24 Questions
What is the minimum number of steps required for an addition polymerization reaction?
Three
What is the role of an initiator in radical polymerization?
To break homolytically into radicals
What is the propagating site in radical polymerization?
The unpaired electron
What happens when two chains combine at their propagating sites in termination steps?
Chain combination occurs
How many subunits are added to the chain in each propagation step?
One
What is the result of disproportionation in termination steps?
One chain is oxidized to an alkene and the other reduced to an alkane
How many mechanisms of polymerization are mentioned in the text?
Three
What is the role of the monomer in radical polymerization?
To react with the initiator
What type of shift can lead to a more stable carbocation during cationic polymerization?
1,2-hydride shift
What is the characteristic of the initiator in anionic polymerization?
A very good nucleophile
What is the purpose of substituents in the monomer during cationic polymerization?
To stabilize the positive charge at the propagating site
What type of polymer is formed during anionic polymerization?
Living polymer
What is the characteristic of the propagating site in unrearranged cationic polymerization?
A secondary carbocation
What is the reason for the nucleophilic attack not occurring readily on an alkene?
Alkenes are electron rich
What is the result of a 1,2-hydride shift during cationic polymerization?
A more stable tertiary carbocation is formed
Why must the alkene contain electron-withdrawing substituents in anionic polymerization?
To decrease the electron density of the double bond
What is the primary mechanism of formation of nylon 6?
Reaction of carboxylic acid group with amino group to form an amide
Which of the following polyesters is formed by the transesterification of dimethyl terephthalate with 1,4-di(hydroxymethyl)cyclohexane?
Kodel
What is the characteristic feature of epoxy resins?
They are extensively cross-linked systems
What is the functional group present in polyurethanes?
Urethane
What is the monomer requirement for the formation of nylon 6?
A monomer with two different functional groups
What is the name of the starting material used for the synthesis of nylon 6?
ε-caprolactam
What is the characteristic feature of nylon 66?
It is formed from two different bifunctional monomers
What is the purpose of the hardener in epoxy cement?
To react with the prepolymer to form a cross-linked polymer
Study Notes
Addition Polymers
- Chain-growth polymerization proceeds by three mechanisms: radical, cationic, and anionic polymerization.
- Each mechanism has three distinct steps: initiation, propagation, and termination.
Radical Polymerization
- Initiation step: a radical initiator is added to the monomer to generate the radical that starts the growth of the polymer chain.
- Propagation steps: the monomer radical reacts with another monomer, converting it into a radical, and the process is repeated.
- Termination steps: may occur by chain combination or disproportionation.
Cationic Polymerization
- Initiation step: a chain-initiating step occurs.
- Propagation steps: chain-propagating steps occur.
- Termination step: the carbocation intermediates undergo rearrangement by either a 1,2-hydride shift or a 1,2-methyl shift.
- The best monomers have substituents that stabilize the positive charge at the propagating site.
Anionic Polymerization
- The initiator is a nucleophile that reacts with the monomer to form an anion propagating site.
- The alkene must contain electron-withdrawing substituents to decrease the electron density of the double bond.
Classes of Step-Growth Polymers
- Polyamides
- Polyesters
- Epoxy Resins
- Polyurethanes
Polyamides
- Nylon 6 is 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.
- Nylon 66 is formed by two different bifunctional monomers—adipoyl chloride and 1,6-hexanediamine.
Polyesters
- Polymers containing many ester groups.
- 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 and are extensively cross-linked systems.
- Epoxy cement is consisting of a low-molecular-weight prepolymer and a hardener that react when mixed to form a cross-linked polymer.
Polyurethanes
- A urethane is a compound that has an OR group and an NHR group bonded to the same carbonyl carbon.
This quiz covers the mechanisms of addition or chain-growth polymerization, including radical, cationic, and anionic polymerization, as well as the three distinct steps involved in each mechanism.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
