Q: Q3. Write the names of monomers of the following polymers:\n(i) Buna-N\n(ii) Buna-S\n(iii) Dacron\n(iv) Neoprene\n(v) Novolac\n(vi) PVC

The names of the monomers for the given polymers are:\n\n(i) **Buna-N:** 1,3-Butadiene and Acrylonitrile\n(ii) **Buna-S:** 1,3-Butadiene and Styrene\n(iii) **Dacron (or Terylene):** Ethylene glycol and Terephthalic acid\n(iv) **Neoprene:** Chloroprene (2-chloro-1,3-butadiene)\n(v) **Novolac:** Phenol and Formaldehyde\n(vi) **PVC (Polyvinyl chloride):** Vinyl chloride (Chloroethene)

Q: Q5. Explain the terms homopolymer and copolymer and give examples of each.

### Homopolymer\nA homopolymer is a polymer formed from only one type of monomer unit. All the repeating structural units in the polymer chain are identical.\n\n**Examples:**\n* **Polythene:** Formed by the polymerization of only ethene monomers.\n* **Polyvinyl chloride (PVC):** Formed by the polymerization of only vinyl chloride monomers.\n* **Polypropylene:** Formed by the polymerization of only propene monomers.\n\n### Copolymer\nA copolymer (or heteropolymer) is a polymer formed from two or more different types of monomer units. The repeating structural units in the polymer chain are derived from different monomers.\n\n**Examples:**\n* **Buna-S:** Formed by the polymerization of 1,3-butadiene and styrene monomers.\n* **Buna-N:** Formed by the polymerization of 1,3-butadiene and acrylonitrile monomers.\n* **Nylon 6,6:** Formed by the polymerization of hexamethylenediamine and adipic acid monomers.\n* **Dacron (Terylene):** Formed by the polymerization of ethylene glycol and terephthalic acid monomers.

Q: Q8. Explain the terms polymer and monomer.

### Explanation of Polymer and Monomer\n\n**1. Monomer**\n * **Definition**: A monomer is a small, simple, reactive molecule that serves as the basic repeating unit from which a polymer is constructed. Monomers typically have functional groups that allow them to form covalent bonds with other monomers.\n * **Etymology**: The term 'mono' means one, and 'meros' means unit.\n * **Characteristics**: Monomers are usually low molecular weight compounds. They undergo polymerization reactions to form long chains or networks.\n * **Examples**: Ethene (monomer for polythene), vinyl chloride (monomer for PVC), glucose (monomer for starch/cellulose), amino acids (monomers for proteins).\n\n**2. Polymer**\n * **Definition**: A polymer is a large molecule (macromolecule) formed by the repetitive bonding of many small, identical or similar, simple molecules called monomers. This process of forming a polymer from monomers is called polymerization.\n * **Etymology**: The term 'poly' means many, and 'meros' means unit.\n * **Characteristics**: Polymers have high molecular weights and often exhibit properties vastly different from their constituent monomers. They can be linear, branched, or cross-linked structures.\n * **Examples**: Polythene (formed from ethene monomers), Polyvinyl chloride (PVC, formed from vinyl chloride monomers), Nylon-6,6 (formed from hexamethylenediamine and adipic acid), Proteins (formed from amino acid monomers), DNA (formed from nucleotide monomers).

Q: Q10. Write the names of monomers of the following polymers: (i) Buna-N (ii) Buna-S (iii) Dacron (iv) Neoprene (v) Novolac (vi) Natural rubber.

The names of the monomers for the given polymers are:\n\n(i) **Buna-N**: 1,3-Butadiene and Acrylonitrile\n(ii) **Buna-S**: 1,3-Butadiene and Styrene\n(iii) **Dacron** (also known as Terylene): Ethylene glycol and Terephthalic acid (or Dimethyl terephthalate)\n(iv) **Neoprene**: Chloroprene (2-Chloro-1,3-butadiene)\n(v) **Novolac**: Phenol and Formaldehyde\n(vi) **Natural rubber**: Isoprene (2-Methyl-1,3-butadiene)

Question 1

Q1. What are polymers?

Accepted Answer

Polymers are high molecular mass macromolecules formed by the joining of a large number of repeating structural units called monomers. This process of forming polymers from monomers is known as polymerization.

