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Questions and Answers

What is the primary function of substituents in the monomers used in cationic polymerization?

To stabilize the positive charge at the propagating site (correct)

To promote anionic polymerization

To reduce the rate of polymerization

To increase the electron density of the double bond

What type of carbocation is formed at the propagating site after a 1,2-hydride shift?

Primary carbocation

Quaternary carbocation

Secondary carbocation

Tertiary carbocation (correct)

Why is a very good nucleophile required as an initiator in anionic polymerization?

To increase the rate of polymerization

To promote cationic polymerization

Because alkenes are electron rich and do not readily undergo nucleophilic attack (correct)

To decrease the electron density of the double bond

What is the role of the initiator in anionic polymerization?

To react with the monomer to form an anion propagating site Signup and view all the answers

What is the purpose of electron-withdrawing substituents in anionic polymerization?

To decrease the electron density of the double bond Signup and view all the answers

What type of carbocation is formed at the propagating site before rearrangement?

Secondary carbocation Signup and view all the answers

Why do carbocation intermediates undergo rearrangement in cationic polymerization?

To form a more stable carbocation Signup and view all the answers

What is the characteristic of a good initiator in anionic polymerization?

It is a very good nucleophile Signup and view all the answers

What is the process of linking monomers together to form a large molecule called?

Polymerization Signup and view all the answers

What is the alternative system of naming polymers, besides the IUPAC structure-based system?

IUPAC source-based system Signup and view all the answers

What is the purpose of the letter 'n' in a polymer formula?

To indicate the number of repeating units is not specified Signup and view all the answers

What is the name of the discipline that involves the creation of new materials with improved properties?

Materials science Signup and view all the answers

What is the type of reaction that produces addition polymers?

Addition reaction Signup and view all the answers

What is the characteristic of monomers that are used to prepare condensation polymers?

They have reactive functional groups at each end Signup and view all the answers

What is the growth pattern of chain-growth polymers?

Monomers add one-by-one to the same end of a growing chain Signup and view all the answers

What is the name of the polymer that is used for hot drink cups, egg cartons, and insulation?

Polystyrene Signup and view all the answers

What is the primary mechanism by which a chain reacts with a molecule XY in radical polymerization?

By homolytic cleavage of the XY bond Signup and view all the answers

What is the role of the substituent attached to the other sp2 carbon in radical polymerization?

It stabilizes the radical by electron delocalization Signup and view all the answers

What is the primary reason for head-to-tail addition being favored in radical polymerization?

Due to the absence of steric hindrance at the unsubstituted sp2 carbon Signup and view all the answers

What is the result of head-to-head addition and some tail-to-tail addition in radical polymerization?

The formation of a polymer with a random chain structure Signup and view all the answers

What is the characteristic of a molecule that can initiate radical polymerization?

It has a weak bond that undergoes homolytic cleavage Signup and view all the answers

What is the primary factor that influences the type of addition (head-to-tail or head-to-head) in radical polymerization?

The size of the substituent Z Signup and view all the answers

What is the result of the growing chain reacting with a molecule XY in radical polymerization?

The termination of the chain Signup and view all the answers

What is the role of the benzene ring in radical polymerization when Z is a phenyl substituent?

It stabilizes the radical by electron delocalization Signup and view all the answers

What is the characteristic of a monomer that forms nylon 6?

It has two different functional groups Signup and view all the answers

What is the reaction involved in the synthesis of Dacron?

Transesterification Signup and view all the answers

What is the common feature of nylon 6 and nylon 66?

They are both polyamides Signup and view all the answers

What is the characteristic of epoxy resins?

They are extensively cross-linked systems Signup and view all the answers

What is the reaction involved in the formation of epoxy cement?

Cross-linking reaction Signup and view all the answers

What is the characteristic of a urethane group?

It has an OR group and an NHR group bonded to the same carbonyl carbon Signup and view all the answers

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

ε-caprolactam Signup and view all the answers

What is the common feature of polyester polymers?

They contain many ester groups Signup and view all the answers

What is the primary reason why living polymers are most common in anionic polymerization?

