Natural and Synthetic like Polythene, Nylon, Polyesters, Bakelite, Rubber — Revision Notes

⚡ 30-Second Revision

Polymers — Large molecules from repeating monomers.
Natural Polymers — Found in nature (e.g., Natural Rubber).

- Natural Rubber: Monomer: Isoprene (

$$ext{CH}_2=\text{C}(\text{CH}_3)-\text{CH}=\text{CH}_2$$

). *cis*-polyisoprene. Vulcanization with sulfur improves properties.

Synthetic Polymers — Man-made (e.g., Polythene, Nylon, Polyesters, Bakelite).

- Polythene: Monomer: Ethene (

$$ext{CH}_2=\text{CH}_2$$

). Addition polymer. LDPE (branched, flexible), HDPE (linear, rigid). - Nylon-6,6: Monomers: Hexamethylenediamine (

$$ext{H}_2\text{N}-(\text{CH}_2)_6-\text{NH}_2$$

) + Adipic acid (

$$ext{HOOC}-(\text{CH}_2)_4-\text{COOH}$$

).

Condensation polymer. Polyamide. High tensile strength. - Nylon-6: Monomer: Caprolactam. Condensation polymer. - Polyesters (Terylene/Dacron/PET): Monomers: Ethylene glycol (

$$ext{HOCH}_2\text{CH}_2\text{OH}$$

) + Terephthalic acid (

$$ext{HOOC}-\text{C}_6\text{H}_4-\text{COOH}$$

).

Condensation polymer. Polyester linkage (

$$-\text{COO}-$$

). - Bakelite: Monomers: Phenol (

$$ext{C}_6\text{H}_5\text{OH}$$

) + Formaldehyde (

$$ext{HCHO}$$

). Condensation polymer. Thermosetting plastic.

Highly cross-linked, rigid, electrical insulator.

2-Minute Revision

Polymers are macromolecules formed from repeating monomer units. They are broadly categorized into natural (e.g., natural rubber) and synthetic (e.g., polythene, nylon, polyesters, Bakelite). Natural rubber, a *cis*-polyisoprene, is derived from isoprene and undergoes vulcanization with sulfur to enhance its elasticity and strength. Synthetic polymers are man-made for specific uses.

Polythene, an addition polymer of ethene, comes in low-density (LDPE, branched, flexible) and high-density (HDPE, linear, rigid) forms. Nylon, a polyamide, includes Nylon-6,6 (from hexamethylenediamine and adipic acid) and Nylon-6 (from caprolactam), both condensation polymers known for high tensile strength in fibers.

Polyesters, like Terylene (PET), are condensation polymers of ethylene glycol and terephthalic acid, forming ester linkages and used in fabrics and bottles. Bakelite, a thermosetting plastic from phenol and formaldehyde, forms a rigid, cross-linked structure that is heat-resistant and an excellent electrical insulator, ideal for switches and handles.

Key distinctions include addition vs. condensation polymerization and thermoplastic vs. thermosetting behavior.

5-Minute Revision

Polymers are high molecular mass compounds formed by linking numerous small molecules called monomers through a process known as polymerization. This topic is fundamental for NEET, requiring a clear understanding of monomer-polymer relationships, polymerization types, and properties.

Natural Polymers: The prime example is Natural Rubber. Its monomer is isoprene (2-methyl-1,3-butadiene), and it's essentially *cis*-polyisoprene. Raw natural rubber is soft and sticky. To improve its properties, it undergoes vulcanization, a process of heating with sulfur.

Sulfur forms cross-links between the polymer chains, significantly increasing its elasticity, tensile strength, and resistance to temperature changes. This makes it suitable for tires and other durable products.

Synthetic Polymers: These are man-made and designed for specific applications.

1
Polythene (Polyethylene): — Formed by the addition polymerization of ethene (
$$ext{CH}_2=\text{CH}_2$$
). There are two main types:

* LDPE (Low-Density Polythene): Highly branched structure, low density, flexible, used in plastic bags, squeeze bottles. * HDPE (High-Density Polythene): Linear structure, high density, rigid, tough, used in buckets, pipes, bottles.

1
Nylon: — A class of polyamides, characterized by amide linkages (
$$-\text{CONH}-$$
). They are formed by condensation polymerization.

* Nylon-6,6: Monomers are hexamethylenediamine (

$$ext{H}_2\text{N}-(\text{CH}_2)_6-\text{NH}_2$$

) and adipic acid (

$$ext{HOOC}-(\text{CH}_2)_4-\text{COOH}$$

). Known for high tensile strength, elasticity, used in fabrics, ropes, tire cords. * Nylon-6: Monomer is caprolactam. Used in tire cords, fabrics.

1
Polyesters (e.g., Terylene/Dacron/PET): — Contain ester linkages (
$$-\text{COO}-$$
). Formed by condensation polymerization.

* Terylene (PET): Monomers are ethylene glycol (

$$ext{HOCH}_2\text{CH}_2\text{OH}$$

) and terephthalic acid (

$$ext{HOOC}-\text{C}_6\text{H}_4-\text{COOH}$$

). Possesses high tensile strength, wrinkle resistance, used in fabrics (often blended), safety belts, bottles.

