Polymers – Chemistry for AIIMS Nursing
Prepared for AIIMS Nursing Entrance Exam – Chemistry
1. Simple Explanation
Polymers are long, chain‑like molecules made up of many repeating units called monomers.
- Monomer: a small molecular unit that can join with others.
- Polymerization: the chemical process that links monomers to form a polymer.
Polymers can be natural (produced by living organisms) or synthetic (made in laboratories/industries). They are the basis of many everyday materials and many medical/clinical supplies.
2. Key Points
| Category | Details | Nursing Relevance |
|---|---|---|
| Types of Polymerization | 1. Addition (Chain‑growth) – monomers add one‑by‑one (e.g., polyethylene, PVC). 2. Condensation (Step‑growth) – monomers join with elimination of a small molecule (e.g., water, methanol) (e.g., nylon, polyester). |
Understanding how medical devices are manufactured (e.g., PVC tubing). |
| Natural Polymers | • Cellulose – plant cell walls, used in gauze, wound dressings. • Proteins (e.g., collagen) – structural support, sutures. • Polysaccharides (e.g., starch, glycogen) – energy stores. • DNA/RNA – genetic material. |
Gauze, sutures, natural wound dressings, biocompatibility. |
| Synthetic Polymers | • Polyethylene (PE) – flexible, low friction, used in IV bags. • Polyvinyl Chloride (PVC) – rigid, used in catheters, tubing. • Polystyrene (PS) – rigid, used in test tubes. • Polyurethane (PU) – elastic, used in wound dressings, foam. |
Sterilization methods, biocompatibility, drug delivery systems. |
| Properties to Know | • Molecular weight (MW) – influences strength, melting point. • Glass transition temperature (Tg) – softening point. • Elongation at break – flexibility. • Biodegradability – important for implants. |
Choosing materials for dressings, implants, and devices. |
| Common Medical Polymers | • Polyethylene oxide (PEO) – used in drug delivery. • Polylactic acid (PLA) – resorbable sutures. • Polyethylene glycol (PEG) – used for PEGylation to reduce immunogenicity. |
Drug formulations, resorbable sutures, coating of implants. |
| Sterilization & Polymers | Some polymers (e.g., PE, PVC) are heat‑stable and can be steam‑sterilized; others (e.g., PU, PLA) are heat‑sensitive and require ethylene oxide or radiation. | Selecting sterilization method for disposable devices. |
3. Worked Example
Problem:
A medical company is producing a synthetic polymer dressing made from polyethylene terephthalate (PET). Two monomers are involved: ethylene glycol (EG) and terephthalic acid (TPA). The reaction is a condensation polymerization:
[ n \text{EG} + n \text{TPA} ;\xrightarrow{\text{heat}}; -[OCH_2CH_2OCOC_6H_4COO]_{n} - + 2nH_2O ]
If the final polymer has an average degree of polymerization (n = 50), calculate:
- The approximate molecular weight (MW) of the polymer.
- The number of water molecules eliminated.
Step‑by‑Step
| Step | Calculation | Result |
|---|---|---|
| 1. MW of EG (C₂H₆O₂) | (2×12.01 + 6×1.008 + 2×16.00 = 62.07) g/mol | 62.07 g/mol |
| 2. MW of TPA (C₈H₆O₄) | (8×12.01 + 6×1.008 + 4×16.00 = 166.13) g/mol | 166.13 g/mol |
| 3. MW of repeat unit (EG + TPA – 2H₂O) | (62.07 + 166.13 – 2×18.02 = 192.14) g/mol | 192.14 g/mol |
| 4. MW of polymer (n = 50) | (50 × 192.14 = 9,607) g/mol | ~9.6 kDa |
| 5. Water eliminated | (2n = 2 × 50 = 100) molecules | 100 H₂O molecules |
Answer:
- The average MW ≈ 9.6 kDa.
- 100 water molecules are removed during polymerization.
4. Quick Revision Summary
- Polymers = long chains of repeating monomers.
- Polymerization: Addition (chain‑growth) vs Condensation (step‑growth).
- Natural polymers: cellulose, collagen, DNA.
- Synthetic polymers: PE, PVC, PS, PU, PLA.
- Key properties: MW, Tg, elongation, biodegradability.
- Medical uses: gauze, sutures, IV bags, tubing, drug delivery.
- Sterilization: heat‑stable polymers → steam; heat‑sensitive → EO or radiation.
- Remember:
- PEG → reduces immunogenicity.
- PLA → resorbable suture.
- PET → used for durable dress