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Related Concept Videos

Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth 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.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
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Polymer Classification: Architecture01:14

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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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Polymers: Molecular Weight Distribution01:10

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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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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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Polymers: Defining Molecular Weight01:01

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Unlike small molecules with definite molecular weights, polymers are a mixture of individual polymer chains of varying lengths, each with a unique molecular weight.  So, the molecular weight of a polymer is expressed as an average value based on the average size of the polymer chains. The two most common forms of averages used for polymers are the number average molecular weight and weight average molecular weight.
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Polymers02:34

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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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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Chain-Length-Dependent Correlated Molecular Motion in Polymers.

Matthew Reynolds1, Daniel L Baker1, Peter D Olmsted2

  • 1University of Leeds, School of Physics and Astronomy, Leeds LS2 9JT, United Kingdom.

Physical Review Letters
|December 5, 2025
PubMed
Summary
This summary is machine-generated.

Dynamic heterogeneities in polymers depend on chain flexibility and length. Highly flexible polymers show correlated motion independent of molecular weight, while less flexible ones exhibit complex behavior linked to relaxation dynamics.

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Area of Science:

  • Polymer physics
  • Materials science
  • Condensed matter physics

Background:

  • Dynamic heterogeneities (DHs) are crucial for understanding glass-forming materials.
  • The relationship between DHs and polymer properties like chain flexibility and length is not fully understood.

Purpose of the Study:

  • To investigate how dynamic heterogeneities (DHs) in polymers are influenced by chain flexibility and molecular weight.
  • To explore the connection between DH length scale and relaxation dynamics in polymers.

Main Methods:

  • Computational modeling and simulation of polymer dynamics.
  • Analysis of monomeric correlated motion at the glass transition temperature (Tg).
  • Comparison of DH behavior across different polymer flexibilities and molecular weights.

Main Results:

  • Highly flexible polymers exhibit a constant number of correlated monomers (Nc) around 500 at Tg, irrespective of molecular weight.
  • Less flexible polymers display a three-regime Nc(M) behavior, correlating with Tg and chain conformation.
  • A direct link was found between Nc(M) and the ratio of activation barriers for structural (α) and secondary (β) relaxations in poly(methyl methacrylate).

Conclusions:

  • DH length scale is directly related to the number of β relaxation events needed for α relaxation.
  • Chain flexibility significantly impacts the nature and molecular weight dependence of dynamic heterogeneities in polymers.
  • The observed correlation between Nc and relaxation barriers suggests a general mechanism for cooperative motion in glass-forming polymers.