Polymer Science Quiz

MMET 206 Lecture Notes 4: Polymers

• Polymers are substances composed of large molecules with repeating structural units (monomers) connected by covalent bonds.
• Synthetic polymers are artificially created via chemical synthesis, not derived from natural sources.
• Examples of synthetic polymers include fibers (aramid, Nomex, Kevlar, nylon, polyester), plastics (acrylics, PET, styrene butadiene), elastomers (rubbers), protective coatings (paint, varnish), and adhesives (cyanoacrylates).
• Crude oil and natural gas are natural resources used to produce polymers.
• Crude oil is a mixture of various hydrocarbons (HCs) with varying molecular sizes.
• Part 1 of the lecture focuses on Crude Oil/Monomers, outlining its composition and preparation.
  • Refining crude oil by fractional distillation breaks it into various hydrocarbon fractions.
  • Cracking breaks larger HCs to smaller ones, including producing monomers.
• Part 2 (Step 3) details Polymerization/Polymers, the process connecting monomers into a polymer.
  • This step uses polymerization processes such as addition (chain growth) and condensation (step growth).
• Polymerization methods:
  • Addition Polymerization (Chain Growth): This process involves rapid reactions between chemically active monomers to form long-chain polymers.
  • Condensation Polymerization (Step Growth): This process involves the individual chemical reactions between pairs of reactive monomers, often with water as a byproduct, and results in a slower polymerization process.
• Part 3 focuses on Synthetic Fibers.
  • Polyester (PET) — used in fibers for curtains, dress fabrics, and fillers for various products.
  • Polyamide (PA, aramid fibers)— includes Nomex and Kevlar, known for heat resistance use in space shuttles, fire protection gear, and race cars.
  • Polyacrylonitrile (PAN, acrylic fibers)— synthetic fibers having a wool-like feel, commonly used for sweaters, hats, and rugs.
• Part 4 focuses on Plastics.
  • Thermoplastics— materials that can be repeatedly heated and reshaped. They include:
    • Commodity Plastics: Common-use plastics (PET, HDPE, PVC, LDPE, PP, PS).
    • Engineering Plastics: Specialized plastics with superior mechanical properties and used in engineering applications(e.g., nylon).
    • Plastic Alloys: These are mixtures of two or more polymers, which can enhance specific properties.
    • Thermosets: Materials that undergo irreversible changes and form strong, permanent crosslinks during curing, making them non-recyclable. They include Phenolics (PF), Amino Plastics (UF, MF), Unsaturated Polyesters (UP), Vinyl Esters (VE), Epoxies (EP), Thermoset Polyimides (PI), and Polyurethane (PU or PUR).
• Part 5 focuses on Rubbers (aka Elastomers) and their properties.
  • Types of synthetic rubbers include polyisoprene (IR), butadiene rubber (BR), nitrile rubber (NBR), styrene butadiene rubber (SBR), chloroprene/neoprene rubber (CR), butyl rubber (IIR), silicone rubber (SI), and ethylene propylene diene monomer (EPDM) rubber.
    • Rubber aging or degradation due to weather cracking is mainly caused by direct sunlight, UV light, and heat.
  • Different applications of these types of rubbers include:
    • Tire components.
    • Car weather seals.
    • Protective equipment.
  • Thermoplastic rubbers are also described.

Other Key Concepts

• Degree of Polymerization (DP): The average number of repeating units in a polymer molecule, significantly influencing properties.
• Crystallinity of Polymers: Polymers can have crystalline regions, amorphous regions, or mixtures of both.
• Glass Transition Temperature (Tg): The temperature at which amorphous polymers change from a hard, brittle state to a rubbery state.
• Additives: Substances added to polymers to modify or enhance properties.
• Manufacturing Processes: Common methods for making plastic products include injection molding, extrusion, blow molding, cast film extrusion, vacuum thermoforming, and rotation molding.