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Questions and Answers
What type of polymerization is primarily used to synthesize polynorbornenes?
Endo–exo isomerism does not affect the tacticity of polynorbornenes.
False
What type of catalysts yield predominantly cis-polynorbornene?
Grubbs-type, ruthenium-based catalysts
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?
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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.
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Polynorbornenes can be synthesized in __________ forms based on stereochemistry.
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Which isomer of polyacetylene has greater conductivity?
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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?
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Trans-polyacetylene is more __________ than cis-polyacetylene.
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Match the terms with their appropriate descriptions:
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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.
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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.
