylene acetal (POM), polyamides (PA) better known as nylon, etc.

                                                                

-Thermoplastic and Thermosetting Polymers:

A thermoplastic is a plastic that, at relatively high temperatures, becomes deformable or flexible, melts when heated, and hardens to a glass transition state when sufficiently cooled. Most thermoplastics are high molecular weight polymers. Thermoplastic polymers differ from thermosetting or thermosetting polymers in that after being heated and molded they can be re-melted to form another part.

A thermosetting polymer can also be the result of the chemical reaction of two components or a component and a catalyst that, when reacted, form a different product that, when reheated, simply burns.

Examples of thermosetting polymers are bakelite (phenol formaldehyde), epoxies, silicones, etc.

The pre-polymer, so called before crosslinking, has a structure very similar to that of a thermoplastic polymer.

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-Crosslinked Polymers:

Crosslinks or crosslinks give a more rigid structure to a polymer, the crosslinking of a polymer is usually achieved from a chemical reaction with a catalyst and heat in vulcanizable or curable elastomers and in thermosetting polymers although there are a few polymers thermoplastics with thermoreversible crosslinking, such as ionomeric resins.

                                                                    

-Common, Functional, Engineering and Specialty Polymers:       

This type is derived from the physical properties offered by the different polymers, generally the highly specialized polymers are those with the greatest mechanical, thermal, chemical resistance or a combination of properties and are synthesized or formulated in a very unique way as liquid crystal polymers. .

Engineering polymers also have excellent physical properties but are a bit more common, examples of these resins are polyamides (PA), acetal or polyoxymethylene (POM), some engineering grade crystalline polyethylene terephthalate (PET) polyesters, etc.

Functional polymers are those that, although they do not have high physical properties, offer some benefit over common polymers, for example, a polycarbonate offers a very good impact resistance or an ethylene vinyl acetate (EVA) offers a better seal to the packaging than a polyethylene. 

                                                                       

-Homopolymers, Copolymers, Terpolymers:     

Polymers containing only one type of repeating unit are called homopolymers while polymers containing a mixture of 2 repeating units are known as copolymers. Polyethylene, for example, is composed solely of ethylene monomers and is therefore a homopolymer, and on the other hand, a polymer such as ethylene vinyl acetate (EVA) that is composed of ethylene and vinyl acetate monomers is known as a copolymer.     

-Bio-Polymers:

Plastics are important materials that make a significant contribution to protecting the environment. When compared to alternatives in typical applications, they can:

-reduce energy costs by up to 40%

-reduce waste by 75 – 80%

-reduce emissions by 70%

-reduce water pollution by up to 90% (2)

However, due to recent concerns about fossil resource depletion and environmental pollution, efforts have been made to replace conventional oil and gas-based plastics with hydrocarbon-based ones derived from renewable resources such as biomass.

• Depending on their origin, polymers can be:

NATURAL POLYMERS: They are of natural origin, coming from nature. For example: nucleic acids or proteins.

SEMI-SYNTHETIC POLYMERS: They are obtained from the transformation of natural polymers. For example: nitrocellulose.

SYNTHETIC POLYMERS: They are obtained industrially by handling organic monomers. For example: nylon or polyvinyl chloride (PVC).

• According to their chemical structure, polymers can be:

ORGANIC POLYMERS: They are those whose main chain of molecules is composed primarily of carbon (C).

VINYL ORGANIC POLYMERS: They only have carbon atoms in their main chain, although they can also contain halogens and styrenes in their structure.

NON-VINYL ORGANIC POLYMERS: They present in their main chain oxygen (O) and nitrogen (N) in addition to carbon atoms.

INORGANIC POLYMERS: They can be based on sulfur (S) or silicon (Si).

Depending on their structure, polymers can be:

HOMOPOLYMERS: They are composed of the same type of molecule that is repeated.

copolymers. They are composed of two or more types of molecules that are repeated successively in the chain.

• Depending on the structure of their chains, polymers can be:

LINEAR CHAIN POLYMERS: They are made up of long chains of monomers in a straight line.

RADIAL POLYMERS: They are made up of circular structures.

BRANCHED POLYMERS: They are made up of divergent chains of polymers, like the branches of a tree.