Polymers and Their Classification
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Questions and Answers

What is the glassy state of a polymer characterized by?

  • High thermal energy
  • Long range rotational motion
  • Short range vibrational motion (correct)
  • Flexible chain movement

Which of the following factors increases the glass transition temperature (Tg) of a polymer?

  • Increased chain mobility
  • Lower percentage of crystallinity
  • Heating the polymer above Tg
  • Presence of bulky side groups (correct)

What is the primary difference between the rubbery state and the glassy state of polymers?

  • Chain movement ability (correct)
  • Molecular weight
  • Temperature dependency
  • Color and appearance

How does the presence of aromatic rings affect the Tg of a polymer?

<p>It increases Tg due to increased stiffness (D)</p> Signup and view all the answers

Which state is a polymer in when it is above its Tg?

<p>Viscoelastic state (D)</p> Signup and view all the answers

What happens to the Tg of a polymer with increased crystallinity?

<p>Tg increases due to reduced mobility (C)</p> Signup and view all the answers

What effect does chain stiffness have on the glass transition temperature (Tg)?

<p>Stiff chains increase Tg (C)</p> Signup and view all the answers

Which of the following statements accurately describes the conditions for using hard plastics like polystyrene?

<p>They are used in the glassy state at room temperature. (C)</p> Signup and view all the answers

What is the primary purpose of catalysts in thermosetting plastics?

<p>To accelerate polymerization (D)</p> Signup and view all the answers

Which of the following substances can be used as catalysts in thermosetting plastics?

<p>Benzoyl peroxide (B)</p> Signup and view all the answers

What role do antioxidants play in the processing of polymers?

<p>They inhibit undesirable oxidation (A)</p> Signup and view all the answers

Liquid crystals are characterized by which of the following properties?

<p>Anisotropy of properties without a crystal lattice (B)</p> Signup and view all the answers

Which of the following additives improves the thermal stability of polymers during processing?

<p>Stabilizers (B)</p> Signup and view all the answers

Who is credited with the discovery of the liquid crystal phase?

<p>Friedrich Reinitzer (A)</p> Signup and view all the answers

Which of these compounds is an example of a pigment used in polymers?

<p>Antimony sulphide (C)</p> Signup and view all the answers

The term 'mesophase' in reference to liquid crystals describes which characteristic?

<p>Their behavior between solid and isotropic liquid (B)</p> Signup and view all the answers

What is a characteristic feature of conductive element filled polymers?

<p>They contain a polymer binder holding conducting elements. (A)</p> Signup and view all the answers

Which type of polymer is created by blending an insulator with a conducting polymer?

<p>Blended conducting polymer (B)</p> Signup and view all the answers

In what application is polyaniline primarily used?

<p>As a sensor for ammonia. (D)</p> Signup and view all the answers

Which polymer type shows increased conductivity when doped cis-forms are compared to their trans analogues?

<p>Polyacetylenes (B)</p> Signup and view all the answers

What is one of the notable applications of conducting polymers in current technology?

<p>For light weight rechargeable batteries. (A)</p> Signup and view all the answers

What characteristic do coordination conducting polymers exhibit due to the combination with coordination complexes?

<p>They demonstrate conductive properties. (A)</p> Signup and view all the answers

Which of the following describes the process of forming polyacetylene?

<p>It forms at the gas-liquid interface with acetylene and a catalyst. (D)</p> Signup and view all the answers

What is compounding of plastics primarily concerned with?

<p>Adding additives to enhance characteristics of plastics. (D)</p> Signup and view all the answers

What action must occur for vertically polarized light to pass through a horizontal polarized filter?

<p>The light must be rotated 90 degrees. (D)</p> Signup and view all the answers

What role does the liquid crystal layer play in a LCD?

<p>It twists the molecules to control light orientation. (A)</p> Signup and view all the answers

What happens to the light when no voltage is applied between the electrodes?

<p>The light passes through and appears white. (D)</p> Signup and view all the answers

How are different gray levels produced on the LCD screen?

<p>By varying the amount of voltage applied between layers. (A)</p> Signup and view all the answers

What is the function of the color filters in front of the outer polarization plate?

<p>To produce different color images by varying intensity. (A)</p> Signup and view all the answers

What causes a pixel to appear black when voltage is applied?

<p>The liquid crystal molecules untwist and block the light. (D)</p> Signup and view all the answers

What is a characteristic of liquid crystal polymers?

