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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

3.7K
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
3.7K
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

2.9K
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
2.9K
Stability of Substituted Cyclohexanes02:30

Stability of Substituted Cyclohexanes

13.2K
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
13.2K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.2K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.2K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.5K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.5K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

10.9K
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
10.9K

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Related Experiment Video

Updated: Sep 24, 2025

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
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Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

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Associative behavior of polyimide/cyclohexanone solutions.

Hongxiang Chen1,2, Wei Liu1, Mei Hong1,2

  • 1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences Changchun 130022 People's Republic of China zhangensong@fudan.edu.cn xlji@ciac.ac.cn.

RSC Advances
|May 9, 2022
PubMed
Summary
This summary is machine-generated.

Modifying solvent quality transforms low molecular weight polyimide (PI) into associative polymers, exhibiting gelation and unique shear thickening behaviors. This research deepens understanding of PI solution properties for advanced material processing.

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Area of Science:

  • Polymer Science
  • Rheology
  • Materials Science

Background:

  • Soluble polyimides (PI) can transition from neutral to associative polymers by increasing molecular weight.
  • Varying solvent quality offers an alternative method to modulate polymer interactions.

Purpose of the Study:

  • To investigate the viscoelastic behavior of a low molecular weight polyimide (PI) in cyclohexanone (CYC) by altering solvent quality.
  • To explore the potential for inducing associative polymer behavior in PI through controlled interactions.

Main Methods:

  • Rheological measurements (viscosity, oscillatory tests) to analyze viscoelastic properties.
  • Synchrotron radiation small-angle X-ray scattering (SAXS) to probe solution structure.
  • Dynamic and steady rheological experiments to study shear thickening and thinning mechanisms.

Main Results:

  • Viscosity scaling aligned with associative polymer theory.
  • PI solutions exhibited gelation tendencies with increasing concentration.
  • SAXS revealed dense aggregate formation in concentrated solutions.
  • Observed shear thickening and thinning behaviors, with shear thickening being a novel finding for PI solutions.

Conclusions:

  • Enhancing interaction strength, even in low molecular weight polyimides, can induce associative polymer characteristics.
  • The study provides insights into polyimide solution properties across different concentrations.
  • Findings guide the preparation of polyimide solutions for diverse processing applications.