Synthesis and self assembly of poly(2-isopropyl-2-oxazoline)-b-poly(2-phenyl-2-oxazoline)-b-poly(2-isopropyl-2-oxazoline)

Turan, Çağrı
Polymersomes are polymeric vesicles formed through self-assembly of amphiphilic polymers. They can be used as nanoreactors for providing a stable compartment with a high concentration of the reactive enzymes or nanocarriers which may simultaneously release hydrophilic and hydrophobic drugs. Poly(2-alkyl-2-oxazolines) (PAOXs) are used in biomedical applications due to their important biological properties such as biocompatibility, antifouling, and stealth behavior. Besides, PAOXs with short alkane side chains exhibit temperature responsive behavior, making them promising materials for controlled release applications. Among PAOX family, poly(2-isopropyl-2-oxazoline) (PiPOX) has attracted attention due to its lower critical solution temperature behaviour at temperatures close to human body temperature. This thesis study reports on synthesis of a PAOX-based triblock copolymer, namely poly(2-isopropyl-2-oxazoline)-b-poly(2-phenyl-2-oxazoline)-b-poly(2-isopropyl-2-oxazoline) (PiPOX-b-PPhOX-b-PiPOX), by a three-step sequential monomer addition through cationic ring opening polymerization (CROP). PiPOX:PPhOX ratio was calculated as 1:1.7 through 1H Nuclear Magnetic Resonance (1H NMR) Spectroscopy. Molecular weight of PiPOX-b-PPhOX-b-PiPOX was determined through Gel Permeation Chromatograpy (GPC). The number average and weight average molecular molecular weights were found as ~8500 g/mol and ~9700 g/mol with a polydispersity index (PDI) of 1.14. The self-assembly of PiPOX-b-PPhOX-b-PiPOX was triggered in aqueous solution through solvent shifting or water-in-oil-in water double emulsion (W/O/W) methods. Hydrodynamic size of the aggregates was measured through dynamic light scattering (DLS) technique. Aggregates obtained through double emulsion method (~219 nm) were smaller in size than those prepared through solvent shifting method (~280 nm). Transition electron microscopy (TEM) and fluorescence microscopy (FM) imaging showed polymersome morphology for the aggregates for both methods. Water soluble PiPOX blocks are suggested to form the hydrophilic inner and outer region of polymersomes, whereas the hydrophobic PPhOX block is expected to form the polymersome membrane. The effect of temperature on aqueous solution behaviour of PiPOX-b-PPhOX-b-PiPOX polymersomes was examined by measuring the size of particles as a function of temperature using DLS technique. Above 40℃, polymersomes merged and formed polymersome clusters and this association among the polymersomes was found to be irreversible. Finally, encapsulation capability of PiPOX-b-PPhOX-b-PiPOX polymersomes was examined using glucose oxidase (GOx) as a model enzyme. TEM imaging indicated that GOx was encapsulated in the inner core region of polymersomes. In summary, this thesis study generated fundamental information about synthesis, self-assembly and temperature-responsive aqueous solution behavior of a PAOX-based triblock copolymer. Use of PiPOX-b-PPhOX-b-PiPOX polymersomes as temperature-responsive nanoreactors for enzymatic reactions will be further explored in future studies.


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Citation Formats
Ç. Turan, “Synthesis and self assembly of poly(2-isopropyl-2-oxazoline)-b-poly(2-phenyl-2-oxazoline)-b-poly(2-isopropyl-2-oxazoline),” M.S. - Master of Science, Middle East Technical University, 2022.