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Related Concept Videos

Radical Chain-Growth Polymerization: Mechanism01:09

Radical Chain-Growth Polymerization: Mechanism

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The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this species into...
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Polymers02:34

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Polymers02:34

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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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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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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.
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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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Updated: Feb 24, 2026

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties
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Nomadic Molecular Key-Driven Instantaneous Covalent Reconstruction Enables Ultrahigh Impact-Stiffening Polymeric

Xiao-Yun Li1, Fu-Rong Zeng1,2, Jian-Wen Ma1

  • 1The Collaborative Innovation Center for Eco-Friendly and Fire-Safety Polymeric Materials (MoE), National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), State Key Laboratory of Advanced Polymer Materials, College of Chemistry, Sichuan University, Chengdu, China.

Advanced Materials (Deerfield Beach, Fla.)
|February 23, 2026
PubMed
Summary

Researchers developed a novel impact-stiffening polymer using a molecular key strategy. This material offers exceptional strength and energy dissipation, significantly reducing impact force for advanced protective applications.

Keywords:
covalent reconstructionenergy dissipationimpact‐stiffeningintelligent polymeric armormolecular key‐driven

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Area of Science:

  • Materials Science
  • Polymer Chemistry
  • Nanotechnology

Background:

  • Impact-stiffening materials are crucial for safety but face challenges like high activation strain/rate and poor energy dissipation.
  • Current materials struggle to meet the demands of extreme impact events.

Purpose of the Study:

  • To develop an ultrahigh impact-stiffening strategy using a nomadic molecular key-driven approach.
  • To overcome limitations of existing materials, such as activation thresholds and stiffening hysteresis.

Main Methods:

  • Designed poly(styrene-thioctic acid) (PSTx) incorporating thioctic acid (TA) as a molecular key.
  • Leveraged strain-rate-sensitive molecules to trigger covalent reconstruction and nanodomain agglomeration.
  • Utilized disulfide/hydrogen bonds for energy dissipation and phenyl groups for physical crosslinking.

Main Results:

  • PSTx demonstrated an ultralow relaxation time (15.8 ms) and a 2925-fold stiffening response with >4000% stretchability.
  • Achieved high modulus (5.8 GPa), record strength (84.3 MPa), and excellent energy dissipation (12.4 MJ/m³), reducing impact force by 97%.
  • Developed wearable composites with over 957% impact force attenuation and 360% puncture resistance.

Conclusions:

  • The molecular key-switchable strategy effectively addresses activation thresholds and stiffening hysteresis in impact-stiffening materials.
  • PSTx offers a promising paradigm for intelligent armor and protective systems.
  • This breakthrough enables efficient impact resistance and energy dissipation through controlled molecular mechanisms.