Polymers - Types, Classification, Properties, and Uses of Polymers

What Are Polymers?

A polymer is a large molecule or a macromolecule, which essentially is a combination of many subunits. The term polymer in Greek means ‘many parts’. Polymers can be found all around us, from the strand of our DNA, which is a naturally occurring biopolymer, to polypropylene which is used throughout the world as plastic.

Polymers can be naturally found in plants and animals (natural polymers) or can be human-made (synthetic polymers). Different polymers have a number of unique physical and chemical properties, due to which they find usage in everyday life.

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Table of Contents

• Classification of Polymers
• Structure
• Types
• Properties
• Polymers and Their Monomers
• Polymerization Reactions
• Molecular Mass of Polymers
• Uses of Polymers
• FAQs

Polymers are created by the process of polymerization, wherein their constituent elements, called monomers, are reacted together to form polymer chains, i.e., 3-dimensional networks forming the polymer bonds.

The type of polymerization mechanism used depends on the type of functional groups attached to the reactants. In the biological context, almost all macromolecules are either completely polymeric or are made up of large polymeric chains.

Classification of Polymers

Polymers cannot be classified under one category because of their complex structures, different behaviours and vast applications. We can, therefore, classify polymers based on the following norms.

Classification of Polymers Based on the Source of Availability

There are three types of classification under this category, namely, natural, synthetic, and semi-synthetic polymers.

Natural Polymers

They occur naturally and are found in plants and animals. For example, proteins, starch, cellulose and rubber. To add up, we also have biodegradable polymers called biopolymers.

Semi-synthetic Polymers

They are derived from naturally occurring polymers and undergo further chemical modification. For example, cellulose nitrate and cellulose acetate.

Synthetic Polymers

These are human-made polymers. Plastic is the most common and widely used synthetic polymer. It is used in industries and various dairy products. For example, nylon-6, 6, polyether, etc.

Also Read: Natural Polymers vs Synthetic Polymers

Classification of Polymers Based on the Structure of the Monomer Chain

This category has the following classifications:

Linear Polymers

The structure of polymers containing long and straight chains falls into this category. PVC, i.e., polyvinyl chloride, is largely used for making pipes, and an electric cable is an example of a linear polymer.

Branched-chain Polymers

When linear chains of a polymer form branches, then such polymers are categorised as branched chain polymers. For example, low-density polythene.

Cross-linked Polymers

They are composed of bifunctional and trifunctional monomers. They have a stronger covalent bond in comparison to other linear polymers. Bakelite and melamine are examples of cross-linked polymers.

Other Ways to Classify Polymers

Classification Based on Polymerization

• Addition Polymerization: For example, poly ethane, Teflon, polyvinyl chloride (PVC), etc.
• Condensation Polymerization: Examples include nylon -6, 6, perylene, polyesters, etc.

Classification Based on Monomers

• Homomer: In this type, a single type of monomer unit is present. For example, polyethene.

• Heteropolymer or co-polymer: It consists of different types of monomer units. For example, nylon -6, 6.

Classification Based on Molecular Forces

• Elastomers: These are rubber-like solids, and weak interaction forces are present in them. For example, rubber.
• Fibres: Strong, tough, high tensile strength and strong forces of interaction are present. For example, nylon -6, 6.
• Thermoplastics: These have intermediate forces of attraction. For example, polyvinyl chloride.
• Thermosetting polymers: These polymers greatly improve the material’s mechanical properties. It provides enhanced chemical and heat resistance. For example, phenolics, epoxies and silicones.

Structure of Polymers

Most of the polymers around us are made up of a hydrocarbon backbone. A hydrocarbon backbone is a long chain of linked carbon and hydrogen atoms, possibly due to the tetravalent nature of carbon.

A few examples of hydrocarbon backbone polymers are polypropylene, polybutylene and polystyrene. Also, there are polymers which, instead of carbon, have other elements in their backbone. For example, nylon contains nitrogen atoms in the repeated unit backbone.

Types of Polymers

On the basis of the type of backbone chain, polymers can be divided into

• Organic Polymers: Carbon backbone
• Inorganic Polymers: Backbone constituted by elements other than carbon

On the basis of their synthesis:

• Natural Polymers
• Synthetic Polymers

Biodegradable Polymers

Polymers which are degraded and decayed by microorganisms, like bacteria, are known as biodegradable polymers. These types of polymers are used in surgical bandages, capsule coatings, etc. For example, poly hydroxybutyrate co vel [PHBV]

High-temperature Polymers

These polymers are stable at high temperatures. Due to their high molecular weight, these are not destroyed even at very high temperatures. They are extensively used in the healthcare industries, for making sterilisation equipment and in the manufacturing of heat and shock-resistant objects.

A few of the important polymers are

Polypropylene: It is a type of polymer that softens beyond a specific temperature allowing it to be moulded, and on cooling, it solidifies. Due to its ability to be easily moulded into various shapes, it has a lot of applications.

A few of which are in stationary equipment, automotive components, reusable container speakers and much more. Due to its relatively low energy surface, the polymer is fused with the welding process and not using glue.

Polyethene: It is the most common type of plastic found around us. Mostly used in packaging, from plastic bags to plastic bottles. There are different types of polyethene, but their common formula is (C₂H₄)_n.

Properties of Polymers

Physical Properties

• As chain length and cross-linking increase, the tensile strength of the polymer increases.
• Polymers do not melt, and they change state from crystalline to semi-crystalline.

