This protocol describes the synthesis, characterization, and the chemical recycling of a chemical recyclable polymer system developing our lamp, which we think have the potential to address the challenges associated with the sustainable use of plastics. Compared with chemically recyclable polymers developed so far, the advantage of our system is that it enables the chemical recycling of polymers with hydrocarbon backbone, which has excellent hydrolytic stability. Demonstrating the procedure will be Devavrat Sathe and Hanlin Chen, graduate students from my laboratory.
To begin, add maleic anhydride, cyclooctadiene, and 150 milliliters of dry acetone to a quartz tube. Seal the quartz flask with a rubber septum and insert a 6-inch needle connected to the nitrogen on a Schlenk line and a smaller bleed needle. Stir the solution on a magnetic stir plate while bubbling with nitrogen for around 30 minutes.
After that, remove the needles. Equip the photoreactor with 300-nanometer lamps, and place the flask in it, clamped to a vertical support. Make sure to cover the top of the photoreactor loosely and turn on the cooling fan and UV lamps.
After irradiating overnight, concentrate the mixture on a rotavap until most of the solvent is removed. Add cotton and silver nitrate-impregnated silica gel to a circulation column, and fill the rest of the column with untreated silica gel. Add another another piece of cotton, wrap the column with aluminum foil, and connect with tubing on either end.
Connect one end of the column to a metering pump for circulation, with another piece of tubing coming out of the metering pump. Put either end of the tubing into a flask with 200 millimeters diethyl ether/hexane solvent mixture and circulate for 2 hours to pack the column tight. Check any possible leaking.
Next, dissolve dimethyl ester monomer, or M1, and methyl benzoate in diethyl ether/hexane solvent mixture in a quartz tube. Equip the photoreaction chamber with 254-nanometer wavelength lamps. Replace the flask with the quartz tube, place it in the photoreaction chamber, and continue circulation under irradiation for 16 hours.
After turning off the photoreactor, pull the tubing up above the solution level and circulate for an additional 1 hour to dry the column. Pack another column with a silica gel layer at the bottom and silver nitrate-impregnated silica gel at the top. After emptying the circulation column, load its contents to the normal column.
Collect the solution from the quartz tube and concentrate. Add this concentrated solution to the silica column. Wash the column with diethyl ether/hexane solvent mixture to collect methyl benzoate and M1, followed by washing with acetone to collect EM1 silver complex.
After acetone is removed on a rotavap, add a mixture of 200 milliliters of DCM and 200 milliliters of concentrated aqueous ammonia to the residue and stir for 15 minutes. Add trans-cyclobutane fused cyclooctene monomer M2 and crosslinker XL to a 4-dram glass vial. Then, add 500 microliters of dichloromethane to this and dissolve using a vortex mixer.
Add Grubbs II catalyst, or G2, to this and agitate manually to ensure dissolution. Add the solution to a polytetrafluoroethylene, or PTFE, mold with six cavities using a glass pipette. Allow the network to cure at room temperature for 24 hours and then at 6 degrees Celsius for 24 hours.
Carefully remove the sample from the mold and submerge the sample in a 20-milliliter vial with around 5 milliliter of ethyl vinyl ether for 4 hous. Place the prepared sample in a cellulose thimble and then place it in a Soxhlet extraction apparatus. Affix the Soxhlet extractor onto a 500-milliliter round-bottom flask with 250 milliliter of chloroform and place it in an oil bath.
Attach a condenser to the top of the Soxhlet extractor and allow the solvent to reflux for almost 14 hours. Remove the sample from the thimble, place it on a piece of paper towel placed on a clean surface, cover it, and allow the solvent to evaporate under ambient conditions for almost 6 hours. Place the sample in a 20-milliliter vial and place it under a vacuum to dry completely, weighing periodically until no weight loss is detectable.
Place the polymer P1 in a 3-dram glass vial and dissolve it in 4706 microliters of deuterated chloroform. Weigh G2 in a 1-dram glass vial and add 148.6 microliters of deuterated chloroform to dissolve it. Next, add 50 microliters of the solution of G2 to the solution of P1.The total concentration of olefinic groups is therefore 25 millimolar.
Split the vial's contents into three different vials and place the vials in a water bath at 30 degrees Celsius for almost 16 hours. Then, add 50 microliters of ethyl vinyl ether to this to quench G2.Follow the same procedure for the depolymerization of the polymer network PN1. Structures of trans-cyclobutane fused cyclooctene monomers for chemically recyclable polymers are shown here.
Photochemical 2 2 cycloaddition of 1, 5-cyclooctadiene and maleic anhydride affords the anhydride 1, which can be readily converted to M1 and XL, M2, and M3.Reaction schemes for the synthesis of trans-cyclobutane fused cyclooctene small molecules and monomers and the synthesis of P1 by conventional and by living ring-opening metathesis polymerization are shown here. The representative image shows the GPC traces for polymer P1 prepared by living ROMP in the presence of G1 and triphenyl phosphine and conventional ROMP in the presence of G2.The depolymerization reaction scheme of trans-CBCO polymers is presented in this image. The stacked partial proton NMR spectra of polymer P1 after depolymerization and before depolymerization, monomer M1 are shown here.
1H NMR spectra of network PN1 after depolymerization, crosslinker XL, and monomer M2 are presented in this figure. The representative images show the stress vs. strain curves of polymer network PN1 and polymer P3.When setting up the photocycloaddition reaction, it's important to remember to spark the reaction mixture with nitrogen.
It's also important to quench the catalyst right after polymerization or depolymerization before workup. Finally, after Soxhlet extraction of the network P1, it should be dried gradually to avoid the evaporation-induced fraction. These methods can be adapted to make tCBCO polymers with many different functional groups and to prepare depolymerizable polymers with diverse material properties and to understand the substituent effect on polymerization behavior.
