Sustainable routes to conjugated polymers and non-halogenated flame retardents

Sustainable design and development of advanced functional materials has gained prominence over the last two decades. In the field of "Green chemistry", the use of enzyme and biomimetic catalysts have facilitated certain unique transformations and polymerization reactions in environmentally benign conditions. Sustainability considerations have also promoted the use of bio-based feedstocks for the creation of functional materials. The work presented in this research explores the use of sustainable approaches for the development of conjugated polymers based on polypyrrole and non-halogenated polyphenol based flame retardant (FR) materials.;Polypyrrole (PPy) is an extensively studied conducting polymer due to its potential biocompatibility and promising opto-electronic properties. Recently, enzymatic polymerization of pyrrole and its derivatives using soybean peroxidase has been successfully accomplished to yield a conducting polymer. The use of enzyme facilitated a one-pot reaction under mild aqueous conditions. However enzyme catalysts suffer from low stability under acidic/basic conditions and high costs. With the objective of using other low cost, biomimetic catalysts, this thesis explores the use of hematin (an iron porphyrin from porcine) for the polymerization of pyrrole and its derivatives. The inadequacies of hematin with respect to solubility and strong aggregation were offset by the use of a micellar environment created using anionic surfactants like dodecylbenzenesulfonate (DBSA). This micellar environment in an aqueous media enables interaction of water insoluble monomers with hematin. Low temperature (4°C) synthesis and acidic conditions favored the formation of a molecular complex of PPy/DBSA with conductivity of the order of 0.01 S/cm. This approach has been extended to the polymerization of alkyl-pyrrole derivatives like 3 -methylpyrrole and 3,4-diethylpyrrole to yield semi-conducting polymers. The unique micellar media has also aided the synthesis of a fluorescent poly(3-heptypyrrole), that can be potentially used in sensing applications. These results suggest new opportunities for the use of cost-effective biomimetic catalysts in place of enzymes for the creation of novel semi- conducting and fluorescent polymers.;In addition to synthesis of conjugated polymers with interesting electrical and optical properties, the possibility of using enzyme catalysts, enzyme-mimics and chemical catalysts for the polymerization of phenols have also been explored in this thesis. The polyphenols synthesized can possibly be used in FR applications as an alternative to toxic halogenated FR.;In the field of FR additives for polymers, halogenated FR compounds have come under heavy scrutiny due to their undesirable environmental and health impact. This has spurred the need for the development of less toxic, efficient non-halogenated FR systems. In this research, polymers of phenol compounds are evaluated as possible alternatives to halogenated FR. From a flame retardancy perspective, the use of a polymeric system significantly reduces toxicity and remains stable at high temperatures, both of which are desirable attributes for effective FR.;The exploration for polyphenols for FR applications began with the synthesis of polymers of hydroxydeoxybenzoins. Enzymatic methods have been utilized for the synthesis of 4,4'-Bishydroxydeoxybenzoin and 4-methoxy,4'-hydroxydeoxybenzoin based homopolymers and copolymers. The polymers exhibit excellent char formation and very low heat release capacities (15-20 J/gK) and are characteristic of ultra-high fire resistant materials. Cardanol, a bio-based starting material, was polymerized using enzymatic, biomimetic and chemical oxidative polymerization methods. Chemically synthesized polycardanol was moderately fire retardant with heat release capacities in the range of 200-250 J/gK. In addition, naturally occurring silicate clays were modified using polyphenols and demonstrated synergistic FR action upon incorporation in polypropylene blends. In view of its predicted thermodynamic compatibility with polyolefms, polycardanol was tested as FR additive in polyethylene and polypropylene. The performance of the resulting blends in laboratory scale pyrolysis combustion flow calorimetric study compared favorably to commercially used halogenated compounds like decabromodiphenylether and hexabromocyclododecane. These results suggest great possibilities in the use of polyphenols as effective replacements in place of toxic halogenated FR in polymer blends. The proposed approach is very cost-effective and remarkably simple and can be easily extended for other applications like fabric coatings to achieve fire retardancy.