Polymers are essential materials in everyday life, found in plastics, rubber, fibers, and biomolecules like proteins and nucleic acids. Their properties depend on the nature of their monomers, the way they are linked, and their overall structure.

Question 2

Q2. How are polymers classified on the basis of structure?

Accepted Answer

On the basis of their structure, polymers can be broadly classified into three main types:

### 1. Linear Polymers
These polymers consist of long and straight chains. The monomer units are linked together to form a single, continuous chain without any branches. Due to their close packing, linear polymers have high density, high tensile strength, and high melting points.

**Examples:** High-density polythene (HDPE), Polyvinyl chloride (PVC), Nylon.

### 2. Branched-Chain Polymers
These polymers have linear chains with some side branches. The branches prevent the polymer chains from packing closely together. As a result, branched-chain polymers have lower density, lower tensile strength, and lower melting points compared to linear polymers.

**Examples:** Low-density polythene (LDPE), Glycogen, Amylopectin.

### 3. Cross-linked or Network Polymers
These polymers are formed from bifunctional and trifunctional monomers and contain strong covalent bonds between various linear polymer chains, forming a three-dimensional network structure. They are generally hard, rigid, and brittle. They are also known as thermosetting polymers because they cannot be reshaped once molded.

**Examples:** Bakelite, Melamine-formaldehyde resin, Vulcanised rubber.

Question 3

Q3. Write the names of monomers of the following polymers:
(i) Buna-N
(ii) Buna-S
(iii) Dacron
(iv) Neoprene
(v) Novolac
(vi) PVC

Accepted Answer

The names of the monomers for the given polymers are:

(i) **Buna-N:** 1,3-Butadiene and Acrylonitrile
(ii) **Buna-S:** 1,3-Butadiene and Styrene
(iii) **Dacron (or Terylene):** Ethylene glycol and Terephthalic acid
(iv) **Neoprene:** Chloroprene (2-chloro-1,3-butadiene)
(v) **Novolac:** Phenol and Formaldehyde
(vi) **PVC (Polyvinyl chloride):** Vinyl chloride (Chloroethene)

Question 4

Q4. Classify the following as addition and condensation polymers:
Terylene, Bakelite, Polyvinyl chloride, Polythene.

Accepted Answer

The classification of the given polymers as addition or condensation polymers is as follows:

**Addition Polymers:**
*   **Polyvinyl chloride (PVC):** Formed by the addition polymerization of vinyl chloride monomers.
*   **Polythene:** Formed by the addition polymerization of ethene monomers.

**Condensation Polymers:**
*   **Terylene (or Dacron):** Formed by the condensation polymerization of ethylene glycol and terephthalic acid, with the elimination of water molecules.
*   **Bakelite:** Formed by the condensation polymerization of phenol and formaldehyde, with the elimination of water molecules.

Question 5

Q5. Explain the terms homopolymer and copolymer and give examples of each.

Accepted Answer

### Homopolymer
A homopolymer is a polymer formed from only one type of monomer unit. All the repeating structural units in the polymer chain are identical.

**Examples:**
*   **Polythene:** Formed by the polymerization of only ethene monomers.
*   **Polyvinyl chloride (PVC):** Formed by the polymerization of only vinyl chloride monomers.
*   **Polypropylene:** Formed by the polymerization of only propene monomers.

### Copolymer
A copolymer (or heteropolymer) is a polymer formed from two or more different types of monomer units. The repeating structural units in the polymer chain are derived from different monomers.

**Examples:**
*   **Buna-S:** Formed by the polymerization of 1,3-butadiene and styrene monomers.
*   **Buna-N:** Formed by the polymerization of 1,3-butadiene and acrylonitrile monomers.
*   **Nylon 6,6:** Formed by the polymerization of hexamethylenediamine and adipic acid monomers.
*   **Dacron (Terylene):** Formed by the polymerization of ethylene glycol and terephthalic acid monomers.

Question 6

Q6. Write the names of monomers of the following polymers: (i) Buna-N (ii) Buna-S (iii) Dacron (iv) Neoprene (v) Novolac (vi) PVC

Accepted Answer

The names of the monomers for the given polymers are as follows:

(i) **Buna-N**
    *   Monomers: 1,3-Butadiene and Acrylonitrile (or Vinyl cyanide)

(ii) **Buna-S**
    *   Monomers: 1,3-Butadiene and Styrene

(iii) **Dacron** (also known as Terylene)
    *   Monomers: Ethylene glycol and Terephthalic acid (or Dimethyl terephthalate)

(iv) **Neoprene**
    *   Monomer: Chloroprene (2-chloro-1,3-butadiene)

(v) **Novolac**
    *   Monomers: Phenol and Formaldehyde

(vi) **PVC** (Polyvinyl chloride)
    *   Monomer: Vinyl chloride (Chloroethene)

Question 7

Q7. Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.

