NEET Important Chapter - Polymers

Since the dawn of time, polymers have been believed to be essential components of commodities. Linoleum fibres, cotton, wool for clothes, and paper reeds for paper are only a few instances of how our forefathers made objects out of polymers containing raw materials. 

The latex sap of cactus plants arrived in Europe in the 16th century, long after Olmec, Aztec, and Maya had begun utilising it to manufacture balls, waterproof fabrics, and containers. Chemical manipulation of polymers extends back to the 19th century, however, the nature of the species was unknown at the time. 

Polymers were first thought to be responsible for the behaviour, according to Thomas Graham's idea, which described them as the colloidal aggregation of tiny molecules held together by unexplained forces. The polymerisation of several tiny molecules known as monomers produces both synthetic and natural polymers. 

Due to their enormous molecular mass in comparison to small molecule molecules, they have unusual physical characteristics. This article provides an example of the types of questions that might be asked about this subject in the JEE 2022 exam. 

Important Topics of Extractive Metallurgy

• Rubber

• Polymers and Polymerisation Process

• Classification of Polymerisation Reaction

Some Important Definitions 

What are Polymers?

A polymer, also known as a macromolecule, is a big molecule made up of numerous subunits. Polymer is a Greek word that means many components.' Polymers may be found in almost every environment. From our DNA strand, which is a naturally occurring biopolymer, to polypropylene, which is utilised as a plastic all over the world.

Polymers can be found naturally in plants and animals (natural polymers) or they can be created artificially (synthetic polymers). Polymers contain a variety of physical and chemical qualities that allow them to be used in everyday life.

The term polymer comes from the Greek words 'polus’, which means many, and ‘meros’, which means parts, and refers to large molecules whose structure is made up of many repeating units, from which a characteristic of higher relative molecules whose structure is made up of multiple properties is derived. 

This unit is made up of polymer drive molecules with a low relative molecular mass, either physically or theoretically. Jons Jacob Berzelius invented the word in 1833, however with a meaning that differed from the contemporary IUPAC definition.

Classification of Polymers

Polymers are difficult to categorise due to their complicated structures, diverse behaviours, and wide range of uses. As a result, we may categorise polymers based on the following criteria.

Polymer Classification Based on the Source of Availability

Natural, synthetic, and semi-synthetic polymers are the three types of polymers included in this category.

• Polymers that occur spontaneously in plants and animals are known as natural polymers. For example, proteins, starch, cellulose, and rubber. To round things off, there are biopolymers, which are biodegradable polymers.

• Semi-synthetic polymers are made from naturally occurring polymers that have been chemically modified. Semi synthetic polymers examples include cellulose nitrate and cellulose acetate.

• Man-made polymers are known as synthetic polymers. The most prevalent and commonly used synthetic polymer is plastic. It's utilised in a variety of industries and dairy products. For example, nylon-6.

Polymer Classification Based on the Structure of the Monomer Chain

Polymers are classified depending on the structure of the monomer chain.

• Polymers with a Linear Structure: Polymers with long and straight chains fall under this group. PVC, or polyvinyl chloride, is a linear polymer that is commonly used to make pipes and electric lines.

• Polymers with Branched Chains: When a polymer's linear chains produce branches, the polymer is classified as a branched-chain polymer.  For example, low-density polythene.

• Polymers that are Cross-Linked: They are made up of monomers with bifunctional and trifunctional functions. Compared to other linear polymers, they have a stronger covalent bond. Bakelite and melamine are both examples of this type of material.

Other Polymer Classification Methods

(A) Polymerisation-Based Classification

Addition Polymerisation: In addition to polymerisation, monomers with double or triple bonds are combined repeatedly to make a polymer. There are no by-products in this sort of reaction. Polyethane, Teflon, and Polyvinyl chloride are just a few examples (PVC).

Condensation Polymerisation: An interaction between two separate bifunctional or trifunctional monomer units produces condensation polymers. Small molecules of simple substances such as HCl (Hydrogen chloride), H2O (Water), alcohol, and others are removed during the condensation reaction that forms polymers from these monomeric components. Nylon-6,6, perylene, and polyesters are examples of condensation polymerisation.

(B) Monomer-Based Classification

Homomer: This kind has only one type of monomer unit. Polyethene Heteropolymer or copolymer, for example, is made up of a variety of monomer units. Nylon-6, 6 is an example.

(C) Molecular Forces-Based Classification

Elastomers are rubber-like substances that have weak contact forces. For example, rubber.

