About this previous year paper
POLYMER SCIENCE & TECHNOLOGY (NOE045)
Section-wise Solved Answers & Notes
SECTION – A (10 × 2 = 20 Marks)
Very short, precise answers
(a) Cross-linked polymers & Branched polymers
• Cross-linked polymers: Chains joined by covalent bonds forming a 3D network (e.g., Bakelite).
• Branched polymers: Main chain with side branches (e.g., LDPE).
(b) Tacticity in polymers
Tacticity refers to the spatial arrangement of side groups along the polymer chain (isotactic, syndiotactic, atactic).
(c) Degree of polymerization & Functionality
• Degree of polymerization (DP): Number of repeating units in a polymer chain.
• Functionality: Number of reactive sites in a monomer molecule.
(d) Repeating unit of ABS polymer
ABS consists of Acrylonitrile, Butadiene, and Styrene units combined in a copolymer structure.
(e) Why Tg is higher for high molecular weight polymers
Higher molecular weight polymers have greater chain entanglement, restricting molecular motion and increasing Tg.
(f) Decrease in elastic behaviour of PVC with impurities
Impurities disturb chain alignment and reduce intermolecular forces, decreasing elasticity.
(g) Inhibitors & their significance
Inhibitors are substances that slow down or stop polymerization by neutralizing free radicals, preventing unwanted reactions.
(h) Condensation vs Addition polymerization
| Condensation | Addition |
|---|---|
| By-product formed | No by-product |
| Stepwise growth | Chain growth |
| Example: Nylon | Example: PVC |
(i) Alternate & Graft copolymers
• Alternate copolymers: Monomers arranged alternately (A-B-A-B).
• Graft copolymers: Side chains of one polymer grafted onto backbone of another.
(j) PTFE behaves like thermoset
PTFE is thermoplastic but shows high thermal stability and rigidity due to strong C–F bonds, resembling thermoset behavior.
SECTION – B (Any 5 × 10 = 50 Marks)
(a) Elastomers & SBR (Buna-S)
Elastomers: Polymers showing rubber-like elasticity.
SBR (Buna-S):
• Preparation: Emulsion polymerization of butadiene and styrene
• Properties: High abrasion resistance, elasticity
• Applications: Tyres, footwear, belts
(b)(i) Initiators & free radical polymerization
Initiators generate free radicals.
Example: Benzoyl peroxide decomposes to form radicals initiating addition polymerization.
(b)(ii) Molecular weight averages
Given:
10% → MW = 10,000 90% → MW = 1,00,000
Mn=∑wi∑(wi/Mi)=≈52,631M_n = \frac{\sum w_i}{\sum (w_i/M_i)} = \approx 52,631Mn=∑(wi/Mi)∑wi=≈52,631 Mw=∑wiMi=91,000M_w = \sum w_i M_i = 91,000Mw=∑wiMi=91,000
(c)(i) Emulsion polymerization
Polymerization occurs in aqueous medium using emulsifier.
Advantages: good heat control, high molecular weight.
(c)(ii) Number average DP
DPn=11−pDP_n = \frac{1}{1-p}DPn=1−p1
(Values calculated for given extent of reaction in exam)
(d) Kinetics of free radical polymerization
Steps: • Initiation
• Propagation • Termination
Degree of polymerization depends on rate of initiation and termination.
(e) High performance polymers (PMMA & PC)
PMMA: • Transparent, rigid
• Used in lenses, aircraft windows
Polycarbonate (PC): • High impact strength
• Used in safety helmets, CDs
(f) Composite polymers Polymers reinforced with fibers or fillers.
Processing methods:
• Hand lay-up • Filament winding
(g)(i) Condensation polymerization mechanism
Step-growth process involving elimination of small molecules like water or HCl.
(g)(ii) Numerical
Given: Styrene = 104 g
Dp = 1000 Moles of styrene = 1
Number of polymer molecules = 11000\frac{1}{1000}10001
(h) Ziegler–Natta Catalyst
Catalyst used in coordination polymerization producing stereoregular polymers.
Advantages: • Better control
• High molecular weight • Less branching
SECTION – C (Any 2 × 15 = 30 Marks)
Q3 Differentiation
(i) Thermoplastic vs Thermosetting
| Thermoplastic | Thermosetting |
|---|---|
| Recyclable | Non-recyclable |
| Linear chains | Cross-linked |
| Example: PVC | Example: Bakelite |
(ii) Suspension vs Emulsion polymerization
| Suspension | Emulsion |
|---|---|
| Larger particles | Very fine particles |
| No emulsifier | Emulsifier used |
(iii) Buna-S vs Buna-N
| Buna-S | Buna-N |
|---|---|
| Styrene + Butadiene | Acrylonitrile + Butadiene |
| Tyres | Oil-resistant goods |
Q4 (Any three)
(i) Vulcanization
Process of heating rubber with sulfur to increase strength and elasticity.
(ii) Polyamides
Nylon polymers formed by condensation polymerization; high strength and toughness.
(iii) Phenol Formaldehyde
Thermosetting polymer with high heat resistance; used in electrical fittings.
(iv) Applications of polymers • Biomedical: artificial joints, syringes
• Space: lightweight composites, insulation
Q5
(i) Effect of polymer structure on properties • Chain length → strength
• Cross-linking → rigidity • Tacticity → crystallinity
(ii) PVA (Polyvinyl Alcohol) • Preparation: Hydrolysis of PVC
• Properties: Water soluble, adhesive • Uses: Films, adhesives
(iii) Factors affecting Glass Transition Temperature
• Molecular weight • Chain flexibility
• Cross-linking • Plasticizers