Design, Synthesis and Self-Assembly Studies of Pyrimidine Derived Amphiphilic Homopolymers and Their Stimuli Responsiveness

Mandal, Piyali (2022) Design, Synthesis and Self-Assembly Studies of Pyrimidine Derived Amphiphilic Homopolymers and Their Stimuli Responsiveness. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Piyali Mandal (15RS001)) 15RS001.pdf - Submitted Version Restricted to Repository staff only Download (10MB)

Abstract

Self-assembly is the only approach through which a wide range of nanostructures can be fabricated. Inspired by nature, nano-scaled self-assembled structures are usually built up with non-covalent bonds. Currently, nano-fabrication via self-assembly is broadly adoptable due to its simplicity, versatility, and spontaneity. Exploiting the promising properties at a low-cost and high-yield, it has extensive applications in scientific as well as technological fields such as nanotechnology, molecular robotics, and molecular computation. Self-assembly is a scalable process within a short timeframe. Macromolecular self-assembly is one of the most important aspects of modern synthetic chemists for its vast application in the industrial field. The objective of my thesis work is to investigate pyrimidine derived self-assembly behavior in the case of homopolymers in an aqueous environment. Chapter 1 described the background of self-assembly and its different types with various interactions. It mainly emphasized the driving forces behind the thiobarbiturate derived homopolymer based self-assembly in an aqueous medium, also elaborated the extraction and synthesis of the natural polymers and synthetic polymers respectively with different polymerization techniques. In chapter 2 the context was focused on natural polymer-based self-assembly. Here, the natural polymer chitosan was conjugated with a hydrophilic thiobarbiturate entity (CS-TBA). A small molecule like thiobarbiturate surprisingly made a relatively high molecular weight chitosan polymer amphiphilic as well as water-soluble. This molecule imparted an interesting vesicular architecture in water. The self-assembled nanostructures were able to encapsulate hydrophobic probes and also responsive towards pH and polarity. Chapter 3 illustrated the self-assembly scenario of thiobarbiturate functionalized ester derivative of biocompatible homopolymer backbone i.e., methyl methacrylic acid which was termed as PMMA-TBA. The synthesized polymer was functionalized through post polymer modifications and thoroughly characterized via different spectroscopic techniques. The thiobarbiturate derived self-assembly phenomena of the hydrophobic polymer backbone were monitored via microscopic studies. Finally, the fluorometric analysis of dye/drug encapsulation and release studies confirmed its materiality in the field of biomedical applications. In chapter 4, A homopolymer of biodegradable aliphatic cyclic ester, i.e., polycaprolactone was chosen. The synthesis, functionalization, and characterizations were well documented here. Next, the self-assembly process of the thiobarbiturate motif attached hydrophobic polymeric backbone (PCL-TBA) was explored in water. Finally, the applicability of the polymeric nanoparticle as a drug delivery vehicle was checked via encapsulation and release studies. Chapter 5 demonstrated a biodegradable as well as bioresorbable polymer backbone, poly(L-lactide). It was functionalized with a thiobarbiturate motif (PLA-TBA). Here the derivative of this polymer was aggregated in a spherical manner via hierarchical self-assembly. The interaction for this self-assembly phenomenon was also explored. The size of the spheres was found to be larger in PLA-TBA than that of the PCL-TBA. The encapsulation ability of these spherical aggregates was investigated with a hydrophobic probe and the release profile was further studied under the external stimulus. Finally, the delivery experiments were performed with Nile red as well as the doxorubicin drug molecule. In chapter 6 the solvent variation morphological studies of the above-synthesized thiobarbiturate derived polymer backbones were investigated. For that purpose, miscible polar protic and aprotic solvents with different polarity indexes were used as a cosolvent with the common solvent water to prepare the 1:1 solvent mixture. Tetrahydrofuran, methanol, acetonitrile and dioxane were the four organic solvents that were used as the cosolvents with water. These solvent mixtures were used for further experiments. As the thiobarbiturate moiety was highly polar, the polar solvents were purposefully chosen to avoid any kind of difficulties to solubilize the functionalized polymers. A detailed exploration of morphology changes with cosolvents as well as the backbones was done in this conclusive chapter.

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