About this previous year paper
Course: B.Tech (All Engineering Branches – Common Elective)
Subject Code: EOE045
Subject Title: Polymer Science & Technology
Exam Type: Theory
Duration: 3 Hours
Maximum Marks: 100
SECTION – A (10 × 2 = 20 Marks)
Concept-based short questions to test theoretical understanding of polymer fundamentals
| No. | Question | Concept Summary |
|---|---|---|
| (a) | Cross-linked vs Branched Polymers | Cross-linked polymers have covalent links between chains (e.g., Bakelite), forming 3D networks; branched polymers have side chains on the main backbone (e.g., LDPE). |
| (b) | Tacticity in Polymers | Refers to stereoregularity — arrangement of side groups along the chain (isotactic, syndiotactic, atactic). |
| (c) | Degree of Polymerization (DP) & Functionality | DP = number of monomer units per chain; functionality = number of reactive sites per monomer. |
| (d) | Structure of ABS Polymer | Acrylonitrile–Butadiene–Styrene copolymer; repeating unit contains –CH₂–CH(CN)– and butadiene segments. |
| (e) | Tg and Molecular Weight | Glass transition temperature (Tg) increases with molecular weight due to restricted segmental motion. |
| (f) | Elastic Behavior of PVC | Decreases with impurities because they disrupt polymer chain alignment and crystallinity. |
| (g) | Inhibitors | Compounds added to prevent unwanted polymerization (e.g., hydroquinone in styrene). |
| (h) | Condensation vs Addition Polymerization | Condensation: byproduct formed (e.g., water, HCl); Addition: no byproduct, occurs via free radicals or ions. |
| (i) | Alternate vs Graft Copolymers | Alternate: monomers alternate regularly (ABAB); Graft: chains of one polymer attached to backbone of another. |
| (j) | PTFE Behavior | Though thermoplastic, strong C–F bonds and high crystallinity make PTFE (Teflon) behave like a thermoset. |
SECTION – B (5 × 10 = 50 Marks)
Descriptive and numerical problems on polymer synthesis and properties
(a) Elastomers – SBR (Buna-S)
Preparation: Copolymerization of butadiene and styrene using emulsion polymerization.
Properties: High elasticity, abrasion resistance, good aging stability.
Applications: Tires, shoe soles, conveyor belts.
(b) Initiators & Free Radical Polymerization
Initiator Example: Benzoyl peroxide decomposes to generate radicals:
- (C6H5CO)2O2→2C6H5COO⋅(C_6H_5CO)_2O_2 \rightarrow 2C_6H_5COO^\cdot(C6H5CO)2O2→2C6H5COO⋅
Steps: Initiation → Propagation → Termination.
Numerical: Molecular weight averages (Mn, Mw) computed for given polymer fractions.
(c) Emulsion Polymerization
Mechanism: Micelles act as reaction sites; monomers emulsified in water with surfactant.
Advantages: High molecular weight polymers with uniform particle size.
Example Calculation: Degree of polymerization for hexamethylene diamine + adipic acid mixtures at various conversions (p values).
(d) Kinetics of Free Radical Polymerization
Overall rate:
- Rp=kp[M][R⋅]R_p = k_p [M][R^\cdot]Rp=kp[M][R⋅]
Degree of polymerization (DP) depends on ratio of propagation to termination rates.
(e) High Performance Polymers
| Polymer | Preparation | Key Properties | Applications |
|---|---|---|---|
| PMMA (Acrylic) | Polymerization of methyl methacrylate | Transparent, weather-resistant | Optical lenses, screens |
| PC (Polycarbonate) | Condensation of bisphenol-A and phosgene | High impact strength, optical clarity | CDs, safety glass |
(f) Composite Polymers
Combination of polymer matrix with reinforcement (fibers or fillers).
Processing Methods: Hand lay-up, filament winding, pultrusion, compression molding.
(g) Condensation Polymerization Mechanism
Step-growth process forming byproducts.
Example: Nylon-6,6 from hexamethylene diamine and adipic acid.
Numerical: Number of molecules of polystyrene formed from given monomer mass and DP.
(h) Ziegler–Natta Catalysts
Catalyst System: TiCl₄ + (C₂H₅)₃Al.
Function: Controls stereoregularity, allowing isotactic polymer formation.
Significance: Produces high-density polymers (e.g., HDPE, polypropylene) not achievable by free-radical methods.
Classification: By origin, stereoregularity, thermal behavior, and ultimate form.
SECTION – C (2 × 15 = 30 Marks)
In-depth analytical questions
Q3. Polymer Comparisons
| Aspect | Thermoplastic | Thermosetting |
|---|---|---|
| Heat Response | Softens on heating | Hardens permanently |
| Structure | Linear / branched | Cross-linked |
| Example | PVC, PE | Bakelite, Epoxy |
Suspension vs Emulsion Polymerization: Differ by particle size, medium, and stabilizer type.
Buna-S vs Buna-N: SBR (butadiene–styrene) vs NBR (butadiene–acrylonitrile); NBR resists oil.
Q4. Detailed Topics
Vulcanization: Heating rubber with sulfur; cross-links improve elasticity and strength.
Polyamides: Formed via condensation (e.g., Nylon-6,6); high tensile and thermal strength.
Phenol–Formaldehyde Resin: Step-growth polymer; thermoset used in coatings, adhesives, laminates.
Polymer Applications: Biomedical (catheters, implants), space (thermal insulation, composites).
Q5. Structure–Property Relationships
Factors Affecting Properties: Chain length, cross-linking, crystallinity, and side groups.
PVA (Polyvinyl Alcohol): Prepared by hydrolysis of polyvinyl acetate; water-soluble, good film-former.
Glass Transition Temperature (Tg): Affected by chain flexibility, intermolecular forces, bulky side groups, and cross-link density.
Summary
This Polymer Science & Technology (EOE045) paper tests:
| Topic | Key Concepts |
|---|---|
| Polymerization Mechanisms | Addition, condensation, emulsion, coordination |
| Polymer Structures | Linear, branched, cross-linked, stereoregular |
| Properties & Processing | Elasticity, Tg, crystallinity, composite techniques |
| Polymer Chemistry | Initiators, inhibitors, degree of polymerization |
| Applications | Engineering plastics, elastomers, biomedical and aerospace uses |