Name: radical chain-growth polymerization steps
Uploaded: 2023-04-30T11:24:11.000Z
Duration: 1 min 10 s
Channel: JoVE

Chain-growth polymerization, or addition polymerization, is the successive addition of monomers in a growing chain.
Free-radical chain-growth polymerization initiates and proceeds via an unpaired electron from a free-radical intermediate.
The free radical originates from a radical initiator. In the process of adding to the first monomer, the unpaired electron moves to the opposite end of the monomer. As this reactive intermediate sequentially adds to other monomers, the polymer chain grows.
The polymer chain&#39;s reactive end, or the propagation site, shifts with each addition to the newly appended monomer. Typically, the number of monomers added to one polymer chain is in the range of one thousand to ten thousand.
To control the chain length of a polymer, a chain transfer reagent is used. It terminates the growth of a polymer chain while simultaneously initiating polymerization by reacting with a monomer.
Inhibitors also can be used to reduce the reactivity of growing polymer chain radicals through stabilization.

radical chain-growth polymerization: overview

Radical Chain-Growth Polymerization: Overview

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is used to minimize radical coupling.
<img alt="Chemical reaction scheme, decarboxylation process, structural formula, thermal decomposition." src="/files/ftp_upload/12920/12920_PT_Figure_1.svg" style="text-align: center; height: 75px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
Figure 1: The homolytic fission reaction of radical initiator dibenzoyl peroxide to generate benzoyloxy radicals and the subsequent decomposition to phenyl radicals
This free radical initiates polymerization by reacting with a monomer molecule. Unsaturated monomers are suitable for radical chain-growth polymerization; a substituent group across the unsaturated bond that stabilizes the free radical increases the reaction feasibility. Ethylene, propylene, vinyl chloride, and styrene are examples of monomers that can be polymerized via free-radical chain-growth polymerization.
The reaction between a monomer and a free radical generates a new free radical. This new radical reacts with another monomer and creates yet another free radical. The polymer chain grows as the reaction between free-radical intermediates and monomers repeats sequentially. Typically, the propagation step repeats one thousand to ten thousand times before the termination of polymerization.
Often, chain transfer reagents, such as thiol, are used to control the molecular weight (Figure 2). A chain transfer agent must be sufficiently reactive to transfer a hydrogen atom to the growing chain to terminate the polymer growth. The resultant radical must add to a double bond in the monomer to initiate polymerization.
<img alt="Chemical reaction mechanism diagram; nucleophilic substitution of sulfur compounds." src="/files/ftp_upload/12920/12920_PT_Figure_2_.svg" style="text-align: center; height: 150px;" data-altupdatedat="1761830439000" data-alt="Figure2" />
Figure 2: (Top): The termination reaction of chain transfer agent thiol and a growing polymer chain; (Bottom): Subsequent reaction of thiol radical and monomer molecule to initiate polymer growth
Inhibitors are the reagents used to reduce the reactivity of radicals in the growing polymer chain. Figure 3 depicts the reaction of benzoquinone as an inhibitor.
<img alt="Polymer synthesis mechanism diagram; molecular formula of rearrangement reaction with structural shifts." src="/files/ftp_upload/12920/12920_PT_Figure_3.svg" style="text-align: center; height: 200px;" data-altupdatedat="1761830439000" data-alt="Figure3" />
Figure 3: The reaction between chain inhibitor benzoquinone and a growing polymer chain to generate a less reactive free radical

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the ...

radical-chain-growth-polymerization-overview

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radical chain-growth polymerization steps

Radical chain-growth polymerization builds a polymer by repeated addition of monomers to a growing chain. It uses a free-radical intermediate, which is the reactive species that keeps the chain moving forward.

The process starts with a radical initiator. These initiators generate free radicals on their own by homolytic fission, or splitting a bond so each atom keeps one electron. Common initiators include organic peroxides such as dibenzoyl peroxide and azo compounds. A low initiator-to-monomer ratio is used to reduce radical coupling.

