Also if it wasn't for my brother, I probably would have finished graduate school a year earlier. There is no way I would have made it to graduate school if not for his selfless and generous gift.
Introduction
Introduction
The process of olefin metathesis occurs when an olefin coordinates to a metal carbene catalyst, upon which a metallocyclobutane is formed as shown in Figure 1.1.3. The metallocyclobutane can either form a new olefin or revert to its original form. Since olefin metathesis is a metal-mediated process, there have been numerous studies and developments of olefin metathesis catalysts.
Ring-Opening Metathesis Polymerization
Although ruthenium catalysts are very tolerant of functional groups, their activities are much lower than those of early transition metal catalysts. group tolerance as shown in Figure 1.3. Since this development, many catalysts have been developed and widely used due to their high activity and tolerance of functional groups.
Synthesis and Characterization of Regioregular Ethylene-Vinyl Alcohol
Introduction
These polymers typically contain some degree of branching, along with a random distribution of alcohol functionality along the polymer backbone.3,8 Consequently, free radical polymerization only allows control over the monomer ratio, which is key to understanding structure–property relationships. of these materials. It was found that the properties of the bulk polymer are strongly influenced by the stereochemistry of the functional groups as well as their barrier properties.13 The synthesis of EVOH cis- and trans-C8-diol copolymers was previously published (Appendix).
Results and Discussion
- Monomer Design and Synthesis
- ROMP of 6a and 6b with 2
- ROMP of 6a/6b with 2 and Chain Transfer Agent (CTA)
- Synthesis of monomer 7a/7b
- ROMP of 7a/7b with 2 and CTA
- Hydrogenation of 8
- Deprotection of 9
- Barrier Testing
1 H NMR and 13 C NMR of the white crystalline precipitate showed this to be 5a in agreement with the literature. Polymerization of the benzoate-protected monomer as shown in Scheme 2.6 was carried out under the same clean conditions as previously described.
Conclusion
The difference in barrier properties between the two polymers was studied by our group.16 It was determined that the cis-C8-diol was prone to intermolecular hydrogen bonding, while the trans-C8-diol polymer was more prone to intramolecular hydrogen bonding. The intermolecular hydrogen bonding of the chains makes it much more difficult for oxygen and water to diffuse through the bulk material.
Future Work
Experimental Section
The reaction mixture was then quenched with 0.1 mL of ethyl vinyl ether and then dissolved in 1 mL of CH2Cl2 and precipitated. The reaction mixture was then quenched with 1.0 mL of CH2Cl2 and then dissolved with an additional 1.0 mL of CH2Cl2 and precipitated into 100 mL of ice-cold MeOH with stirring.
The Synthesis of Regioregular Ethylene-Vinyl Alcohol Copolymers via
- Introduction
- Results and Discussion
- Monomer Design and Synthesis
- ROMP of 4
- Synthesis of 9
- Conclusions
- Living Polymerization of Cyclic-olefins
- Conclusions
- Experimental Section
The reaction mixture was allowed to warm to room temperature and cis-3,4-dichlorobutene was added dropwise with a syringe. The reaction mixture was then placed in a preheated oil bath at 60 °C and allowed to stir under argon for 20 hours. The desired amount of CTA (as needed) was then added to the vial and the reaction was allowed to stir for a few minutes.
The Controlled Living Ring-Opening Metathesis Polymerization of
Introduction
This secondary metathesis is limited by the steric hindrance of the olefins in the polynorbornene polymer backbone. Additionally, living ROMP of monocyclic alkenes has seen limited use due to significant secondary metathesis of unhindered olefins in the polymer backbone. If secondary metathesis can be prevented, the high ring strain of TCO makes it an excellent candidate for controlled living polymerization.
Results and Discussions
- ROMP of Trans-Cyclooctene
- Reaction Time Study
However, as the equivalents of PPh3 increase, a high molecular weight peak is observed, as shown in the GPC of data 7 in Figure 4.3. To limit the formation of the high molecular weight species, we decided to investigate a method to prevent secondary metathesis. This results in the broadening of the PDIs or, in our case, the observed high molecular weight.
