PDMAEMA Shell Research Articles

Dual pH- and temperature-responsive poly(dimethylaminoethyl methacrylate)-coated mesoporous silica nanoparticles as a smart drug delivery system

A robust drug delivery system was created by grafting poly(dimethylaminoethyl methacrylate) (PDMAEMA) onto silica nanoparticles with two different lengths using an in situ atom transfer radical polymerization, resulting in the formation of a pH- and temperature-sensitive shell. The high molecular weight PDMAEMA demonstrated effective controlled drug release, and prevented drug release in healthy cells. Drug release occurred through polymer shell protonation at pH 5. The critical temperature of 41 °C facilitated rapid solvation of the shell polymers in the blood, preventing tissue accumulation and reducing toxicity compared to systems with lower critical solution temperatures. Field-emission scanning electron microscopy analysis and nitrogen adsorption/desorption analysis showed that the nanoparticles have a fine network, mesoporous structure, and a mean size of around 17 nm that show their excellent capacity for loading drugs. Fourier-transform infrared spectroscopy showed that all the modification steps and polymerization were successfully implemented. Thermogravimetric analysis showed PDMAEMA chains with two different lengths grafted onto the nanoparticles. Transmission electron microscopy analysis also showed grafted polymer chains on the hybrid nanoparticles. The release profile of model cancer drugs (doxorubicin and methotrexate) varied with pH and temperature, with high molecular weight PDMAEMA shells effectively preventing drug release at neutral pH. In vitro analysis using the HeLa cell line showed minimal toxicity in blank samples and significant release profile in acidic environment.

A Polymeric Unimolecular CO Dehydrogenase Mimic with both Inner and Outer Spheres for Enhanced Photocatalytic CO2 Reduction in Aqueous Solution.

Inspired by carbon monoxide dehydrogenase (CODH), mimicking its inner and outer spheres is a promising strategy in CO2 reduction catalyst design. However, artificialCODH-like catalysts are generally limited to the inner sphere effect and only applicable in organic solvents or for electrocatalysis. Herein, we report an aqueous CODH mimic with both inner and outer spheres for photocatalysis. In this polymeric unimolecular catalyst, the inner sphere is composed of cobalt porphyrin with four appended amido groups and the outer sphere consists of four poly(2(dimethylamino)ethyl methacrylate) (PDMAEMA) arms. Upon visible light irradiation (λ > 420 nm), the as-prepared photocatalyst exhibits a high turnover number (TONCO = 1731.2) in the reduction of CO2 into CO, which is superior to most reported molecular photocatalysts in aqueous solution. The mechanism studies indicate that, in this water-dispersible and structurally well-defined CODH mimic, the cobalt porphyrin core serves as the catalysis center, amido groups function as hydrogen-bonding pillars helping to stabilize the CO2 adduct intermediate, while PDMAEMA shell renders both the water solubility and a CO2 reservoir through reversibly capturing of CO2. The present work has clarified the significance of inner and outer coordination sphere effects for improving the aqueous photocatalytic CO2 reduction performance of CODH mimics.

Copolymer-Functionalized Cellulose Nanocrystals as a pH- and NIR-Triggered Drug Carrier for Simultaneous Photothermal Therapy and Chemotherapy of Cancer Cells.

As a class of biocompatible and biodegradable naturally derived nanomaterials, cellulose nanocrystals (CNCs) with diverse surface functionalization have aroused considerable attention for a range of biomedical applications in drug or gene delivery, as a fluorescent nanoprobe, in cancer targeting, and in photothermal cancer therapy, among others. Herein, we construct the copolymer-functionalized CNCs as a pH- and near-infrared (NIR)-triggered drug carrier for simultaneous photothermal therapy and chemotherapy of cancer cells. Poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (PCL-b-PDMAEMA) was conjugated onto the surface of CNCs through ring-opening polymerization, followed by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The resultant CNC-based drug carrier can encapsulate doxorubicin (DOX) as a therapeutic agent and indocyanine green (ICG) as an NIR dye in the PCL core and the PDMAEMA shell, respectively, via hydrophobic and electrostatic interactions. In addition to the intrinsic pH response, the release profile of DOX can also be controlled by the duration of laser irradiation due to collapse of the crystal structure of the PCL domain with the increase of temperature induced by photothermal conversion. The drug carrier can exhibit enhanced cytotoxicity toward HepG2, human hepatocyte carcinoma, cells upon laser irradiation, which can be attributed to the synergistic effect arising from NIR-triggered burst release of DOX and photothermal heating. The rod-like morphology of the CNC-based drug carrier may help accelerate the endocytosis in cell membranes compared with its common spherical counterpart. Based on the abovementioned advantages, copolymer-functionalized CNCs can serve as a promising candidate for effective cancer treatment.