Accepted Answer

Polymers can be classified based on their mode of polymerization into addition polymers and condensation polymers.

Here's the classification of the given polymers:

1.  **Terylene (Dacron)**: **Condensation Polymer**
    *   It is formed by the condensation reaction between ethylene glycol and terephthalic acid, with the elimination of small molecules like water.

2.  **Bakelite**: **Condensation Polymer**
    *   It is formed by the condensation reaction between phenol and formaldehyde, with the elimination of water molecules.

3.  **Polyvinyl chloride (PVC)**: **Addition Polymer**
    *   It is formed by the repeated addition of vinyl chloride (chloroethene) monomers without the elimination of any small molecules.

4.  **Polythene**: **Addition Polymer**
    *   It is formed by the repeated addition of ethene monomers without the elimination of any small molecules.

Question 8

Q8. Explain the terms polymer and monomer.

Accepted Answer

### Explanation of Polymer and Monomer

**1. Monomer**
    *   **Definition**: A monomer is a small, simple, reactive molecule that serves as the basic repeating unit from which a polymer is constructed. Monomers typically have functional groups that allow them to form covalent bonds with other monomers.
    *   **Etymology**: The term 'mono' means one, and 'meros' means unit.
    *   **Characteristics**: Monomers are usually low molecular weight compounds. They undergo polymerization reactions to form long chains or networks.
    *   **Examples**: Ethene (monomer for polythene), vinyl chloride (monomer for PVC), glucose (monomer for starch/cellulose), amino acids (monomers for proteins).

**2. Polymer**
    *   **Definition**: A polymer is a large molecule (macromolecule) formed by the repetitive bonding of many small, identical or similar, simple molecules called monomers. This process of forming a polymer from monomers is called polymerization.
    *   **Etymology**: The term 'poly' means many, and 'meros' means unit.
    *   **Characteristics**: Polymers have high molecular weights and often exhibit properties vastly different from their constituent monomers. They can be linear, branched, or cross-linked structures.
    *   **Examples**: Polythene (formed from ethene monomers), Polyvinyl chloride (PVC, formed from vinyl chloride monomers), Nylon-6,6 (formed from hexamethylenediamine and adipic acid), Proteins (formed from amino acid monomers), DNA (formed from nucleotide monomers).

Question 9

Q9. Distinguish between the terms homopolymer and copolymer and give an example of each.

Accepted Answer

### Distinction between Homopolymer and Copolymer

Polymers can be classified based on the type of monomers used in their synthesis:

**1. Homopolymer**
    *   **Definition**: A homopolymer is a polymer formed from only one type of monomeric unit. All the repeating structural units in the polymer chain are identical.
    *   **Formation**: Homopolymers are typically formed by the polymerization of a single type of monomer.
    *   **Structure**: The polymer chain consists of identical repeating units linked together.
    *   **Example**: 
        *   **Polythene**: Formed by the polymerization of only ethene (ethylene) monomers.
            `... -[CH₂-CH₂]- [CH₂-CH₂]- [CH₂-CH₂]- ...`
        *   Other examples include Polyvinyl chloride (PVC), Polypropylene, Polystyrene.

**2. Copolymer (or Heteropolymer)**
    *   **Definition**: A copolymer is a polymer formed from two or more different types of monomeric units. The repeating structural units in the polymer chain are not identical.
    *   **Formation**: Copolymers are formed by the copolymerization of two or more different monomers.
    *   **Structure**: The polymer chain contains a sequence of different monomer units. The arrangement of these different units can be alternating, random, block, or graft.
    *   **Example**: 
        *   **Buna-S**: Formed by the copolymerization of 1,3-butadiene and styrene monomers.
            `... -[CH₂-CH=CH-CH₂]- [CH(C₆H₅)-CH₂]- [CH₂-CH=CH-CH₂]- [CH(C₆H₅)-CH₂]- ...`
        *   Other examples include Buna-N, Nylon-6,6, Terylene (Dacron).