![Table 4.1. Polymerization of TCO in CH 2 Cl 2 [M] 0 /Cat = 300:1.](https://thumb-ap.123doks.com/thumbv2/123dok/10406693.0/68.918.240.736.223.727/table-polymerization-tco-ch-cl-m-cat-300.webp)
Concentration Study
As the initial monomer concentration in CH2Cl2 decreases, the molecular weight remains constant, but the isolated yields are low. Low PDI and isolated yields are obtained by removing these low molecular weight contaminants by fractionation in MeOH. When these same polymerizations are carried out in THF, backbite is suppressed and high isolated yields are achieved, along with constant molecular weights.
Synthesis of Linear High Density Polyethylene
- Diblock Copolymer Syntehesis
- Synthesis of Hydrogenated Norbornene-b-Polyethylene
- Triblock PNB-b-PCO-b-PNB
First, the polynorbornene block was synthesized using catalyst 1 in the presence of two equivalents of PPh3 relative to 1 and was then added as a macroinitiator to a vigorously stirred solution of TCO (0.1 M in THF) as shown in Scheme 4.3. The GPC trace in Figure 4.9 shows traces for polynorbornene homopolymers (PNB, dashed line) and PNB-b-PCO copolymer (solid line) made in THF. First, the polynorbornene block was synthesized using catalyst 1 in the presence of two equivalents of PPh3 relative to 1 and was then added as a macroinitiator to a vigorously stirred solution of TCO (0.1 M in THF).
Conclusions
Acknowledgements
Experimental Section
The reaction mixture was then precipitated in vigorously stirring acetone (100 ml) and a white precipitate formed. A stock solution of catalyst was quickly added to the vigorously stirred norbornene solution via a syringe under argon. After stirring for 10 min at room temperature under an argon flow, a desired amount of solution was taken up in a syringe and added as a macroinitiator to the vigorously stirred solution of TCO (0.1 M in THF with 58 equiv PPh3).
Synthesis of a Photodegradable Polybutadiene using Ring-Opening
Introduction
Results and Discussion
- Monomer Design and Synthesis
- ROMP of 5 with 2
- ROMP of 5 with COD
Conclusions
Experimental Section
Introduction
Results and Discussion
Conclusions
Acknowledgements
Experimental Section
Synthesis of Monomer 6a/6b
In the preparation of the literature it was noted that 5a is a white solid and 5b is a clear oil. With this knowledge in hand, attempts were made to crystallize the 5a, but all attempts failed.
Protection of 5a/5b
Since all attempts to obtain pure 4a and 4b failed, reduction of the epoxide with LiAlH4 to provide the 5a and 5b was carried out on the mixture of diastereomers. Protection of the diol using 2,2'-dimethoxypropane to get to the acetonide cis-protected alcohol also failed.
ROMP of monomer 6a/6b
As a result, the mixture of diols was then protected as acetates and purified by column chromatography to obtain the final monomer in 90% yield.
ROMP of 6a/6b with CTA
The number of problems associated with monomer purification and precipitation of the final polymer lead us to create an isolable monomer and polymer that is easier to purify. Reduction of the epoxide with LiAlH4 gave 70% yield of a white solid after drying under high dynamic vacuum, unlike before where a yellow viscous oil was obtained.
Benzoate protection of 5a/5b to form 7a/7b
From the previous monomer synthesis, it appears that the monomer starting with the epoxidation of MCPBA was very difficult to purify and all attempts to separate the diastereomers failed. Attempts to crystallize the diol failed along with attempts to separate the diasteremers using column chromatography.
ROMP of 7a/7b with 2 and CTA
Hydrogenation of 8 to form 9
Deprotection of 9 to form 10
The reaction mixture was then quenched with 1.0 ml of CH2 Cl2 and then dissolved with another 1.0 ml of CH2 Cl2 and precipitated in 100 ml of stirred hexanes at -78 °C. It was then cooled to room temperature and then precipitated in 50 ml of ice-cold stirred MeOH.
Living ROMP of Substituted Cyclobutenes with a Mo Initiator
ROMP of Bis(acetyloxymethyl)cyclobutene
Due to the exceptionally low yield of the reaction and the prohibitive cost of the starting material ($400 per 5 g), these conditions were unattractive.
Synthesis of monomer 4
After each hydrogenation, the benzylic carbons were still present, as evidenced by the 13C peak at 128 ppm (Figure 3.2b). Therefore, a solution method involving treatment with trimethylsilyl iodide followed by hydrolysis was used. 8,11-13 However, upon hydrolysis, the polymer began to precipitate out of solution, preventing complete deprotection.