Effects of Ionic Strength and Ion Specificity on the Interface Behavior of Poly(dimethylaminoethyl methacrylate)-Poly(lauryl methacrylate).

The ion specificity effect on the water solubility of poly(N-isopropylacrylamide)-containing copolymers complies with the Hofmeister series, which is applicable to other copolymers or not need to be explored. In this work, effects of ionic strength under acidic conditions and ion specificity under alkaline conditions on the air/water interface behavior of two amphiphilic diblock copolymers poly(dimethylaminoethyl methacrylate)-poly(lauryl methacrylate) (PDMAEMA-PLMA) were systematically studied. Under acidic conditions, the surface pressure-area isotherms of a predominantly hydrophilic copolymer are insensitive to ionic strength. In contrast, the isotherms of a predominantly hydrophobic copolymer successively shift to the large, small, and large molecular area with the increase of ionic strength. Under alkaline conditions, the interfacial stretch degrees of PDMAEMA chains of two copolymers change with salt species and concentrations, which do not comply with the Hofmeister series. All of the Langmuir-Blodgett films of the former copolymer exhibit separate circular micelles. Nevertheless, those of the latter copolymer obtained under alkaline conditions exhibit various distinctive morphologies such as separate circular micelles, large separate PLMA cores within large PDMAEMA domains, and large PLMA domains/aggregates surrounded by short PDMAEMA shells. It can be attributed to the high deformability of PLMA chains, the ion specificity effect on the stretch degree of PDMAEMA blocks, and their underwater solubility upon compression.

Seed's morphology-induced core-shell composite particles by seeded emulsion polymerization for drug delivery

Cross-liked poly(2-hydroxyethyl methacrylate-co-methacrylic acid) seeds with different morphologies such as cauliflower-like, lobed spherical, and spherical were used in seeded emulsion polymerization (SEP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA), 2-hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA). The morphological structure of produced composite particles was observed using field emission scanning electron microscopy (FE-SEM). The origin of the formation of different morphologies was discussed using various thermodynamic parameters such as solubility parameters and intermolecular forces between polymeric components involved. Also, the effect of the morphology of seed particles on the resultant structures was investigated. Results showed that morphology of fabricated composite particles is induced from morphology of seed particles with larger sizes. Finally, the fabricated composite particles were utilized in the controlled release of DOX. The effect of morphological changes of synthesized composite particles on the cumulative release behavior at acidic environment indicated the pH-sensitive nature of drug release through carriers. The particles with PDMAEMA shell showed the highest release of DOX at pH = 7.4 whereas PMAA shells displayed the least cumulative release. Inversely, the lowest cumulative release at pH = 1.2 was shown by PDMAEMA-coated carriers. Moreover, particles with spherical morphology had better drug release than cauliflower-like ones originated from smart nature of carriers.

Triple-Responsive Block Copolymer Micelles with Synergistic pH and Temperature Response

Multifunctional, stimuli-responsive block copolymers have been prepared via the sequential atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the in-house synthesized 1′-(2-methacryloxyethyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) (SPMA) monomer. Two PDMAEMA-b-PSPMA diblock copolymers, containing 3 and 14 mol % SPMA, were synthesized. The amphiphilic nature of the PDMAEMA-b-PSPMA diblock copolymers led to the formation of well-defined spherical micelles, comprising a hydrophobic PSPMA core and a hydrophilic PDMAEMA shell, in water. The combination of the pH- and temperature-responsive character of PDMAEMA with the pH-, temperature-, and light-sensitive properties of the PSPMA block has resulted in a complex responsive behavior of the copolymer micelles in aqueous solution, when applying three different external stimuli (i.e., light irradiation, pH, and temperature). More importantly, the synergistic response of the block copolymer micelles ...