### Summary of Distinction:

Question 10

Q10. Write the names of monomers of the following polymers: (i) Buna-N (ii) Buna-S (iii) Dacron (iv) Neoprene (v) Novolac (vi) Natural rubber.

Accepted Answer

The names of the monomers for the given polymers are:

(i) **Buna-N**: 1,3-Butadiene and Acrylonitrile
(ii) **Buna-S**: 1,3-Butadiene and Styrene
(iii) **Dacron** (also known as Terylene): Ethylene glycol and Terephthalic acid (or Dimethyl terephthalate)
(iv) **Neoprene**: Chloroprene (2-Chloro-1,3-butadiene)
(v) **Novolac**: Phenol and Formaldehyde
(vi) **Natural rubber**: Isoprene (2-Methyl-1,3-butadiene)

Question 11

Q11. Classify the following into homopolymer and copolymer: Buna-S, Nylon-6,6, PVC, Orlon, Dacron.

Accepted Answer

Polymers can be classified as homopolymers or copolymers based on the type of monomer units they contain.

*   **Homopolymer**: A polymer formed from a single type of monomer unit.
*   **Copolymer**: A polymer formed from two or more different types of monomer units.

Based on this classification:

1.  **Buna-S**: Copolymer (formed from 1,3-butadiene and styrene)
2.  **Nylon-6,6**: Copolymer (formed from hexamethylenediamine and adipic acid)
3.  **PVC** (Polyvinyl chloride): Homopolymer (formed from vinyl chloride)
4.  **Orlon** (Polyacrylonitrile): Homopolymer (formed from acrylonitrile)
5.  **Dacron** (Terylene): Copolymer (formed from ethylene glycol and terephthalic acid)

Question 12

Q12. How is the functionality of a monomer important for the formation of a polymer?

Accepted Answer

The functionality of a monomer refers to the number of bonding sites or reactive functional groups present in a monomer molecule that are capable of forming covalent bonds with other monomer molecules during polymerization. This concept is crucial because it dictates the type of polymer formed and its resulting structure (linear, branched, or cross-linked).

### Importance of Monomer Functionality:

1.  **Minimum Functionality for Polymerization**: For a polymer to form, the monomer must have a functionality of at least two. This means it must be able to form a bond at two different points. If a monomer has a functionality of one (e.g., methanol, which can only react at one site), it can only terminate a growing chain and cannot initiate or propagate a polymer chain.

2.  **Formation of Linear Polymers**: When monomers have a functionality of exactly two, they typically form linear polymers. Each monomer unit links to two other monomer units, creating long, unbranched chains. Examples include:
    *   **Ethene (functionality 2)**: Forms linear polyethylene.
    *   **Adipic acid and Hexamethylenediamine (each functionality 2)**: Form linear Nylon-6,6.

3.  **Formation of Branched Polymers**: If a monomer has a functionality greater than two, it can lead to branching in the polymer chain. For example, if a monomer has three reactive sites, it can form a bond with two other monomers to extend the main chain and also form a bond with a third monomer, leading to a side branch. Low-density polyethylene (LDPE) is an example where branching occurs due to side reactions during polymerization.

4.  **Formation of Cross-linked Polymers (Network Polymers)**: When monomers with a functionality of three or more are used, they can form extensive three-dimensional networks, resulting in highly cross-linked or thermosetting polymers. These polymers are rigid, brittle, and infusible. Examples include:
    *   **Phenol and Formaldehyde (phenol has functionality 3, formaldehyde 2)**: React to form Novolac (linear) or Bakelite (cross-linked, when excess formaldehyde is used or further heating is done).
    *   **Melamine and Formaldehyde**: Form highly cross-linked melamine-formaldehyde resins.

### Summary:

*   **Functionality = 1**: Cannot form a polymer (acts as chain terminator).
*   **Functionality = 2**: Forms linear or sometimes branched polymers (if side reactions occur).
*   **Functionality ≥ 3**: Forms branched or highly cross-linked (network) polymers.

In essence, the functionality of a monomer determines the number of bonds it can form, which directly influences the architecture of the polymer (linear, branched, or network) and, consequently, its physical and mechanical properties (e.g., strength, flexibility, melting point, solubility).

