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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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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...
2.1K
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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Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

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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...
2.4K
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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Characteristics and Nomenclature of Homopolymers01:00

Characteristics and Nomenclature of Homopolymers

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Polymers that are made up of identical monomer units are called homopolymers. Only one repeating unit is involved in the construction of the homopolymer structure. For example, as depicted in Figure 1, polypropylene is a homopolymer constituted of propylene monomers. Here, the only repeating unit in the polymer chain is propylene.
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Related Experiment Video

Updated: Jun 3, 2025

Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants
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Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants

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Characterization and Rheological Properties of Ultra-High Molecular Weight Polyethylenes.

Alexander Ya Malkin1, Tatyana A Ladygina2, Sergey S Gusarov2

  • 1A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29, Leninskiy Prospect, 119991 Moscow, Russia.

Polymers
|January 8, 2025
PubMed
Summary

Investigating ultra-high molecular weight polyethylene (UHMWPE) reveals molecular weight and rheological properties are method-dependent. UHMWPE exhibits elastic-plastic behavior at high temperatures, not viscous flow, with degradation occurring over time.

Keywords:
GPCMWUHMWPEplasticityrheology

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Area of Science:

  • Polymer Science
  • Materials Science
  • Rheology

Background:

  • Ultra-high molecular weight polyethylene (UHMWPE) is a critical material in various applications.
  • Understanding its molecular characteristics and rheological properties is essential for processing and performance.
  • Existing characterization methods may yield inconsistent results due to calibration and dissolution dependencies.

Purpose of the Study:

  • To investigate the molecular characteristics and rheological properties of three UHMWPE samples.
  • To evaluate the impact of different characterization methods on molecular weight determination.
  • To understand the high-temperature behavior and flow properties of UHMWPE.

Main Methods:

  • High-temperature Gel Permeation Chromatography (GPC) for molecular weight distribution (MWD) and average molecular weight (MW) analysis.
  • Calibration using polystyrene (PS) standards with linear and cubic approximations, and linear polyethylene (PE) data.
  • Rheological property measurements using creep and oscillatory tests at various shear stresses and temperatures (up to 210 °C).

Main Results:

  • Molecular weight assessment is highly dependent on the calibration method and dissolution time, with cubic PS approximation yielding manufacturer-consistent results.
  • UHMWPE exhibits elastic-plastic behavior at 210 °C, with irreversible deformation attributed to plasticity rather than flow.
  • Ultimate plastic deformation decreases with increasing molecular weight, and prolonged high-temperature exposure leads to macromolecular degradation, not viscous flow.

Conclusions:

  • Accurate characterization of UHMWPE requires careful selection of GPC calibration methods and consideration of dissolution effects.
  • UHMWPE does not reach a terminal viscous flow region even at elevated temperatures; it behaves as an elastic-plastic material.
  • High molecular weight and processing conditions significantly influence UHMWPE's mechanical response and stability, with degradation being a key concern.