Nano-container assembled thin films with time-programmed release of hydrophobic dyes

We introduce an all nano-container assembled multilayer thin films for controlling the release of hydrophobic functional materials. Two complementary charged block copolymer micelles were used as a nano-container for layer-by-layer assembly of thin films. Block copolymer micelles were composed of positively charged hairy polystyrene-block-poly(4-vinylpyridine) and negatively charged hairy (long corona region relative to the hydrophobic core part) or crew-cut (huge hydrophobic core chains, compared with the hydrophilic corona region) polystyrene-block-poly(acrylic acid) micelles. Two different fluorescent dye-incorporated block copolymer micelles multilayer films deconstructed when rehydrated in physiological condition, phosphate buffer saline solutions, releasing block copolymer micelles as a hydrophobic material carrier, suggesting that the detachment behavior of block copolymer micelles integrated into the multilayer films differs according to layer-by-layer assembled block copolymer micelle combinations. These results indicate the suitability of thin films for applications including the controlled release of hydrophobic materials. Atomic force microscope analysis suggested the successful preparation of block copolymer micelles. Film growth and release of fluorescence dyes were monitored by UV-Vis spectra.     

Synthesis and thermal responsive properties of P(LA-b-EO-b-PO-b-EO-b-LA) block copolymers with short hydrophobic poly(lactic acid) (PLA) segments

Poly(lactic acid) (PLA) was successfully grafted to both ends of Pluronic F87 block copolymer (PEO-PPO-PEO) to obtain amphiphilic P(LA-b-EO-b-PO-b-EO-b-LA) block copolymers (PLA-F87-PLA) with short PLA blocks. The block composition and structure of PLA-F87-PLA block copolymers were studied by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetric (DSC) and wide angle X-ray diffraction (WXRD) techniques. The aggregation behavior of PLA-F87-PLA block copolymers in aqueous solutions was studied using the laser light scattering (LLS) technique. Various types of particles consisting of small micelles, medium and large aggregates were observed due to the complex structure of these copolymers. Importantly, PLA-F87-PLA block copolymers retain the thermal responsive behavior found in Pluronic systems. The critical micellization temperatures (CMTs) of PLA-F87-PLA were lower than that of F87 because of increased hydrophobicity introduced by the PLA blocks. A reversible sol-gel transition was observed for the hydrogels formed from PLA₆-F87-PLA₆ and PLA₉-F87-PLA₉ block copolymers. Preliminary results from the drug release study using a hydrophilic model drug procain hydrochloride (PrHy) were promising. Constant initial release rate was observed.     

Synthesis of poly(ethylene glycol)-<Emphasis Type="Italic">b</Emphasis>-poly(mercapto ethylacrylamide) diblock copolymer via atom transfer radical polymerization

Atom transfer radical polymerization was used to synthesize a well-defined poly(ethylene glycol)-b-poly(mercapto ethylacrylamide) (PEG-b-PMEAAm) diblock copolymer. Poly(ethylene glycol)-b-poly[N-(acryloxysuccinimide)](PEG-b-PNAS) was synthesized at 80 °C using methoxy-poly(ethylene glycol)-2-bromo propanoate (PEG-Br) and CuBr/2,2′-bipyridine as a macroinitiator and catalyst, respectively. The monomer conversion was determined by ¹H nuclear magnetic resonance (NMR) spectroscopy. The resulting PEG-b-PNAS diblock copolymer was characterized by gel permeation chromatography, Fourier transform infrared (FT-IR), and ¹H NMR spectroscopy. Disulfide groups were introduced by a simple reaction through the N-acryloxysuccinimide (NAS) moieties of the PEG-b-PNAS diblock copolymer with cystamine dihydrochloride in the presence of triethylamine. FT-IR spectroscopy was used to confirm the introduction of disulfide moieties into the polymer repeating units. Subsequently, a thiol-functionalized block copolymer was prepared using DL-dithiothreitol (DTT) as the reducing agent and the reduction step was monitored by ¹H NMR spectroscopy. This thiol group was transformed easily to a disulfide bond using FeCl₃ as an oxidizing agent. The transformation into disulfide could be visualized easily as insoluble polymeric particles formed from a clear solution of PEG-b-PMEAAm after oxidation.     

