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Polymers Overview
World D — Polymers & Biomolecules
39.A — MACROMOLECULES & FORMATION
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R39.01 Monomer to Polymer
- Monomers: Simple, repeating reactive molecules.
- Polymers: Giant macromolecules formed by linking monomers.
- The process of linking them is called Polymerization.
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R39.02 Addition Polymerization
- Monomers contain double or triple bonds (e.g., Ethene).
- Bonds break and link together directly.
- No byproduct is formed. Empirical formula remains the same.
- Example: Polythene, PVC, Teflon.
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R39.03 Condensation Polymerization
- Reaction between two different bi-functional monomers.
- A small molecule (like $H_2O$, $HCl$, or $NH_3$) is eliminated.
- Example: Nylon 6,6 (Hexamethylenediamine + Adipic acid).
R39.04 Homopolymer vs Copolymer
- Homopolymer: Derived from a single type of monomer (A-A-A-A).
- Copolymer: Derived from two or more different monomers (A-B-A-B).
39.B — SOURCE & STRUCTURE
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R39.05 Source Classification
- Natural: Found in nature (Proteins, Cellulose, Natural Rubber, Starch).
- Synthetic: Man-made in labs (Plastics, Nylon, Synthetic Rubbers).
- Semi-Synthetic: Modified natural polymers (Cellulose acetate/Rayon).
R39.06 Linear Polymers
- Long, straight, continuous chains.
- Pack closely together resulting in high density, high melting point, and high tensile strength.
- Example: High-Density Polythene (HDPE), PVC.
R39.07 Branched Chain Polymers
- Linear chains with side branches of varying lengths.
- Branches prevent close packing $\rightarrow$ lower density and lower melting point.
- Example: Low-Density Polythene (LDPE).
R39.08 Cross-Linked Polymers
- Formed from bi- or tri-functional monomers.
- Strong covalent bonds form a massive 3D network.
- Hard, rigid, and brittle. Cannot be remelted.
- Example: Bakelite, Melamine.
39.C — MOLECULAR FORCES
R39.09 Elastomers
- Rubber-like solids with elastic properties.
- Weakest intermolecular forces allow the chains to stretch.
- A few cross-links help the polymer return to its original shape when force is released (Vulcanization).
- Example: Buna-S, Buna-N, Neoprene.
R39.10 Fibers
- Thread-forming solids with high tensile strength.
- Strongest intermolecular forces (Hydrogen bonding or strong dipole-dipole).
- Chains pack closely, leading to crystalline structures.
- Example: Polyamides (Nylon), Polyesters (Terylene).
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R39.11 Thermoplastics
- Linear or slightly branched long chains.
- Intermolecular forces are between elastomers and fibers.
- Soften on heating and harden on cooling. Can be remolded repeatedly.
- Example: Polythene, Polystyrene, PVC.
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R39.12 Thermosetting Polymers
- Heavily branched and cross-linked molecules.
- On heating, they undergo extensive cross-linking in molds to become infusible.
- Cannot be softened, remelted, or reshaped once set.
- Example: Bakelite, Urea-formaldehyde resins.