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

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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