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Questions and Answers
What is the smallest repeating unit in a polymer chain called?
What is the smallest repeating unit in a polymer chain called?
What characteristic defines polymers?
What characteristic defines polymers?
Which of the following is NOT typically associated with tooth colored restorative materials?
Which of the following is NOT typically associated with tooth colored restorative materials?
In the context of restorative dentistry, what is the role of cements?
In the context of restorative dentistry, what is the role of cements?
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How are polymers structured?
How are polymers structured?
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Which of the following are classified as natural polymers?
Which of the following are classified as natural polymers?
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What type of polymers are produced through chemical reactions in a laboratory setting?
What type of polymers are produced through chemical reactions in a laboratory setting?
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Which of the following is an example of a natural polymer?
Which of the following is an example of a natural polymer?
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Which of the following statements is true regarding synthetic polymers?
Which of the following statements is true regarding synthetic polymers?
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Vinyl polymers are derived from which chemical compound?
Vinyl polymers are derived from which chemical compound?
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What happens to materials when they are heated to high temperatures?
What happens to materials when they are heated to high temperatures?
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Which statement best describes the mechanical properties of the materials mentioned?
Which statement best describes the mechanical properties of the materials mentioned?
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What is true about the reusability of these materials?
What is true about the reusability of these materials?
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Which property makes these materials vulnerable when subjected to heat?
Which property makes these materials vulnerable when subjected to heat?
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How do high temperatures generally affect the shape of these materials?
How do high temperatures generally affect the shape of these materials?
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Which of the following methods can activate the initiator for polymerization?
Which of the following methods can activate the initiator for polymerization?
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What is the primary purpose of free radicals in the polymerization process?
What is the primary purpose of free radicals in the polymerization process?
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Which type of light is NOT mentioned as a means to activate the initiator?
Which type of light is NOT mentioned as a means to activate the initiator?
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How does peroxide function in the polymerization process?
How does peroxide function in the polymerization process?
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What role does heat play in the activation of the initiator?
What role does heat play in the activation of the initiator?
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What distinguishes one type of polymer from another based on chain length?
What distinguishes one type of polymer from another based on chain length?
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What characterizes copolymers in terms of their composition?
What characterizes copolymers in terms of their composition?
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Which statement is true about the molecular weight distribution of polymers?
Which statement is true about the molecular weight distribution of polymers?
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What is a key feature of the structure of copolymers?
What is a key feature of the structure of copolymers?
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How can the chain structure of different polymers impact their properties?
How can the chain structure of different polymers impact their properties?
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How do polymers typically behave at a slow rate of loading?
How do polymers typically behave at a slow rate of loading?
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What characteristic of polymers is highlighted due to their viscoelastic nature?
What characteristic of polymers is highlighted due to their viscoelastic nature?
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What is a consequence of polymers behaving in a ductile manner at slow loading rates?
What is a consequence of polymers behaving in a ductile manner at slow loading rates?
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Which statement accurately describes the behavior of polymers under varying loading rates?
Which statement accurately describes the behavior of polymers under varying loading rates?
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Which of the following statements is most accurate regarding the mechanical properties of polymers?
Which of the following statements is most accurate regarding the mechanical properties of polymers?
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Study Notes
Polymers
- Polymers are long chain molecules formed from many repeating units.
- The smallest repeating unit is called a monomer.
- The entire long chain is the polymer.
- The links between the repeating units are covalent bonds.
Nomenclature
- Monomer: The smallest repeating unit in a polymer.
- Polymer: A macromolecule formed by linking repeating monomer units through covalent bonds.
- Homopolymer: A polymer made of only one type of monomer.
- Copolymer: A polymer made of two or more different types of monomers.
- Oligomer: A short polymer chain containing 2 to 10 mers.
Polymerization
- Polymerization is the chemical reaction that creates polymers from monomers.
- Most polymerization reactions are either condensation or addition reactions.
Condensation Polymerization
- A reaction between two molecules that creates a larger molecule and a low molecular weight by-product (e.g., water).
- Composition changes during the reaction.
- Often a slow process.
- May experience early termination (low molecular weight products).
- Examples include polysulfides and silicones, which are used in synthetic rubber impression materials.
Addition Polymerization
- A reaction between two molecules that creates a larger molecule without the formation of a byproduct.
- No change in composition during the reaction.
- The structure of the monomer is repeated numerous times in the polymer.
- Examples include polyethylene, poly(acrylic acid), poly(methacrylic acid), and poly(methyl methacrylate).
Types of Addition Polymerizations
- Free radical: Initiated by free radicals (e.g. benzoyl peroxide)
- Ring opening: Reactive terminal rings open under the influence of an initiator (cationic or anionic).
Stages of Addition Polymerization
- Initiation: Activation (chemical, heat, or light) initiates the reaction and creates free radicals.
- Propagation: The free radical reacts with monomers, creating longer polymer chains.
- Termination: The chain reaction ends, either by direct coupling of two free radicals or by transfer of a hydrogen atom from one chain to another.
Activation and Initiation
- Free Radical (R°): A compound with an unpaired electron makes the radical reactive.
- Initiators (e.g. benzoyl peroxide, diketones) generate free radicals to start the reaction.
- Activation methods: chemical, heat, or electromagnetic waves (UV, blue visible light).
- In this way the peroxide decomposes.
Propagation
- The free radical continues reacting with monomers to form longer chains.
- The chain keeps growing until termination.
Termination
- The chain reaction ends by direct coupling or by transfer of a hydrogen atom.
- Under normal conditions, polymerization is often incomplete, and there is a residual monomer left.
Classification of Polymers
- By origin: Natural (proteins, polyisoprenes, polysaccharides, polynucleic acids) and synthetic (acrylic resin, elastic impression materials, vinyl polymers)
- By spatial structure: linear, branched, cross-linked
- By thermal behavior: Thermoplastic (shaped by heating/cooling, reversible) and Thermosetting (formed by chemical reaction, irreversible)
- By polymerization reaction: condensation, addition
Other Properties
- Molecular Weight: The higher the molecular weight, the higher the degree of polymerization.
- Degree of Polymerization: The number of mer units in the polymer.
- Cross-linking: Joining adjacent polymer chains by covalent bonds, increasing strength, hardness, and resistance to solvents & decreasing water sorption.
- Molecular Weight Distribution: The fraction of low, medium, and high molecular weight molecules in a polymer. Different molecular weight distributions result in varying properties.
- Plasticizers: Substances added to polymers to reduce their secondary forces, increasing flexibility and decreasing glass transition temperature (Tg).
- Inhibitors: Substances that hinder or retard the polymerization reaction, by reacting with free radicals or monomers.
- Fillers: Added agents that can improve the strength, hardness, and rigidity of polymers, creating composite structures.
- Rate of Loading: Polymers respond differently to loading rates (slow = ductile, high = brittle).
- Glass Transition Temperature (Tg): The temperature at which a polymer transitions from a hard, glassy state to a soft, rubbery state.
Additional Notes
- Polymers are molecular solids with strong primary covalent bonds within molecules and weak secondary bonds between molecules.
- They are typically amorphous, having a glass transition temperature (Tg).
- The physical state of dental polymers can be rubbery (elastomers) or hard and amorphous (organic glasses) at room temperature.
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Description
Test your knowledge on polymers and their applications in restorative dentistry. This quiz covers definitions, properties, and classifications of various types of polymers, along with their uses in dental materials. Whether you're a student or a professional, this quiz provides a comprehensive overview of the subject.