<p>They retain molecular order in both liquid and solid states. (D)</p> Signup and view all the answers

Which of the following is NOT a function of the electrodes in the liquid crystal display?

<p>To create a color effect in pixels. (A)</p> Signup and view all the answers

What is a characteristic of long chain, linear polymers?

<p>They retain their shape upon heating. (D)</p> Signup and view all the answers

Which type of polymerization results in the loss of small molecules?

<p>Condensation polymerization (C)</p> Signup and view all the answers

What initiates the addition polymerization process?

<p>Heat, light, pressure, or catalyst (C)</p> Signup and view all the answers

What happens to the structure of a polymer during heating above the glass transition temperature?

<p>It softens into a viscous liquid. (A)</p> Signup and view all the answers

Which of the following is an example of a high molecular weight polymer?

<p>Nylon 6,6 (D)</p> Signup and view all the answers

What is a property of polymers formed by addition polymerization?

<p>They yield an exact multiple of the monomer. (C)</p> Signup and view all the answers

Which of the following characteristics is true for high molecular weight polymers?

<p>Hard and strong. (A)</p> Signup and view all the answers

What is the main difference between addition and condensation polymerization?

<p>Addition focuses on unsaturated bonds; condensation does not. (D)</p> Signup and view all the answers

What is the effect of polar side atoms or groups on the glass transition temperature (Tg) of polymers?

<p>They increase the intermolecular attractive interactions, raising Tg. (C)</p> Signup and view all the answers

How does increasing molecular weight affect Tg and Tm of polymers?

<p>It increases Tg and Tm. (A)</p> Signup and view all the answers

What is the effect of plasticizers when added to polymers?

<p>They decrease the brittleness of the polymer and lower Tg. (A)</p> Signup and view all the answers

What is the result of co-polymerization on the glass transition temperature?

<p>It introduces disorder, which lowers Tg. (A)</p> Signup and view all the answers

How does the presence of flexible pendant groups in a polymer affect its Tg?

<p>It enhances the rotational motion of the chains, lowering Tg. (B)</p> Signup and view all the answers

What characteristic of conducting polymers allows them to exhibit metallic conductivity?

<p>Conjugated double bonds providing delocalized pi electrons. (D)</p> Signup and view all the answers

How does moisture content in a polymer influence its Tg?

<p>It increases the distance between polymer chains, thus lowering Tg. (A)</p> Signup and view all the answers

What effect does cross-linking have on the glass transition temperature of polymers?

<p>It increases the restriction and stiffness, raising Tg. (C)</p> Signup and view all the answers

Flashcards

Condensation Polymerization

A type of polymerization where monomers with polar groups react together, forming a polymer and eliminating small molecules like water. This creates a 3D network of cross-linked structures.

Addition Polymerization

A type of polymerization where monomer molecules with double or triple bonds link together, forming a polymer without losing any material during the process. It's initiated by factors like heat, light, pressure, or catalysts, breaking the double bonds.

Linear Polymer

A long chain polymer with few or no cross-links. It can be easily reshaped compared to cross-linked polymers.

Cross-linked Polymer

A three-dimensional network polymer with strong covalent bonds and cross-links. It retains its shape after being heated and cannot be easily reshaped.

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Glass Transition Temperature (Tg)

The temperature range where a polymer transitions from a hard, brittle state to a soft, flexible, or liquid-like state.

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Melting Point (Tm)

The temperature at which a polymer changes from a solid state to a liquid state.

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Low Molecular Weight Polymer

Polymers with smaller chains. Often soft, weak, and brittle.

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High Molecular Weight Polymer

Polymers with longer chains. Often hard, strong, and more brittle.

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Tg (Glass Transition Temperature)

The temperature at which amorphous polymer chains gain enough thermal energy to begin sliding past each other, becoming more flexible.

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Glassy State

A hard and brittle state of amorphous polymers in which the chains have limited motion.

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Rubbery State

A soft and flexible state of amorphous polymers above the Tg, where segments can move freely.

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Viscoelastic State

The state of an amorphous polymer above its Tg, exhibiting both viscous (liquid-like) and elastic (solid-like) properties.

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Crystallinity Effect on Tg

Increased crystallinity in a polymer leads to a higher Tg.

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Chain Mobility and Tg

More mobile polymer chains have lower Tg values, meaning they transition to a rubbery state at lower temperatures.