Smart pH-sensitive micelles based on redox degradable polymers as DOX/GNPs carriers for controlled drug release and CT imaging

An amphiphilic copolymer poly(ε-caprolactone)-ss-poly(2-(dimethylamino) ethyl methacrylate), PCL-SS-PDMAEMA, was designed and synthesized using ROP and ARGET ATRP methods. Dual stimulus responsive micelles were prepared by the self-assembly of PCL-SS-PDMAEMA. PDMAEMA could respond to acid conditions with protonation, followed by enhanced hydrophilicity and swelling of the micellar shell. In addition, the cleavable joint disulfide bond between the core and shell was disrupted when exposed to an abundance of the reductant reductive glutathione GSH, leading to the disassembly of the micellar structure. The smart response behavior can be used for intracellular controlled drug release in tumor cells. In terms of “theranostics” with higher therapy effect, the tool for tumor imaging and diagnose through computed tomography (CT) was considered with the loading of gold nanoparticles (GNPs). GNPs with good distribution were prepared by means of in situ reduction by PDMAEMA block and stabilized by the micelles. Polymeric micelles were used to load the anticancer drug doxorubicin (DOX) in the hydrophobic core and GNPs in the hydrophilic PDMAEMA shell. Subsequently, the micellar theranostics platform combining chemotherapy and CT diagnose was obtained. The pH- or redox-triggered drug release profiles suggesting that the DOX/GNPs-loaded micelles facilitated controlled release in response to different simulated microenvironments. Cellular uptake study was carried out, indicating that the micelles could be fast internalized within several hours. MTT assay showing significant inhibition against HepG2 and MCF-7 cells for the DOX/GNPs-loaded micelles. Finally, the in vitro CT imaging assay indicated the good CT diagnosis potential of DOX/GNPs-loaded micelles. The micelle simultaneously loaded with DOX and GNPs represent a promising theranostics platform for efficient cancer chemotherapy and diagnosis.

Template‐Directed Fabrication of Anatase TiO2 Hollow Nanoparticles and Their Application in Photocatalytic Degradation of Methyl Orange

Polymerization‐induced self‐assembly (PISA) was used to fabricate polymeric nanoparticles via reversible addition‐fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) using diblock copolymer poly(glycerol monomethacrylate)‐block‐poly(2‐dimethylaminoethyl methacrylate) (PGMMA‐ PDMAEMA‐CTA) as the macro RAFT agent. The dispersion of polymeric nanoparticles with a final concentration of about 210 mg/g (solid content of 21%) was obtained via this efficient method (PISA). The resultant polymeric nanoparticles consisting of corona‐shell‐core three layers with weak polyelectrolyte PDMAEMA as the shell were used as sacrificial template to fabricate TiO2 hollow nanoparticles. The negatively charged titanium precursor was absorbed into the PDMAEMA shell via the electrostatic interaction, and hydrolyzed to form polymer/TiO2 hybrid nanoparticles. Anatase TiO2 hollow nanoparticles were formed after removing the polymeric templates by calcination at 550 °C. The experiments of photocatalytic degradation of methyl orange showed that the resultant anatase TiO2 hollow nanoparticles had high photocatalytic activity and good reusability.

Synthesis of star-like hybrid POSS-(PDMAEMA-b-PDLA)8 copolymer and its stereocomplex properties with PLLA

Although poly(lactide) (PLA), when used as biomaterials, possesses many good properties, its high hydrophobicity and slow degradation may hinder its applications. In this work, a novel star-like oligomeric silsesquioxane-(poly(2-dimethylaminoethyl methacrylate)-b-poly(d-lactide))8 (POSS-(PDMAEMA-b-PDLA)8) was first synthesized through a three-step procedure that involves Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization of DMAEMA initiated by the macroinitiator POSS-8-CTA, and then conversion of the trithiocarbonated end groups on PDMAEMA arms into hydroxyl groups by a combination of aminolysis and Michael addition followed by controlled ring-opening polymerization of D-LA. In the next step, the synthesized hybrid copolymer POSS-(PDMAEMA-b-PDLA)8 was blended with PLLA in solution to form nanocomposites to further modify the thermo-mechanical and degradation properties of PLLA. It was noted that the outer PDLA shell could facilitate POSS-(PDMAEMA-b-PDLA)8 to be well-dispersed in PLLA matrix through stereocomplex (SC) interaction, and the inner PDMAEMA shell endowed PLLA with good hydrophilicity. The SC formation between POSS-(PDMAEMA-b-PDLA)8 and PLLA was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The surface wettability of the PLLA was enhanced due to the presence of hydrophilic PDMAEMA segments and the contact angle values decreased with increasing amount of PDMAEMA in the nanocomposites. Meanwhile, controlled degradation of PLLA in a faster pace was achieved when the nanocomposites were incubated in different pH solutions, indicating its potential in specific biomedical applications.