CMC and dynamic properties of poly(VA-<Emphasis Type="Italic">b</Emphasis>-St) copolymer micelles for drug delivery

The polymeric micelles from amphiphilic block copolymer poly(vinyl alcohol-b-styrene) (poly(VA-b-St)) with different syndiotacticity of poly(vinyl alcohol) (PVA) block were prepared by dialysis against water. Critical micelle concentration (CMC) and dynamic properties of poly(VA-b-St) copolymeric micelles were investigated by fluorescence techniques. From the fluorescence emission spectrum measurements using pyrene as a fluorescence probe, the observed CMC value was in the range of 0.125–4.47 mg/L. The CMC value increased with decreasing the weight ratio of PS to PVA block and with increasing the syndiotacticity of PVA block. The rate of pyrene release was very slow for block copolymers containing PVA block with higher syndiotacticity, which indicates that their micelles have increased kinetic stability. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007.     

Preparation of block-brush PEG-b-P(NIPAM-g-DMAEMA) and its dual stimulus-response

Well-defined dually responsive block-brush copolymer of poly(ethylene glycol)-b-[poly(N-isopropylacrylamide)-g-poly(N,N-dimethylamino-ethylmethacrylate)], [PEG-b-P(NIPAM-g-PDMAEMA)] was successfully prepared by the combination of atom transfer radical polymerization (ATRP) and click chemistry based on azide-capped PDMAEMA and alkyne-pending PEG-b-PNIPAM copolymer. Azide-capped PDMAEMA was synthesized through ATRP of DMAEMA monomer using an azide-functionalized initiator of β-azidoethyl-2-bromoisobutyrate. Alkyne-pending PEG-b-PNIPAM copolymer was obtained through ATRP copolymerization of NIPAM with propargyl acrylate. The final block-brush copolymer was synthesized by the click reaction between these two polymer precursors. Because of characteristics of three different blocks, the copolymer exhibited dually thermo- and pH-responsive behavior. The responsive behaviors of block-brush copolymer were studied by laser light scattering, temperature-dependent turbidity measurement and micro differential scanning calorimetry. The phase transition temperature of block-brush copolymer increased with the decrease of pH value. At pH = 5.0, the copolymer displayed weak thermo-responsive behavior and might form uni-molecular micelles upon heating. At higher pH values, the block-brush copolymer aggregated intermolecularly into the micelles during the phase transition.     

Complex micelles with a responsive shell for controlling of enzymatic degradation

Complex polymeric micelles with a PLA core and a mixed PEG/PNIPAM shell were prepared by self-assembly of two block copolymers: poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) and poly(N-isopropylacrylamide)-b-poly(lactic acid) (PNIPAM-b-PLA). Using ¹H NMR spectroscopy and dynamic light scattering, the micellization and the enzymatic degradation status were characterized. At 25 °C, the PNIPAM block is hydrophilic and the PLA core is prone to the enzymatic degradation, resulting in the disassembly of the micelles. While increasing the temperature to 45 °C, the PNIPAM collapsed onto the PLA core, protecting the PLA core from the attack by the enzyme, and the micelles exhibit a resistance to the enzymatic degradation. Furthermore, the enzymatic degradation rate of the micelles can also be tuned by changing the ratio of PEG to PNIPAM. With increasing content of PNIPAM, the conformation of the collapsed PNIPAM changes from patchy domains to a continuous and dense layer, and the enzyme accessibility to the PLA core is changed.     