Question 13

Q13. Elaborate the differences between the following: (a) Addition and condensation polymerisation (b) Homopolymers and copolymers (c) Elastomers and thermosetting polymers.

Accepted Answer

Let's elaborate on the differences between the given pairs:

### (a) Addition and Condensation Polymerisation

| Feature             | Addition Polymerisation                               | Condensation Polymerisation                               | | :------------------ | :---------------------------------------------------- | :-------------------------------------------------------- | | **Definition**      | Monomers add to one another in a chain reaction without the elimination of any small molecules. | Monomers react to form a polymer with the elimination of small molecules like water, alcohol, HCl, etc. | | **Monomers**        | Typically unsaturated compounds (alkenes, alkynes, dienes) or their derivatives. | Typically bifunctional or polyfunctional monomers (containing -OH, -COOH, -NH₂, -X functional groups). | | **By-products**     | No by-products are formed; the polymer is an exact multiple of the monomer unit. | Small molecules are eliminated as by-products.            | | **Molecular Mass**  | The molecular mass of the polymer is an integral multiple of the monomer's molecular mass. | The molecular mass of the polymer is not an integral multiple of the monomer's molecular mass due to loss of small molecules. | | **Mechanism**       | Usually proceeds via free radical, cationic, or anionic mechanisms. | Usually proceeds via step-growth mechanism.               | | **Examples**        | Polyethylene, Polypropylene, PVC, Teflon, Orlon, Buna-S, Buna-N. | Nylon-6,6, Nylon-6, Dacron (Terylene), Bakelite, Melamine-formaldehyde resin. |

### (b) Homopolymers and Copolymers

| Feature             | Homopolymers                                          | Copolymers                                                | | :------------------ | :---------------------------------------------------- | :-------------------------------------------------------- | | **Definition**      | Polymers formed from a single type of monomer unit.   | Polymers formed from two or more different types of monomer units. | | **Monomer Units**   | All repeating units in the polymer chain are identical. | The repeating units in the polymer chain are derived from different monomers. | | **Structure**       | Simple, uniform repeating structure.                  | More complex repeating structure, often with alternating, random, block, or graft arrangements of monomer units. | | **Properties**      | Properties are determined by the single monomer type. | Properties are often a blend of the properties of the constituent monomers, or can be unique and superior. | | **Examples**        | Polyethylene, Polypropylene, PVC, Orlon, Natural rubber, Polystyrene. | Buna-S, Buna-N, Nylon-6,6, Dacron (Terylene), ABS rubber. |

### (c) Elastomers and Thermosetting Polymers

| Feature             | Elastomers                                            | Thermosetting Polymers                                    | | :------------------ | :---------------------------------------------------- | :-------------------------------------------------------- | | **Definition**      | Polymeric solids with elastic properties, meaning they can be stretched to many times their original length and return to their original shape upon release of stress. | Polymers that undergo extensive cross-linking upon heating and become hard, rigid, and infusible. | | **Intermolecular Forces** | Weakest intermolecular forces (van der Waals forces) between polymer chains. | Strong covalent bonds forming extensive 3D networks (cross-links) between polymer chains. | | **Structure**       | Long, coiled polymer chains with a few cross-links (vulcanization enhances this). | Highly cross-linked, rigid, three-dimensional network structure. | | **Heating Effect**  | Can be softened on heating (thermoplastic elastomers exist, but general elastomers are often cross-linked to improve properties). They retain elasticity over a wide temperature range. | Cannot be softened or remoulded on heating once cured. Heating causes further cross-linking and eventually degradation. | | **Reversibility**   | Elastic deformation is largely reversible.            | Once formed, the structure is irreversible.               | | **Mechanical Properties** | High elasticity, low tensile strength, high extensibility. | High rigidity, high tensile strength, brittle, hard.      | | **Examples**        | Natural rubber, Buna-S, Buna-N, Neoprene.             | Bakelite, Melamine-formaldehyde resin, Urea-formaldehyde resin. |

Question 14

Q14. Write the names of monomers of the following polymers:
(i) Buna-N
(ii) Buna-S
(iii) Dacron
(iv) Neoprene
(v) Novolac
(vi) PVC

Accepted Answer

The names of the monomers for the given polymers are:

(i) **Buna-N:** Buta-1,3-diene and Acrylonitrile (or Prop-2-enenitrile)

(ii) **Buna-S:** Buta-1,3-diene and Styrene (or Phenylethene)