1
Bakelite: — A classic thermosetting plastic (cannot be remolded once set). Formed by condensation polymerization of phenol (
$$ext{C}_6\text{H}_5\text{OH}$$
) and formaldehyde (
$$ext{HCHO}$$
). It forms a highly cross-linked, rigid, three-dimensional network structure. It is hard, heat-resistant, and an excellent electrical insulator, making it ideal for electrical switches, utensil handles, and non-breakable crockery.

Key Distinctions: Remember that addition polymers form without loss of small molecules, while condensation polymers involve elimination of small molecules. Thermoplastics (Polythene, Nylon, Polyesters) can be remolded, while thermosetting plastics (Bakelite) cannot.

Prelims Revision Notes

Polymers: Natural & Synthetic (NEET Quick Recall)

1. Basic Definitions:

Polymer: — Macromolecule formed by repeating monomer units.
Monomer: — Smallest repeating unit of a polymer.
Polymerization: — Process of forming polymers from monomers.

2. Classification by Origin:

Natural Polymers: — Found in nature. E.g., Natural Rubber, Proteins, Starch, Cellulose.
Synthetic Polymers: — Man-made. E.g., Polythene, Nylon, Polyesters, Bakelite.

3. Classification by Polymerization Mode:

Addition Polymerization: — Monomers add without loss of small molecules. Usually involves unsaturated monomers. E.g., Polythene, Natural Rubber.
Condensation Polymerization: — Monomers react with elimination of small molecules (e.g., H₂O, NH₃). Involves monomers with two or more functional groups. E.g., Nylon-6,6, Terylene, Bakelite.

4. Classification by Thermal Behavior:

Thermoplastics: — Soften on heating, harden on cooling. Can be remolded. Linear/branched chains. E.g., Polythene, Nylon, Polyesters.
Thermosetting Plastics: — Undergo irreversible chemical change on heating, form rigid cross-linked network. Cannot be remolded. E.g., Bakelite.

5. Specific Polymers (Monomers, Type, Properties, Uses):

Natural Rubber:

* Monomer: Isoprene (2-methyl-1,3-butadiene) (

$$ext{CH}_2=\text{C}(\text{CH}_3)-\text{CH}=\text{CH}_2$$

). * Type: Natural, Addition Polymer, *cis*-polyisoprene. * Process: Vulcanization (heating with sulfur) improves elasticity, strength, and resistance to temperature changes by forming cross-links. * Uses: Tires, elastic bands.

Polythene (Polyethylene):

* Monomer: Ethene (

$$ext{CH}_2=\text{CH}_2$$

). * Type: Synthetic, Addition Polymer, Thermoplastic. * LDPE (Low-Density): Branched, flexible, transparent. Uses: Plastic bags, squeeze bottles. * HDPE (High-Density): Linear, rigid, tough. Uses: Buckets, pipes, bottles.

Nylon-6,6:

* Monomers: Hexamethylenediamine (

$$ext{H}_2\text{N}-(\text{CH}_2)_6-\text{NH}_2$$

) and Adipic acid (

$$ext{HOOC}-(\text{CH}_2)_4-\text{COOH}$$

). * Type: Synthetic, Condensation Polymer, Polyamide, Thermoplastic, Fiber. * Properties: High tensile strength, elasticity, abrasion resistance. * Uses: Fabrics, ropes, bristles, tire cords.

Nylon-6:

* Monomer: Caprolactam. * Type: Synthetic, Condensation Polymer, Polyamide, Thermoplastic, Fiber. * Uses: Tire cords, fabrics.

Polyesters (Terylene/Dacron/PET):

* Monomers: Ethylene glycol (

$$ext{HOCH}_2\text{CH}_2\text{OH}$$

) and Terephthalic acid (

$$ext{HOOC}-\text{C}_6\text{H}_4-\text{COOH}$$

). * Type: Synthetic, Condensation Polymer, Polyester linkage (

$$-\text{COO}-$$

), Thermoplastic, Fiber. * Properties: High tensile strength, wrinkle resistance, low moisture absorption. * Uses: Fabric blends, safety belts, bottles (PET).

Bakelite:

* Monomers: Phenol (

$$ext{C}_6\text{H}_5\text{OH}$$

) and Formaldehyde (

$$ext{HCHO}$$

). * Type: Synthetic, Condensation Polymer, Thermosetting Plastic. * Properties: Hard, rigid, heat-resistant, excellent electrical insulator, non-fusible. * Uses: Electrical switches, utensil handles, non-breakable crockery.

Vyyuha Quick Recall

Polymers Need Precise Building Rules:

Polythene: Ethene (Addition)
Nylon-6,6: Hexamethylenediamine + Adipic Acid (Condensation)
Polyesters (Terylene): Ethylene Glycol + Terephthalic Acid (Condensation)
Bakelite: Phenol + Formaldehyde (Condensation, Thermosetting)
Rubber (Natural): Isoprene (Addition, *cis*)