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Related Concept Videos

Radical Chain-Growth Polymerization: Chain Branching01:17

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...
Ziegler–Natta Chain-Growth Polymerization: Overview01:17

Ziegler–Natta Chain-Growth Polymerization: Overview

Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta catalyst, high molecular...
Radical Chain-Growth Polymerization: Mechanism01:09

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...
Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
Radical Chain-Growth Polymerization: Overview01:10

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...
Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.

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Related Experiment Video

Updated: Jul 7, 2026

DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
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DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers

Published on: October 25, 2017

Metastable tight knots in a wormlike polymer.

Alexander Y Grosberg1, Yitzhak Rabin

  • 1Department of Physics, University of Minnesota, 116 Church Street SE, Minneapolis, Minnesota 55455, USA.

Physical Review Letters
|February 1, 2008
PubMed
Summary

Knot entropy in semiflexible polymers predicts compact knots that diffuse along the chain. This finding aligns with experimental data for knotted DNA, suggesting a universal behavior for polymer knots.

Area of Science:

  • Polymer Physics
  • Statistical Mechanics
  • Biophysics

Background:

  • Semiflexible polymers exhibit complex topological states.
  • Understanding polymer knot dynamics is crucial for various biological and material science applications.
  • Previous models have not fully captured the interplay between bending energy and confinement entropy in polymer knots.

Purpose of the Study:

  • To predict the behavior of knots in wormlike chains based on knot entropy.
  • To investigate the role of bending energy and confinement entropy in knot configuration.
  • To compare theoretical predictions with experimental data for knotted DNA.

Main Methods:

  • Theoretical estimation of knot entropy for a wormlike chain.
  • Modeling the interplay of bending energy and confinement entropy.

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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

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DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
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  • Analyzing the diffusion of compact metastable knot configurations.

    • Main Results:

    • A compact metastable knot configuration is predicted.
    • Knots diffuse along the polymer contour without spreading.
    • The estimated knot size as a function of topological invariant matches experimental dsDNA data.

    Conclusions:

    • The interplay of bending energy and confinement entropy dictates polymer knot behavior.
    • The predicted knot diffusion mechanism offers a new perspective on polymer topology.
    • Further experimental validation is proposed to confirm these findings.