ROMP, Hydrogenation, and Deprotection
Synthesis of monomer 9
ROMP of 9 with 2
The reaction was allowed to stir under argon for 3 hours, by which time the reaction had turned clear orange. If the polymerization was to be heated, the reaction flask was placed on a 55 °C aluminum heating block with stirring under argon for 24 h. The reaction mixture was then dissolved in 1 mL of CH2Cl2 and precipitated into 50 mL of stirring MeOH.
ROMP of Trans-Cyclooctene
Both Wu and Register also observed this high-molecular-weight species in the ROMPs of cyclobutene and cyclopentene, respectively. Photodegradable polymers have been the subject of much research due to their potential applications as photoresists and environmentally friendly materials.1 The incorporation of oxygen-containing molecules such as hydroperoxide, peroxide, and various carbonyl groups into polymers to form photodegradable materials has been extensively investigated. . In recent years, ring-opening metathesis polymerization (ROMP) has emerged as a powerful tool for polymer chemists.6-8 The development of late transition metal olefin metathesis catalysts 19 and 210, shown in Figure 5.1, has enabled the polymerization of a wide range of monomers with complex architectures and functionality.
A clear shift towards the lower molecular weight polymer is observed, as well as a broadening of the peaks. Ethylene vinyl alcohol (EVOH) copolymers have found commercial utility in food packaging and in the biomedical and pharmaceutical industries due to their excellent barrier properties for gases and hydrocarbons.1-6 The structures of EVOH copolymers affect the ability of materials to limit the diffusion of gases or hydrocarbons through a membrane. .7,8 The current commercial route to these materials involves free radical polymerization of vinyl acetate and ethylene monomers followed by saponification.9 As a result of free radical polymerization, the overall architecture is impossible to control and EVOH produced in this way contains a similar degree of branching such as low density polyethylene (LDPE). the placement of the alcohol functionality along the polymer backbone cannot be controlled.8 This has led to a poor understanding of the structure-property relationships in EVOH.
ROMP of TCO with excess PPh 3
Block copolymers of Norbornene and Trans-cyclooctene
The reaction was allowed to proceed for 30 minutes before quenching, after which the desired amount of norbornene was added. 2 equiv. PPh3 to catalyst was added to the vial containing norbornene, and 58 equiv. PPh3 to catalyst was added to the vial containing TCO. Each reaction mixture was then precipitated into two separate flasks containing vigorously stirred acetone (100 mL).
Mechanism of Norrish type II reaction
One of the most useful methods for synthesizing photodegradable polymers is the incorporation of carbonyl groups into copolymers, which can undergo a Norrish type II reaction2,3. The Norwegian type II reactions of aryl ketones involve "-hydrogen abstraction by the n,#* triplet excited state of the "-carbonyl group. Products originate from fragmentation and/or cyclization of the resulting 1,4-biradical, namely acetophenone, enol/alkene and/or cyclobutanols (Scheme 5.1).4,5.
Synthesis of aryl ketone containing monomer 5
ROMP of 5 with 2
The thermal properties of the corresponding EVOH copolymers have been reported and suggest that changes in the stereochemistry of the diol significantly affect the polymer morphology. To produce completely linear EVOH materials that differed only in the relative stereochemistry between neighboring 1,2-diols along the polymer backbone, diol protection was used to increase the solubility of monomers 3 and 4. Due to the limited solubility of diols in organic solvents suitable for ROMP, the free alcohols are protected before polymerization.
To arrive at the final EVOH structure, deprotection of the acetonide groups was necessary. This allowed for direct investigation of the effect of relative stereochemistry on EVOH copolymer properties.
![Figure 2.3. Molecular weight increases linearly with increasing [M] 0 /CTA. 7a/7b (circles, solid line), 7a/7b in toluene (4.0 M) (triangle, dashed line), 6a/6b (diamonds dash dot line)](https://thumb-ap.123doks.com/thumbv2/123dok/10406693.0/32.918.236.744.171.652/figure-molecular-increases-linearly-increasing-circles-triangle-diamonds.webp)
![Table 3.2. ROMP of 9 with 2. [M] 0 /2=600:1.](https://thumb-ap.123doks.com/thumbv2/123dok/10406693.0/49.918.206.778.195.277/table-3-2-romp-9-2-m-600.webp)
