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Related Concept Videos

Polymer Classification: Architecture01:14

Polymer Classification: Architecture

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Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
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Radical Chain-Growth Polymerization: Chain Branching01:17

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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...
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Radical Chain-Growth Polymerization: Mechanism01:09

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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...
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Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

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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.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
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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.
Many natural and synthetic polymers are produced by...
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Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

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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.
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Updated: Dec 2, 2025

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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Heat conduction in polymer chains with controlled end-to-end distance.

Mohammadhasan Dinpajooh1, Abraham Nitzan1

  • 1Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.

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|November 3, 2020
PubMed
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Stretching polymer chains significantly enhances their thermal conductivity by shifting heat transport from diffusive to ballistic mechanisms. This transition depends on mechanical tuning and chain length, offering insights into polymer material properties.

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Area of Science:

  • Materials Science
  • Polymer Physics
  • Computational Chemistry

Background:

  • Low thermal conductivity is a key limitation for many polymer applications.
  • Individual polymer chains, when stretched, can exhibit surprisingly high thermal conductivity.

Purpose of the Study:

  • To investigate how mechanical tension affects thermal conductance in single polymer chains.
  • To understand the mechanisms of heat transport in polymers under varying mechanical conditions.

Main Methods:

  • Non-equilibrium molecular dynamics simulations were employed.
  • Steady-state thermal conductance was studied along finite macromolecules.
  • Mechanical control of the end-to-end distance was applied.

Main Results:

  • Thermal conductance is highly dependent on mechanical tuning, showing distinct behaviors in compressed versus stretched states.
  • A threshold phenomenon was observed where thermal conductance increases sharply beyond critical end-to-end distances.
  • Heat transport transitions from diffusive (compressed) to ballistic (stretched) mechanisms, evidenced by temperature profiles and length dependence.

Conclusions:

  • Mechanical stretching is a critical factor in enhancing polymer thermal conductivity.
  • The observed behavior is robust across different molecular structures and force fields.
  • Understanding these mechanics offers pathways to engineer polymers with improved thermal management properties.