Anionic Polymerization: Living Polymers
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Questions and Answers

What is necessary for an anionic polymerization reaction to occur?

  • A moderate nucleophile and an alkene with an electron-donating substituent
  • A weak nucleophile and an alkene with a neutral substituent
  • A strong acid and an alkene with a basic substituent
  • A very good nucleophile and an alkene with an electron-withdrawing substituent (correct)

    • Why do living polymers commonly form in anionic polymerization?

  • Because the chains cannot be terminated by proton loss from the polymer (correct)
  • Because the chains can be terminated by proton loss from the polymer
  • Because the chains can be terminated by the initiator
  • Because the chains can be terminated by chain combination or disproportionation

    • What type of substituent on the alkene is necessary for an anionic polymerization reaction to occur?

  • Electron-donating substituent
  • No substituent
  • Neutral substituent
  • Electron-withdrawing substituent (correct)

    • What is necessary to initiate anionic polymerization of methyl α-cyanoacrylate?

    <p>A moderately good nucleophile</p> Signup and view all the answers

    What initiates the polymerization reaction when using Super Glue?

    <p>A nucleophilic group on the surface of the skin</p> Signup and view all the answers

    What is the result when using Super Glue?

    <p>Two fingers can be firmly glued together</p> Signup and view all the answers

    Why is anionic polymerization necessary for the formation of some polymers?

    <p>Because it produces living polymers</p> Signup and view all the answers

    What is unique about the initiator in anionic polymerization?

    <p>It is a very good nucleophile</p> Signup and view all the answers

    What type of reaction occurs between molecules with a functional group at each end to form condensation polymers?

    <p>Intermolecular reaction</p> Signup and view all the answers

    Which of the following is NOT a class of step-growth polymers?

    <p>Acrylics</p> Signup and view all the answers

    What is the monomer used to form nylon 6?

    <p>6-aminohexanoic acid</p> Signup and view all the answers

    What is the starting material for the synthesis of nylon 6?

    <p>ε-caprolactam</p> Signup and view all the answers

    What is the name of the polyamide formed from adipoyl chloride and 1,6-hexanediamine?

    <p>Nylon 66</p> Signup and view all the answers

    What is the process by which Dacron is made?

    <p>Transesterification</p> Signup and view all the answers

    What is the property of epoxy resins that makes them useful as adhesives?

    <p>Extensive cross-linking</p> Signup and view all the answers

    What is the polyester formed by the transesterification of dimethyl terephthalate with 1,4-di(hydroxymethyl)cyclohexane?

    <p>Kodel polyester</p> Signup and view all the answers

    What is the mechanism of polymerization of epoxides when the initiator is a nucleophile?

    <p>Anionic mechanism</p> Signup and view all the answers

    What is the process of hardening rubber by heating it with sulfur known as?

    <p>Vulcanization</p> Signup and view all the answers

    What type of copolymer has a random distribution of monomers?

    <p>Random copolymer</p> Signup and view all the answers

    What is the natural rubber a polymer of?

    <p>2-Methyl-1,3-butadiene (isoprene)</p> Signup and view all the answers

    What is the problem with natural and most synthetic rubbers?

    <p>They are too soft and sticky</p> Signup and view all the answers

    What is the result of heating rubber with sulfur?

    <p>Cross-linking of polymer chains through disulfide bonds</p> Signup and view all the answers

    What type of polymerization occurs in the presence of a Lewis acid?

    <p>Cationic mechanism</p> Signup and view all the answers

    What is a graft copolymer composed of?

    <p>Branches derived from one monomer grafted onto a backbone from another monomer</p> Signup and view all the answers

    Study Notes

    Anionic Polymerization

    • Initiator is a nucleophile that reacts with the monomer to form an anion propagating site
    • Nucleophilic attack on an alkene does not occur readily due to the electron-rich nature of alkenes
    • Initiator must be a very good nucleophile, such as sodium amide or butyllithium, and the alkene must contain electron-withdrawing substituents to decrease the electron density of the double bond

    Mechanism of Anionic Polymerization

    • Initiating step: involves the reaction of the nucleophile with the monomer
    • Propagation steps: involve the reaction of the anion propagating site with additional monomers

    Living Polymers

    • Most common in anionic polymerization
    • Chains cannot be terminated by proton loss from the polymer (as they can in cationic polymerization) or by chain combination or disproportionation (as they can in radical polymerization)

    Examples of Alkenes That Undergo Anionic Polymerization

    • Methyl α-cyanoacrylate (Super Glue)

    Ring-Opening Polymerizations

    • Some compounds can polymerize well rather than ethylene and substituted ethylenes in chain-growth polymerizations
    • Epoxides undergo chain-growth polymerization
    • If the initiator is a nucleophile, polymerization occurs by an anionic mechanism
    • If the initiator is a Lewis acid, epoxides are polymerized by a cationic mechanism

    Polymerization of Dienes

    • The manufacture of rubber
    • Natural rubber is a polymer of 2-methyl-1,3-butadiene (isoprene)
    • Synthetic rubbers have been made by radical polymerization of dienes other than isoprene

    Vulcanization

    • A problem with both natural and most synthetic rubbers is that they are soft and sticky
    • They can be hardened by vulcanization (heating of rubber with sulfur)
    • Heating rubber with sulfur causes cross-linking of the separate polymer chains through disulfide bonds

    Copolymers

    • Formed from two or more different monomers
    • Both chain-growth polymers and step-growth polymers can be copolymers
    • Four types of copolymers:
      • Alternating copolymer: the two monomers alternate
      • Block copolymer: consists of blocks of each kind of monomer
      • Random copolymer: has a random distribution of monomers
      • Graft copolymer: contains branches derived from one monomer grafted onto a backbone from another monomer

    Condensation Polymers (Step-Growth Polymers)

    • Formed by the intermolecular reaction of molecules with a functional group at each end
    • In most cases, a small molecule such as H2O, alcohol, or HCl is lost
    • Can be formed by the reaction of a single compound with two different functional groups, A and B, or by the reaction of two different compounds

    Classes of Step-Growth Polymers

    • Polyamides
    • Polyesters
    • Epoxy Resins
    • Polyurethanes

    Polyamides

    • Nylon 6: an example of a step-growth polymer formed from a monomer with two different functional groups
    • Nylon 6 is formed from the polymerization of 6-aminohexanoic acid, which contains six carbons
    • The starting material for the synthesis of nylon 6 is ε-caprolactam

    Polyesters

    • Polymers containing many ester groups
    • Dacron is the most common polyesters polymer
    • Dacron is made by the transesterification of dimethyl terephthalate with ethylene glycol
    • Kodel polyester is formed by the transesterification of dimethyl terephthalate with 1,4-di(hydroxymethyl)cyclohexane

    Epoxy Resins

    • They are the strongest adhesives known
    • They are extensively cross-linked systems
    • They can adhere to almost any surface and are resistant to solvents and high temperature

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    Description

    This quiz covers the process of anionic polymerization, including the role of nucleophilic initiators and electron-withdrawing substituents in forming living polymers.

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