Sethumadhavan Ravichandran

Halogen-free ultra-high flame retardant polymers through enzyme catalysis

Over the past few years, the use of certain types of halogenated flame retardant additives such as decabromodiphenylether has come under intense scrutiny due to their toxicity, environmental persistence and bio-accumulation. There is an immediate need for the development of non-toxic alternative flame retardant materials and fire resistant polymers with comparable or better efficacies, obtained using benign synthetic approaches. Enzymatic polymerization is being used increasingly as an environmentally friendly alternative method for the synthesis of functional materials including polymers and additives. Here, we report a biocatalytic synthesis of a new class of thermally stable, ultra-fire resistant polyphenols based on deoxybenzoins. In calorimetric studies, these polyphenols exhibit very low heat release capacities (comparable to Nomex™) and form a large amount of carbonaceous char rendering them suitable for flame retardant applications.

Horseradish Peroxidase Catalyzed Synthesis of Polycardanol Microcapsules

Polymers synthesized from naturally derived monomers are valuable since they decrease the reliance on petroleum based feed stocks. Cashew nut shell oil (CNSL) is a side-product from processing of edible Cashew nuts of Annacardium occidentale. One of the major components of CNSL is cardanol, which is a phenol derivative having an unsaturated pentadecyl substituent in the ‘meta’ position with varying amount of unsaturation (no double bonds to three double bonds). The substituent in the meta position can also be hydrogenated to yield completely saturated hydrogenated cardanol. Cardanol can be utilized to stabilize the dispersions of oil in water and vice versa since it displays amphiphilic behavior owing to the phenolic head and the C15 aliphatic tail. Here we report the horseradish peroxidase (HRP) catalyzed polymerization of cardanol at oil water interface to obtain polycardanol microcapsules. A synthetic analogue of hydrogenated cardanol, 3-pentadecylphenol (3PDP), was also oxidatively polymerized at the oil-water interface to obtain Poly(3-pentadecylphenol) microcapsules.

Oxidoreductase Catalyzed Polymerization of 3-Methylpyrrole

A one-pot, environmentally friendly enzymatic method is described for the synthesis a polypyrrole derivative, poly(3-methylpyrrole) (poly(3-MP)) in an aqueous solvent system. The enzyme, soybean peroxidase (SBP), was shown to successfully polymerize the beta functionalized pyrrole monomer. The resulting polymer was semiconducting, thermally stable, and exhibited bipolaron absorptions when synthesized in the presence of poly(sodium 4-styrenesulfonate) (PSS). Polymers synthesized in the presence of 10-camphor sulfonic acid (CSA) were found to exhibit slightly higher conductivity values, but were less thermally stable compared to poly(3-MP) polymerized in the presence of PSS. This work should stimulate further interest in expanding the use of enzymes as catalysts for the polymerization of other pyrrole derivatives, as well as other classes of conjugated polymers.

Biocatalytic Synthesis of Two-Photon Active Resveratrol Oligomer

Resveratrol (3,5,4′ trihydroxy trans-stilbene) is a plant based phenolic compound. Enzymatic oligomerization of trans-resveratrol using horseradish peroxidase followed by characterization of the oligomer is presented. The oligomerization reaction was monitored using UV-Visible absorption and fluorescence spectroscopies. The oligomer exhibits strong two-photon-induced fluorescence. Computational modeling using spin-density calculations was performed to investigate the most probable reaction sites and the nature of products formed in the oligomerization process.