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Chain Stiffness and Tg

Stiff polymer chains have higher Tg values, as they require more energy to become flexible.

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Side Groups Impact on Tg

Bulky side groups increase Tg by hindering chain movement due to steric hindrance.

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What affects Tg?

Several factors influence the glass transition temperature (Tg) of a polymer, including the presence of polar groups, molecular weight, copolymerization, cross-linking, plasticizers, and flexible pendant groups.

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Polar groups and Tg

The presence of polar side groups or atoms in a polymer increases the attractive forces (like dipole-dipole interactions) between polymer chains, resulting in higher Tg.

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Molecular weight and Tg

Increasing the molecular weight of a polymer generally leads to a higher Tg and melting point (Tm).

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Copolymerization and Tg

Random copolymerization often reduces Tg because the different monomers create a less ordered structure, hindering chain packing.

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Cross-linking and Tg

Cross-linking, which creates strong, covalent bonds between polymer chains, significantly increases Tg due to the introduction of rigidity and stiffness.

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Plasticizers and Tg

Plasticizers, generally low molecular weight compounds, reduce Tg by slipping between polymer chains, decreasing intermolecular forces and increasing chain mobility.

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Flexible pendant groups and Tg

Flexible side groups, like aliphatic chains, can hinder chain packing and increase rotational motion, leading to a lower Tg.

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What are conducting polymers?

Conducting polymers are materials that exhibit electrical conductivity properties similar to semiconductors or even metals. They possess delocalized pi electrons due to conjugated double bonds, enabling charge transport.

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What are catalysts in polymers?

Catalysts are substances added to thermosetting plastics to speed up the process of forming a solid, cross-linked structure during molding.

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What's the purpose of antioxidants in polymers?

Antioxidants are additives used to prevent polymers from breaking down due to exposure to high temperatures during molding or storage.

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What are pigments and dyes in polymers?

Pigments are colorants that give polymers a solid, opaque color. Dyes are used to give transparent polymers a bright color.

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What do stabilizers do for polymers?

Stabilizers improve the thermal stability of polymers during processing, protecting them from degradation caused by heat, oxygen, and sunlight.

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What is a liquid crystal?

A liquid crystal is a state of matter with properties between a liquid and a solid. It can flow like a liquid, but its molecules can align like a solid.

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What was Reinitzer's contribution to liquid crystals?

Reinitzer observed that a material called cholesteryl benzoate had two distinct melting points, indicating a new phase of matter: the liquid crystal phase.

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Conductive Polymer

A material that combines a polymer (often an insulator) with conducting elements like carbon black, metallic fibers, or metal oxides. This results in a lightweight, strong, and conductive material.

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What is the scientific name for the liquid crystal phase?

The scientific name for the liquid crystal phase is 'mesophase'.

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Blended Conducting Polymer

A polymer created by mixing a conventional insulator polymer with a conducting polymer. This combination enhances the electrical conductivity of the material without significantly changing its mechanical properties.

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How are liquid crystals characterized?

Liquid crystals are characterized by their anisotropic properties, meaning their properties vary depending on direction, but they don't have a fixed, three-dimensional crystal structure.

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Coordination Conducting Polymer

A material formed by combining a polymer with a coordination complex, usually involving a metal atom bound to a polydentate ligand. This interaction allows the polymer to become conductive due to electron transitions.

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Why are Conducting Polymers Used in Rechargeable Batteries?

Conducting polymers, like polypyrrole, are used in rechargeable batteries because their structure allows them to undergo oxidation and reduction reactions during charging and discharging, facilitating the storage and release of electrical energy.

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Polyacetylene - A Pioneer in Conducting Polymers

Polyacetylene is a simple yet significant conductive organic polymer. Its discovery sparked a boom in the research and development of conductive polymers.

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Cis vs. Trans Polyacetylene

Polyacetylene exists in two forms: cis and trans. The cis form is generally more conductive than the trans form due to its less stable configuration.

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What are LCDs?

LCDs (Liquid Crystal Displays) are screens that use liquid crystal molecules to control light passage and display images. They are commonly found in TVs, monitors, and mobile devices.

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How do LCDs work?

LCDs work by applying voltage to liquid crystal molecules sandwiched between polarizing filters. Voltage alters molecule orientation, controlling light passage for pixel brightness.

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What is polarization?