Poly(ionic liquids) hollow nanospheres with PDMAEMA as joint support of highly dispersed gold nanoparticles for thermally adjustable catalysis

A smart hollow hybrid system was prepared by introducing poly(2-(1-methylimidazolium 3-yl)-ethyl methacrylate chloride) (PMIMC) network, the temperature-responsive PDMAEMA brushes, and Au nanoparticles into silica nanoparticles through two-step surface-initiated atom transfer radical polymerization. TEM, FTIR, EDX, XRD, XPS, and TGA were used to characterize the morphology and structure of air@PMIMC–PDMAEMA–Au hairy hollow nanospheres. The result showed that Au nanoparticles with an average diameter of 1.5 ± 0.2 nm were homogeneously embedded inside the PMIMC–PDMAEMA shell. Catalytic activity of the as-synthesized air@PMIMC–PDMAEMA–Au hairy hollow nanospheres were investigated using the reduction of 4-nitrophenol with NaBH4 as a model reaction. It was found that the joint structures of PMIMC hollow nanospheres and PDMAEMA brushes lead to production of the highly active and stable catalyst for reduction of 4-nitrophenol. Furthermore, the obtained air@PMIMC–PDMAEMA–Au hairy hollow nanospheres were found to have a thermally adjustable catalytic activity for the reduction of 4-nitrophenol.

Developing recyclable pH-responsive magnetic nanoparticles for oil–water separation

Hybrid magnetic nanoparticles (MNPs) with well-defined core-shell structure, pH-tunable interfacial activity and strong magnetic responsiveness were developed as recyclable stabilizers for oil–water separation. The Fe3O4 magnetic core was synthesized using a solvothermal method involving hydrolysis of Fe(II) and Fe(III) salts in basic condition, followed by surface-initiated atom transfer radical polymerization (SI-ATRP) of dimethylaminoethyl methacrylate to grow the PDMAEMA shell. The magnetic core allowed rapid separation of the oil droplets from emulsions under external magnetic field, while the pH-responsive polymer shell offered the hybrid MNPs tunable interfacial activity to form and break Pickering emulsion reversibly for recyclable use of the hybrid MNPs. Results showed that MNPs with longer PDMAEMA arms exhibited broader suitable pH range to form Pickering emulsion, but slower magnetic responsiveness. An optimized sample MNP3 with DP of PDMAEMA ca. 65 was screened out and tested to prove efficient separation of diesel emulsion droplets from water and the recyclability of the hybrid MNPs.

Synthesis of multifunctional microspheres having polymer brush with magnetism, fluorescence, and pH-responsiveness

Multifunctional magnetite@silica-fluorescein isothioxylate-g-poly(dimethyl amino ethyl methacrylate) (Fe3O4@SiO2-FITC-g-PDMAEMA) tri-layer microspheres with magnetism, fluorescence, and pH-responsive PDMAEMA shell were designed and prepared. The functional PDMAEMA brush was grafted from Fe3O4@SiO2-FITC nanoparticles by the surface-induced atom transfer radical polymerization (SI-ATRP) onto the alkylbromide-modified Fe3O4@SiO2-FITC fluorescent templates, which were synthesized by the co-precipitation of Fe(II) and Fe(III) under basic condition together with the subsequently modified Stober sol–gel technique. These nanoparticles were characterized by transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), fluorescence spectrum, dynamic light scattering (DLS), and zeta potentials.

Polymer/TiO₂ hybrid vesicles for excellent UV screening and effective encapsulation of antioxidant agents.

Presented in this paper is a hybrid polymer/titanium dioxide (TiO2) vesicle that has excellent UV-screening efficacy and strong capacity to encapsulate antioxidant agents. Poly(ethylene oxide)-block-poly(2-(dimethylamino)ethyl methacrylate)-block-polystyrene (PEO-b-PDMAEMA-b-PS) triblock terpolymer was synthesized by atom transfer radical polymerization (ATRP) and then self-assembled into vesicles. Those vesicles showed excellent UV-screening property due to the scattering by vesicles and the absorption by PS vesicle membrane. The selective deposition of solvophobic tetrabutyl titanate in the PDMAEMA shell and the PS membrane of the vesicles led to the formation of polymer/TiO2 hybrid vesicles, resulting in an enhanced UV-screening property by further reflecting and scattering UV radiation. The vesicles can effectively encapsulate antioxidant agents such as ferulic acid (up to 57%), showing a rapid antioxidant capability (within 1 min) and a long-lasting antioxidant effect.

