The overall goal of this procedure is to produce well-defined polymethyl methacrylate using perylene as a visible light photocatalyst for atom transfer radical polymerization. The overall goal of this procedure is to produce well-defined polymethyl methacrylate using perylene as an organic photocatalyst for atom transfer radical polymerization. This method can help answer key questions in the field of organic catalysis and photoredox catalysis such as, can we replace transition metal complexes with organic dyes such as perylene?
The main advantage of this technique is that the metal catalyst commonly used in atom transfer radical polymerization can be replaced with perylene, a common organic dye. Visual demonstration of this method is critical to ensure reproducibility among research groups, as the exact reaction setup can have a substantial impact on the outcome of the experiment. Prepare all reagents as described in the text protocol, and allow them to come to room temperature.
Inspect all reagents prior to use to ensure there is no sign of contamination such as discoloration or formation of solid particles. In a nitrogen atmosphere glove box, place a small stir bar in a 100 milliliter reaction tube. Add 9.5 milligrams of perylene, and then 4.00 milliliters of dimethylformamide, or DMF.
To this mixture, add 4.00 milliliters of methyl methacrylate, or MMA. Place the vial on a stir plate set to 900 rpm inside a 400 milliliter beaker illuminated by strips of white light-emitting diodes. Limit any illumination from other light sources.
To initiate the reaction, add 65.6 microliters of ethyl alpha-bromophenylacetate, or EBP, via pipette. Stir the reaction for twenty-four hours under constant illumination. On the bench top, dispense 0.70 milliliters of the butylated hydroxytoluene, or BHT, in deuterated chloroform solution into a two milliliter vial, and seal with a septum cap.
Bring this vial into the glove box where the polymerization is being performed. Use a syringe to remove 0.20 milliliters of the reaction mixture. Inject the contents of the syringe into the two milliliter vial containing the 250 ppm solution of BHT and deuterated chloroform.
Draw back and push in the plunger several times to ensure thorough quenching of the polymerization. Next, transfer the contents of the two milliliter vial to an NMR spectroscopy tube. Analyze this sample via proton NMR spectroscopy for percent conversion.
After analysis, pour the contents of the NMR spectroscopy tube into a clean 20 milliliter scintillation vial. Evaporate the solvent under reduced pressure. Then, redissolve the sample in 1.00 milliliters of tetrahydrofuran.
Send the sample through a 0.45 micron syringe filter into a clean two milliliter vial. Analyze the sample via gel permeation chromatography, or GPC, coupled with multi-angle light scattering, to determine number average molecular weight, weight average molecular weight, and dispersity. To isolate and purify the product polymethyl methacrylate, first quench the polymerization reaction by pouring the contents of the reaction mixture into a fifty-fold excess of methanol and letting stir for at least one hour.
Isolate the polymethyl methacrylate from the methanol by vacuum filtration. Then, rinse the polymer with an additional 100 milliliters of methanol. Redissolve the polymer in dichloromethane and repeat these steps twice.
In a nitrogen atmosphere glove box, place 544 milligrams of polymethyl methacrylate macroinitiator into a 20 milliliter scintillation vial fitted with a small stir bar. Next, add 2.4 milligrams of perylene to the scintillation vial followed by 4.00 milliliters of dimethylformamide. Place the vial on a stir plate set to 900 rpm inside a beaker illuminated by strips of white LEDs.
Limit any illumination from other light sources. To this mixture, add 4.96 milliliters of styrene via pipette and stir the reaction for twenty-four hours under constant illumination. Finally, isolate and purify the polymethyl methacrylate block polystyrene product, as before.
Shown here are representative results of the polymerization of functionalized vinyl monomers using this technique. Tuning of reaction parameters can have a significant effect on the outcome of the polymerization. This figure shows the results of block copolymerization using an isolated polymethyl methacrylate macroinitiator, as described in the video procedure.
The ability to chain extend in this fashion lends support to an atom transfer mechanism. After watching this video, you should have a working understanding of how to produce and isolate well-defined polymers and block copolymers using perylene as a visible light photocatalyst for atom transfer radical polymerization.
