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Related Concept Videos

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...
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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: 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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Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

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The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
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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...
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Tuning High-Density Polyethylene Microstructure and Properties from Known Distributions of Dynamic Bonds.

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Researchers developed dynamic high-density polyethylene (HDPE) using urethane bonds. This innovation enhances mechanical properties and offers a new path for recycling polyolefin plastics, a major waste contributor.

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Area of Science:

  • Polymer Science
  • Materials Chemistry
  • Sustainable Plastics

Background:

  • Polyolefins, including high-density polyethylene (HDPE), constitute over 50% of plastic waste.
  • Current recycling methods often degrade the molecular mass distribution crucial for polyolefin properties.
  • Preserving molecular characteristics is key to maintaining processability and mechanical strength in recycled plastics.

Purpose of the Study:

  • To investigate the incorporation of urethane-based dynamic bonds into HDPE.
  • To enhance the mechanical properties of HDPE while maintaining its desirable characteristics.
  • To explore new strategies for toughening semicrystalline polymers and designing advanced recycling processes.

Main Methods:

  • Synthesized dynamic HDPE polymers with urethane-based dynamic bonds.
  • Characterized polymer properties including crystallinity, melting temperature, and lamellar/amorphous thicknesses.
  • Utilized polymer physics theories to predict material properties based on bond-to-bond spacing.

Main Results:

  • Dynamic bonds strengthened the amorphous phase via supramolecular interactions, bypassing reliance on high molecular mass chains.
  • Key properties were found to be dependent on the distribution of bond-to-bond spacings along the polymer backbone.
  • A mixed backbone dynamic HDPE polymer demonstrated superior mechanical properties, approaching ultrahigh molecular weight polyethylene behavior.
  • Observed long-range supramolecular order that remained stable even in the melt state.

Conclusions:

  • The placement of dynamic bonds significantly influences the bulk properties of semicrystalline polymers.
  • This approach provides a framework for toughening polymers and designing chemical recycling methods.
  • Controlling bond-spacing distributions is a key factor in developing advanced polymer materials and recycling strategies.