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Questions and Answers
What is the ultimate tensile strength of high-cis materials?
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?
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?
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?
What has been identified as a potential application of switchable cis-trans photoisomerization?
Which characteristic of 100% trans (Z)-double-bond-containing polymer was noted?
Which characteristic of 100% trans (Z)-double-bond-containing polymer was noted?
What has not been thoroughly investigated in stereocontrolled thiol-yne polymerization studies?
What has not been thoroughly investigated in stereocontrolled thiol-yne polymerization studies?
What common limitation was highlighted regarding the comparisons of isomeric polymers?
What common limitation was highlighted regarding the comparisons of isomeric polymers?
What type of polymers has switchable cis-trans photoisomerization been applied to specifically?
What type of polymers has switchable cis-trans photoisomerization been applied to specifically?
What effect does stereochemistry have on the optoelectronic properties of polymers?
What effect does stereochemistry have on the optoelectronic properties of polymers?
What was observed about the elongation at break of high-trans materials compared to normal values?
What was observed about the elongation at break of high-trans materials compared to normal values?
What is the primary advantage of the nucleophilic addition pathway in thiol–yne reactions?
What is the primary advantage of the nucleophilic addition pathway in thiol–yne reactions?
Which metals are commonly used as catalysts in the thiol–yne click reaction?
Which metals are commonly used as catalysts in the thiol–yne click reaction?
What role does the base play in the nucleophilic addition pathway of the thiol–yne reaction?
What role does the base play in the nucleophilic addition pathway of the thiol–yne reaction?
How can the stereochemistry of the resultant alkene in thiol–yne reactions be influenced?
How can the stereochemistry of the resultant alkene in thiol–yne reactions be influenced?
What type of elastomers are produced through the control of double-bond stereo-chemistry in thiol–yne addition step-growth polymers?
What type of elastomers are produced through the control of double-bond stereo-chemistry in thiol–yne addition step-growth polymers?
What characteristic did wide-angle X-ray scattering (WAXS) confirm about high-cis-content materials?
What characteristic did wide-angle X-ray scattering (WAXS) confirm about high-cis-content materials?
In the thiol–yne click reaction, which mechanism is responsible for leading to unsaturated, monofunctionalized products?
In the thiol–yne click reaction, which mechanism is responsible for leading to unsaturated, monofunctionalized products?
What is a notable property of polymers with significant trans content (>30%) from thiol–yne reactions?
What is a notable property of polymers with significant trans content (>30%) from thiol–yne reactions?
What experimental technique was used to analyze the crystallinity of the high-cis-content materials?
What experimental technique was used to analyze the crystallinity of the high-cis-content materials?
Which factor is NOT mentioned as influencing the tuning of stereochemistry in thiol–yne reactions?
Which factor is NOT mentioned as influencing the tuning of stereochemistry in thiol–yne reactions?
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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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