Polarization refers to the direction of light waves' oscillation. A polarization filter allows only light waves oscillating in a specific direction to pass.

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How does a liquid crystal layer work?

The liquid crystal layer is composed of molecules that can be twisted. This twisting lets vertically polarized light pass through and become horizontally polarized.

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What happens when no voltage is applied?

Without voltage, the liquid crystal molecules stay twisted. This lets light pass through both polarizing filters, resulting in a white pixel.

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What happens when voltage is applied?

When voltage is applied, the liquid crystal molecules untwist. This blocks light from passing through the second polarizing filter, making the pixel appear black.

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How does a liquid crystal polymer work?

A liquid crystal polymer retains molecular order in both liquid and solid states. This property allows for the creation of displays with unique properties.

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How are color images displayed on LCDs?

Color images are produced by placing color filters (red, green, blue) in front of each pixel. Varying the intensity of each color creates a full spectrum.

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Study Notes

Polymers

  • A polymer is a large molecule formed by repeating small molecules (monomers)
  • Degree of polymerization is the number of repeating units in a polymer chain.
  • Functionality is the number of reactive sites in a monomer.
  • Functionality of 2 creates linear polymers, and functionality greater than 2 creates 3-D polymers.
  • Polymers are classified by availability (natural, semi-synthetic, synthetic), types of monomers (homopolymer, copolymer), chain structure (linear, branched, cross-linked), tacticity (isotactic, atactic, syndiotactic), and polymerization reaction (addition or condensation).
  • Natural polymers include protein, natural rubber, silk, and polysaccharides.
  • Examples of synthetic polymers include nylon, terylene, and PVC.
  • Homopolymers are made of identical monomers. Examples include polyethylene and PMMA.
  • Copolymers are made of different monomers. Examples include BUNA-S and nylon 66.

Classification of Polymers

  • Based on availability: Natural, semi-synthetic, synthetic
  • Based on monomers: Homopolymer (same monomer), copolymer (different monomers)
  • Based on chain structure: Linear, branched, cross-linked
  • Based on tacticity: Isotactic, atactic, syndiotactic
  • Based on effect of heating: Thermoplastic, thermosetting

Thermoplastic and Thermosetting Polymers

  • Thermoplastics: Soften on heating and harden on cooling. They are easily reshaped and reused. Formed by addition polymerization. Examples: PE, PVC, PMMA
  • Thermosetting polymers: Harden on heating and cannot be softened again. They are formed by condensation polymerization. Examples: Urea formaldehyde, phenol formaldehyde, epoxy resins, polyester.

Types of Polymerisations

  • Addition polymerization: Chain polymerization in which no small molecules are eliminated. Monomers yield a polymer that is an exact multiple of the original molecule.
  • Condensation polymerization: Step-growth polymerization where small molecules like water are eliminated. It involves polyfunctional monomers and forms network polymers.

Effect of Heat on Polymers

  • Glass Transition Temperature (Tg): The temperature at which a glassy/brittle polymer transitions to a viscous liquid/rubbery state.
  • Melting Point (Tm): The temperature at which a crystalline polymer melts to a liquid state.

Factors Affecting Tg and Tm

  • Crystallinity
  • Polymer chain mobility
  • Chain stiffness
  • Presence of bulky side groups, multiple bonds, aromatic rings, or polar side atoms.
  • Co-polymerization
  • Cross-linking
  • Plasticizers
  • Water/moisture content

Conducting Polymers

  • Some polymers can exhibit conductivity similar to semiconductors or metals.
  • Conductivity depends on delocalized π electrons.
  • Intrinsic conducting polymers (ICPs) have extensive conjugation in their backbone which is responsible for electron conduction.
  • Doped conducting polymers (DCPs): Increase in conductivity by addition or removal of electrons to give negative or positive charge on backbone.

Liquid Crystals

  • Liquid crystals are a state of matter with properties in between liquids and solids.
  • They exhibit anisotropy of properties (e.g. optical) without a crystalline lattice.
  • Types of liquid crystals depend on factors like phase transition (thermotropic, lyotropic) and arrangement of molecules (nematic, smectic, cholesteric).1

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Description

This quiz explores the fascinating world of polymers, covering their definitions, formation, and various classifications. Test your knowledge on topics such as monomers, polymerization, and examples of natural and synthetic polymers. Discover the intricacies of polymer functionality and structure in this comprehensive quiz.

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