Novel Approaches to Biodegradable Polymers: Synthesis and Biodegradation Studies

Biodegradable polymers have opened an emerging area of great interest because they are the ultimate solution for the disposal problems of synthetic polymers used for short time applications in the environmental and biomedical field. The biodegradable polymers available until recently have a number of limitations in terms of strength and dimensional stability. Most of them have processing problems and are also very expensive. Recent developments in biodegradable polymers show that monomers and polymers obtained from renewable resources are important owing to their inherent biodegradability, biocompatibility and easy availability. The present study is, therefore, mostly concemed with the utilization of renewable resources by effecting chemical modification/copolymerization on existing synthetic polymers/natural polymers for introducing better biodegradability and material properties.The thesis describes multiple approaches in the design of new biodegradable polymers: (1) Chemical modification of an existing nonbiodegradable polymer, polyethylene, by anchoring monosaccharides after functionalization to introduce biodegradability. (2) Copolymerization of an existing biodegradable polymer, polylactide, with suitable monomers and/or polymers to tailor their properties to suit the emerging requirements such as (2a) graft copolymerization of lactide onto chitosan to get controlled solvation and biodegradability and (2b) copolymerization of polylactide with cycloaliphatic amide segments to improve upon the thermal properties and processability.

Synthesis and Photochemistry of a few Olefin appended Dibenzobarrelenes and Bisdibenzobarrelenes

The thesis entitled: ‘Synthesis and Photochemistry of a few Olefin appended Dibenzobarrelenes and Bisdibenzobarrelenes’ is divided into 5 chapters.In Chapter 1, the fundamental concepts of Diels-Alder reaction, di-r:methane rearrangement and energy transfer process in organic photochemistry is discussed.Chapter 2 presents the synthesis of 9-olefin appended anthracenes and bisanthracenes. The target of synthesising various bridgehead olefin appended dibenzobarrelenes and some novel bisdibenzobarrelenes, led us to the synthesis of the appropriate alkenylanthracenes and bisanthracenes as precursor molecules. Diels-Alder reaction was the synthetic tool for the preparation of the target olefin appended dibenzobarrelenes and bisdibenzobarrelenes. This chapter attempts to throw light on our endeavours in synthesising the various 9-alkenylanthracenes and bisanthracenes.Chapter 3 deals with the synthesis of olefin appended dibenzobarrelenes and bisdibenzobarrelenes. Ever since the discovery of di-It-methane rearrangement dibenzobarrelenes, tailored with dijferent substituents at various positions have always been a tool to photochemists in unravelling the mechanisms of light induced reactions. Our intention of analysing the role of a It-moiety at the bridgehead position of the dibenzobarrelene, was synthetically envisaged via the Diels-Alder reaction. Bisdibenzobarrelenes were synthesised through tandem Diels-Alder reaction. Various alkenylanthracenes and bisanthracenes were employed as dienes and the dienophiles used were dimethyl acetylenedicarboxylate and dibenzoylacetylene. In this chapter, we report our venture in synthesising the various olefin appended dibenzobarrelenes and bisdibenzobarrelenes. Chapter 4 describes the preliminary time-resolved fluorescence studies of some olefin appended dibenzobarrelenes and bisdibenzobarrelenes.To understand the primary and secondary physicochemical processes in a photochemical reaction it is necessary to characterise the excited states and the transient intermediates during their short lifetime. A number of methods developed on the basis of the physical properties of the transient species are available for their detection. Time-correlated single-photon counting technique has been utilised in the present study of the excited states of olefin appended dibenzobarrelenes and bisdibenzobarrelenes. To understand the primary and secondary physicochemical processes in a photochemical reaction it is necessary to characterise the excited states and the transient intermediates during their short lifetime. A number of methods developed on the basis of the physical properties of the transient species are available for their detection. Time-correlated single-photon counting technique has been utilised in the present study of the excited states of olefin appended dibenzobarrelenes and bisdibenzobarrelenes.Chapter 5 portrays the photochemistry of olefin appended dibenzobarrelenes and bisdibenzobarrelenes. Dibenzocyclooctatetraene and dibenzosemibullvalene are the photoproducts obtained respectively through the singlet excited state and the triplet excited state of dibenzobarrelenes. Chemical literature shows evidences of the photoreactivity of dibenzobarrelenes generating both the singlet and triplet mediated photoproducts, in a single photoreaction. Our research target in synthesising various bridgehead olefin appended dibenzobarrelenes and bisdibenzobarrelenes, was based on the perception that olefins are eflicient triplet quenchers, thereby quenching intramolecularly the triplet excited state of the barrelenes. A It-moiety at the bridgehead position of the dibenzobarrelene, creates a tetra tr-methane system, which similar to a 6li—7l' or tri-tr-methane systems, could be the fertile ground for interesting photochemical rearrangements. Our attempts in deciphering the photochemistry of the olefin appended dibenzobarrelenes and bisdibenzobarrelenes is the substance of this chapter.

