Polymers are natural or synthetic materials whose molecular structure consists of a large number of repeating molecules (monomers).
Starch, cellulose, rubber, and proteins are examples of natural polymers.
The number of synthetic polymers today exceeds tens of thousands.
Polymers are classified into different types. Their classification in terms of application and physical properties is as follows:
Plastics
Elastomers
Fibers
Resins
Classification of types of polymers
Polymers are classified into subcategories based on their origin.
Natural polymers: These are polymers that are produced only from natural materials found in nature, such as wool, silk, starch, protein, natural rubber, cellulose, etc.
Synthetic polymer: Synthetic polymer, also known as synthetic polymer, is produced in laboratories from molecules with low molecular weight, such as nylons, polyethylene, polyester, PVC, Teflon, synthetic rubbers, etc.
Semi-synthetic polymer: This type of polymer is made from a combination of natural polymers to modify properties and also simple chemical modification, such as cellulose acetate, cellulose nitrate, etc.
Polymers are classified into two categories based on their behavior against heat and high temperatures.
Thermoplastics: Thermoplastics or thermosets are polymers that are easily molded into various shapes by heat and then cooled at room temperature and used. This means that these types of polymers soften when heated and harden again when cooled, such as polyethylene, PVC, polypropylene, polystyrene, etc.
Thermosets: Thermosets or thermosets are hard and insoluble polymers when heated. These polymers do not soften when heated and cannot be re-molded. Thermosets are polymers with cross-links that cannot be reused. The most important thermosets include phenolics, urea, melamine, epoxy, alkyds, silicone, urethane, polyester, etc.
Linear polymer: In linear polymers, monomers are linked together to form long chains. In this type of polymer, there are no side branches and their molecules are close together and usually have high density, melting point and tensile strength. Such as HDPE and nylon
Branched polymer: Branched polymers have long and straight chains but also have different side branches. For this reason, their molecules are arranged irregularly and therefore have lower density, tensile strength and low melting point.
Cross-linked and network-linked polymers: This type of polymer has repeating units and forms three-dimensional networks when connected. The connection between them is made by cross-links. This type of polymer has a hard, rigid and brittle network structure due to the type of connection to the units. These polymers include melamines, formaldehyde resin, cured rubbers, etc.
