THEORY EXAMINATION (SEM–IV) 2016-17 POLYMER SCIENCE & TECHNOLOGY

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

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(C6​H5​CO)2​O2​→2C6​H5​COO⋅

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

(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

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: