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Related Concept Videos

Aldehydes and Ketones with Amines: Imine Formation Mechanism01:23

Aldehydes and Ketones with Amines: Imine Formation Mechanism

8.7K
Imine formation involves the addition of carbonyl compounds to a primary amine. It begins with the generation of carbinolamine through a series of steps involving an initial nucleophilic attack and then several proton transfer reactions. The second part includes the elimination of water, as a leaving group, to give the imine.
Imines are formed under mildly acidic conditions. A pH of 4.5 is ideal for the reaction.
If the pH is low or the solution is too acidic, the reaction slows down in the...
8.7K
Structure of Amines01:19

Structure of Amines

3.4K
The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are...
3.4K
Structure of Benzene: Molecular Orbital Model01:18

Structure of Benzene: Molecular Orbital Model

13.2K
According to the molecular orbital (MO) model, benzene has a planar structure with a regular hexagon of six sp2 hybridized carbons. As shown in Figure 1, each carbon is bonded to three other atoms with C–C–C and H–C–C bond angles of 120°. The C–H bond length is 109 pm, and the C–C bond length is 139 pm which is midway between the single bond length of sp3 hybridized carbons (154 pm) and sp2 hybridized carbons (133 pm).
13.2K
Structure of Benzene: Kekulé Model01:07

Structure of Benzene: Kekulé Model

12.7K
In 1865, August Kekule suggested the structure of benzene according to the structural theory of organic chemistry based on the three assertions—formula of benzene is C6H6, all the hydrogens of benzene are equivalent, and each carbon must have four bonds due to its tetravalency.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.
12.7K
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

7.1K
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
7.1K
Structural Isomerism02:34

Structural Isomerism

22.0K
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...
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Time Scale-Dependent Structure-Property Relationships in Dynamic Imine-Benzoxazine Networks.

John J Peyrefitte1, Levi J Hamernik1, Elaina M Booker1

  • 1School of Polymer Science and Engineering, The University of Southern Mississippi, 118 College Dr. #5050, Hattiesburg, Mississippi 39406, United States.

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Summary

This study explores dynamic polymer networks called vitrimers, focusing on how their structure affects material properties. Researchers found that varying the polymer backbone and cross-link density significantly impacts relaxation times and activation energies, highlighting the complexity in tuning these dynamic materials.

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Area of Science:

  • Polymer Chemistry
  • Materials Science
  • Rheology

Background:

  • Dynamic polymer networks, or vitrimers, feature labile cross-links enabling network rearrangement through bond exchange, influenced by heat and strain.
  • The linear viscoelasticity of vitrimers depends on both local segmental motions and the kinetics of dynamic exchange mechanisms.
  • Imine-containing benzoxazine (iBOX) networks, with high glass transition temperatures, mimic structural thermosets but possess dynamic capabilities.

Purpose of the Study:

  • To investigate the linear viscoelasticity of imine-containing benzoxazine (iBOX) vitrimer networks.
  • To understand how polymer architecture, including backbone structure (PPO, PEO, PE) and molecular weight between cross-links, influences viscoelastic response.
  • To elucidate the impact of structural variations on relaxation dynamics and apparent activation energies.

Main Methods:

  • Synthesis of nine iBOX monomers via condensation of aldehyde-functionalized benzoxazine with difunctional amines.
  • Cationic ring-opening polymerization to create iBOX vitrimer networks with varied backbone structures and molecular weights.
  • Application of time-temperature superposition (TTS) to small-amplitude oscillatory shear (SAOS) and stress relaxation data.

Main Results:

  • Distinct temperature dependences for short- and long-time dynamics necessitated separate shift factors.
  • Both short- and long-time dynamics exhibited Arrhenius temperature dependence, yielding different apparent activation energies (Ea).
  • Structural variations resulted in nonuniform changes in Ea across different time scales, indicating complex tuning of exchange kinetics.

Conclusions:

  • The viscoelastic behavior of iBOX vitrimers is significantly influenced by polymer architecture.
  • Separate relaxation processes with distinct temperature dependencies and activation energies were observed.
  • Tuning the exchange kinetics in dynamic polymer networks is complex and requires careful consideration of structural variations.