Addition Polymers

Have you ever wondered why plastic wrap stretches while water pipes remain rigid? This difference arises from addition polymers and their distinct properties.

Addition Polymers: Formed by the repetitive addition of monomer units.

Addition Polymerisation: Involves the use of unsaturated monomers such as alkenes, which join through the breaking of double bonds.

Understanding Addition Polymers

• Monomers containing double bonds connect to form polymer chains.
• The process is straightforward and efficient compared to alternative methods.

Role of Catalysts

• Catalysts enhance the rate and efficiency of polymerisation.
• Ziegler-Natta catalysts influence the polymer's molecular weight and branching.

Structural Overview

Polymer	Structure	Key Functional Groups
PE	$(CH_2-CH_2)_n$	None
PVC	$(CH_2-CHCl)_n$	Chloride
PS	$(C_8H_8)_n$	Phenyl
PTFE	$(CF_2-CF_2)_n$	C-F Bonds

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Polyethylene

Structure of Polyethylene

Polyethylene (PE): A widely used plastic formed by linking ethylene units in a chain.

LDPE vs. HDPE

• Low-Density Polyethylene (LDPE):

  • Structure: Visualise LDPE as a tree with branches.
  • Properties: Lower tensile strength, suitable for cling wraps and bags.

• High-Density Polyethylene (HDPE):

  • Structure: Imagine HDPE as a straight pole.
  • Properties: High tensile strength, used in bottles and tanks.

Common Uses

• LDPE: Utilised for supermarket bags and cling wraps, commonly found at home.
• HDPE: Employed in milk jugs and detergent bottles.

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Polyvinyl Chloride (PVC)

Structure and Composition

Polyvinyl Chloride (PVC) is polymerised from vinyl chloride monomer. The chlorine atoms in PVC contribute to its resistance to fire and chemicals.

Forms of PVC

• Flexible PVC: Made pliable by plasticisers, used in garden hoses.
• Rigid PVC: Strengthened with stabilisers, suitable for pipes.

Properties and Uses

• Chemical Resistance: Ideal for industrial chemical containment.
• Durable: Common in construction, such as window frames.

Environmental Considerations

• Production releases harmful dioxins.

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Polystyrene (PS)

Structure of Polystyrene

Polystyrene: Derived from the monomer styrene. Its phenyl groups restrict chain mobility, providing rigidity.

Applications

• EPS (Expanded Polystyrene): Used in packaging and insulation.
• Solid PS (Crystal): Utilised for clear, rigid products.

Properties

• Brittleness: Tends to shatter under impact.
• Thermal Insulation: Air within EPS makes it an excellent insulator.

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Polytetrafluoroethylene (PTFE)

Introduction to PTFE

PTFE, also known as Teflon, is renowned for its heat resistance. Discovered in 1938 by Roy Plunkett, it is a staple in non-stick cookware and industrial applications.

Properties

• Thermal Resistance: Crucial for high-temperature applications, such as cookware.
• Chemical Resistance & Non-Stick Surface: Attributed to strong carbon-fluorine bonds.

Applications of PTFE

• Cookware: Provides easy maintenance and cleaning.
• Electrical Insulators: Valued for dielectric properties.

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Environmental Challenges and Recycling

Environmental Impact

• Polyethylene (PE): A major contributor to plastic pollution.
• Polyvinyl Chloride (PVC): Produces harmful emissions during manufacturing.
• Polystyrene (PS): Persistently remains in ecosystems, challenging to recycle.
• PTFE: Recycling complicated by its strong chemical bonds.

Recycling Advancements

• PE: Technological improvements enhance recovery processes.
• PVC: Innovations like Vinyloop improve recycling capabilities.
• PS: Chemical breakthroughs make component breakdown more efficient.
• PTFE: Pyrolysis offers promise for recovery.

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Exam Tips

Identifying the properties of polymers aids in making informed material selections:

• For high thermal stability or chemical resistance, PTFE is the optimal choice.
• If flexibility is required, LDPE is the best candidate.
• For safe and effective pipe materials, consider PVC.

Key Takeaways for Exams:

• Comprehending properties is pivotal for application efficiency.
• Progress in recycling polymer materials is gaining traction.