(iii) **Dacron (also known as Terylene):** Ethane-1,2-diol and Terephthalic acid (or Benzene-1,4-dicarboxylic acid)

(iv) **Neoprene (also known as Polychloroprene):** Chloroprene (or 2-Chloro-buta-1,3-diene)

(v) **Novolac:** Phenol and Formaldehyde (or Methanal)

(vi) **PVC (Polyvinyl chloride):** Vinyl chloride (or Chloroethene)

Question 15

Q15. Classify the following polymers as natural and synthetic polymers:
Nylon-6,6, Buna-S, Polyethene, Starch, Cellulose, Natural rubber, DNA, PVC.

Accepted Answer

Polymers can be broadly classified into natural and synthetic categories based on their origin.

**Natural Polymers:** These polymers are found in nature, primarily in plants and animals.
*   Starch
*   Cellulose
*   Natural rubber
*   DNA

**Synthetic Polymers:** These polymers are man-made and are synthesized in laboratories or industries.
*   Nylon-6,6
*   Buna-S
*   Polyethene (or Polyethylene)
*   PVC (Polyvinyl chloride)

Question 16

Q16. Explain the terms plastics, elastomeric polymers, fibres and thermosetting polymers on the basis of intermolecular forces. Classify the following polymers in each of these classes:

Accepted Answer

Polymers can be classified into different categories based on the magnitude of intermolecular forces present between their polymer chains. These forces dictate their mechanical properties such as tensile strength, elasticity, and melting behavior.

### Explanation based on Intermolecular Forces:

1.  **Elastomeric Polymers (Elastomers):**
    *   **Intermolecular Forces:** These polymers have the weakest intermolecular forces of attraction among all polymer types. The polymer chains are held together by weak van der Waals forces, allowing them to be easily stretched.
    *   **Structure and Properties:** They possess elastic properties, meaning they can be stretched to many times their original length and return to their original shape when the stretching force is released. This is due to the presence of a few cross-links between the polymer chains, which help the polymer to retract to its original position after the force is removed. These cross-links prevent permanent deformation.
    *   **Example:** Buna-S

2.  **Plastics (Thermoplastics):**
    *   **Intermolecular Forces:** These polymers have intermolecular forces that are intermediate between those of elastomers and fibres. They are stronger than the forces in elastomers but weaker than those in fibres.
    *   **Structure and Properties:** Thermoplastics are capable of repeatedly softening on heating and hardening on cooling. This reversible behavior is due to the absence of extensive cross-linking. The polymer chains can slide past each other when heated, allowing them to be molded into different shapes. They are generally linear or slightly branched polymers.
    *   **Example:** Polythene

3.  **Fibres:**
    *   **Intermolecular Forces:** Fibres possess very strong intermolecular forces of attraction, such as hydrogen bonding and strong dipole-dipole interactions. These strong forces lead to close packing of chains.
    *   **Structure and Properties:** Due to strong intermolecular forces and close packing, fibres have high tensile strength and high modulus. They are long, thin, thread-like structures that can be woven into fabrics. They have sharp melting points and are generally crystalline in nature.
    *   **Example:** Nylon-6,6

4.  **Thermosetting Polymers:**
    *   **Intermolecular Forces:** These polymers are characterized by extensive cross-linking between polymer chains, forming a rigid, three-dimensional network structure. The cross-links are strong covalent bonds.
    *   **Structure and Properties:** Once molded and set (usually by heating), they become hard and infusible. They cannot be softened or remolded upon subsequent heating because the extensive cross-links prevent the chains from moving. Heating them further leads to degradation rather than softening. They are typically brittle.
    *   **Example:** Melamine-formaldehyde resin

### Classification of Given Polymers:

*   **Nylon-6,6:** Fibres (due to strong hydrogen bonding)
*   **Buna-S:** Elastomeric polymers (due to weak intermolecular forces and some cross-links)
*   **Polythene:** Plastics (Thermoplastics) (due to intermediate intermolecular forces)
*   **Melamine-formaldehyde resin:** Thermosetting polymers (due to extensive cross-linking)

Question 17

Q17. What is the repeating unit in the polymer Nylon-6?

Accepted Answer

Nylon-6 is a polyamide formed by the ring-opening polymerization of caprolactam. The repeating unit in Nylon-6 is derived from caprolactam and contains six carbon atoms and one nitrogen atom.

