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Related Concept Videos

Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

2.8K
The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the...
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Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

2.4K
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael...
2.4K
Radical Chain-Growth Polymerization: Mechanism01:09

Radical Chain-Growth Polymerization: Mechanism

3.3K
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...
3.3K
Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

2.4K
The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
2.4K
Anionic Chain-Growth Polymerization: Overview01:20

Anionic Chain-Growth Polymerization: Overview

2.5K
The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
2.5K
Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

3.1K
Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
3.1K

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

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Chain ends excite polymer cooperative motion.

Quanyin Xu1, Zhenghao Wu2, Katelyn Randazzo3

  • 1School of Chemistry and Chemical Engineering, State Key Laboratory of Bio-Based Fiber Materials, Key Laboratory of Surface and Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou 310018, China.

Science Advances
|November 26, 2025
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Summary
This summary is machine-generated.

Polymer chain ends significantly influence glass transition temperature (Tg) and dynamic fragility (m). Shorter polymer chains with more chain ends exhibit reduced Tg and m due to faster relaxation, simplifying polymer glass formation mechanisms.

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Area of Science:

  • Polymer Science
  • Materials Science
  • Soft Condensed Matter Physics

Background:

  • Polymers exhibit unique glass formation properties influenced by chain connectivity.
  • Key properties like glass transition temperature (Tg) and dynamic fragility (m) vary with polymer chain length.

Purpose of the Study:

  • To elucidate the chain length-dependent behaviors in polymer glass formation.
  • To reveal the correlation between chain ends and glassy properties (Tg, m).

Main Methods:

  • Analysis of the number of chain ends within the cooperatively rearranging region.
  • Correlation studies linking chain ends to Tg and m.
  • Introduction of an index of rigidity to categorize end group roles.

Main Results:

  • A strong correlation was found between chain end concentration and polymer glassy properties.
  • Fast-relaxing chain ends reduce cooperativity requirements for structural rearrangement.
  • Reduced chain length leads to decreased Tg and m.

Conclusions:

  • Polymer chain ends play a crucial role in glass formation by facilitating cooperative motion.
  • A unifying mechanism for polymer glass formation is proposed, considering chain end effects, length, and topology.
  • Findings have broad implications for chemistry, soft-condensed matter, and material science.