Polyhedral Oligomeric Silsesquioxane (POSS) Based Hybrid Polymeric Architectures via Controlled/Living Polymerization Technique

Haldar, Ujjal (2016) Polyhedral Oligomeric Silsesquioxane (POSS) Based Hybrid Polymeric Architectures via Controlled/Living Polymerization Technique. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Recently, organic/inorganic (O/I) hybrid materials have been used to develop highly efficient multi-synergetic functional materials. Among the various hybrid materials (such as nanoparticles, clay, fullerene, carbon nanotubes, graphene, etc.), polyhedral oligomeric silsesquioxanes (POSSs) are one of most intriguing examples of nanostructured O/I hybrid building blocks.In this Thesis, we want to focus on the current investigations on the self-assembling behaviour of POSS-containing novel hybrid polymers prepared by RAFT technique. Their synthesis, self-assembly (both in aqueous/organic medium), and finally their potential applications in various fields have been discussed. It focuses on the recent advances of POSS based various macromolecular architectures and their potential biomedical and industrial application. Later, the synthesis, characterization and solution behavior of tadpole-shaped amphiphilic polymers with hydrophobic polyhedral oligomeric silsesquioxane (POSS) chain-end and hydrophilic mainchain having leucine pendants were investigated. Expulsion of side chain Boc groups produced pH responsive amphiphilic cationic polymers, which exhibited self-assembly in aqueous medium, confirmed by dynamic light scattering (DLS) and field-emission scanning electron microscopy (FE-SEM). The aggregation behavior of POSS end-capped polymeric nanoparticles was further investigated through nile red encapsulation as a hydrophobic probe in aqueous medium. To understand the effect of polyhedral oligomeric silsesquioxane (POSS) moieties on the rheological properties of thermoresponsive hydrogels, poly(ethylene glycol) methyl ether methacrylate (PEGMA) based gels have been synthesized via conventional free radical polymerization (FRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization techniques. The mechanical behavior of the swollen hydrogels has been investigated through rheological measurements. Interestingly, we find that the mechanical stability of the hydrogels improved by both cross-linking density and total net fraction of the POSS moieties. We report the rational design of a new polyhedral oligomeric silsesquioxane (POSS) containing “inimer” and employed in reversible additionfragmentation chain transfer (RAFT) copolymerization with various vinyl monomers such as styrene (St), polyethylene glycol methyl ether methacrylate (PEGMA) and N,N-dimethyl acrylamide (DMA) to develop novel hybrid hyperbranched copolymers. Interestingly, a wide spectrum of morphologies including sphere, ellipsoid and vesicle could be achieved simply via tuning the availability of POSS moiety, DB of the methanophobic hyperbranched core and/or the length of methanophilic arms. We have synthesized organic/inorganic hybrid peptide-poly(ɛ-caprolactone) (PCL) conjugates via coordination-insertion ring opening polymerization (ROP) of ɛ-caprolactone (CL) in the presence of two sequence defined amine terminated peptide initiators. Spherulitic morphologies of POSS/OMe-peptide-PCL conjugates were fully destroyed after inclusion complexation with α-CyD and tiny nano-objects were produced. We have synthesized sequence registered peptide-polypeptide conjugates via ring opening polymerization (ROP) of γ- benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) employing two amine terminated peptide initiators. Interestingly, a morphological switch from sphere to square shaped micelles could be achieved simply by adjusting net fraction of POSS moiety and/or the length of benzyl deprotected segment.

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