Synthesis and characterization of Tellurium oxide glasses for photonic applications

Tellurite glasses are photonic materials of special interest to the branch of optoelectronic and communication, due to its important optical properties such as high refractive index, broad IR transmittance, low phonon energy etc. Tellurite glasses are solutions to the search of potential candidates for nonlinear optical devices. Low phonon energy makes it an efficient host for dopant ions like rare earths, allowing a better environment for radiative transitions. The dopant ions maintain majority of their individual properties in the glass matrix. Tellurites are less toxic than chalcogenides, more chemically and thermally stable which makes them a highly suitable fiber material for nonlinear applications in the midinfrared and they are of increased research interest in applications like laser, amplifier, sensor etc. Low melting point and glass transition temperature helps tellurite glass preparation easier than other glass families. In order to probe into the versatility of tellurite glasses in optoelectronic industry; we have synthesized and undertaken various optical studies on tellurite glasses. We have proved that the highly nonlinear tellurite glasses are suitable candidates in optical limiting, with comparatively lower optical limiting threshold. Tuning the optical properties of glasses is an important factor in the optoelectronic research. We have found that thermal poling is an efficient mechanism in tuning the optical properties of these materials. Another important nonlinear phenomenon found in zinc tellurite glasses is their ability to switch from reverse saturable absorption to saturable absorption in the presence of lanthanide ions. The proposed thesis to be submitted will have seven chapters

Design Of Metal Architectures: Synthesis And Study Of Their Photophysical And Biomolecular Recognition Properties

Design and study of molecular receptors capable of mimicking natural processes has found applications in basic research as well as in the development of potentially useful technologies. Of the various receptors reported, the cyclophanes are known to encapsulate guest molecules in their cavity utilizing various non–covalent interactions resulting in significant changes in their optical properties. This unique property of the cyclophanes has been widely exploited for the development of selective and sensitive probes for a variety of guest molecules including complex biomolecules. Further, the incorporation of metal centres into these systems added new possibilities for designing receptors such as the metallocyclophanes and transition metal complexes, which can target a large variety of Lewis basic functional groups that act as selective synthetic receptors. The ligands that form complexes with the metal ions, and are capable of further binding to Lewis-basic substrates through open coordination sites present in various biomolecules are particularly important as biomolecular receptors. In this context, we synthesized a few anthracene and acridine based metal complexes and novel metallocyclophanes and have investigated their photophysical and biomolecular recognition properties.

Synthesis and characterization of eco-friendly inorganic yellow pigments for coloring applications

Research in the fields of ceramic pigments is oriented towards the enlargement of the chromatic set of colors together with a replacement for more expensive and less stable organic pigments. Novel non-toxic inorganic pigments have been required to answer environmental laws to remove elements like lead, chromium, cobalt entering in the composition of usual pigments widely used in paints and plastics. Yellow is particularly an important color in the pigment industry and consumption of yellow exceeds that of any other colored pigments. Apart from this, high infrared reflective pigments are now in great demand for usage in coatings, cement pavements, automotives and camouflage applications. They not only impart color to an object, but also reflect the invisible heat from the object to minimize heat build–up, when exposed to solar radiation. With this in view, the present work aims at developing new functional yellow pigments for these applications. A series of IR reflecting yellow pigments have been synthesized and analyzed for their crystalline structure, morphological, composition and optical characteristics, coloring and energy saving applications

Synthesis and characterization of Tellurium oxide glasses for photonic applications

Tellurite glasses are photonic materials of special interest to the branch of optoelectronic and communication, due to its important optical properties such as high refractive index, broad IR transmittance, low phonon energy etc. Tellurite glasses are solutions to the search of potential candidates for nonlinear optical devices. Low phonon energy makes it an efficient host for dopant ions like rare earths, allowing a better environment for radiative transitions. The dopant ions maintain majority of their individual properties in the glass matrix. Tellurites are less toxic than chalcogenides, more chemically and thermally stable which makes them a highly suitable fiber material for nonlinear applications in the midinfrared and they are of increased research interest in applications like laser, amplifier, sensor etc. Low melting point and glass transition temperature helps tellurite glass preparation easier than other glass families.In order to probe into the versatility of tellurite glasses in optoelectronic industry; we have synthesized and undertaken various optical studies on tellurite glasses. We have proved that the highly nonlinear tellurite glasses are suitable candidates in optical limiting, with comparatively lower optical limiting threshold. Tuning the optical properties of glasses is an important factor in the optoelectronic research. We have found that thermal poling is an efficient mechanism in tuning the optical properties of these materials. Another important nonlinear phenomenon found in zinc tellurite glasses is their ability to switch from reverse saturable absorption to saturable absorption in the presence of lanthanide ions. The proposed thesis to be submitted will have seven chapters.