Synthesis of Terpolymers at Mild Temperatures Using Dynamic Sulfur Bonds in Poly(S-Divinylbenzene)

Summary

The goal of this protocol is to initiate polymerization using dynamic sulfur bonds in poly(S-divinylbenzene) at mild temperatures (90 °C) without using solvents. Terpolymers are characterized by GPC, DSC and ¹H NMR, and tested for changes in solubility.

Abstract

Elemental sulfur (S₈) is a byproduct of the petroleum industry with millions of tons produced annually. Such abundant production and limited applications lead to sulfur as a cost-efficient reagent for polymer synthesis. Inverse vulcanization combines elemental sulfur with a variety of monomers to form functional polysulfides without the need for solvents. Short reaction times and straight forward synthetic methods have led to rapid expansion of inverse vulcanization. However, high reaction temperatures (>160 °C) limit the types of monomers that can be used. Here, the dynamic sulfur bonds in poly(S-divinylbenzene) are used to initiate polymerization at much lower temperatures. The S-S bonds in the prepolymer are less stable than S-S bonds in S₈, allowing radical formation at 90 °C rather than 159 °C. A variety of allyl and vinyl ethers have been incorporated to form terpolymers. The resulting materials were characterized by ¹H NMR, gel permeation chromatography, and differential scanning calorimetry, as well as examining changes in solubility. This method expands on the solvent-free, thiyl radical chemistry utilized by inverse vulcanization to create polysulfides at mild temperatures. This development broadens the range of monomers that can be incorporated thus expanding the accessible material properties and possible applications.

Introduction

Conversion of organosulfur compounds to S₈ during petroleum refinement has led to the amassing of large stockpiles of sulfur¹. Elemental sulfur is primarily used for the production of sulfuric acid and phosphates for fertilizers². The relative abundance provides a readily available and inexpensive reagent making elemental sulfur an ideal feedstock for materials development.

Inverse vulcanization is a relatively new polymerization technique that repurposes sulfur into functional materials³. The S₈ ring converts to a diradical, linear chain upon heat....

Protocol

1. Synthesis of poly(S-divinylbenzene)

1. To prepare poly(S-divinylbenzene), combine elemental sulfur (S₈) and divinylbenzene (DVB) at various weight ratios (30:70, 40:60, 50:50, 60:40, 70:30, 80:20, and 90:10 of S₈:DVB). Prepare the reaction according to prior methods described below^3,25.
   NOTE: All reactions here were conducted on a 1.00 g scale. A typical reaction contains 500 mg of S₈ and 500 mg of DVB.
   1. Place the reagents in a 1-dram vial equipped with a magnetic stir bar. Insert the vials in an oil bath at 185 °C for 30 min.
   2. Remov....

Results

Poly(S-DVB) was synthesized according to published protocols using high temperatures (185 °C) to initiate S₈ ring cleavage forming radicals³. These radicals then initiate polymerization with DVB. The molten sulfur and liquid DVB eliminate the need for solvents. Within 30 min, sulfur and DVB react completely for form poly(S-DVB). Upon removal from the vial, the polymer is a hard, brittle material at lower sulfur content (30-40%). Mid-range sulfur content .......

Discussion

The primary benefit of this method is the ability to form polysulfides at mild temperatures, 90 °C versus >159 °C for traditional inverse vulcanization. The extended sulfur chains and sulfur loops in poly(S-DVB) are less stable than S-S bonds in S₈^23,26. Lower temperatures can then be used to cause homolytic scission and thiyl radical formation²⁴. For monomers with melting points well below the reaction temperature.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sulfur, 99.5%, sublimed, ACROS Organics	Fisher Scientific	AC201250250SDS
divinylbenzene	Fisher Scientific	AA4280422
1,4-Cyclohexanedimethanol divinyl ether, mixture of isomers	Sigma Aldrich	406171
Cyclohexyl vinyl ether	Fisher Scientific	AC395420500
Allyl ether	Sigma Aldrich	259470
maleimide	Sigma Aldrich	129585
dichlormethane	Fisher Scientific	D37
N,N-dimethylformamide	Fisher Scientific	D119
Auto sampler Aluminum Sample Pans, 50µL, 0.1mm, Sealed	Perkin Elmer	B0143017
Auto sampler Aluminum Sample Covers	Perkin Elmer	B0143003
EMD Millipore 13mm Nonsterile Millex Syringe Filters - Hydrophobic PTFE Membrane, 0.45 um	Fisher Scientific	SLFHX13NL