Chemical Properties

• Compared to conventional molecules with different side molecules, the polymer is enabled by hydrogen bonding and ionic bonding resulting in better cross-linking strength.
• Dipole-dipole bonding side chains enable the polymer for high flexibility.
• Polymers with Van der Waals forces linking chains are known to be weak but give the polymer a low melting point.

Optical Properties

• Due to their ability to change their refractive index with temperature, as in the case of PMMA and HEMA: MMA, they are used in lasers for applications in spectroscopy and analytical applications.

Some Polymers and Their Monomers

• Polypropene, also known as polypropylene, is made up of monomer propene.
• Polystyrene is an aromatic polymer, naturally transparent, made up of monomer styrene.
• Polyvinyl chloride (PVC) is a plastic polymer made of monomer vinyl chloride.
• The urea-formaldehyde resin is a non-transparent plastic obtained by heating formaldehyde and urea.
• Glyptal is made up of monomers ethylene glycol and phthalic acid.
• Bakelite or polyoxybenzylmethylenglycolanhydride is a plastic which is made up of monomers phenol and aldehyde.

Types of Polymerization Reactions

Addition Polymerization

This is also called chain growth polymerization. In this, small monomer units join to form a giant polymer. In each step, the length of the chain increases. For example, polymerization of ethane in the presence of peroxides.

Condensation Polymerization

In this type, small molecules like H₂O, CO, NH₃, are eliminated during polymerization (step growth polymerization). Generally, organic compounds containing bifunctional groups, such as idols, dials, diamines and dicarboxylic acids, undergo this type of polymerization reaction. For example, preparation of nylon -6, 6.

What Is Copolymerization?

In this process, two different monomers join to form a polymer. Synthetic rubbers are prepared by this polymerization. For example, BUNA – S.

How to Calculate the Molecular Mass of Polymers?

There are two types of average molecular masses of polymers.

• Number Average Molecular Masses
• Weight Average Molecular Mass

Number Average Molecular Masses

If N₁, N₂, N₃…. are the number of macromolecular with molecular masses. M₁, M₂, M₃….., respectively, then the number average molecular masses of the polymer is given by

The number average molecular mass

Weight Average Molecular Mass

If m₁, m₂, m₃…. are the masses of a macromolecule with molecular masses M₁, M₂, M₃…, respectively, then the weight average molecular mass of the polymer is given by

Polydispersive index: It is the ratio of the weight average molecular mass and the number average molecular mass of polymers.

Uses of Polymers

Here, we will list some of the important uses of polymers in our everyday life.

• Polypropene finds usage in a broad range of industries, such as textiles, packaging, stationery, plastics, aircraft, construction, rope, toys, etc.
• Polystyrene is one of the most common plastic actively used in the packaging industry. Bottles, toys, containers, trays, disposable glasses and plates, TV cabinets and lids are some of the daily-used products made up of polystyrene. It is also used as an insulator.
• The most important use of polyvinyl chloride is the manufacture of sewage pipes. It is also used as an insulator in electric cables.
• Polyvinyl chloride is used in clothing and furniture and has recently become popular for the construction of doors and windows as well. It is also used in vinyl flooring.
• Urea-formaldehyde resins are used for making adhesives, moulds, laminated sheets, unbreakable containers, etc.
• Glyptal is used for making paints, coatings and lacquers.
• Bakelite is used for making electrical switches, kitchen products, toys, jewellery, firearms, insulators, computer discs, etc.

Commercial Uses of Polymers

FAQs on Polymers

How do polymers have different physical properties? Give examples.

In polymers, monomers are bonded by different molecular interactions. The nature of these interactions yields polymers of varying elasticity, tensile strength, toughness, thermal stability, etc.

1. Monomers form a linear chain with weak bonding. These polymers exhibit elasticity and are called elastomers. Examples: neoprene, Buna-S and Buna-R.
2. Polymers with strong forces of interaction between the monomer in both linear and between the chains have higher tensile strength and are used as fibres. Examples: Polyamides (nylon6,6) and polyesters (terylene).
3. Polymers having their intermolecular force in between the elastomers and fibres are thermoplastics. They can be repeatedly reprocessed without much change in their polymeric properties. Examples: Polythene and polyvinyl.
4. Monomers that undergo heavy branching get fused on heating and cannot be reused or reprocessed. Such materials are thermosetting plastics. Bakelite and Urea-formaldehyde are examples.

What is the vulcanization of rubber?

Natural rubber is highly elastic to be of poor physical stability. Adding 5% of sulphur enhances the crosslinking of the linear chains and, thus, improves the stiffening of the rubber for an application like vehicle tires.

Match column A with B.

Answer:

What are biodegradable polymers? Give examples.

These polymers have functional groups found in natural polymers. Example: Poly β-hydroxybutyrate -co-β-hydroxy valerate (PHBV). This can be degraded by bacterial presence.

What do you mean by engineering plastics and synthetic metal?

These polymers possess high strength and resistance to chemical, thermal and abrasion, similar to ceramics and metals for use in engineering applications. Examples: silicone, polycarbonate, ABS and polysulfone.

The polymer that is similar to the metal in terms of its electrical, electronic, magnetic and optical properties is termed an ‘intrinsically conducting polymer (ICP)’ or ‘synthetic metal’.

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