We've developed a method to initiate polymerization using dynamic sulfur bonds in poly(sulfur-divinylbenzene)at 90 degrees Celsius without the need for solvents. This is substantially lower than traditional methods which require temperatures above 160 degrees Celsius. Lowering the polymerization temperature broadens the range of monomers that can be incorporated into polysulfides by inverse vulcanization.
This expands possible materials'properties and possible applications. Inverse vulcanization has produced polysulfides that have been used in lithium sulfide batteries, as infra-red transparent lenses, as mercury and oil sorbents among other applications. This method would enable the development of new materials and likely additional applications.
One of the key benefits of this method is the relative ease of the synthesis. This video provides the opportunity to demonstrate how the reaction progresses over time, as well as showing how much the polymers can vary based on the sulfur content and the ratio of the monomers present. To prepare poly(S-divinylbenzene)combine elemental sulfur and divinylbenzene at the desired weight ratio in a one-dram vial equipped with a magnetic stir bar.
Place the vial in an oil bath at 185 degrees Celsius for 30 minutes. After the reaction is complete, remove the vial from the oil bath and immediately quench by placing the vial in liquid nitrogen. Then break open the vial to remove the polymer, and repeat this step for each polymer prepared.
To synthesize terpolymers, first crush the poly(S-divinylbenzene)with a mortar and pestle for higher surface area interaction with the monomer 1, 4-Cyclohexanedimethanol divinyl ether, or CDE. Then combine the poly(S-divinylbenzene)and CDE at the desired weight ratio on a 600-milligram scale. Place the sample in a oil bath at 90 degrees Celsius for 24 hours.
Then cool the sample to room temperature. For reactions that do not result in complete monomer incorporation, dissolve the soluble polymer portions in dichloromethane, and precipitate in cold methanol. For samples with limited solubility, wash the solid polymer samples with cold methanol to remove any unreacted monomer.
To synthesize terpolymers using maleimide, combine sulfur and divinylbenzene at a 30-to-70 weight ratio on a five-gram scale as previously described. Combine the pre-polymer with maleimide at a three-to-one weight ratio in a one-dram glass vial equipped with a magnetic stir bar. Dissolve the mixture in 10 milligrams per microliter of dimethylformamide.
Then place the vial in an oil bath at 100 degrees Celsius for 24 hours. Next combine poly(S-divinylbenzene)and the desired monomer at a one-to-one weight ratio as described previously to prepare various terpolymers. Remove a sample of the mixture at various time points during the reaction, and dissolve the polymer in 600 microliters of deuterated chloroform for proton NMR analysis.
To confirm that sulfur from the polymer rather than elemental sulfur is required for polymerization, prepare samples of sulfur alone, and with CDE, divinylbenzene, and allyl ether as previously described. Analyze the polymers by proton NMR in deuterated chloroform. Integrate the resulting proton NMR spectra to determine the extent of the reaction.
Due to the relative low solubility and high polydispersity of most terpolymers, dissolve each polymer in dichloromethane at a high concentration of 75 milligrams per milliliter. Then remove particulates from the soluble portion using a 0.45-micron hydrophobic filter. Analyze the samples by gel permeation chromatography using dichloromethane as the eluent, two MesoPore columns in sequence, and a refractive index detector for analysis.
Determine the number average and weight average molecular weights based on the calibration curve of polystyrene standards. To study thermal properties, fill aluminum pans with 30 to 50 milligrams of each polymer, providing enough sample to adequately discern the glass transition temperature from the resulting thermograms. Scan the samples and obtain the thermogram values from the second scan.
For solubility studies, weigh approximately 150 milligrams of each polymer into a pre-weighed vial, and dissolve in dichloromethane to reach a concentration of 75 milligrams per milliliter. After eight hours, remove the soluble portion, and wash the insoluble portion with dichloromethane two times. Dry the remaining insoluble sample in an oven for 10 minutes to remove the remaining solvent.
After cooling the vial to room temperature, weigh it, and calculate the percent solubility by determining the difference in starting and final weights. Poly(S-divinylbenzene)was synthesized using high temperatures to initiate sulfur ring cleavage-forming radicals, which then initiate polymerization with divinylbenzene. Dynamic sulfur bonds within poly(S-divinylbenzene)can be utilized to initiate polymerization with additional monomers at much lower temperatures.
Mono-functional and di-function vinyl and allyl monomers were evaluated, and all were successfully polymerized as confirmed by NMR. The monomer content for all polymerizations were monitored over the course of 48 hours. Control reactions were performed to determine the role of poly(S-divinylbenzene)versus sulfur in the polymerization.
The products were examined by proton NMR and TLC to examine changes to the polymer structure, monomer incorporation, and to determine if sulfur was fully incorporated. Various polymerizations were conducted to examine the polymer structure of poly(S-divinylbenzene)CDE. Both increased sulfur content, and the addition of CDE led to a decrease in the glass transition temperature.
After an initial decrease in the molecular weight, the addition of CDE led to an overall increase in chain length. Maximum solubility was achieved for poly(s-divinylbenzene)synthesized with 40%to 50%sulfur. The addition of CDE led to decreased polymer solubility.
For high-sulfur-content poly(S-divinylbenzene)low solubility was observed, but incorporating CDE substantially improved the solubility. Developing a solvent-free polymerization that occurs at substantially lower temperatures than previously reported broadens the range of monomers that can be incorporated into polysulfides. This may open the door to new applications, or allow materials to be better tailored for a desired function.
A small amount of gas is produced during the synthesis of poly(sulfur-divinylbenzene)Vials should only be filled half-full to prevent a buildup of pressure. Samples should be vented prior from removing them from the hood to ensure the gas is not inhaled.
