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Related Concept Videos

Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

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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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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...
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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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The process of surrounding a solute with solvent is called solvation. It involves evenly distributing the solute within the solvent. The rule of thumb for determining a solvent for a given compound is that like dissolves like. A good solvent has molecular characteristics similar to those of the compound to be dissolved. For example, polar solutions dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent is a solvent that has a high dielectric constant (ϵ...
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The VSEPR theory can be used to determine the electron pair geometries and molecular structures as follows:
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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...
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Related Experiment Video

Updated: Oct 20, 2025

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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Spatial correlations of entangled polymer dynamics.

Jihong Ma1, Jan-Michael Y Carrillo1, Changwoo Do2

  • 1Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

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Entangled polymer dynamics show initial similarities to unentangled systems but reveal long-tail spatial correlations due to topological constraints. Existing models fail to fully capture these dynamics, suggesting a critical role for incompressibility.

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Area of Science:

  • Polymer Physics
  • Soft Matter Science
  • Computational Materials Science

Background:

  • Entangled polymer dynamics are crucial for material properties.
  • Understanding topological constraints is key to polymer behavior.
  • Existing models struggle to accurately describe complex polymer dynamics.

Purpose of the Study:

  • To investigate spatial correlations in entangled polymer dynamics.
  • To compare simulation and experimental results with theoretical models.
  • To identify limitations in current polymer dynamics theories.

Main Methods:

  • Molecular dynamics simulations were employed.
  • Neutron spin-echo spectroscopy was utilized for experimental validation.
  • Analysis of intermediate scattering functions and spatial correlations was performed.

Main Results:

  • Initial spatial decays of entangled chains resemble unentangled systems.
  • Entanglements manifest as long tails in reciprocal-space correlations.
  • A weak but persistent dynamic localization was observed in real space.
  • Existing theoretical models inadequately describe the observed spatial correlations.

Conclusions:

  • Current theoretical models, including the tube model, are insufficient.
  • Incompressibility may play a critical role in polymer melt dynamics.
  • Dynamic spatial correlation analysis is a valuable tool for studying entangled polymers.