Syntheses of Novel Biodegradable Materials from Biorenewable Resources through Nitroxide Mediated Polymerization; Green, Sustainable and Environmentally Benign Materials.

We have depended on petroleum or fossil sources for raw materials to synthesize polymers in order to meet the high demand of polymeric materials for over a century. Notwithstanding, polymers derived from these sources (synthetic polymers) are toxic to the environment. They are also expensive and are scarce sometimes because their raw material sources are nonrenewable. Biodegradable polymers (BDP) derived from biorenewable resources on the other hand are ecofriendly, cost-effective and sustainable. The raw materials which are mainly from agricultural and forestry products and the shells of crustaceans are readily available, cheap and renewable. The final polymers derived from these raw materials are potential replacement to synthetic polymers. As appealing as biodegradable polymers derived from biorenewable resources might be, there a number of challenges surrounding their synthesis and their properties sometimes do not meet the demands of certain applications. Some applications require very strong mechanical properties which may not be in possession of some biodegradable polymers derived from biorenewable resources. Copolymerization of these polymers with synthetic ones produces novel versatile polymeric materials which are biodegradable and possess robust mechanical properties suitable for different applications. Nitroxide mediated polymerization (NMP) is one of the most effective and efficient free radical living polymerization technique employed in chemical grafting of polymers. NMP as well as other free radical polymerization techniques can be used in tuning polymers into macromolecular architectures of different shapes, sizes and structures as opposed to conventional condensation polymerization. The advantage of NMP is that, it is a facile metal free process and therefore greener than other free radical techniques. This process is also viable for employment in the commercial production of polymers. In this light, the exploitation of the NMP technique for the production of biodegradable polymers from biorenewabe resources is essential and further research is required. The first chapter discusses elaborately the objectives of replacing synthetic polymers from petroleum sources with biodegradable ones from biorenewable resources, underlining the main reasons for this work. It further states the development in the research and production of biodegradable polymers from biorenewable resources. xiii In the second chapter, the art of NMP and its role in the synthesis and development of biodegradable polymers from renewable resources was discussed. It also entails a brief discussion on nitroxides and alkoxyamines which are the most important species involved in the NMP process. Chapter three constitutes the experimental synthesis of nitroxides, macro(alkoxyamines), monomers from biorenewable resources and graft copolymers. 2-phenyl-3-(phenylimino)-3Hindole 1-oxide (DPAIO) and its alkoxyamine were synthesized. N-tert-butyl-N-(1-diethyl phosphono-2,2-dimethylpropyl) nitroxide (SG1) nitroxide and its alkoxyamine, commercial BlocBuilder MA were mostly employed in the NMP process to produce the copolymers. The monomers derived from biorenewable resources included corn starch, cellulose, chitosan, castor oil, maleic acid, acrylamide and amino acids. Polystyrene (PS) and methyl methacrylate (MMA) are some synthetic polymers which were grafted onto the polymers from biorenewable resources. The copolymers in this chapter where synthesized through atom transfer radical addition (ATRA) and NMP. The products synthesized in chapter three were characterized and the results discussed in chapter four. The characterization techniques used were near magnetic resonance (NMR), Fourier Transform Infra-red (FTIR), differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR). FTIR analyses confirmed the formation of several copolymers were formed but only cellulose acetate-g-poly (methyl methacrylate) (CA-g-PMMA) was further confirmed by NMR and DSC. Chapter five is a summary of chapter one to four. It provides an elaborate argument on the replacement of synthetic polymers with biodegradable polymers from biorenewable resources. Chapter six discusses a specific project carried out at Aix-Marseille Université, centre de la recherche scientifique (CNRS), institute chimie radicalaire (ICR). The aim of this project was to develop hydrogels for the treatment and recovery of ischemic stroke. A novel blockgraft amphiphilic copolymer, polylactide-block-poly(N-isopropylamide-co-polyethylene glycol methacrylate) (PLA-b-P(NIPAAm-co-PEGMA)) was synthesized. 15wt% of the hydrogel formed by the polymer in phosphate buffer saline solution undergoes a sol-gel transition between 25°C and 37°C through micelle packing/rearrangement upon heating. The xiv synthesis of this biomaterial was based on the strategies of ring opening polymerization (ROP), intermolecular radical addition (IRA) and nitroxide mediated polymerization (NMP). Characterization of the copolymers was done by size exclusion chromatography (SEC), dynamic light scattering (DLS) and NMR. 15wt% of the hydrogel degrades after 48 h at 37°C by hydrolysis. The biomaterial also showed good mechanical properties since it did not shrink or break after heating at 50°C. Key words: Biodegradable; Polymer; Nitroxide Mediated Polymerization, Biorenewable resources, cellulose, polylactide, poly( N-isopropylamide), SG1, BlocBuilder MA, hydrogel.