Irakli Javakhishvili

Gold Nanoparticles Protected with Thiol-Derivatized Amphiphilic Poly(ϵ-caprolactone)-b-poly(acrylic acid)

Amphiphilic poly(epsilon-caprolactone)-b-poly(acrylic acid) (HS-PCL-b-PAA) with a thiol functionality in the PCL terminal has been prepared in a novel synthetic cascade. Initially, living anionic ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) employing the difunctional initiator, 2-hydroxyethyl 2-bromoisobutyrate, followed by esterification with 2,4-dinitrophenyl- or 4-monomethoxytrityl-protected mercaptoacetic acids (Prot-), provided well-defined PCL macroinitiators capped with protected thiols. The macroinitiators allowed atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) in a controlled fashion by use of NiBr2(PPh3)2 catalyst to produce Prot-PCL-b-PtBA with narrow polydispersities (1.17-1.39). Subsequent mild deprotection protocols provided HS-PCL-b-PAA. Reduction of a gold salt in the presence of this macroligand under thiol-deficient conditions afforded stable, aggregation-free nanoparticles, as evidenced from UV-vis spectroscopy and transmission electron microscopy (TEM), the latter revealed nanoparticles with a mean diameter of 9.0+/-3.1 nm.

Synthesis of telechelic vinyl/allyl functional siloxane copolymers with structural control

Multifunctional siloxane copolymers with terminal vinyl or allyl functional groups are synthesised through the borane-catalysed polycondensation of hydrosilanes and alkoxysilanes. Copolymers of varying molecular weights (w = 13 200–70 300 g mol−1), spatially well-distributed functional groups and high end-group fidelity are obtained in a facile and robust synthetic scheme involving polycondensation, end-group transformation and different functionalisation reactions such as Cu(I)-mediated azide–alkyne cycloaddition. Pendant alkyl chloride, alkyl azide, bromoisobutyryl, 4-nitrobenzene and 1-ethyl-imidazolium chloride fragments with programmable spatial distributions are incorporated in the copolymer backbones. NMR and FTIR spectroscopy as well as size exclusion chromatography corroborate the efficacy and versatility of this modular approach.

Facile synthesis of linear-dendritic cholesteryl-poly(ε-caprolactone)-b-(L-lysine)G2 by thiol-ene and azide-alkyne “click” reactions

The construction of a linear-dendritic block copolymer consisting of terminal cholesteryl moiety, poly(e-caprolactone), and a second generation L-lysine dendron has been accomplished by the combination of copper(I) catalyzed azide-alkyne and UV-triggered thiol-ene “click” reactions. Ring-opening polymerization of e-caprolactone initiated by 5-hexyn-1-ol and Mitsunobu coupling with 4-pentenoic acid provide hetero-telechelic poly(e-caprolactone) bearing terminal alkyne and alkene groups. It is then employed in the sequential “click” reactions with the azide-functionalized dendritic wedge and thiocholesterol. Near to quantitative functionalization of the intermediate and final products has been attained as confirmed by NMR spectroscopy and MALDI-TOF spectrometry.

Adsorption and aqueous lubricating properties of charged and neutral amphiphilic diblock copolymers at a compliant, hydrophobic interface.

We have investigated the adsorption and lubricating properties of neutral and charged amphiphilic diblock copolymers at a hydrophobic polydimethylsiloxane (PDMS) interface in an aqueous environment. The diblock copolymers consist of a hydrophilic block of either neutral poly(ethylene glycol) (PEG) or negatively charged poly(acrylic acid) (PAA) and of a hydrophobic block of polystyrene (PS) or poly(2-methoxyethyl acrylate) (PMEA), thus generating PEG-b-X or PAA-b-X, where X block is either PS or PMEA. The molecular weight ratios were roughly 1:1 with each block ca. 5 kDa. Comparing the neutral PEG and charged PAA buoyant blocks with all other conditions identical, the former showed superior adsorption onto nonpolar, hydrophobic PDMS surfaces from a neutral aqueous solution. PEG-based copolymers showed substantial adsorption for both PS and PMEA as the anchoring block, whereas PAA-based copolymers showed effective adsorption only when PMEA was employed as the anchoring block. For PAA-b-PS, the poor adsorption properties are chiefly attributed to micellization due to the high interfacial tension between the PS core and water. The poor lubricating properties of PAA-b-PS diblock copolymer for a PDMS-PDMS sliding contact was well correlated with the poor adsorption properties. PAA-b-PMEA copolymers, despite their sizable amount of adsorbed mass, showed insignificant lubricating effects. When the charges of the PAA-b-PMEA diblock copolymers were screened by either adding NaCl to the aqueous solution or by lowering the pH, both the adsorption and lubricity improved. We ascribe the poor adsorption and inferior aqueous lubricating properties of the PAA-based diblock copolymers compared to their PEG-based counterparts mainly to the electrostatic repulsion between charged PAA blocks, hindering the facile formation of the lubricating layer under cyclic tribological stress at the sliding PDMS-PDMS interface.

