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