The free radical then reacts with a monomer molecule to begin polymer formation. Unsaturated monomers work well for this reaction, especially when a substituent group across the double bond helps stabilize the radical. Examples include ethylene, propylene, vinyl chloride, and styrene.

After initiation, the chain grows through propagation. Each time the radical adds to another monomer, a new radical forms at the end of the chain. That pattern repeats many times, often about one thousand to ten thousand steps, before the reaction ends.

The polymer size can be adjusted with chain transfer reagents such as thiol. A chain transfer agent must be reactive enough to transfer a hydrogen atom to the growing chain and stop its growth. The radical that remains must then add to a monomer double bond to start a new chain.

Inhibitors are also used to slow radical reactivity in the growing polymer chain. Benzoquinone is one example of a chain inhibitor. It reacts with the chain radical and produces a less reactive free radical, which reduces further polymer growth.

Radical Chain-Growth Polymerization Steps

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characteristics and nomenclature of homopolymers

characteristics-and-nomenclature-of-homopolymers

Naming Homopolymers from Their Monomers

Homopolymers are polymers made from identical monomer units. They contain only one repeating unit in the polymer chain. A clear example is polypropylene, which is built from propylene monomers. The name of a homopolymer is usually formed by adding the prefix poly to the monomer name. That is why the polymer from propylene is called polypropylene. When the monomer has multiple parts or substituents, the monomer name may be placed in parentheses after poly. Examples include...

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Radical chain-growth polymerization builds a polymer by repeated addition of monomers to a growing chain. It uses a free-radical intermediate, which is the reactive species that keeps the chain moving forward. The process starts with a radical initiator. These initiators generate free radicals on their own by homolytic fission, or splitting a bond so each atom keeps one electron. Common initiators include organic peroxides such as dibenzoyl peroxide and azo compounds. A low...

radical chain-growth polymerization: mechanism

radical-chain-growth-polymerization-mechanism

Radical Polymer Chain Growth and Ending

Radical chain-growth polymerization builds polymers through initiation, propagation, and termination. A free radical from the initiator adds to the unsaturated bond in a monomer. The unpaired electron from the radical and one pi electron from the double bond form a sigma bond. The other pi electron then becomes a new free radical on the growing molecule. The initiation step can be shown with a phenyl free radical reacting with vinyl chloride. After initiation, the new radical adds to another...

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Anionic chain-growth polymerization builds a polymer through initiation, propagation, and termination. It begins when a nucleophilic anion, such as butyl lithium, attacks the pi bond of a vinylic monomer. This creates a carbanion, which is a carbon atom with a negative charge. The electron-withdrawing group on the monomer helps stabilize that carbanion. The carbanion then drives the propagation step. It acts as a Michael donor and attacks a second vinylic monomer, which serves as the Michael...

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olefin metathesis polymerization: overview

olefin-metathesis-polymerization-overview

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Olefin metathesis polymerization creates polymers by rearranging double bonds in olefins with a catalyst. The metathesis reaction moves substituents between two alkene molecules, and that same chemistry can be used to build polymer chains. Ruthenium-based Grubbs catalyst is the most common catalyst for this process. Grubbs catalyst contains a carbon-metal double bond called a carbene. The reaction is reversible and starts when the catalyst reacts with an alkene in a [2+2] cycloaddition. This...

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ROMP Polymerization Driven by Ring Strain

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ADMET Polymerization for Linear Polymers

ADMET polymerization is a type of olefin metathesis used to build linear unsaturated polymers from terminal dienes. In this reaction, molecules such as 1,8-nonadiene react with each other and release ethylene gas. The process is reversible, so the ethylene must be removed from the reaction mixture for polymerization to continue. ADMET works through a metallacyclobutane intermediate, which forms when one double bond in a terminal diene undergoes [2+2] cycloaddition with a Grubbs catalyst. The...

key terms and concepts

Explore how radical chain-growth polymerization starts, grows, and stops, including initiators, monomers, chain transfer agents, and inhibitors.

Radical Chain-Growth Polymerization Steps | JoVE K12

organic chemistry

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Radical Chain-Growth Polymerization Steps

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