The repeating unit of Nylon-6 is: **[-NH-(CH₂)₅-CO-]**

This unit is formed when the amide bond in caprolactam breaks, and the molecule polymerizes to form a linear chain.

Question 18

Q18. Write the names of monomers of the following polymers: (i) Buna-N (ii) Buna-S (iii) Dacron (iv) Neoprene (v) Novolac (vi) PVC

Accepted Answer

The names of the monomers for the given polymers are as follows:

(i) **Buna-N**: 1,3-Butadiene and Acrylonitrile
(ii) **Buna-S**: 1,3-Butadiene and Styrene
(iii) **Dacron** (also known as Terylene): Ethylene glycol and Terephthalic acid (or Dimethyl terephthalate)
(iv) **Neoprene**: Chloroprene (2-chloro-1,3-butadiene)
(v) **Novolac**: Phenol and Formaldehyde
(vi) **PVC** (Polyvinyl chloride): Vinyl chloride (Chloroethene)

Question 19

Q19. Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.

Accepted Answer

Polymers can be classified into addition and condensation polymers based on their mode of formation.

**Addition Polymers:** These are formed by the repeated addition of monomer units without the elimination of any small molecules (like H₂O, HCl, CH₃OH, etc.). The empirical formula of the polymer is the same as that of the monomer.

**Condensation Polymers:** These are formed by the repeated condensation reaction between two or more bi-functional or tri-functional monomer units with the elimination of small molecules such as water, alcohol, hydrogen chloride, etc.

Based on this classification:

1.  **Terylene** (Dacron): Condensation polymer (formed from ethylene glycol and terephthalic acid with the elimination of water).
2.  **Bakelite**: Condensation polymer (formed from phenol and formaldehyde with the elimination of water).
3.  **Polyvinyl chloride** (PVC): Addition polymer (formed from vinyl chloride monomers).
4.  **Polythene**: Addition polymer (formed from ethene monomers).

Question 20

Q20. Explain the term copolymerisation and give two examples.

Accepted Answer

**Copolymerisation**
Copolymerisation is a polymerisation process in which two or more different monomeric units are allowed to polymerise together to form a polymer. The resulting polymer contains multiple types of monomer units in its chain. The polymer formed is called a copolymer.

This process can occur via both addition and condensation mechanisms. For addition copolymerisation, the monomers must have double or triple bonds. For condensation copolymerisation, the monomers must have at least two functional groups capable of undergoing condensation.

**Examples of Copolymerisation:**

1.  **Buna-S:** It is a copolymer of 1,3-butadiene and styrene. The polymerisation involves the addition of these two different monomers to form a synthetic rubber.
    Monomers: CH₂=CH-CH=CH₂ (1,3-Butadiene) and C₆H₅-CH=CH₂ (Styrene)

2.  **Buna-N:** It is a copolymer of 1,3-butadiene and acrylonitrile. This copolymer is also a synthetic rubber known for its resistance to oils and fuels.
    Monomers: CH₂=CH-CH=CH₂ (1,3-Butadiene) and CH₂=CH-CN (Acrylonitrile)

3.  **Nylon 6,6:** It is a copolymer formed by the condensation polymerisation of hexamethylenediamine and adipic acid, with the elimination of water molecules.
    Monomers: H₂N-(CH₂)₆-NH₂ (Hexamethylenediamine) and HOOC-(CH₂)₄-COOH (Adipic acid)

Question 21

Q21. Write the structures of the monomers of the following polymers: (i) Nylon 6,6 (ii) Nylon 6 (iii) Polythene

Accepted Answer

The structures of the monomers for the given polymers are as follows:

(i) **Nylon 6,6**
Nylon 6,6 is a copolymer formed from two different monomers:
*   **Hexamethylenediamine:** H₂N-(CH₂)₆-NH₂
*   **Adipic acid:** HOOC-(CH₂)₄-COOH

(ii) **Nylon 6**
Nylon 6 is a homopolymer formed from a single monomer:
*   **Caprolactam:** A cyclic amide with the formula (CH₂)₅CONH. During polymerization, the ring opens to form the polymer chain.

(iii) **Polythene**
Polythene is a homopolymer formed from a single monomer:
*   **Ethene (Ethylene):** CH₂=CH₂

Chapter 15: Polymers