Papers by Keyword: Block Copolymer

Abstract: Doxycycline was loaded with synthesized micelles composed of methyl Poly (ethylene glycol-block-poly (L-alanine–co–L-aspartate), or mPEG–Ala–Asp, and then characterized as a drug delivery carrier. The synthesis of the temperature-sensitive mPEG–Ala–Asp block copolymer was carried out by two-step ring-opening polymerization: firstly, the mPEG reacts with L-alanine N-carboxylic anhydride, and secondly the resulting mPEG–Ala reacts with benzyl aspartate N-carboxylic anhydride. The molecular structure of the copolymers obtained was determined by FT-IR and NMR spectroscopy methods and the micelles were characterized by SEM, TEM and DLS, respectively. The controlled release of Dox from hydrogel in the presence of PBS (8 to 9% by weight) lasts 6 to 7 days exhibiting stable release rates. The drug release mechanisms were studied: Higuchi and zero order models. The results and correlation coefficients applied to the Higuchi and zero-order models. The findings show the potential use of mPEG–Ala–Asp as an effective depot matrix to deliver anthracycline class drugs.

Abstract: The self-assembly of block copolymers has attracted attention for many decades because it can yield polymeric nanoobjects with a wide range of morphologies. Membrane emulsification is a fairly novel technique for preparation of various types of emulsions, which relies on the dispersed phase passing through a membrane in order to effect droplet formation. In this study, we have prepared polymeric nanoparticles of different morphologies using self-assembly of asymmetric block copolymers in connection with membrane emulsification. Shirasu Porous Glass (SPG) membranes has been employed as the membrane emulsification equipment, and poly (oligoethylene glycol acrylate)-block-poly (styrene) (POEGA-b-PSt) copolymers prepared via RAFT polymerization. It has been found that a number of different morphologies can be achieved using this novel technique, including spheres, rods, and vesicles. Interestingly, the results have shown that the morphology can be controlled not only by adjusting experimental parameters specific to the membrane emulsification step such as membrane pore size and pressure, but also by changing the nature of organic solvent. As such, this method provides a novel route to these interesting nanoobjects, with interesting prospects in terms of exercising morphology control without altering the nature of the block copolymer itself.

Abstract: In this report, s-1-dodecyl-s’-(α,α’-dimethyl-α’’-dimethyl-α’’-aceticacid) trithiocarbonate (RAFT-COOH) was successfully synthesized by phase transfer catalyst reaction, which was then amidated with diaminopropyl terminated polydimethylsiloxane (NH₂-PDMS-NH₂) to synthesize PDMS-based macro-RAFT agent to control the synthesis of tri-block copolymer PDMA-b-PDMS-b-PDMA. The successful synthesis of small and macro chain transfer has been confirmed by techniques of FTIR. Moreover, the polymerization to synthesize tri-block copolymer proceeded with first-order kinetics, which showed the reaction system was a controlled/‘living’ polymerization. The triblock copolymers have also been characterized by FTIR, ¹HNMR, and GPC techniques, which confirmed the successful synthesis of triblock copolymer.

Abstract: Polystyrene-b-Polylactide (PS-b-PLA) was dissolved in chlorobenzene, and the development of the micro-phase separation morphology in asymmetric PS-b-PLA thin films was investigated by AFM. The thin films were prepared by spinning casting at the speed of 6000 r/min for 60s on Si substrates. We get different morphologies of PS-b-PLA thin film by changing the annealing temperature from 150 °C to 170 °C. In addition, the annealing time influences the morphology of the film. When the annealing time increased from 2 hours to 15 hours and 30 hours, the morphology transformed from parallel to perpendicular to the substrate. By applying temperature gradients, we can control the morphology and orientation of the Block copolymer film self-assembly.

Abstract: Different nanocomposite materials consisting of semiconducting CdSe nanocrystals (NCs) and a low band gap copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4-b’]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) were prepared, morphologically characterized, and tested in hybrid solar cells. In addition, a PCPDTBT-based rod-coil diblock copolymer was synthesized through a grafting-onto approach and a preliminary evaluation of the morphology of the hybrid nanocomposites with CdSe NCs was performed.

Abstract: Three biodegradable amphiphilic triblock copolymers: polylactide-poly (ethylene glycol)-polylactide (PLA-PEG-PLA), poly (ε-caprolactone)-poly (ethylene glycol)-poly (ε-caprolactone) (PCL-PEG-PCL) and poly (lactide-glycolide)-poly (ethylene glycol)-poly (lactide-glycolide) (PLGA-PEG-PLGA) were synthesized. Their chemical structures were characterized. In aqueous solution, their self-assembly and degradation were studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Spherical micelles were formed in aqueous solution via self-assembly of the amphiphilic triblock copolymers. After degradation, the PLA-PEG-PLA and PCL-PEG-PCL micelles became smaller and the PLGA-PEG-PLGA micelles change to vesicles, which should mainly attribute to their different degradation speed.

Abstract: Pluronic F87/Poly (lactic acid) block copolymer (PLA-F87-PLA) was synthesized by bulk polymerization. Paclitaxel-loaded PLA-F87-PLA nanoparcticles were prepared by a dialysis method. The loading efficiency was determined by UV. The results showed that the loading efficiency of paclitaxel for PLA-F87-PLA nanoparticles was 69%. In vitro release behavior of paclitaxel-loaded PLA-F87-PLA nanoparticles was studied by HPLC. In vitro release behavior showed an initial rapid release followed by a slow release. The biocompatibility of nanoparticles was measured by MTT. The viability of paclitaxel-loaded PLA-F87-PLA nanoparticles was less than that of free paclitaxel. The results indicated that PLA-F87-PLA copolymer has good biocompatibility.

Abstract: Diameters of self-assembled micelles were discussed carefully in this paper. When block copolymer was crossed by Eu (III) ions, they could be assembled into micelles. Then diameters of micelles increased with increasing molar ratios of Phen.

Abstract: The development of the morphology in asymmetric Polystyrene-b-Polylactide (PS-b-PLA) thin films was investigated by Tapping-mode AFM. The thin films were prepared by solution casting with different evaporation rates. Films were cast onto hydrophobic Si wafers. When PS-b-PLA was dissolved in chloroform, fast evaporation (~110nL/s) produced hexagonally packed perpendicular PLA cylinders in the PS matrix; intermediate evaporation (~25nL/s) generated mixed microstructures of PLA cylinders of either vertical or parallel to the substrate; slow evaporation (~9nL/s) produced the PLA cylinders that were fully parallel to the substrate. This simple one step route is shown where highly oriented, ordered arrays of cylindrical domains of PS-b-PLA can be produced over large distance.