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Related Concept Videos

Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

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.
Determination of Molar Masses of Polymers I01:24

Determination of Molar Masses of Polymers I

Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...
Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

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...
Determination of Molar Masses of Polymers II01:27

Determination of Molar Masses of Polymers II

Polymer samples typically consist of macromolecular chains with a distribution of lengths, resulting in a range of molar masses rather than a single discrete value. Conventional descriptors such as the number-average molar mass and weight-average molar mass quantify this distribution but do not fully capture polymer behavior in solution..The viscosity-average molar mass provides a more realistic description of polymer behavior in solution because it accounts for the enhanced contribution of...
Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

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...
Polymers02:34

Polymers

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 properties that they exhibit. Additionally,...

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Related Experiment Video

Updated: Jul 3, 2026

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
06:55

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

Published on: September 26, 2016

Molecular physics of a polymer engineering instability: experiments and computation.

D G Hassell1, M R Mackley, M Sahin

  • 1Department of Chemical Engineering, University of Cambridge, Cambridge CB2 3RA, United Kingdom.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|July 23, 2008
PubMed
Summary

Flow instabilities in entangled polymer melts hinder industrial production. This study reveals a viscoelastic disturbance at the slit outlet, driven by chain stretch, offering insights into improving polymer processability.

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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

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Related Experiment Videos

Last Updated: Jul 3, 2026

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
06:55

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

Published on: September 26, 2016

DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
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DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers

Published on: October 25, 2017

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
16:24

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

Published on: August 2, 2012

Area of Science:

  • Polymer physics
  • Rheology
  • Fluid dynamics

Background:

  • Entangled polymer melts are prone to flow instabilities, limiting manufacturing efficiency.
  • Understanding these instabilities is crucial for optimizing polymer processing.

Purpose of the Study:

  • To investigate the formation and development of a specific flow instability in entangled polymer melts.
  • To identify the underlying physical mechanisms and key parameters governing this instability.

Main Methods:

  • Experimental flow of monodisperse linear polystyrenes in a contraction-expansion geometry.
  • Computational linear stability analysis using the Rolie-Poly model.

Main Results:

  • Observed a viscoelastic disturbance at the slit outlet, leading to upstream fluid motion.
  • Confirmed the instability numerically and identified critical parameters.
  • Determined that chain stretch plays a key role in the instability mechanism.

Conclusions:

  • Chain stretch is a critical factor in polymer melt flow instabilities.
  • This understanding can inform strategies to enhance polymer blend processability, such as incorporating low-molecular weight tails.