Azobenzene Polyesters Used as Gate‐Like Scaffolds in Nanoscopic Hybrid Systems

The synthesis and characterisation of new capped silica mesoporous nanoparticles for on-command delivery applications is reported. Functional capped hybrid systems consist of MCM-41 nanoparticles functionalised on the external surface with polyesters bearing azobenzene derivatives and rhodamine B inside the mesopores. Two solid materials, Rh-PAzo8-S and Rh-PAzo6-S, containing two closely related polymers, PAzo8 and PAzo6, in the pore outlets have been prepared. Materials Rh-PAzo8-S and Rh-PAzo6-S showed an almost zero release in water due to steric hindrance imposed by the presence of anchored bulky polyesters, whereas a large delivery of the cargo was observed in the presence of an esterase enzyme due to the progressive hydrolysis of polyester chains. Moreover, nanoparticles Rh-PAzo8-S and Rh-PAzo6-S were used to study the controlled release of the dye in intracellular media. Nanoparticles were not toxic for HeLa cells and endocytosis-mediated cell internalisation was confirmed by confocal microscopy. Furthermore, the possible use of capped materials as a drug-delivery system was demonstrated by the preparation of a new mesoporous silica nanoparticle functionalised with PAzo6 and loaded with the cytotoxic drug camptothecin (CPT-PAzo6-S). Following cell internalisation and lysosome resident enzyme-dependent gate opening, CPT-PAzo6-S induced CPT-dependent cell death in HeLa cells.

Miktoarm core-crosslinked star copolymers with biologically active moieties on peripheries

Miktoarm core-crosslinked star (CCS) copolymers featuring hydrophobic inner compartment based on poly(e-caprolactone) (PCL), and hydrophilic multivalent exterior consisting of L-lysine dendritic wedges and estradiol or ferrocene moieties have been synthesized. Ring-opening polymerization (ROP) of e-caprolactone (e-CL) initiated by functional alcohols provides alkyne or azide end-capped linear PCL chains. Further derivatization of the hydroxyl chain ends of these hetero-telechelic macromolecules by methacrylic acid (MA), and subsequent Cu(I) mediated “click” coupling of terminal alkyne and azide groups with azide-functionalized dendritic wedge, 17α-ethynylestradiol and ethynylferrocene afford well-defined linear-dendritic and linear macromonomers (MMs), respectively. Atom transfer radical polymerization (ATRP) of the MMs together with a difunctional monomer 1,4-butanediol dimethacrylate (BDMA) results in miktoarm CCS copolymers. Elucidation of the structure and composition of the intermediate and final products demonstrates effectiveness, versatility, and high degree of control displayed by the proposed synthetic sequence.

