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Identifier 000370246
Title Synthesis of multiresponsive copolymers for the development of "smart" organic-inorganic hybrids
Alternative Title Σύνθεση συμπολυμερών αποκρινόμενων σε πολλαπλά ερεθίσματα για την ανάπτυξη "έξυπνων" οργανικών/ανόργανων υβριδίων
Author Αχιλλέως, Δήμητρα Σ.
Thesis advisor Βαμβακάκη, Μαρία
Abstract The aim of this work is the synthesis and the investigation of the responsive behavior of a range of spiropyran (SP)-based materials including random copolymers, spherical polymer brushes and hollow nanoparticles. The ability of these materials to respond to a variety of applied external stimuli such as light, pH, temperature and solvent polarity renders them excellent candidates for various applications. Multiresponsive SP-based random copolymers which vary in the content of the SP moieties, were synthesized by the random copolymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) or methyl methacrylate (MMA) with the in-house synthesized SP monomer 1',3',3'-trimethyl-6-methacryloyloxy-spiro(2H-1-benzopyran-2,2'-indoline) by ATRP in solution. The PDMAEMA-co-PSP copolymers exhibited “reverse photochromism” and “negative solvatochromism” upon increasing the polarity of the solvent, in contrast to the PMMA-co-PSP analogue. Moreover, the PDMAEMA-co-PSP copolymers exhibited a reversible pH-responsive character in aqueous media with an acid-induced the SP-to-merocyanine (MC) isomerization and the formation of [MC-OH]+ and [SP-NH]+ species. The lower critical solution temperature (LCST) of the copolymers increased with their content in hydrophilic MC moieties, while the recovery of the hydrophobic SP species decreased the LCST. Finally, the copolymers exhibited a first-order photoinduced bleaching of the chromophore units in water and acetonitrile, with a slower decoloration rate in the aqueous medium due to the effective stabilization of the bipolar MC form. A PDMAEMA-co-(1΄-(2-methacryloxyethyl)-3΄,3΄-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2΄-indoline)) (PSPMA) random copolymer which exhibited “normal photochromism”, that is the SP-to-MC isomerization upon stimulation with UV light was also synthesized using the in-house synthesized monomer SPMA. The stimulation of the PDMAEMA-co-PSPMA copolymer with UV light in water resulted in the generation of three switterionic moieties from the same parent SP molecule; namely the non-planar X isomer and two different planar MC species, MC1 and MC2 which differ in polarity. The photo-isomers followed a biexponential thermal bleaching mechanism originated from localized barriers inherent in the polymer matrix which establish a non-homogeneous microenvironment around the chromophores. Moreover, the copolymer exhibited an intra- and inter-chain fluorescence resonance energy transfer (FRET) upon the photo-induced generation of both X and MC species which are FRET donor-acceptor pairs, respectively, from the SP isomers. The photo-regulated energy transfer was favored by the close proximity of the bipolar isomers promoted by the association of the random copolymers in water and the spectral overlap of the emission and absorption bands of X and MC isomers, respectively. The FRET process is interrupted by the thermal MC-to-SP isomerization which is retarded by the polar microenvironment and enabled before relaxation of the acceptors the read-out process. In the second part of this work, SiO2-g-(PDMAEMA-co-PSPMA) spherical brushes were synthesized from the surface of silica particles via copper-mediated ATRP in bulk. Stimulation of the hybrids with UV light resulted in the isomerization of the SP units to two different bipolar species; the cisoid non-planar X and the planar MC isomers which followed a biexponential thermal relaxation process to reform the SP isomers due to variations in the microenvironment polarity and the free volume in the polymer brush layer. The generation of two different bipolar species, X and MC, in aqueous media from the same parent SP molecule upon UV irradiation of the hybrids provided the unique property to the system of exhibiting FRET between X and MC residues. In this case, the proximity of the donor-acceptor pairs was promoted by the steric crowding within the polymer brush layer. The energy transfer was switched “off” upon the thermal fading of the MC species which exhibited adequate kinetic rates and enabled the monitoring of the process. This property of the nanohybrids can be successfully applied for the detection of biological substances such as proteins and aminoacids. In particular, the presence of bovine serum albumin (BSA) in the aqueous dispersion of the hybrids was proved to enhance significantly the FRET efficiency of the system, due to the accelerated MC formation catalyzed by the protein, while L-histidine did not affect the FRET efficiency of the hybrids however it retarded the MC bleaching by interaction with the MC dipoles. Finally, the light-driven supramolecular engineering of fluorescent nanocapsules (NCPs) utilizing the appropriate phototrigger to stimulate the SiO2-g-(PDMAEMA-co-PSPMA) spherical brushes, was also studied. The fabrication of the nanospheres was based on the formation of π-π H-type interactions between the MC photoisomers being in close proximity within the sterically crowded environment of the polymer brushes by applying UV irradiation which enabled the SP-to-MC isomerization of the photosensitive species. HF etching of the inorganic core resulted in the formation of dual-responsive polymeric vesicles whose wall’s robustness is provided by the MC-MC cross-link points. The disruption of the NCPs could be achieved remotely and progressively by applying a harmless trigger such as visible light irradiation. The hydrophilic nature of the DMAEMA comonomer not only provided dispersability of the vesicles in the environmentally benign aqueous media but also enabled the controlled alteration of the NCPs size stimulated by variations in the solution pH. The inherent ability of the NCPs to fluoresce in water opens new possibilities for the development of addressable nanoscale capsules for biomedical applications.
Language English
Subject Förster resonance energy transfer
atom transfer radical polymerization
core-shell hybrid particles
hollow nanocapsules
negative solvatochromism
random copolymers
reverse and normal photochromism
ανάστροφος και κανονικός φωτοχρωμισμός
αρνητικός διαλυτοχρωμισμός
οργανικά-ανόργανα υβρίδια
ριζικός πολυμερισμός μεταφοράς ατόμου
συντονιζόμενη μεταφορά ενέργειας Förster
τυχαία συμπολυμερή
Issue date 2011-11-21
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
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