Aqueous lubricating properties of charged (ABC) and neutral (ABA) triblock copolymer chains

Application of charged polymer chains as additives for lubricating neutral surfaces in aqueous environment, especially via polymer physisorption, is generally impeded by the electrostatic repulsion between adjacent polymers on the surface. In this study, we have investigated the adsorption and aqueous lubricating properties of an amphiphilic triblock copolymer, comprised of a neutral poly(ethylene glycol) (PEG) block, a hydrophobic poly(2-methoxyethyl acrylate) (PMEA) block, and a charged poly(methacrylic acid) (PMAA) block, namely PEG-b-PMEA-b-PMAA. After adsorption onto a nonpolar hydrophobic surface from aqueous solution, an equal and homogeneous mixture of neutral PEG and charged PMAA chains is formed on the surface, with an adsorbed polymer mass comparable to its fully neutral counterpart, PEG-b-PMEA-b-PEG. The lubricity of PEG-b-PMEA-b-PMAA showed significant improvement compared to fully charged polymer chains, e.g. poly(acrylic acid)-block-poly(2-methoxyethyl acrylate) (PAA-b-PMEA), which is attributed to dilution of charged moieties on the surface and subsequent improvement of the lubricating film stability.     

Synthesis and characterization of biodegradable amphiphilic triblock copolymers methoxy-poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-lactic acid)

Starting from MPEG-NH₂, a series of amphiphilic triblock copolymers MPEG-b-PLL-b-PLA were synthesized through PEG-NH₂-initiated ring-open polymerization of N ^ε-benzyloxycarbonyl-L-lysine, followed by acylation coupling between the amino-terminated MPEG-b-PZLL-NH₂ and carboxyl-terminal PLA and the deprotection of amines. The block copolymers were characterized by FT-IR, ¹H NMR, GPC, DSC and TEM. The copolymer functional groups, molecular and block structures were verified by FT-IR, ¹H NMR and DSC, respectively. The GPC results indicate that the chain lengths of each block can be controlled by varying the feed ratios of the monomer and initiator, providing the polymer samples with a narrow molecular weight distribution (M _w /M _n = 1.10 ~ 1.25). The TEM analysis shows that the triblock polymers can self-assemble into polymeric micelles in aqueous solution with spherical morphology. The cell-cytotoxicity assay indicates that the triblock polymers show no obvious cytotoxicity against Bel7402 human hepatoma cells.     

Dissipative particle dynamics study on the multicompartment micelles self-assembled from the mixture of diblock copolymer poly(ethyl ethylene)-block-poly(ethylene oxide) and homopolymer poly(propylene oxide) in aqueous solution

Dissipative particle dynamics (DPD) method is applied to model the self-assembly of diblock copolymer poly(ethyl ethylene)-block-poly(ethylene oxide) (PEE-b-PEO) and homopolymer poly(propylene oxide) (PPO) in aqueous solution. In this study, several segments are coarse-grained into a single simulation bead based on the experimental density. For the self-assembly of pure diblock copolymer PEE-b-PEO in dilute solution, the DPD simulation results are in good agreement with experimental data of micelle morphologies and sizes. The chain lengths of the block copolymers and the volume ratios between PPO and PEE-b-PEO are varied to find the conditions of forming multicompartment micelles. The micelles with core-shell-corona structure and the micelles with two compartments are both formed from the mixture of PEE-b-PEO and PPO in aqueous solution.     

Functionalization of amphiphilic coil-rod-coil triblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine) with florescence moiety and C60

We recently achieved quantitative synthesis of an amphiphilic coil-rod-coil triblock copolymer, poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine), by coupling in situ living diblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (P2VP-b-PHIC) using malonyl chloride in the presence of pyridine. This led to the introduction of an active methylene group that is a site for further functionalization in the rod block. The Michael addition reaction of the triblock copolymer with 7-(4-trifluoromethyl) coumarin acrylamide led to copolymer bearing a fluorescent pendent in the rod block. The fluorescent labeled copolymers were isolated in ∼94% yields. Similarly C₆₀ pendent was introduced to the rod block by the Bingel reaction. The yields of C₆₀ functionalized copolymers were ∼54%. The precursor and functionalized amphiphilic coil-rod-coil copolymer show diverse morphologies, such as micelles and vesicles by simply changing the solvent. For the C₆₀ functionalized block copolymer, structural constraints in micelles and vesicles prevented C₆₀ pendents to aggregate.     

