Chemistry
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A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes
Chapters
Summary February 27th, 2017
We describe the catalytic insertion polymerization of 5-norbornene-2-carboxylic acid and 5-vinyl-2-norbornene to form functional polymers with a very high glass transition temperature.
Transcript
The overall goal of this synthetic procedure is to prepare functional insertion polynorbornenes, which are highly functional polymers with a very high glass transition temperature. The main advantage of this technique is that it's possible to access high performance polymers bearing highly reactive functional groups such as epoxy groups or acid groups via a simple experimental protocol. Generally, researchers that are new to catalytic polymer synthesis will struggle because the synthesis must be performed using very high standards of purity, but here, in the process we're going to describe, the synthesis can be performed easily with no special purification step.
Demonstrating part of the procedure will be Moubarak Compaore, a graduate student in the Claverie laboratory. To begin this procedure, set up a one liter round bottom flask with a condenser and stir bar. Add 327 grams of acrylic acid and 4.9 grams of hydroquinone to the flask.
Then use a heating block to heat the mixture to 150 degrees Celsius. Once the refluxing has settled, add 300 grams of DCPD. Then increase the temperature to 170 degrees Celsius for 16 hours.
The solution color will change from clear to yellow-brown. Using a Pasteur pipette, extract a sample. Analyze by proton NMR, using deuterated chloroform as the solvent.
Next, remove the condenser from the round bottom flask. Replace it with a simple distillation setup connected to a condenser circulating cold water. Place the reaction setup under vacuum and set the pressure to one millimeter mercury.
Then heat to 100 degrees Celsius for approximately one hour. Collect and discard the clear liquid that boils off. Replace the collection flask with a 250 milliliter round bottom flask.
Heat to 155 degrees Celsius for seven hours to distill the NBE carboxylic acid. Analyze the distilled liquid by proton NMR to determine the purity and endo to exo proportions. Then add 300 grams of NBE carboxylic acid to a 500 milliliter round bottom flask equipped with a magnetic stir bar.
Degas the NBE carboxylic acid by bubbling nitrogen for 40 minutes using a slow stirring rate for the stir bar. Add 76 milligrams of allylpalladium(II)chloride dimer. Then add 180 milligrams of silver antimonate.
Increase the stirring rate and heat the solution to 70 degrees Celsius under a slight nitrogen flux for 36 hours. Next, cool the flask with liquid nitrogen. Using a spatula, break the polymer into small pieces.
Add 750 milliliters of ethyl acetate to a two liter beaker equipped with a magnetic stir bar. Then add the polymer chunks under vigorous stirring. Allow the solution to continue stirring for two hours.
After stirring is complete, filter the solution using a Buchner funnel equipped with filter paper. Wash the polymer with 500 milliliters of ethyl acetate three times, then dry the polymer in a vacuum oven at 50 degrees Celsius for 12 hours. Separately degas 100 grams of toluene and 100 grams of NBE(vinyl)by bubbling with nitrogen gas for 30 minutes.
After that, place both in the glove box. In the glove box, add the toluene into a 250 milliliter round bottom flask. Next, successively add 76 milligrams of PD2(DBA)3, 68 milligrams of silver antimonite and 43 milligrams of triphenylphosphine to the toluene solution.
Then add the degassed NBE(vinyl)and stir at 70 degrees Celsius for 72 hours. Once stirring is complete, remove the solution from the glove box and transfer it into a one liter glass bottle equipped with a magnetic stir bar. Add 200 milliliters of fresh toluene and stir.
Then add 10 grams of silica powder and continue stirring at room temperature for 16 hours. After stirring is complete, let the solution settle for two hours to allow the silica particles to sedimentate. Filter the settled solution through a Buchner funnel equipped with filter paper.
Rinse the silica particles with fresh toluene and filter it through the Buchner funnel. Next, add 1.2 liters of methanol to a fresh four liter beaker equipped with a magnetic stir bar. Gradually add this solution of toluene and polymer to the beaker under vigorous stirring.
Continue stirring for 30 minutes. After stirring is complete, filter the polymer using a Buchner funnel and filter paper. Wash the polymer with 400 milliliters of methanol three times.
Analyze the polymer purity by proton NMR to determine if the residual monomer is present. If so, perform one additional wash with methanol. After washing is complete, dry the PNBE(vinyl)under vacuum at room temperature overnight.
Add 150 grams of dichloromethane to a 500 milliliter round bottom flask equipped with a magnetic stir bar and a condenser. Then add 15 grams of PNBE(vinyl)with stirring. Once the polymer has completely dissolved, place the flask in an ice bath to cool for 15 minutes.
In a fresh beaker, mix 30 grams of formic acid and five grams of acetic acid. Add this acid solution to the flask and let it cool for 15 minutes. Next, add 75 grams of a 30%aqueous solution of hydrogen peroxide and stir the solution for 18 hours.
After this, remove a small sample. Precipitate the polymer with acetone and analyze with proton NMR as outlined in the text protocol. If the signal for the double bond has not decreased sufficiently, continue stirring the reaction, analyzing by proton NMR hourly.
Once the signal for the double bond has decreased sufficiently, add 750 milliliters of acetone to a fresh four liter beaker equipped with a magnetic stir bar. Gradually add the polymer solution under vigorous stirring. Let the solution continue to stir for 15 minutes.
After that, filter the polymer using a Buchner funnel and filter paper. Wash the polymer with 200 milliliters of acetone four times. Finally, dry the polymer under vacuum at room temperature overnight.
In this procedure, polymers are obtained by catalyzed polymerization and collected in the form of dry powders. Representative results for the proton NMR analysis of the polymers can be seen here. This analysis confirms the epoxidation of PNBE(vinyl)The decreasing ratio between the integrals of the vinyl group and the other protons in the PNBE(epoxy)spectrum proves the efficacy of this epoxidation procedure, with 97%of PNBE(vinyl)being converted to PNBE(epoxy)FTIR spectroscopy is also used to confirm the outcome of the epoxidation reaction.
This is seen by the apparition of a characteristic peak at 875 inverse centimeters and the disappearance of the 904 inverse centimeter and 992 inverse centimeter peaks, which are observed in the PNBE(vinyl)polymer. So once mastered, an ordinary scale of either polymer, be it polynorbornene epoxy or polynorbornene acid, can be prepared in less than a week with minimal manipulation time.
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