Podcast
Questions and Answers
What type of polymerization is primarily used to synthesize polynorbornenes?
What type of polymerization is primarily used to synthesize polynorbornenes?
Endo–exo isomerism does not affect the tacticity of polynorbornenes.
Endo–exo isomerism does not affect the tacticity of polynorbornenes.
False
What type of catalysts yield predominantly cis-polynorbornene?
What type of catalysts yield predominantly cis-polynorbornene?
Grubbs-type, ruthenium-based catalysts
The simplest polymer in the field of conducting polymers is __________.
The simplest polymer in the field of conducting polymers is __________.
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Which type of polymerization method is most commonly used for polyacetylene?
Which type of polymerization method is most commonly used for polyacetylene?
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Match the catalyst type with the polynorbornene structure they predominantly produce:
Match the catalyst type with the polynorbornene structure they predominantly produce:
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Stereochemistry has been extensively investigated for its influence on the material properties of polynorbornenes.
Stereochemistry has been extensively investigated for its influence on the material properties of polynorbornenes.
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Polynorbornenes can be synthesized in __________ forms based on stereochemistry.
Polynorbornenes can be synthesized in __________ forms based on stereochemistry.
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Which isomer of polyacetylene has greater conductivity?
Which isomer of polyacetylene has greater conductivity?
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Cis-stilbene has a long lifetime and is stable under light exposure.
Cis-stilbene has a long lifetime and is stable under light exposure.
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What is the main issue that limits the application of stilbene in conjugated polymers?
What is the main issue that limits the application of stilbene in conjugated polymers?
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Trans-polyacetylene is more __________ than cis-polyacetylene.
Trans-polyacetylene is more __________ than cis-polyacetylene.
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Match the terms with their appropriate descriptions:
Match the terms with their appropriate descriptions:
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What term describes the special type of bond present in poly(azomethine)s?
What term describes the special type of bond present in poly(azomethine)s?
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Stereochemistry has been fully explored in the context of poly(azomethine)s.
Stereochemistry has been fully explored in the context of poly(azomethine)s.
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What can result from the extended conjugated systems of stilbene?
What can result from the extended conjugated systems of stilbene?
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Study Notes
Polynorbornenes
- Polynorbornenes are a significant class of commodity polymers, synthesized primarily through ring-opening metathesis polymerization (ROMP) of norbornenes.
- The stereochemistry of the resulting C=C bonds in the backbone can be tuned by selecting catalysts and controlling reaction conditions.
- Stereopure polynorbornene can be achieved by using Grubbs-type, ruthenium-based catalysts, especially with bulkier monomers, leading to predominantly cis-polynorbornene.
- Schrock-type molybdenum or tungsten catalysts can also produce stereocontrolled materials.
- Consideration of tacticity is crucial due to endo–exo isomerism, which can yield four possible stereoisomeric structures, all obtainable in stereopure form.
- Most research has concentrated on synthetic methods while the influence of stereochemistry on material properties is less explored, presenting opportunities for characterization of stereopure polynorbornenes.
Polyacetylene
- ROMP methodologies can extend to create polyacetylene, a method not yet fully explored, but polyacetylene is primarily obtained through coordination–insertion polymerization.
- Polyacetylene serves as a fundamental material in the realm of conducting polymers, with its stereochemistry playing a vital role in physical properties.
- The geometry of polyacetylene can be controlled to yield either cis or trans configurations.
- Cis-polyacetylene exhibits rubbery and elastomeric characteristics, while trans-polyacetylene is brittle and crystalline, with significantly higher conductivity due to better electron delocalization from increased orbital overlap.
Stilbene and Photochemical Stability
- Stilbene (1,2-diphenylethylene) has potential for incorporation into conjugated polymers due to its photoisomerizable C=C bond but lacks widespread application.
- The cis-stilbene form is known to have a short lifetime and displays photochemical instability, leading to issues like photocrosslinking and oxidation side products.
- Extended conjugated systems can exacerbate photooxidation problems associated with stilbenes.
Poly(azomethine)s
- Poly(azomethine)s contain –HC=N– moieties, isoelectronic to HC=CH groups in traditional conjugated polymers, which theoretically allows for cis–trans isomerism.
- Unlike stilbenes, poly(azomethine)s avoid photooxidative and chemical instabilities due to the conjugated stabilization of the imine bond.
- A recent aza-Wittig protocol produced crystalline trans-poly(azomethine)s capable of supramolecular self-assembly.
- The stereochemistry of the imine bond is rarely discussed; research mainly focuses on the more stable trans isomer.
- Developing synthetic methods to synthesize high-cis-content polymers could unveil significant opportunities in the study of poly(azomethine)s and their properties.
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Description
This quiz explores the important class of polynorbornenes, focusing on their synthesis through ring-opening metathesis polymerization (ROMP). Participants will learn about the tuning of C=C bond stereochemistry and the impact of catalysts in achieving stereopure polynorbornene. Dive into the fascinating chemistry behind this significant polymer.