Fabrication of biofunctional complex micelles with tunable structure for application in controlled drug release

In acidic solution, complex micelles were formed by diblock copolymers of poly (ethylene glycol)-b-poly (e-caprolactone) (PEG-b-PCL) and folate-poly (2-(dimethylamino) ethyl methylacrylate)-b-poly (e-caprolactone) (Fol-PDMAEMA-b-PCL) with a PCL core, a mixed PEG/Fol-PDMAEMA shell. The surface charge of the complex micelles was positive at acidic surroundings for the protonated PDMAEMA. With increasing pH value to 7.4 (above pK a of PDMAEMA), these micelles could convert into a core-shell-corona (CSC) structure composing a hydrophobic PCL core, a collapsed PDMAEMA shell, and a soluble PEG corona. Compared to core-shell micelles formed by PEG-b-PCL, micelles with CSC structure can prolong degradation by enzyme. Doxorubicin was physically loaded into the PCL core. The drug release rate was pH-dependent. At pH 5.5, complex micelles with core-shell structure showed faster drug release rate, while at pH 7.4, complex micelles gained CSC structure which control the drug release at a lower rate. The multifunctional complex micelles were prepared for enhanced tumor therapy.

Fabrication and characterization of silica nanotubes with controlled dimensions

Silica nanotubes with controlled diameters and lengths were fabricated by a template-directed method. Nanowires composed of poly(2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA–PS), which were fabricated by RAFT dispersion polymerization of styrene in methanol using PDMAEMA as a macro-RAFT agent, were used as sacrificial templates. The diameter of the polymeric nanowires can be adjusted by changing the degree of polymerization (DP) of the hydrophilic PDMAEMA block. As the chain length of the hydrophilic PDMAEMA block increases, the DP of the PS block for formation of the nanowires increases, leading to the diameter increase of the corresponding nanowires. Moreover, the polymeric nanowires with controlled lengths and diameters of the core and the shell can be fabricated on a large scale through polymerization-induced self-assembly and reorganization, conveniently. The weak polyelectrolyte, PDMAEMA shell, is an ideal nanoreactor for deposition of silica to form hybrid nanowires. Silica nanotubes were prepared by calcination of the hybrid nanowires.

Functionalized Stimuli-Responsive Nanocages from Photocleavable Block Copolymers

The light-induced formation of pH and temperature-responsive poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) nanocages is demonstrated here. The strategy is based on the self-assembly in aqueous solutions of a photocleavable poly(tert-butyl acrylate)-hv-poly[2-(dimethylamino)ethyl methacrylate] block copolymer (PtBA-hv-PDMAEMA, where -hv- is the photocleavable junction) into spherical micelles, followed by first PDMAEMA cross-linking by a bis-iodo compound and then by UV light irradiation. The exposure to light induces the cleavage of the junction between the PtBA core and the cross-linked PDMAEMA shell of the micelles. The PtBA block is then extracted to obtain the desired nanocages. The size change of the nanocages in response to pH and temperature is investigated by dynamic light scattering. Finally, the ability to functionalize the internal cavity of the nanocages is demonstrated.

Synthesis and properties of bifunctional magnetic-optical nanomaterials: Fe2O3@Pdmaema-capped II–VI semiconductor quantum dots nanocomposites

A facile route to synthesize a new type of multifunctional nanocomposites is reported. Here, PDMAEMA (poly[2-(dimethylamino)ethyl] methacrylate) is a key macromolecule serving as a bridge between magnetic Fe2O3 nanoparticles and luminescent quantum dots. Both Fe2O3 nanoparticles and II–VI semiconductor quantum dots with a narrow size distribution are synthesized through a two-phase thermal approach. Subsequently, the atom transfer radical polymerization (ATRP) technique was applied to prepare magnetic Fe2O3@PDMAEMA core-shell nanoparticles. The thickness of PDMAEMA shell can be easily controlled by adjusting the reaction time. Finally, the ligand exchange method was exploited to modify II-VI quantum dot with amine-containing polymer of PDMAEMA, which led to quantum dot securely bound by Fe2O3@PDMAEMA core-shell nanoparticle to form a multifunctional nanocomposite. The resulting nanocomposite remains variable emission by tuning the II–VI semiconductor type and particle size and shows H c at 49 kA/m and T b at 16 K from Fe2O3 nanoparticles. The self-assembled behavior for the resulting samples is also discussed.

