Anionic Polymerization Mechanism
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Questions and Answers

Why doesn't nucleophilic attack on an alkene occur readily?

  • Because the initiator is not a good nucleophile
  • Because the alkene must contain electron-donating substituents
  • Because alkenes are electron poor
  • Because alkenes are electron rich (correct)

    • What is the role of the initiator in anionic polymerization?

  • To increase the electron density of the double bond
  • To terminate the polymer chain
  • To react with the monomer to form an anion propagating site (correct)
  • To decrease the electron density of the double bond

    • Why are living polymers more common in anionic polymerization?

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

    • What type of nucleophile is required to initiate anionic polymerization?

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

    What happens when a nucleophilic group on the surface of the skin initiates the polymerization reaction?

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

    What is the role of electron-withdrawing groups in anionic polymerization?

    <p>To decrease the electron density of the double bond</p> Signup and view all the answers

    What is the monomer that is used to make Super Glue?

    <p>Methyl α-cyanoacrylate</p> Signup and view all the answers

    What is the reason why surface-absorbed water can initiate anionic polymerization of methyl α-cyanoacrylate?

    <p>Because water is a moderately good nucleophile</p> Signup and view all the answers

    What is the role of the nucleophile in the anionic mechanism of ring-opening polymerization of epoxides?

    <p>To initiate the polymerization reaction by attacking the less sterically hindered carbon of the epoxide</p> Signup and view all the answers

    What type of polymerization is used to manufacture synthetic rubbers from dienes other than isoprene?

    <p>Radical polymerization</p> Signup and view all the answers

    What is the purpose of vulcanization in the manufacture of rubber?

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

    What type of copolymer is formed when two monomers are polymerized in an alternating sequence?

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

    Which type of polymerization is characterized by the formation of a new bond between two monomers?

    <p>Step-growth polymerization</p> Signup and view all the answers

    What is the result of heating rubber with sulfur in the vulcanization process?

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

    What is the main difference between anionic and cationic mechanisms of ring-opening polymerization?

    <p>The type of initiator used</p> Signup and view all the answers

    What is the purpose of using a Lewis acid as an initiator in ring-opening polymerization of epoxides?

    <p>To initiate a cationic mechanism</p> Signup and view all the answers

    What is a characteristic of condensation polymers?

    <p>They are formed by the reaction of a single compound with two different functional groups.</p> Signup and view all the answers

    What is the name of the polyamide formed from the polymerization of 6-aminohexanoic acid?

    <p>Nylon 6</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 by the reaction of adipoyl chloride and 1,6-hexanediamine?

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

    What is the process by which Dacron polyester is made?

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

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

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

    What is a characteristic of epoxy resins?

    <p>They are resistant to solvents and high temperature.</p> Signup and view all the answers

    What is the type of polymers that are formed by the intermolecular reaction of molecules with a functional group at each end?

    <p>Step-growth polymers</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

    Learn about the mechanism of anionic polymerization, including the initiators and conditions required for the reaction to occur. Understand the roles of nucleophiles and electron-withdrawing substituents.

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