Synthesis and Applications of Polymers Made by Inverse Vulcanization

Polysulfides Synthesized from Renewable Garlic Components and Repurposed Sulfur Form Environmentally Friendly Adhesives

Natural materials have been used as glues throughout human history. Over the last century, society has come to rely heavily on synthetic, petroleum-based adhesives instead, consuming ∼14 million tons per year. In recent years, however, there has been a resurgence of glues formed with renewable materials. This work seeks to integrate the two to form strong adhesives. Here, elemental sulfur was combined with diallyl sulfide (DAS), diallyl disulfide (DADS), and garlic essential oil (GEO) to form adhesive polymers from recycled petroleum waste and renewable monomers. The labile sulfur bonds in DADS and GEO allowed these monomers to be homopolymerized, forming polysulfides entirely from renewable monomers. Heating these materials causes them to transition from viscous liquids to hardened solids. A family of copolymers containing different garlic components and varying sulfur-to-monomer ratios were synthesized, characterized, and tested for this study. Polymer structures were confirmed by ¹H NMR. Changes to the polysulfide material properties upon curing were examined by gel permeation chromatography and differential scanning calorimetry. Characterization data of cured polymers were used to choose the optimal cure temperature for adhesion studies. The adhesion strength of polysulfides with varying compositions was determined by single-lap shear testing. Strong bonding was obtained for all garlic-based polysulfides with strengths 3 times higher than commercial hide glue.

Gas Permeation of Sulfur Thin-Films and Potential as a Barrier Material

Elemental sulfur was formed into poly(ether sulfone)-supported thin-films (ca. 10 µm) via a melt-casting process. Observed permeabilities of C2H4, CO2, H2, He, and N2 through the sulphur thin-films were <1 barrer. The sulfur thin-films were observed to age over a period of ca. 15 days, related to the reversion of polymerized sulfur to the S8 allotrope. This structural conversion was observed to correlate with an increase in the permeability of all gases.

Combining polybenzoxazines and polybutadienes via simultaneous inverse and direct vulcanization for flexible and recyclable thermosets by polysulfide dynamic bonding

Simultaneous inverse and direct vulcanization of a benzoxazine and a polybutadiene gave recyclable films through dynamic S–S bonding.