Fabrication of pDMAEMA-coated silica nanoparticles and their enhanced antibacterial activity

Thin pDMAEMA shells were formed on the surface of silica nanoparticles via vapor deposition polymerization. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis have been used to characterize the resulting pDMAEMA-coated silica nanoparticles. Electron microscopy studies reveal that the thin polymer shell is formed on the silica surface. In this work, the particle diameter can be controlled (from ∼19 to ∼69nm) by varying the size of silica core. The antibacterial performance of the core–shell nanoparticles was investigated against both Gram-positive (Escherichia coli) and Gram-negative (Staphylococcus aureus) bacteria. Importantly, the nano-sized pDMAEMA particles presented antibacterial activity against both bacteria without additional quaternization due to its enlarged surface area. Additionally, the bactericidal efficiency was enhanced by reducing the particle size, because the expanded surface area of the cationic polymer nanoparticles provides more active sites that can kill the bacteria.

Self-assembly of PBzMA-b-PDMAEMA diblock copolymer films at the air–water interface and deposition on solid substrates via Langmuir–Blodgett transfer

The aggregation behavior and morphological characteristics of amphiphilic block copolymer polybenzyl methacrylate-block-poly(dimethylamino)ethyl methacrylate (PBzMA-b-PDMAEMA) at the air–water interface were investigated through surface pressure measurements, atomic force microscopy (AFM) imaging, electrochemical measurements and X-ray reflectivity. Ionization of PDMAEMA blocks significantly affects the isotherms of the surface films at the air–water interface and, consequently, originates different morphologies of Langmuir–Blodgett films obtained under different experimental conditions. At low pH the PDMAEMA blocks are fully protonated and therefore dissolved in the aqueous subphase. Under this condition, the effects of the solubility and electrostatic repulsion of submerged PDMAEMA chains prevail over hydrophobic interactions and the Langmuir film exhibits low surface pressure at large molecular area values. Upon compression, the isotherm shows a pseudoplateau corresponding to the “pancake-to-brush” transition followed by an increase in surface pressure at smaller MMA values. These results were correlated with the morphological features of Langmuir–Blodgett films transferred onto silicon substrates, where dispersed dot-like domains that gradually transformed into an island-like structure, followed by further percolation into a continent-like morphology, were observed through AFM imaging. On the other hand, at high pH the isotherm is more expanded and the film exhibits higher surface pressure at relatively high MMA values due to the strong repulsive interactions between interface-confined hydrophobic aggregates constituted of PBzMA cores and neutral PDMAEMA shells. In this case, the AFM results show a structural evolution from circular and quasi-hexagonally packed micelles, followed by a worm-like structure that collapses into a homogeneous film. Furthermore, the study of the copolymer behavior under different subphase ionic strength conditions confirmed the critical role of electrostatic interactions in determining the characteristics of the isotherm. We could also demonstrate that our system follows accurately the scaling relationship for surface pressure of annealed brushes. Complementary studies performed by means of X-ray reflectivity were carried out to probe the buried interfacial structure of the diblock copolymer film, corroborating that the organization of both blocks on the silicon substrates is strongly dependent on the pH conditions of the subphase during the LB transfer.

Template-Directed Synthesis of Silica Nanowires and Nanotubes from Cylindrical Core–Shell Polymer Brushes

We report the synthesis and characterization of core-degradable core–shell cylindrical polymer brushes (CPBs) that can be used as a molecular soft template for the fabrication of uniform one-dimensional silica nanostructures with tunable dimensions and morphologies. The silica nanostructures were templated from CPBs consisting of a densely grafted poly(ε-caprolactone) core and a poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) shell. According to the degree of polymerization of both the backbone and the side chains, silica nanostructures with varying lengths and diameters were obtained. The weak polyelectrolyte shell acted as an ideal nanoreactor for the deposition of silica. Calcination or treatment with an acid of the as-synthesized silica hybrids led to the removal of the core and consequently to hollow silica nanotubes. Calcined nanotubes were microporous and exhibited high pore volumes and high specific surface areas. Furthermore, metal salts immobilized within the PDMAEMA shell can be fully embedded into the silica shell. Accessibility of the embedded nanoparticles was demonstrated via the catalysis of the reduction of 4-nitrophenol by sodium borohydride in the presence of nanoparticle-doped silica hybrids.