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Anionic Chain-Growth Polymerization: Mechanism

Anionic Chain-Growth Polymerization: Mechanism

The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.

Radical Chain-Growth Polymerization: Mechanism

Radical Chain-Growth Polymerization: Mechanism

The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this species into the...

Anionic Chain-Growth Polymerization: Overview

Anionic Chain-Growth Polymerization: Overview

The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...

Free-Radical Chain Reaction and Polymerization of Alkenes

Free-Radical Chain Reaction and Polymerization of Alkenes

The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.

Radical Chain-Growth Polymerization: Chain Branching

Radical Chain-Growth Polymerization: Chain Branching

The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...

Cationic Chain-Growth Polymerization: Mechanism

Cationic Chain-Growth Polymerization: Mechanism

The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...

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Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

Published on: September 1, 2018

A backbone lever-arm effect enhances polymer mechanochemistry.

Hope M Klukovich¹, Tatiana B Kouznetsova, Zachary S Kean

¹Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.

Nature Chemistry

|January 25, 2013

Summary

Mechanical forces in polymers can activate chemical reactions. The polynorbornene polymer backbone more efficiently transfers force, enabling reactions with less energy compared to polybutadiene.

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Area of Science:

Polymer Chemistry
Mechanochemistry
Materials Science

Background:

Mechanical forces can induce chemical transformations in polymers.
Understanding how polymer backbones transmit force is crucial for mechanochemistry.

Purpose of the Study:

To quantify and compare force transmission in different polymer backbones.
To investigate the chemomechanical coupling efficiency of cis-polynorbornene and cis-polybutadiene.

Main Methods:

Single-molecule force spectroscopy was employed.
The ring opening of cyclopropane derivatives was studied.
Computational support was utilized.

Main Results:

The critical force for isomerization decreased by approximately one-third in the polynorbornene scaffold compared to polybutadiene.
Polynorbornene demonstrated more efficient chemomechanical coupling.
Polynorbornene exhibited a greater mechanical advantage.

Conclusions:

The polymer backbone significantly influences mechanochemical reactivity.
Polynorbornene is a superior scaffold for efficient force transmission in mechanochemistry.
These findings provide a basis for designing novel mechanochemical reactions.