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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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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...
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Force driven transition of a globular polyelectrolyte.

Keerthi Radhakrishnan1, Sunil P Singh1

  • 1Department of Physics, Indian Institute of Science Education and Research, Bhopal 462 066, Madhya Pradesh, India.

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A flexible polyelectrolyte chain transitions from a globule to a coil state under force. This globule-coil transition force shows surprising nonmonotonic behavior, influenced by counterion interactions and chain properties.

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Area of Science:

  • Polymer Physics
  • Soft Matter Physics
  • Computational Chemistry

Background:

  • Flexible polyelectrolytes (PEs) are polymers with charged groups.
  • Their behavior is significantly influenced by counterions and external forces.
  • Understanding PE chain conformations is crucial for various applications.

Purpose of the Study:

  • To investigate the force-induced globule-coil transition in a flexible polyelectrolyte with explicit counterions.
  • To analyze the nonmonotonic behavior of the critical transition force (Fc).
  • To elucidate the underlying physical mechanisms driving this transition.

Main Methods:

  • Systematic molecular dynamics simulations of a flexible polyelectrolyte chain.
  • Application of a constant force at the chain's terminal ends.
  • Analysis of polymer shape fluctuations, end-to-end distance (Re), and free energy.

Main Results:

  • A critical force (Fc) was identified, triggering an abrupt globule-to-coil transition in the hydrophobic regime.
  • Large-scale fluctuations and bimodal distributions of Re indicate coexistence of globule and coil states at the transition.
  • The critical force (Fc) exhibited nonmonotonic dependence on Bjerrum length (lB), decreasing at small lB and increasing at large lB.

Conclusions:

  • The study reveals a novel nonmonotonic force-induced globule-coil transition in flexible polyelectrolytes.
  • This behavior is driven by the interplay of intrachain repulsion, counterion entropy, and adsorption energy.
  • Simulation results were validated by theoretical predictions for polyelectrolyte behavior.