Fibres are the strong, tough, high tensile strength, and strong interaction forces. For example, Nylon-6.

Thermoplastics are materials that exhibit intermediate attraction forces. For example, Polyvinyl chloride.

Thermosetting polymers significantly increase the mechanical characteristics of the material. It has improved chemical and thermal resistance.

Polymer Structures

The majority of the polymers we encounter have a hydrocarbon backbone. Due to the tetravalent nature of carbon, a hydrocarbon backbone is a lengthy chain of connected carbon and hydrogen atoms.

Polypropylene, polybutylene, and polystyrene are examples of hydrocarbon backbone polymers. There are other polymers with other elements in their backbones instead of carbon. Nylon, for example, has nitrogen atoms in its repeating unit backbone.

Types of Polymers

Natural Polymers: A polymer is created by combining tiny molecules or components into a single large molecule through a chemical reaction. Monomer refers to the tiny molecules that are employed to make a polymer. Natural Polymers are compounds that can be found in nature. The procedure of addition polymerisation or condensation polymerisation is used to create these polymers. Natural polymers examples include Proteins, Polypeptides etc.

Synthetic Polymers: The procedure of addition polymerisation or condensation polymerisation is used to create these polymers. Human-made polymers are known as synthetic polymers. Polymers are made up of monomers, which are repeating structural units. Polyethylene is one of the most basic polymers; it is made up of ethylene as the monomer unit, and the linear polymer is called high-density polyethylene-HDPE. Many polymeric compounds resemble polyethylene in that they have chain-like structures.

Characteristics of Polymers 

Physical Characteristics

The tensile strength of the polymer improves as the chain length and cross-linking increase. Polymers do not melt; instead, they transition from crystalline to semi-crystalline form.

Chemical Characteristics

The polymer is enabled with hydrogen bonding and ionic bonding, resulting in improved cross-linking strength when compared to ordinary molecules with distinct side molecules. The polymer's great flexibility is due to the dipole-dipole bonding side chains. Van der Waals interactions between chains in polymers are known to be weak, yet they provide the polymer with a low melting point.

Optical Characteristics

They are utilised in lasers for spectroscopic and analytical applications because of their capacity to vary their refractive index with temperature, as in the case of PMMA and HEMA: MMA.

Examples of Polymer in Everyday Life

We'll go through some of the most common applications of polymers in our daily lives.

• Textiles, packaging, stationery, plastics, aviation, construction, rope, and toys are just a few of the sectors that use polypropene.

• Polystyrene is a popular plastic that is used extensively in the packaging sector. Polystyrene is utilised in everyday items such as bottles, toys, containers, trays, disposable glasses and plates, television cabinets, and lids. It's also a great insulator.

• The most common application for polyvinyl chloride is the production of sewage pipes. It's also used in electric wires as an insulator.

• Polyvinyl chloride is utilised in the manufacture of clothes and furnishings, and it has lately gained popularity in the manufacture of doors and windows. It's also a component of vinyl flooring.

• Adhesives, moulds, laminated sheets, unbreakable containers, and other products are made with urea-formaldehyde resins.

• Paints, coatings, and lacquers are made from glyptal.

• Bakelite is used in the manufacture of electrical switches, food items, toys, jewellery, guns, insulators, and computer discs, among other things.

Degree of Polymerisation

The frequency of repeating units in a polymer can be characterised as the degree of polymerisation. For example, if a polymer P is composed of 5 monomers (M), its degree of polymerisation will be 5. This is the most important property of a polymer, as it also specifies its physical properties.

You can also calculate its degree by following the methods outlined below.

You must first write down the chemical formula of the polymer. Take the case of tetrafluoroethylene [-(CF2-CF2)n-], for example. The monomer unit is indicated by the element contained in parentheses.

After that, you'll need to collect the atomic masses of the elements that make up a monomer. Carbon and Fluorine are implicated in this example. Fluorine and Carbon have atomic masses of 19 and 12, respectively.

Using the Techniques below, Calculate the Monomer's Molecular Weight.

• To determine molecular weight, multiply the atomic mass by the number of atoms in the molecule (Carbon or Fluorine atoms).

• To get the molecular weight, add both products together. It's (19 x 4) + (12 x 2) = 100 for Tetrafluoroethylene.

• Finally, divide the molecular mass of the polymer by the monomer's predicted molecular weight. If the molecular mass of Tetrafluoroethylene is 1,20,000, the degree of polymerisation will be 1200.

As a result, the degree of polymerisation formula may be defined as the ratio of the polymer's molecular mass to the molecular weight.