Preparation of core cross-linked micelles using a photo-cross-linking agent

A new method for preparing polymeric, core cross-linked (CCL) micelles has been developed using a bifunctional photo-cross-linking agent of di(4-hydroxyl benzophenone) dodecanedioate (BPD). An amphiphilic diblock copolymer of poly(ethylene glycol)-b-poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PEG-b-P(HEMA-co-MMA)) was synthesized via atom-transfer radical polymerization (ATRP) using a PEG macroinitiator at 85 °C. The core domains of the PEG-b-P(HEMA-co-MMA) micelles containing BPD in aqueous solution were successfully photo-cross-linked by UV irradiation for only 30 min. The HEMA units incorporated in the hydrophobic block of PEG-b-P(HEMA-co-MMA) donated labile hydrogens to excited-state BP groups in BPD, and they were subsequently cross-linked by BPD through radical-radical combination. A sufficient degree of cross-linking was obtained at an equivalent ratio of the BP groups to the HEMA units.     

Preparation of hydrogel nanoparticles by atom transfer radical polymerization of N-isopropylacrylamide in aqueous media using PEG macro-initiator

PEG-b-PNIPAM block copolymers are synthesized by the atom transfer radical polymerization of NIPAM using PEG macro-initiator. When the polymerization temperature is 25 °C, the block copolymer is soluble in water, whereas the block copolymer is phase-separated to form micelles during polymerization as the polymerization temperature is raised to 50 °C, the temperature above the LCST of PEG-b-PNIPAM. To prepare stable hydrogel nanoparticles in water at room temperature, a small amount of N,N′-ethylenebisacrylamide is added as a cross-linker to the reaction system, where the size of nanoparticles is controlled by the composition of mixed solvent.     

Comparison of micelles formed by amphiphilic poly(ethylene glycol)‐b‐poly(trimethylene carbonate) star block copolymers

In this article, we describe the synthesis and solution properties of PEG‐b‐PTMC star block copolymers via ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) monomer initiated at the hydroxyl end group of the core PEG using HCl Et₂O as a monomer activator. The ROP of TMC was performed to synthesize PEG‐b‐PTMC star block copolymers with one, two, four, and eight arms. The PEG‐b‐PTMC star block copolymers with same ratio of between hydrophobic PTMC and hydrophilic PEG segments were obtained in quantitative yield and exhibited monomodal GPC curves. The amphiphilic PEG‐b‐PTMC star block copolymers formed spherical micelles with a core–shell structure in an aqueous phase. The mean hydrodynamic diameters of the micelles increased from 17 to 194 nm with increasing arm number. As arm number increased, the critical micelle concentration (CMC) of the PEG‐b‐PTMC star block copolymers increased from 3.1 × 10^?3 to 21.1 × 10^?3 mg/mL but the partition equilibrium constant, which is an indicator of the hydrophobicity of the micelles of the PEG‐b‐PTMC star block copolymers in aqueous media, decreased from 4.44 × 10⁴ to 1.34 × 10⁴. In conclusion, we confirmed that the PEG‐b‐PTMC star block copolymers form micelles and, hence, may be potential hydrophobic drug delivery vehicles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of poly(ethylene glycol)-b-poly (l-lactide)-b-poly(l-glutamic acid) triblock copolymer

A biodegradable amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(l-glutamic acid) (PEG-b-PLLA-b-PLGA) was obtained by catalytic hydrogenation of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(γ-benzyl-l-glutamic acid) (PEG-b-PLLA-b-PBLGA) synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with amino-terminated MPEG-b-PLLA-NH₂ as a macroinitiator. MPEG-b-PLLA-NH₂ converted from MPEG-b-PLLA-OH first reacted with tert-Butoxycarbonyl-l-phenylalanine (Phe-^NBOC) and dicyclohexylcarbodiimide (DCC) and then deprotected the tert-butoxycarbonyl group. MPEG-b-PLLA-OH was prepared by ROP of l-lactide with monomethoxy poly(ethylene glycol) in the presence of stannous octoate. The triblock copolymer and its diblock precursors were characterized by ¹H NMR, FTIR, GPC and DSA (drop shape analysis) measurements. The lengths of each block polymers could be tailored by molecular design and the ratios of feeding monomers. The triblock polymer PEG-b-PLLA-b-PLGA containing carboxyl groups showed obviously improved hydrophilic properties and could be a good potential candidate as a drug delivery carrier.     

