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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.
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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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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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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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Polymer Classification: Crystallinity01:21

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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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Polymer Classification: Stereospecificity01:26

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Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...
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Related Experiment Video

Updated: Sep 22, 2025

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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Molecular Weight Dependence of Polymer Chain Mobility within Multilayer Films.

Li Xu1, Victor Selin1, Aliaksandr Zhuk1

  • 1Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030, United States.

ACS Macro Letters
|May 24, 2022
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Summary

This study reveals how polymer chain diffusion in layer-by-layer films depends on molecular weight. Lateral diffusion of polymethacrylic acid (PMAA) decreases with increasing molecular weight.

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Area of Science:

  • Polymer science
  • Materials science
  • Physical chemistry

Background:

  • Layer-by-layer (LbL) films are versatile materials with tunable properties.
  • Understanding polymer dynamics within LbL films is crucial for their application.
  • Previous studies have not fully elucidated the molecular weight dependence of polymer diffusion in LbL films.

Purpose of the Study:

  • To investigate the molecular weight (Mw) dependence of lateral diffusion for polymer chains within LbL films.
  • To determine the relationship between polymer diffusion and molecular weight in these nanostructured films.
  • To quantify diffusion coefficients using advanced characterization techniques.

Main Methods:

  • Fluorescence recovery after photobleaching (FRAP) was employed to measure diffusion.
  • Neutron reflectometry was used to characterize film structure and composition.
  • Polyelectrolyte multilayers (PEMs) of polymethacrylic acid (PMAA) with varying molecular weights were assembled.

Main Results:

  • Similar diffusion of PMAA was observed perpendicular to the film surface, irrespective of molecular weight.
  • Layer intermixing remained minimal (<1.0 nm) even at salt concentrations that unfroze chains.
  • The lateral diffusion coefficient (D) exhibited a clear inverse relationship with PMAA molecular weight: D ~ Mw^-1±0.05.

Conclusions:

  • Lateral polymer chain diffusion in LbL films is significantly influenced by molecular weight.
  • The findings provide quantitative insights into polymer dynamics within LbL assemblies.
  • This research contributes to the fundamental understanding of polymer behavior in confined environments.