Polymerization and Properties of Polyurethanes

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Questions and Answers

What is the reason why an alkene does not readily undergo nucleophilic attack?

Alkenes have a high molecular weight

Alkenes have a low molecular weight

Alkenes are electron poor

Alkenes are electron rich (correct)

What type of initiator is required for anionic polymerization of an alkene?

A strong acid

A very good nucleophile (correct)

A strong base

A moderately good nucleophile

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

Chains can be terminated by chain combination

Chains cannot be terminated by proton loss (correct)

Chains can be terminated by disproportionation

Chains can be terminated by proton loss

What is the monomer of Super Glue?

Methyl a -cyanoacrylate Signup and view all the answers

What is the purpose of polymers similar to Super Glue in medical applications?

To close wounds Signup and view all the answers

What type of polymerization occurs when an epoxide is polymerized?

Ring-opening polymerization Signup and view all the answers

What is the mechanism of anionic polymerization of epoxides?

Anionic mechanism Signup and view all the answers

What is the requirement for an alkene to undergo anionic polymerization?

Electron-withdrawing groups Signup and view all the answers

What is the primary method of preparing polyurethanes?

Treating an isocyanate with an alcohol Signup and view all the answers

What is a distinctive feature of Dyneema?

It is stronger than Kevlar Signup and view all the answers

How do microorganisms degrade biodegradable polymers?

Through enzymatic hydrolysis Signup and view all the answers

What is the byproduct of lactic acid polymerization?

A molecule of water Signup and view all the answers

What is the primary mechanism of PHA degradation?

Enzymatic hydrolysis Signup and view all the answers

What is the most common PHA?

Polyhydroxybutyrate (PHB) Signup and view all the answers

What is the characteristic of oriented polymers?

Parallel arrangement of polymer chains Signup and view all the answers

What is the advantage of Dyneema compared to steel?

Dyneema is lighter and stronger than steel Signup and view all the answers

What is the estimated amount of synthetic polymers manufactured annually in the United States?

50 trillion pounds Signup and view all the answers

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

Polymerization Signup and view all the answers

What is the more widely used system for naming polymers?

IUPAC source-based system Signup and view all the answers

How are polymer formulas typically written?

By enclosing the repeating unit within brackets, followed by the letter n Signup and view all the answers

What is the term for polymers synthesized by cells?

Biopolymers Signup and view all the answers

What is the name of the polymer commonly known as Teflon?

Polytetrafluoroethylene Signup and view all the answers

What are examples of biopolymers?

DNA, RNA, and polysaccharides Signup and view all the answers

How can polymers be broadly classified?

Into synthetic polymers and biopolymers Signup and view all the answers

Study Notes

Urethanes

Urethanes can be prepared by treating an isocyanate with an alcohol in the presence of a catalyst such as a tertiary amine.
The most common polyurethanes are prepared by the polymerization of toluene-2,6-diisocyanate and ethylene glycol.

Oriented Polymers

Polymer chains obtained by conventional polymerization can be stretched and packed together again in a more ordered, parallel arrangement than originally, resulting in polymers that are stronger than steel.
Dyneema is an oriented polyethylene polymer with a molecular weight 100 times greater than that of high-density polyethylene.
Dyneema is lighter than Kevlar and at least 40% stronger.
A rope made of Dyneema can lift almost 119,000 pounds, whereas a steel rope of similar size fails at 13,000 pounds.

Biodegradable Polymers

Biodegradable polymers can be degraded by microorganisms such as bacteria and fungi.
Polylactide (PLA) is a biodegradable polymer of lactic acid, widely used.
Lactic acid is converted to a cyclic dimer, which can form a polymer without loss of water by ring-opening polymerization.
Polyhydroxyalkanoates (PHAs) are also biodegradable polymers.
PHAs are condensation polymers of 3-hydroxycarboxylic acids.
The most common PHA is PHB, a polymer of 3-hydroxybutyric acid; it can be used as polypropylene.
PHAs are degraded by bacteria to CO2 and H2O.

Anionic Polymerization

Nucleophilic attack on an alkene does not occur readily because alkenes are electron-rich.
The 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.
Living polymers are most common in anionic polymerization because the chains cannot be terminated by proton loss from the polymer.
Examples of anionic polymerization include the polymerization of methyl α-cyanoacrylate, which is used in Super Glue.

Ring-Opening Polymerizations

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

Synthetic Polymers

Synthetic polymers are a multibillion-dollar industry, with over 50 trillion pounds manufactured each year in the United States alone.
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

Polymers can be named according to their structure, but an alternative source-based system is more widely used.
Source-based names are generated by adding the prefix poly- to the name of the monomer.
When the name of the monomer consists of two words, both words are enclosed in parentheses following poly-.
The 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.

Classification of Polymers

Polymers can be divided into two broad groups: synthetic polymers and biopolymers.
Synthetic polymers are synthesized by scientists, whereas biopolymers are synthesized by cells.
Examples of biopolymers include DNA, RNA, proteins, and polysaccharides.