Neutral, anionic, cationic, and zwitterionic diblock copolymers featuring poly(2-methoxyethyl acrylate) “hydrophobic” segments

Amphiphilic diblock copolymers incorporating “hydrophobic” poly(2-methoxyethyl acrylate) (PMEA) and hydrophilic neutral poly(ethylene glycol) monomethyl ether (mPEG), anionic poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA), cationic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA), and zwitterionic poly(3-(N-(2-methacryloyloxyethyl)-N,N-dimethylammonio)propane sulfonate) (PDMAPS) blocks are constructed. mPEG, poly(tert-butyl acrylate) (PtBA), and poly(tert-butyl methacrylate) (PtBMA) macroinitiators are chain extended with 2-methoxyethyl acrylate (MEA) employing copper-mediated atom transfer radical polymerization (ATRP) garnishing well-defined diblock copolymers with narrow polydispersities (1.11–1.30). Selective cleavage of the tert-butyl esters affords PAA-b-PMEA and PMAA-b-PMEA. ATRP of 2-dimethylaminoethyl methacrylate (DMAEMA) from the PMEA macroinitiator results in PMEA-b-PDMAEMA while the betainisation of the latter provides zwitterionic diblock amphiphile PMEA-b-PDMAPS. Inspection of these macromolecular architectures by NMR spectroscopy and size exclusion chromatography (SEC) confirms a fairly high degree of control over the reactions emphasizing flexibility and precision of the approach.

Synthesis of Graft Copolymers Based on Poly(2‐Methoxyethyl Acrylate) and Investigation of the Associated Water Structure

Graft copolymers composed of poly(2-methoxyethyl acrylate) are prepared employing controlled radical polymerization techniques. Linear backbones bearing atom transfer radical polymerization (ATRP) initiating sites are obtained by reversible addition-fragmentation chain transfer copolymerization of 2-methoxyethyl acrylate (MEA) and 2-(bromoisobutyryloxy)ethyl methacrylate (Br(i) BuEMA) as well as 2-hydroxyethyl methacrylate and Br(i) BuEMA in a controlled manner . MEA is then grafted from the linear macroinitiators by Cu (I)-mediated ATRP. Fairly high molecular weights (>120 000 Da) and low polydispersity indices (1.17-1.38) are attained. Thermal investigations of the graft copolymers indicate the presence of the freezing bound water, and imply that the materials may exhibit blood compatibility.

Holographic storage and multiplexing in azopolyester blends using low energy pulses down to 2 ms

Three different blends containing side-chain azobenzene polyesters and poly(methyl methacrylate) homopolymers have been prepared for recording volume holographic polarization gratings using 488 nm light pulses. The final azo content in the blends has been decreased down to 0.2 wt. %, and their morphologies have been investigated by transmission electron microscopy. Stable and rewritable polarization gratings have been recorded, and 20 gratings have been multiplexed using 2 ms pulses of low energy (4 mJ/cm2). The equilibrium values of the diffraction efficiency were higher than 5 × 10−5.

Controlled immobilization of palladium nanoparticles in two different fluorinated polymeric aggregate cores and their application in catalysis

AbstractFluoroalkyl end-capped betaine-type cooligomeric nanocomposites-immobilized palladium nanoparticles were prepared by the reactions of palladium chloride with sodium acetate in the presence of sodium chloride and the corresponding fluorinated cooligomers. Outer blocks of poly(2,3,4,5,6-pentafluorostyrene)-containing ABA-triblock copolymeric nanocomposites-immobilized palladium nanoparticles were prepared by the use of the corresponding block copolymers under similar conditions. TEM images showed that palladium nanoparticles can be immobilized outside the fluorinated cooligomeric nanocomposite cores; in contrast, palladium nanoparticles can be effectively immobilized inside these fluorinated ABA-triblock copolymeric nanocomposite cores. Thus, these two different fluorinated copolymers enabled the controlled immobilization of palladium nanoparticles in the fluorinated nanocomposite cores. These fluorinated nanocomposites-immobilized palladium nanoparticles were also applied to the catalysts for Suzuki-Miyaura cross-coupling reaction, and the different reactivity between these nanocomposites was observed. FigureControlled immobilization of palladium nanoparticles in two different flourinated nanocomposite cores was observed. Palladium nanoparticles were immobilized onto fluorinated betaine-type cooligomeric nanocomposite cores; in contrast, palladium nanoparticles were effectively immobilized inside poly(2,3,4,5-pentafluorostyrene)-containing copolymeric nanocomposite cores. These fluorinated nanocomposites-immobilized palladium nanoparticles were applied to the catalysts for Suzuki-Miyaura cross-coupling reaction