Durable, acid-resistant copolymers from industrial by-product sulfur and microbially-produced tyrosine

The search for alternative feedstocks to replace petrochemical polymers has centered on plant-derived monomer feedstocks. Alternatives to agricultural feedstock production should also be pursued, especially considering the ecological damage caused by modern agricultural practices. Herein, l-tyrosine produced on an industrial scale by <i>E. coli</i> was derivatized with olefins to give tetraallyltyrosine. Tetraallyltyrosine was subsequently copolymerized <i>via</i> its inverse vulcanization with industrial by-product elemental sulfur in two different comonomer ratios to afford highly-crosslinked network copolymers TTS <i>_x</i> (<i>x</i> = wt% sulfur in monomer feed). TTS <i>_x</i> copolymers were characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis (DMA). DMA was employed to assess the viscoelastic properties of TTS <i>_x</i> through the temperature dependence of the storage modulus, loss modulus and energy damping ability. Stress-strain analysis revealed that the flexural strength of TTS <i>_x</i> copolymers (>6.8 MPa) is more than 3 MPa higher than flexural strengths for previously-tested inverse vulcanized biopolymer derivatives, and more than twice the flexural strength of some Portland cement compositions (which range from 3-5 MPa). Despite the high tyrosine content (50-70 wt%) in TTS <i>_x</i> , the materials show no water-induced swelling or water uptake after being submerged for 24 h. More impressively, TTS <i>_x</i> copolymers are highly resistant to oxidizing acid, with no deterioration of mechanical properties even after soaking in 0.5 M sulfuric acid for 24 h. The demonstration that these durable, chemically-resistant TTS <i>_x</i> copolymers can be prepared from industrial by-product and microbially-produced monomers <i>via</i> a 100% atom-economical inverse vulcanization process portends their potential utility as sustainable surrogates for less ecofriendly materials.