The chains cannot be terminated by proton loss from the polymer Signup and view all the answers

What type of group is required to initiate anionic polymerization of methyl α-cyanoacrylate?

A moderately good nucleophile Signup and view all the answers

What is the mechanism of polymerization involved in the reaction of epoxides?

Anionic polymerization Signup and view all the answers

What is the result of the polymerization reaction initiated by a nucleophilic group on the surface of the skin?

Two fingers can become firmly glued together Signup and view all the answers

What is the characteristic of living polymers that distinguishes them from other types of polymers?

They cannot be terminated by proton loss or chain combination Signup and view all the answers

What is the primary difference between anionic polymerization and cationic polymerization?

The ability of the polymer to be terminated Signup and view all the answers

What is the role of surface-absorbed water in the initiation of anionic polymerization of Super Glue?

It acts as a nucleophile to initiate the reaction Signup and view all the answers

What is the characteristic of epoxides that allows them to undergo chain-growth polymerization?

They have a low degree of sterical hindrance Signup and view all the answers

Study Notes

Polymers

A polymer is a large molecule made by linking together repeating units of small molecules called monomers.
The process of linking them together is called polymerization.

Polymer Nomenclature

The IUPAC has set forth rules for naming polymers according to structure.
An alternative IUPAC source-based system names polymers according to the monomers from which they are prepared.
Polymer formulas are written by enclosing the repeating unit within brackets, followed by the letter n to indicate that the number of repeating units is not specified.
Many polymers are referred to by their common names or trade names.

Classification of Polymers

Synthetic polymers are synthesized by scientists.
Biopolymers are synthesized by cells.
Polymer chemistry is part of the larger discipline of materials science, which involves the creation of new materials with improved properties.

Classification of Polymers: Type of Reaction

Addition polymers are made by addition reactions.
Polystyrene is an example of an addition polymer, used for hot drink cups, egg cartons, and insulation.
Condensation polymers are made by linking monomers by removing a small molecule, such as water or an alcohol.

Classification of Polymers: Polymer Growth

Chain-growth process: Monomers add one-by-one to the same end of a growing chain. Each chain has only one growth point.

Addition Polymers

Radical polymerization is a mechanism of addition polymers.
Termination steps may occur by one of the following pathways: chain transfer, combination, or disproportionation.
Head-to-tail addition is favored due to two factors: less steric hindrance at the unsubstituted sp2 carbon of the alkene, and radicals formed by addition to the unsubstituted sp2 carbon can be stabilized by the substituent attached to the other sp2 carbon.
Head-to-head addition and some tail-to-tail addition occurs when Z is small and is less able to stabilize the growing end of the chain.
The initiator for radical polymerization can be any compound with a weak bond that undergoes homolytic cleavage by heat or ultraviolet light.

Addition Polymers: Cationic Polymerization

Mechanism: chain-initiating step, chain-propagating steps, and termination.
The carbocation intermediates formed during cationic polymerization undergo rearrangement by either a 1,2-hydride shift or a 1,2-methyl shift if rearrangement leads to a more stable carbocation.
The best monomers in cationic polymerization have substituents that stabilize the positive charge at the propagating site either by hyperconjugation or by donating electrons by resonance.

Addition Polymers: Anionic Polymerization

Mechanism: initiating step, propagation steps, and termination.
Living polymers are most common in anionic polymerization because the chains cannot be terminated by proton loss from the polymer or by chain combination or disproportionation.
Examples of alkenes that undergo anionic polymerization include methyl α-cyanoacrylate, which is the monomer used to make Super Glue.

Addition Polymers: Ring-Opening Polymerizations

Some compounds can polymerize well rather than ethylene and substituted ethylenes in chain-growth polymerizations.
Epoxides undergo chain-growth polymerization, which can occur by an anionic mechanism.

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.
The carboxylic acid group of one monomer reacts with the amino group of another monomer to form an amide.
Nylon 66 is an example of a step-growth polymer formed by two different bifunctional monomers.

Polyesters

Polymers containing many ester groups.
Dacron is the most common polyesters polymer, 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, consisting of extensively cross-linked systems.
They can adhere to almost any surface and are resistant to solvents and high temperature.
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.

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