Study Notes on Polymers

Definition of Polymers:
- The term 'polymer' is derived from Greek words, where "poly" means several and "meros" means parts.
- Polymers are high molecular weight substances made up of large molecules of colloidal dimensions (10^-4 to 10^-7 cm).
- Composed predominantly of long chain macromolecules.
- Chains are made of similar or different repeating units on a backbone of carbon or other polyvalent atoms.
Monomers:
- The smallest units of a polymer known as monomers or repeating units or building blocks.
- Monomers are joined through covalent bonding.
Importance of Polymers:
- Key components of modern civilization and critical products of chemical industries.
- Ability to modify physical properties through additives while maintaining inherent characteristics.
- Ubiquitous impact on daily life from household products to applications in space.
Distinction Between Polymers and Macromolecules:
- While both are high molecular weight substances, all polymers consist of repeating structural units, whereas macromolecules may vary in structure.
- Examples:
- Starch is both a polymer and macromolecule (made from repeating glucose).
- Nucleic acids are macromolecules but not considered polymers (composed of different units: phosphoric acid, sugar, nitrogen base).
- Polyvinyl chloride (PVC) is a polymer but can be regarded as a macromolecule.
- Haemoglobin is a macromolecule but does not have repeated units.

High molecular weight implies polymers have extensive chain lengths and different extents of cross-linking.
Methods to Determine Molecular Weight:
- Number-average molecular weight (Mn):
- Formula:
  $M_n = \frac{M_1n_1 + M_2n_2 + M_3n_3 + \ldots}{n_1 + n_2 + n_3 + \ldots}$
- Each species contributes equally to colligative properties (freezing point depression, boiling point elevation, osmotic pressure).
- Weight-average molecular weight (Mw):
- Formula:
  $M_w = \frac{w_1M_1 + w_2M_2 + w_3M_3 + \ldots}{w_1 + w_2 + w_3 + \ldots}$
- Determined by light scattering, ultracentrifugation methods focusing more on size than number of molecules.
- Poly Dispersity Index (PDI):
- Ratio of weight average to number average:
  $PDI = \frac{M_w}{M_n}$
- Natural polymers are monodisperse (PDI = 1) whereas synthetic have a wide mass range (PDI > 1).

Based on Occurrence:
- Natural Polymers: Proteins, cellulose, starch, natural rubber.
- Synthetic Polymers: Created in laboratories; examples include Bakelite, PVC, polyethene.
Based on Monomeric Unit:
- Homopolymers: Composed of a single type of monomer (e.g., polyethylene, polypropylene).
- Copolymers: Made from two or more monomers (e.g., nylon 66, bakelite).
Based on Structure:
- Linear Polymers: Monomers linked in straight chains (e.g., polyethylene).
- Branched Polymers: Chains with side branches.
- Cross-linked Polymers: Chains connected at multiple points.
Based on Backbone Composition:
- Organic Polymers: Backbone contains predominantly carbon.
- Inorganic Polymers: Backbone includes elements like silicon, phosphorus (e.g., silicones).
Based on Tacticity:
- Isotactic: All side groups on the same side.
- Syndiotactic: Alternating side groups.
- Atactic: Random arrangement of side groups.
Based on Synthesis Method:
- Addition Polymers: Formed from monomers with double/triple bonds.
- Condensation Polymers: Join monomers with loss of small molecules (e.g., water).

Functionality: Number of bonding sites in monomers critical for polymerization.
Monomers must have at least 2 active sites to polymerize:
- Bifunctional: e.g., ethylene glycol, adipic acid.
- Trifunctional: e.g., melamine.
Bifunctional monomers yield linear polymers; multifunctional monomers yield branched/cross-linked structures.

Two main types:
- Addition Polymerization (Chain Growth): Monomers add without losing atoms.
- Condensation Polymerization: Monomers combine with loss of small molecules (e.g., H2O).
Process Steps in Addition Polymerization:
1. Initiation: Generation of free radicals.
2. Propagation: Continuous addition of monomers to radical.
3. Termination: Various methods including coupling, disproportionation.
Example of Addition Polymerization:
- Polyvinyl chloride (PVC) synthesis from vinyl chloride.
- Condensation Polymerization: Requires bifunctional monomers, producing polymer with byproducts (e.g., water).

Definition: Organic macromolecular materials that can be shaped with heat, pressure.
Types of Plastics:
- Natural Plastics: Derived from natural sources (e.g., amber).
- Synthetic Plastics: Man-made (e.g., PVC, polyethene).
Important classifications:
- Thermoplastics: Soft when heated, reversible hardening (e.g., polyethylene, PVC).
- Thermosetting Plastics: Irreversibly set, cannot be remelted (e.g., Bakelite, urea-formaldehyde).

Polythene (Polyethylene):
- Types:
  - Low-Density Polyethylene (LDPE): Branched structure, soft, used in bags and films.
  - High-Density Polyethylene (HDPE): Linear structure, stronger, used in containers.
Polyvinyl Chloride (PVC):
- Used in plumbing, cables, and as a durable container material.
Polypropene (Polypropylene): Strong, used in packaging, ropes.
Polytetrafluoroethylene (PTFE): Non-stick coatings (Teflon), high chemical resistance.
Polystyrene: Lightweight, used in packaging, insulations.
Polymethyl Methacrylate (PMMA): Transparent, shatter-resistant, used in lenses.
Polyurethanes: Flexible foams, resistant to environmental factors.

Bakelite: Formed from phenol and formaldehyde, used in electrical insulations.
Epoxy Resins: Formed from epichlorohydrin and bisphenol, known for adhesive properties.
Urea-Formaldehyde Resins: Clear, good adhesive properties, used in wood and textiles.

Definition of Elastomers: Polymers with elastic properties (e.g., natural rubber).
- Natural Rubber: Polymer of isoprene, structure leads to weak intermolecular forces.
- Vulcanization: Process of treating rubber with sulfur to create cross-links, enhancing elasticity and strength.

Process that improves rubber's properties: heating with sulfur forms cross-links, making vulcanized rubber hard and elastic.

Types of synthetic fibers include polyesters (e.g., terylene) and nylon (e.g., nylon-6, nylon-66).
Each type has applications based on its strength and durability, from textiles to engineering components.