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Related Concept Videos

Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

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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.
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Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
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Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
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Cationic Chain-Growth Polymerization: Mechanism00:57

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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...
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Polymers

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The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the...
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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...
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Updated: Sep 4, 2025

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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Delayed collapse transitions in a pinned polymer system.

Keerti Chauhan1, Ankit Singh1

  • 1Department of Physics, Banaras Hindu University, Varanasi 221005, India.

Physical Review. E
|July 20, 2022
PubMed
Summary
This summary is machine-generated.

Pinning a monomer in a polymer chain significantly alters its collapse kinetics. While central pinning has minimal effect, end-monomer pinning substantially delays polymer collapse, impacting the transition dynamics.

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Area of Science:

  • Polymer Physics
  • Computational Biophysics
  • Soft Matter Science

Background:

  • Understanding polymer collapse transitions is crucial for various fields, including materials science and biophysics.
  • The kinetics of polymer collapse are influenced by factors such as chain length and external constraints.
  • The theta-point represents a critical temperature where polymer chains transition between coil and globule states.

Purpose of the Study:

  • To investigate the effect of pinning a specific monomer on the kinetics of polymer collapse.
  • To compare the collapse dynamics of pinned polymers with those of free polymers.
  • To elucidate the underlying mechanisms and scaling laws governing the collapse process under confinement.

Main Methods:

  • Langevin dynamics simulations were employed to model polymer chains of varying lengths (N).
  • The equilibrium theta-point was determined by analyzing the crossover in the mean squared radius of gyration per monomer.
  • The influence of pinning a monomer at position X on collapse time and cluster size evolution was systematically studied.

Main Results:

  • Polymer collapse follows a three-stage mechanism: pearl formation, pearl coarsening, and globule formation, for both free and pinned polymers.
  • Pinning the central monomer (X=N/2) shows negligible effect on collapse kinetics, similar to a free polymer.
  • Pinning monomers away from the center, particularly end monomers (X=1 or N), delays collapse by a factor proportional to X, with collapse time scaling as τ_c ~ N^1.60.

Conclusions:

  • Monomer pinning introduces asymmetry, significantly impacting polymer collapse kinetics, especially when pinning occurs near chain ends.
  • The collapse time is maximized for end-monomer pinning and minimized for central monomer pinning.
  • Cluster size evolution exhibits distinct early-time dynamics for pinned polymers compared to free polymers, indicating altered aggregation pathways.