Polymerization Classifications

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Questions and Answers

What happens to the concentration of monomer over time?

It decreases gradually (correct)

It remains constant

It fluctuates randomly

It increases rapidly

What is the primary characteristic of step growth polymerization?

Oligomers react together to form longer chains (correct)

Monomers react in a single step

The reaction is reversible

Chain growth is rapid and continuous

What is the main difference between linear and branched polymers?

Branched polymers have a network structure

Branched polymers have a backbone with short branches (correct)

Linear polymers have a single chain structure

Linear polymers have cross-links

What is the main characteristic of cross-linked polymers?

They have covalently bonded linking units between chains Signup and view all the answers

What is the primary factor that determines the physical properties of a polymer?

The arrangement of individual chains Signup and view all the answers

What is the primary type of force that holds polymer chains together?

Van der Waals forces Signup and view all the answers

What are the regions of a polymer where the chains are highly ordered called?

Crystallites Signup and view all the answers

What happens to the density of a polymer when it has substituents or branches that prevent close packing?

It decreases Signup and view all the answers

What type of polymers have both ordered crystalline regions and amorphous noncrystalline regions?

Thermoplastic polymers Signup and view all the answers

What is the reason thermosetting polymers cannot be remelted by heating?

Because the cross-links are covalent bonds Signup and view all the answers

What happens to the polymer chains when elastomers are stretched?

They stretch out and crystallize Signup and view all the answers

What type of polymers are rubber and spandex examples of?

Elastomers Signup and view all the answers

What type of polymerization is involved in the formation of addition polymers?

Chain-growth polymerization Signup and view all the answers

What is the common monomer used to form vinyl polymers?

Ethylene Signup and view all the answers

Why do elastomers return to their original state after the stretching force is removed?

Because of weak van der Waals forces Signup and view all the answers

What is the characteristic of thermoplastic polymers that allows them to be molded when heated?

Chain slippage Signup and view all the answers

What is the purpose of molecule XY in radical polymerization?

To terminate the growing chain Signup and view all the answers

Why is head-to-tail addition favored in radical polymerization?

Due to the radical stabilization by the substituent Signup and view all the answers

What type of bond is required for molecule XY to react with the growing chain?

Bond that can readily be cleaved homolytically Signup and view all the answers

What is the role of the initiator in radical polymerization?

To initiate a new chain Signup and view all the answers

Why does head-to-head addition occur when Z is small?

Due to the lack of radical stabilization Signup and view all the answers

What is the effect of a phenyl substituent on the radical?

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

What type of cleavage occurs in radical polymerization?

Homolytic cleavage Signup and view all the answers

What is the result of chain transfer in radical polymerization?

Termination of the growing chain Signup and view all the answers

What is the role of the initiator in anionic polymerization?

It acts as a nucleophile to react with the monomer. Signup and view all the answers

What type of shift can occur in the propagating site during cationic polymerization?

1,2-hydride shift Signup and view all the answers

What is the characteristic of the monomers that undergo cationic polymerization?

They have substituents that stabilize the positive charge. Signup and view all the answers

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

Secondary carbocation Signup and view all the answers

What is the reason for the difficulty in nucleophilic attack on an alkene in anionic polymerization?

Alkenes are electron-rich. Signup and view all the answers

What is the characteristic of the initiator in anionic polymerization?

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

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

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

What is the result of a 1,2-hydride shift in the propagating site during cationic polymerization?

A more stable tertiary carbocation is formed. Signup and view all the answers

What is the functional group that reacts with the carboxylic acid group in the formation of nylon?

Amino group Signup and view all the answers

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

Nylon 6 Signup and view all the answers

What is the common name of the polyester polymer formed by the transesterification of dimethyl terephthalate with ethylene glycol?

Dacron Signup and view all the answers

What is the characteristic of epoxy resins that makes them resistant to solvents and high temperature?

Extensive cross-linking Signup and view all the answers

What is the functional group that defines a polyurethane?

Urethane group (carbamate) 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 name of the polyamide formed from two different bifunctional monomers—adipoyl chloride and 1,6-hexanediamine?

Nylon 66 Signup and view all the answers

What is the reaction that forms Kodel polyester?

Transesterification Signup and view all the answers

Study Notes

Polymerization

The concentration of monomer decreases gradually until it is depleted during polymerization.

Classification of Polymers: Growth

Step growth: Chains have at least two growth points, forming oligomers that react to give longer chains, associated with condensation polymerization.
Chain growth: Associated with addition polymerization.

Classification of Polymers: Structure

Linear polymers: Continuous chain of repeating units.
Branched polymers: Short branches connected to the main chain.
Cross-linked polymers: Covalently bonded linking units between chains.

Classification of Polymers: Physical Properties

Physical properties of polymers are a result of individual chain arrangement.
Regions of highly ordered chains (crystallites) are interspersed with amorphous, noncrystalline regions.
Polymers classified according to properties:
- Thermoplastic polymers: Have both ordered crystalline and amorphous noncrystalline regions, can be molded when heated.
- Thermosetting polymers: Cross-linked, rigid, and cannot be remelted by heating.
- Elastomers: Flexible, can be stretched and return to original state, have some cross-linking.

Addition Polymers

Formed from ethylene or substituted ethylenes (vinyl polymers).
Radical polymerization:
- Termination steps: Chain transfer, may occur by reaction with a molecule XY.
- Favored head-to-tail addition due to steric hindrance and stabilization by substituents.
- May undergo head-to-head or tail-to-tail addition in some cases.
Cationic polymerization:
- Mechanism involves chain-initiating, chain-propagating, and termination steps.
- Carbocation intermediates can undergo rearrangement by 1,2-hydride or 1,2-methyl shift.
- Best monomers have substituents that stabilize the positive charge.

Anionic Polymerization

Initiator is a nucleophile that reacts with the monomer to form an anion propagating site.
Nucleophilic attack on an alkene requires a very good nucleophile and electron-withdrawing substituents on the alkene.

Classes of Step-Growth Polymers

Polyamides
Polyesters
Epoxy resins
Polyurethanes

Polyamides

Nylon 6: Formed from 6-aminohexanoic acid, a polyamide.
Nylon 66: Formed from adipoyl chloride and 1,6-hexanediamine.
Starting material for nylon 6 synthesis is ε-caprolactam.

Polyesters

Containing many ester groups.
Dacron: Made by transesterification of dimethyl terephthalate with ethylene glycol.
Kodel polyester: Formed by transesterification of dimethyl terephthalate with 1,4-di(hydroxymethyl)cyclohexane.

Epoxy Resins

Strongest adhesives known, extensively cross-linked systems.
Adhere to almost any surface, resistant to solvents and high temperature.
Epoxy cement: Consisting of a low-molecular-weight prepolymer and a hardener that react to form a cross-linked polymer.

Polyurethanes

Containing urethane (carbamate) groups.
Formed by reaction of a prepolymer with a hardener.

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Description

This quiz covers the classifications of polymers, including chain growth and step growth polymerization. It explores the formation of oligomers and their role in polymerization reactions.