Synthesis,characterization, and application of novel amphiphilic poly(D‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐ poly(D‐gluconamidoethyl methacrylate) triblock copolymers

Novel amphiphilic ABA‐type poly(D ‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐poly(D ‐gluconamidoethyl methacrylate) (PGAMA‐b‐PU‐b‐PGAMA) tri‐block copolymers were successfully synthesized via the combination of the step‐growth and copper‐catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO‐PU‐OH) was synthesized by the step‐growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA‐b‐PU‐b‐PGAMA block copolymers were synthesized via copper‐catalyzed ATRP of GAMA in N, N‐dimethyl formamide at 20°C in the presence of 2, 2′‐bipyridyl using Br‐PU‐Br as macroinitiator and characterized by ¹H‐NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by ¹H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo‐gravimetric analysis, and differential scanning calorimetric study. Spherical Ag‐nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri‐block copolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nanostructured thermosetting epoxy systems modified with poly(isoprene‐b‐methyl metacrylate) diblock copolymer and polyisoprene‐grafted carbon nanotubes

Nanostructured thermosetting composites based on an epoxy matrix modified with poly(isoprene‐b‐methyl methacrylate) (PI‐b‐PMMA) block copolymer were prepared through PI block segregation. Morphological structures were examined by means of atomic microscopy force microscopy. As epoxy/pristine multi‐walled carbon nanotubes (MWCNT) systems were found to present big agglomerations, with a very poor dispersion of the nanofiller, epoxy/PI‐b‐PMMA/MWCNT systems were prepared by using polyisoprene‐grafted carbon nanotubes (PI‐g‐CNT) to enhance compatibility with the matrix and improve dispersion. It was found that the functionalization of MWCNT with grafted polyisoprene was not enough to totally disperse them into the epoxy matrix but an improvement of the dispersion of carbon nanotubes was achieved by nanostructuring epoxy matrix with PI‐b‐PMMA when compared with epoxy/MWCNT composites without nanostructuring. Nevertheless, some agglomerates were still present and the complete dispersion or confinement of nanotubes into desired domains was not achieved. Thermomechanical properties slightly increase with PI‐g‐CNT content for nanostructured samples, whereas for nonnanostructured epoxy/PI‐g‐CNT composites they appeared almost constant and even decreased for the highest nanofiller amount due to the presence of agglomerates. Compression properties slightly decreased with block copolymer content, while remained almost constant with nanofiller amount. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermosensitive self‐assembly micelles from A2BA2‐type poly(N‐isopropyl acrylamide)2‐b‐Poly(lactic acid)‐b‐Poly(N‐isopropyl acrylamide)2 four‐armed star block copolymers and their applications as drug carriers

A novel A₂BA₂‐type thermosensitive four‐armed star block copolymer, poly(N‐isopropyl acrylamide)₂‐b‐poly(lactic acid)‐b‐poly(N‐isopropyl acrylamide)₂, was synthesized by atom transfer radical polymerization and characterized by ¹H‐NMR, Fourier transform infrared spectroscopy, and size exclusion chromatography. The copolymers can self‐assemble into nanoscale spherical core–shell micelles. Dynamic light scattering, surface tension, and ultraviolet–visible determination revealed that the micelles had hydrodynamic diameters (D_h) below 200 nm, critical micelle concentrations from 50 to 55 mg/L, ζ potentials from ?7 to ?19 mV, and cloud points (CPs) of 34–36°C, depending on the [Monomer]/[Macroinitiator] ratios. The CPs and ζ potential absolute values were slightly decreased in simulated physiological media, whereas D_h increased somewhat. The hydrophobic camptothecin (CPT) was entrapped in polymer micelles to investigate the thermo‐induced drug release. The stability of the CPT‐loaded micelles was evaluated by changes in the CPT contents loaded in the micelles and micellar sizes. The MTT cell viability was used to validate the biocompatibility of the developed copolymer micelle aggregates. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4137–4146, 2013     

Amphiphilic block copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene: synthesis and self‐assembly

