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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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Radical Chain-Growth Polymerization: Chain Branching01:17

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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...
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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...
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Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

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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...
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Ziegler–Natta Chain-Growth Polymerization: Overview01:17

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Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta...
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Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

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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...
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Molecular Stiffening by Macrocycle Clustering.

Hang Yin1, Qian Cheng1, Roselyne Rosas2

  • 1State Key Laboratory of Quality Research in Chinese Medicine, Institute of Chinese Medical Sciences, University of Macau Taipa, Macau, China.

Angewandte Chemie (International Ed. in English)
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Summary

Cucurbit[n]uril macrocycles selectively stiffen guest molecules by controlling their dynamics. This host-guest interaction offers new strategies for bioinspired systems, room temperature phosphorescence, and organocatalysis.

Keywords:
CucurbiturilMacrocyclesRigidificationSupramolecularTetratopic

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Area of Science:

  • Supramolecular Chemistry
  • Chemical Biology
  • Materials Science

Background:

  • Allosteric stiffening regulates protein function by controlling oligomerization.
  • Selective control over molecular dynamics in synthetic compounds is challenging.
  • Nature utilizes allosteric mechanisms for cellular regulation.

Purpose of the Study:

  • To investigate cucurbit[n]uril (CB[n]) macrocycles for selective control of guest molecule dynamics.
  • To explore the potential of host-guest interactions in stiffening molecular portions.
  • To demonstrate a new strategy for allosteric control in synthetic systems.

Main Methods:

  • 1H-NMR (1D, 2D), DOSY, and VT-NMR spectroscopy.
  • Isothermal titration calorimetry (ITC) and mass spectrometry.
  • Molecular modeling and computational analysis.

Main Results:

  • Cucurbit[n]uril (CB[n]) macrocycles bind extensively to tetratopic guest molecules.
  • Host-guest interactions selectively stiffen different parts of the guest molecule.
  • Cucurbit[8]uril (CB[8]) binding is crucial for selective hardening of guest molecule segments.

Conclusions:

  • Cucurbit[n]urils can allosterically control molecular dynamics, mimicking natural systems.
  • This approach has potential applications in enhancing room temperature phosphorescence.
  • The strategy may enable allosteric control of organocatalysis in aqueous media.