Introduction to Polymer Science

LECTURE 1

• Introduction to polymers

LECTURE 2

• Polymer Basics
  • Polymers are formed by the polymerization of monomers.
  • Step-growth polymerization: Every monomer can start polymerization thanks to an initiator.
  • Chain-growth polymerization: Few monomers can initiate growth, but it happens extremely quickly.
  • Classification: Synthetic or semi-synthetic, usually used in plastics.
  • Additives: Commonly incorporated into polymers.
  • Applications: Electronics, safety equipment, and medical devices.
  • Issues: Production (plants/oil), usage (microplastics), and waste management (recycling/incineration/landfill).
• Polymer Morphology
  • Definition: The spatial arrangement of polymer chains (crystalline and amorphous regions); affects mechanical, thermal, and optical properties.
  • Types:
    • Linear Polymers: Flexible, interact via van der Waals and hydrogen bonding.
    • Branched Polymers: Side chains off the main chain; lower density due to less packing.
    • Cross-linked Polymers: Covalent bonds between chains (e.g., vulcanization of elastomers).
    • Networked Polymers: Formed via physical or chemical interactions.
• Thermoplastics and Thermosets
  • Thermoplastics: Can be melted and reshaped; easy to recycle as they don't lose integrity when melted
  • Thermosets: Decompose before melting (e.g., cured or cross-linked polymers).
• Copolymers
  • Definition: Polymers composed of two or more different monomers.
  • Types:
    • Random Copolymers: Monomers are randomly distributed along the chain. The sequence does not follow any particular order, leading to varied properties.

LECTURE 3

• Crystallinity in Polymers
  • Discovery and Basics: Polymers cannot be 100% crystalline due to molecular imperfections.
  • Typical degree: 30% to 80%, depending on the polymer type.
  • Requirements for Crystallization:
    • Regular configurations: (isotactic or syndiotactic) promote crystallization while atactic polymers struggle.
    • Symmetrical binding: Head-to-tail configurations favor crystal formation over head-to-head.
    • Short & sparse side chains: Support crystallization; bulky/irregular chains impede it.
    • Intermediate chain flexibility is necessary; very rigid or highly flexible polymers cannot crystallize effectively.
  • Factors Affecting Crystallinity:
    • Regular copolymer structures increase crystallization chances.
    • Linear polymers have higher chances of crystallizing.
    • Higher molecular weights generally increase crystallinity.
    • Strong inter- and intra-molecular forces (e.g., hydrogen bonds) enhance crystallinity.
    • Cooling rates, evaporation, and annealing conditions affect crystallinity.

LECTURE 4

• Glass Transition Temperature (Tg)
  • Definition: The temperature range between glassy and rubbery states where chain segments gain coordinated motion.
  • Glassy State: Hard, rigid, brittle; limited atomic motion.
  • Rubbery State: Soft, flexible; long-range rotational motion of chain segments.
• Analysis Techniques
  • GPC/SEC: Measures molecular weight distribution using hydrodynamic volume.
  • Other Methods: Viscosimetry, ultracentrifugation, light scattering, and more.

LECTURE 5

• Mechanical Properties of Polymers
  • Types of Deforming Forces: Tensile, Compressive, Shear, Bending, Impact, Creep, and Stress Relaxation.
  • Thermal Effects: Heat deflection temperature, softening temperature and thermal expansion.
  • Failure Mechanisms: Ductile and brittle failure, crazing.
  • Common Failure Modes: Creep failure, fatigue failure, and impact failure.
  • Improving Failure Resistance: Using fibers, crosslinking, and polymer blending.
  • Mechanical Testing: Tensile, compressive, shear, flexural, and impact tests for characterizing mechanical behavior.

LECTURE 6

• Compressive Testing
  • Definition: Measures material response under compression.
  • Measured Properties: Compressive modulus, yield point, compressive strength
  • Thermoplastics Behavior: Excessive deformation before failure, reported as stress at specific deformations (e.g., 1%, 2%, or 10%).
• Shear and Bending Properties
  • Shear Testing: Measures material response to parallel forces.
  • Shearing forces: Distort the object rather than pulling or compressing it.
  • Measurement Techniques: Various instruments depending on fluid properties for measuring viscosity, elasticity, and flow behavior.

LECTURE 7

• Thermal Properties of Polymers
  • Key Temperatures: Melting temperature (Tm), glass transition temperature (Tg), and crystallization temperature (Tc).
  • Heat Deflection Temperature (HDT): The highest temperature at which a polymer can withstand a specific load without significant deformation.
  • Test Procedure: Immerse sample in silicone oil bath, and increase temperature gradually while applying a load.

LECTURE 8

• Introduction to Rheology

  • Definition: The science of how liquids flow and solids deform
  • Measurement Methods (Rheometry): Experimental methods to measure rheological properties (e.g., viscosity).

• Viscosity:

  • Definition: Resistance of a material to shearing forces
  • Newton's Law: τ = η γ [shear stress = viscosity × shear rate]
  • Factors Affecting Viscosity: Temperature (higher temp → lower viscosity), pressure, time, molecular weight, and additives (e.g., fillers).

LECTURE 9

• Bingham Model & Yield Stress: Material behaves as solid at low stress, flows as liquid above threshold (yield stress)
• Benefits of Bingham Flow: Prevents phase separation, reduce sedimentation and flocculation, enhance stability of emulsions and suspensions.
• Types of Non-Newtonian Flows: Shear thinning (pseudoplasticity), shear thickening (dilatancy), Bingham flow, Bingham pseudoplastic, Bingham dilatant.

LECTURE 10

• Rheological Measurement Methods: Description of techniques for measuring rheological properties of various materials (e.g., viscosity, elasticity, and flow behavior).
• Common Measurement Techniques: Descriptions of common laboratory techniques (e.g., Ostwald viscometer).

LECTURE 11

• Oscillating analysis measurement Techniques: Amplitude sweep and frequency sweep used to determine material behavior in different regions.
• Cox-Merz Rule: Steady-state shear viscosity at a given shear rate ≈ complex viscosity at the same frequency; valid for polymer melts, concentrated/semi-dilute solutions.
• Deborah Number (De): Determines material behavior as solid-like or liquid-like (De < 1: viscous response, De ~1: viscoelastic response, De>>1: elastic response).

Additional Topics (From other Sections)

• Tensile Testing and Stress-Strain Behavior: Procedure, output, and key terms to understand tensile testing of materials.
• Factors Affecting Polymer Modulus: Key factors like temperature and molecular weight affecting a polymer's modulus.
• Yielding and Plastic Deformation: Yield point, plastic deformation, necking, and descriptions of ductile/brittle behaviours.
• Fatigue Failure: Definition and description of crack growth due to cyclic loading.
• Crazing: Description of microcavities formed in glassy polymers under excessive tensile stress before yielding.
• Brittle Failure: Description of fracture with minimal deformation.
• Surface Properties: Hardness, friction, and wear resistance.
• Material Modification: Toughening polymers with rubber phases.