Polymer Chemistry and Click Reactions

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Questions and Answers

What is the ultimate tensile strength of high-cis materials?

1,495 ± 66 MPa

2.8 ± 0.4 MPa

54.3 ± 6.5 MPa (correct)

3.5 ± 1.0 MPa

How does the elongation at break for high-trans materials compare to high-cis materials?

Elongation at break is irrelevant to material toughness.

High-trans materials have a lower elongation at break. (correct)

High-trans materials have a higher elongation at break.

Both have the same elongation at break.

What primary factor is suggested to affect the mechanical properties of the materials?

Molecular weight distribution.

Temperature variations.

Chemical composition of the monomers.

Altered chain packing. (correct)

What has been identified as a potential application of switchable cis-trans photoisomerization?

Alteration of stereochemical configuration in polymers. Signup and view all the answers

Which characteristic of 100% trans (Z)-double-bond-containing polymer was noted?

It has higher optical application potential than lower cis/trans ratio polymers. Signup and view all the answers

What has not been thoroughly investigated in stereocontrolled thiol-yne polymerization studies?

The effects of stereochemistry on polymer properties. Signup and view all the answers

What common limitation was highlighted regarding the comparisons of isomeric polymers?

Variability in molecular weights and material compositions. Signup and view all the answers

What type of polymers has switchable cis-trans photoisomerization been applied to specifically?

Sulfur-rich acetylenic polymers. Signup and view all the answers

What effect does stereochemistry have on the optoelectronic properties of polymers?

It significantly influences the properties. Signup and view all the answers

What was observed about the elongation at break of high-trans materials compared to normal values?

Higher values than expected. Signup and view all the answers

What is the primary advantage of the nucleophilic addition pathway in thiol–yne reactions?

It typically results in high yields of unsaturated products. Signup and view all the answers

Which metals are commonly used as catalysts in the thiol–yne click reaction?

Ru, Ir, Ni, Pd, Pt, Au, and Zr Signup and view all the answers

What role does the base play in the nucleophilic addition pathway of the thiol–yne reaction?

It facilitates the nucleophilic attack. Signup and view all the answers

How can the stereochemistry of the resultant alkene in thiol–yne reactions be influenced?

By selecting the solvent polarity, catalyst choice, and substrate. Signup and view all the answers

What type of elastomers are produced through the control of double-bond stereo-chemistry in thiol–yne addition step-growth polymers?

Crystalline materials with stereochemically dependent properties. Signup and view all the answers

What characteristic did wide-angle X-ray scattering (WAXS) confirm about high-cis-content materials?

They are crystalline in nature. Signup and view all the answers

In the thiol–yne click reaction, which mechanism is responsible for leading to unsaturated, monofunctionalized products?

Transition metal catalysed and Michael addition pathways. Signup and view all the answers

What is a notable property of polymers with significant trans content (>30%) from thiol–yne reactions?

They demonstrate amorphous characteristics. Signup and view all the answers

What experimental technique was used to analyze the crystallinity of the high-cis-content materials?

Wide-angle X-ray scattering (WAXS) Signup and view all the answers

Which factor is NOT mentioned as influencing the tuning of stereochemistry in thiol–yne reactions?

Polymerization rate Signup and view all the answers

Study Notes

Click Chemistry in Polymer Science

Click chemistry methods have gained prominence in polymer synthesis and modification, particularly post-introduction by Kolb, Finn, and Sharpless.
Thiol–ene and thiol–yne addition reactions are crucial, allowing thiols to interact with unsaturated carbon–carbon bonds.

Mechanistic Pathways of Thiol–Yne Reaction

Three mechanistic pathways for thiol–yne clicks:
- Radical mediated (photo or thermally initiated)
- Transition metal catalyzed
- Michael addition (nucleophilic addition)
Only transition metal catalyzed and Michael addition yield unsaturated monofunctionalized products.

Transition Metal Catalysts

Catalysts like Ru, Ir, Ni, Pd, Pt, Au, and Zr facilitate the formation of stereoregular vinyl sulfides via a migratory insertion mechanism.
Transition metal catalysis has been effectively applied in polymer chemistry.

Nucleophilic Addition Pathway

Requires a base (tertiary amine or phosphine) and typically results in higher yields of unsaturated products.
The stereochemistry of the alkene can be controlled through catalyst choice, solvent polarity, substrate selection, and post-polymerization treatments.

Stereochemistry in Polymers

Nucleophilic addition is preferred for creating stereochemically defined polymers due to enhanced control over double-bond stereochemistry.
High-cis-content elastomers (80% cis) exhibit crystalline structure, confirmed via wide-angle X-ray scattering and DSC, with a melting temperature of 80 °C.
Polymers with >30% trans content are amorphous, showing a lower glass transition temperature (ΔTg = 20 °C).

Mechanical Properties

High-cis materials demonstrate toughness and ductility (ultimate tensile strength: 54.3 MPa, elongation: 1,495%).
High-trans materials are softer (ultimate tensile strength: 2.8 MPa, elongation: 2,970%).
Differences in properties attributed to altered chain packing linked to alkene stereochemistry.

Contrasting Effects of Stereochemistry

The impact of cis–trans stereochemistry on mechanical properties is distinct from traditional polyolefins (like natural rubber), emphasizing unique behavior of sulfur-rich acetylenic polymers.

Photoisomerization Techniques

Switchable cis–trans photoisomerization can modify stereochemical configuration in polymers post-synthesis.
A 100% trans polymer exhibits significantly enhanced optoelectronic properties compared to those with lower cis:trans ratios.

Further Investigations

Previous studies explored stereocontrolled thiol–yne polymerizations but lacked insights into the relationship between stereochemistry and polymer properties.
Other nucleophilic addition reactions (e.g., phenol–yne, amino–yne) yielded stereocontrolled unsaturated polymers, yet similarly unexplored structure–property correlations exist due to challenges in cis:trans ratio control.

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Description

Explore the fascinating world of polymer chemistry, focusing on click chemistry methods introduced by Kolb, Finn, and Sharpless. This quiz delves into thiol–ene and thiol–yne addition reactions, their mechanisms, and applications in polymer synthesis and modification.