The triblock energetic copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene (PLA‐b‐GAP‐b‐PS) was synthesized successfully through atom‐transfer radical polymerization (ATRP) of styrene and ring‐opening polymerization of d,l ‐lactide. The energetic macroinitiator GAP‐Br, which was made from reacting equimolar GAP with α‐bromoisobutyryl bromide, firstly triggered the ATRP of styrene with its bromide group, and then the hydroxyl group on the GAP end of the resulting diblock copolymer participated in the polymerization of lactide in the presence of stannous octoate. The triblock copolymer PLA‐b‐GAP‐b‐PS had a narrow distribution of molecular weight. In the copolymer, the PS block was solvophilic in toluene and improved the stability of the structure, the PLA block was solvophobic in toluene and served as the sacrificial component for the preparation of porous materials, and GAP was the basic and energetic material. The three blocks of the copolymer were fundamentally thermodynamically immiscible, which led to the self‐assembly of the block copolymer in solution. Further studies showed that the concentration and solubility of the copolymer and the polarity of the solvent affected the morphology and size of the micelles generated from the self‐assembly of PLA‐b‐GAP‐b‐PS. The micelles generated in organic solvents at 10 mg mL^?1 copolymer concentration were spherical but became irregular when water was used as a co‐solvent. The spherical micelles self‐assembled in toluene had three distinct layers, with the diameter of the micelles increasing from 60 to 250 nm as the concentration of the copolymer increased from 5 to 15 mg L^?1. © 2017 Society of Chemical Industry     

Oval cuboid TiO2 particles with mesoporous structure fabricated by using fluorinated block copolymers as templates with photocatalytic performance

In this work, a poly(ethylene glycol)-b-poly(1H,1H,7H-dodecafluoroheptyl methacrylate) (PEG-b-PDFMA) block copolymer was first synthesized by the reversible addition−fragmentation chain transfer (RAFT) polymerization. Then a novel facile approach was developed to fabricate oval cuboid TiO₂ particles with mesoporous structure by using the PEG-b-PDFMA block copolymer as a template and titanium tetrabutoxide (TBOT) as a precursor, followed by evaporation-induced self-assembly (EISA) process and calcination process. The results show that the PEG-b-PDFMA block copolymer can control the oriented assembly of nanoparticles and act as templates for the formation of a mesopore. It is found that the mass ratio of TBOT/PEG-b-PDFMA and water content in the solution have a significant influence on the morphology of TiO₂ particles. When the mass ratio of TBOT/PEG-b-PDFMA is 0.25/1, oval cuboid TiO₂ particles with mesopores are obtained, which exhibits a high photocatalytic activity for the degradation of methylene blue (MB) dye under UV light irradiation.     

Synthesis and characterization of dual stimuli-responsive block copolymers based on poly(N-isopropylacrylamide)-b-poly(pseudoamino acid)

The current study synthesized amphiphilic thermal/pH-sensitive block copolymers PNiPAAm-b-PHpr by condensation polymerization of trans-4-hydroxy-l-proline (Hpr) initiated from hydroxy-terminated poly(N-isopropylacrylamide) (PNiPAAm) as the macroinitiator in the presence of the catalyst, SnOct₂. ¹H NMR, FTIR, and gel permeation chromatography (GPC) characterized these copolymers. Their solutions showed reversible changes in optical properties: transparent below a lower critical solution temperature (LCST) and opaque above the LCST. The LCST values depended on the polymer composition and the media. With critical micelle concentrations (CMCs) in the range of 1.23-3.73 mg L⁻¹, the block copolymers formed micelles in the aqueous phase owing to their amphiphilic characteristics. Increased hydrophobic segment length or decreased hydrophilic segment length in an amphiphilic diblock copolymer produced lower CMC values. The current work proved the core-shell structure of micelles by ¹H NMR analyses of the micelles in D₂O. Transmission electron microscopy analyzed micelle morphology, showing a spherical core-shell structure. The micelles had an average size in the range of 170˜210 nm (blank), and 195˜280 nm (with drug). Observations showed high drug entrapment efficiency and drug-loading content for the drug micelles.