Solved Examples from the Chapter: Polymers

Example 1: Polymer formation from monomers starts by

(1) Condensation reaction between monomers

(2) Coordinate reaction between monomers

(3) Conversion of monomer to monomer ions by protons 

(4) Hydrolysis of monomers

Solution: 

Repeated condensation processes of bi- and tri-functional monomers produce these polymers. Small molecules such as water, alcohol, and others are removed during this procedure. Condensation polymers, such as nylon-6,6, are generated by repeated condensation processes and are referred to as such.

Among the choices for the above issue, we know that polymer formation occurs when monomers are added repeatedly or when monomers undergo repeated condensation reactions and tiny molecules are eliminated.

Therefore option (1) is the answer.

Key point to remember:  Polymers are divided into addition polymers and condensation polymers based on their mechanism of polymerisation.

Example 2: Which of the following is fully fluorinated polymer?

(1) Neoprene

(2) Teflon

(3) Thiokol

(4) PVC

Solution:

Teflon is a fluorinated polymer that is completely fluorinated. Tetrafluoroethylene is its monomer. A chloroprene monomer is used to make neoprene (2-chlorobuta-1,3-diene). Thiokol is a polymer made up of organic polysulfide molecules. Polyvinyl chloride (PVC) is a kind of plastic. Vinyl chloride is the monomer.

(C2H3Cl)n is the chemical formula for PVC.

As a result, option (2) is right.

Key point to remember: To know the monomers of the following polymers.

Solved Questions from the Previous Years’ Question Papers

Question 1: The polymer containing strong intermolecular forces e.g. hydrogen bonding, is

(1) Teflon

(2) Nylon 6,6

(3) Polystyrene

(4) Natural rubber

Solution: 

Teflon is a chemical compound made of tetrafluoroethylene. Since the H atom isn't linked to N, O, or F, it can't create H bonds. Nylon 6, 6 is a kind of polyamide because the H atom is connected to the amide N atom, it may establish hydrogen bonds. 

Polystyrene is a styrene polymer because the H atom isn't linked to N, O, or F, it can't create H bonds. 

Natural rubber is 1,4-polyisoprene (cis-polyisoprene) because the H atom isn't linked to N, O, or F, it can't create H bonds. Nylon-6,6 is a polymer with strong intermolecular forces (e.g. hydrogen bonding).

As a result, (2) is the right answer.

Trick: Nylon-6,6 is a polyamide made from adipic acid and hexamethylenediamine condensation polymerisation. Because of the amide connections, Nylon-6,6 has hydrogen bonding interactions.

Question 2: Which one is classified as a condensation polymer?

(1) Acrylonitrile

(2) Dacron

(3) Neoprene

(4) Teflon

Solution: 

Dacron is a polymer that is formed through condensation of ethylene glycol and methyl terephthalate. Addition polymers include Teflon, neoprene, and acrylonitrile.

As a result, (2) is the right answer.

Trick: No molecule is lost during addition polymerisation. Condensation polymerisation, on the other hand, eliminates a tiny molecule such as water, ethanol, or hydrogen chloride.

Question 3: Which polymer is used in the manufacture of paints and lacquers?

(1) Bakelite

(2) Glyptal

(3) Polypropene

(4) Polyvinyl Chloride

Solution:

Glyptal is a polyester made from glycerol and phthalic anhydride that has been condensation polymerised. It's used to make paints and lacquers, among other things.

Hence option (2) is correct.

Trick: Glyptal, commonly known as alkyd resins, is made by the condensation polymerisation of ethylene glycol with phthalic acid monomer units.

Practice Questions

Question 1: Nylon threads are made of

(1) Polyester polymer

(2) Polyamide polymer

(3) Polyethylene polymer

(4) Polyvinyl polymer

Answer: (2) Polyamide polymer

Question 2: The formation of which of the following polymers involves hydrolysis reaction?

(1) Nylon 6

(2) Bakelite

(3) Nylon 6, 6

(4) Terylene

Answer:  (1) Nylon 6

Conclusion

Thus, the study of the polymer which is a chemical molecule consists of a large number of similar building components that are all connected together by an ionic or covalent connection. Polymers are always made by a process called polymerisation, in which monomers are reacted together to produce polymer chains, which are three-dimensional networks that form the polymer links.

The sort of polymerisation process utilised is determined by the reactive groups' functional groups. Almost all macromolecules in biology are either entirely polymeric or composed of massive polymeric chains.

Hence, this is important for competitive exams like JEE or NEET.