Biodegradable and thermoresponsive micelles of triblock copolymers based on 2-(N,N-dimethylamino)ethyl methacrylate and ε-caprolactone for controlled drug delivery

Amphiphilic triblock copolymers, poly(2-(N,N-dimethylamino)ethyl methacrylate)_x-block-poly(caprolactone)-block-poly(2-(N,N-dimethylamino)ethyl methacrylate)_x, PDMAEMA_Co, were synthesized. Polymerization and structural features of the polymers were analyzed by different physicochemical techniques (GPC, ¹H NMR and FTIR). Formation of hydrophobic domains as cores of the micelles was studied by ¹H NMR and further confirmed by fluorescence. Dynamic light scattering measurements showed a monodispersed size distribution only for the copolymer with the lowest degree of polymerization, while increasing the length of PDMAEMA blocks leads to a bimodal size distribution. The micelles showed reversible dispersion/aggregation in response to temperature cycles through an outer polymer shell lower critical solution temperature (LCST) for PDMAEMA at temperatures between 54 and 87 °C. The triblock copolymer micelles were loaded with the sparingly water-soluble anticancer drug, chlorambucil, by a dialysis procedure. The drug release profile monitored by fluorescence showed that the release of chlorambucil from PDMAEMA nanoparticles is controlled by a combined degradation-diffusion mechanism.     

A recyclable polyoxometalate-based supramolecular chemosensor for efficient detection of carbon dioxide

A new type of supramolecular chemosensor based on the polyoxometalate (POM) Na₉DyW₁₀O₃₆ (DyW₁₀) and the block copolymer poly(ethylene oxide-b-N,N-dimethylaminoethyl methacrylate) (PEO₁₁₄-b-PDMAEMA₁₆) is reported. By taking advantage of the CO₂ sensitivity of PDMAEMA blocks to protonate the neutral tertiary amino groups, CO₂ can induce the electrostatic coassembly of anionic DyW₁₀ with protonated PDMAEMA blocks, and consequently trigger the luminescence chromism of DyW₁₀ due to the change in the microenvironment of Dy³⁺. The hybrid complex in dilute aqueous solution is very sensitive to CO₂ content and shows rapid responsiveness in luminescence. The luminescence intensity of the DyW₁₀/PEO-b-PDMAEMA complex increases linearly with an increasing amount of dissolved CO₂, which permits the qualitative and quantitative detection of CO₂. The complex solution also shows good selectivity for CO₂, with good interference tolerance of CO, N₂, HCl, H₂O and SO₂. The supramolecular chemosensor can be recycled through disassembly of the hybrid complex by simply purging with inert gases to remove CO₂.     

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 (ε-caprolactone) (PEG-b-PCL) and folate-poly (2-(dimethylamino) ethyl methylacrylate)-b-poly (ε-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.     

HPW/PDMAEMA‐b‐PMAA/ZIF‐8 Ternary Lamellar Composite and the Photocatalytic Degradation of Methylene Blue

PDMAEMA‐b‐PMAA block copolymers were prepared by the sequential RAFT polymerization of DMAEMA and tBMA, followed by hydrolysis. Phosphotungstic acid (HPW) was anchored to the PDMAEMA blocks through electrostatic interactions and the as‐obtained HPW/PDMAEMA‐b‐PMAA was added to the synthesis of ZIF‐8. During the formation of ZIF‐8, the PMAA blocks coordinated to the Zn²⁺ ions through their carboxy groups, along with the HPW groups that were anchored to the PDMAEMA blocks. In this way, the block copolymer could consolidate the interactions between HPW and ZIF‐8 and prevent the leakage of HPW. Finally, the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 ternary lamellar composite was obtained and the structure of the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 hybrid material was characterized by using powder X‐ray diffraction (PXRD), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). As a photocatalyst, the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 ternary lamellar composite showed excellent photoactivity for the degradation of methylene blue (MB). The rate of degradation of MB was 0.0240 min^?1, which was 7.5‐times higher than that of commercially available P25 (0.0032 min^?1). In the presence of H₂O₂, the kinetic degradation parameters of the composite reached 0.0634 min^?1, which was about 19.8‐times higher than that of P25.     

Synthesis of Amphiphilic Azobenzene Functionalized Branched-Type Copolymer Based on Branched Poly(2-(Dimethylamino) ethyl methacrylate) and Investigation of Its Drug Release Properties

Here, we reported the synthesis of branched poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) via a combination of activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) and self-condensing vinyl polymerization (SCVP) techniques. The typical linear kinetics of the AGET ATRP of DMAEMA with the initiation of 2-(2-bromoisobutyryloxy) ethyl methacrylate (BIEM) was observed. The molecular weight (M_n ) of the branched PDMAEMA increased with the monomer conversion. The GPC traces of these polymers were unimodal and the molecular weight distributions (M_w/M_n ) were in the range of 1.30–2.10. The degree of branching (DB) determined by NMR spectra agreed with theoretical value. The branched amphiphilic copolymer functionalized with azobenzene was then prepared via AGET ATRP chain-extension of branched PDMAEMA with azobenzene monomer, 6-[4-(4-methoxyphenylazo)phenoxy]hexyl(meth)acrylate as the second monomer. The GPC traces of these branched copolymers showed the mono-peaks, which proved the successful preparation of copolymers. The properties of this branched copolymer in controlling drug release were also investigated. It was found that the drug release rate of chlorambucil can be controlled by various factors, such as polymer structure, light, temperature and pH values.     

Novel block ionomers II. Synthesis and characterization of polyisobutylene‐based block cationomers

Various novel block cationomers consisting of polyisobutylene (PIB) and poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) segments were synthesized and characterized. The specific targets were various molecular weight diblocks (PIB‐b‐PDMAEMA⁺) and triblocks (PDMAEMA⁺‐b‐PIB‐b‐PDMAEMA⁺), with the PIB blocks in the DP_n = 50–200 range (number‐average molecular weight = 3,000–9000 g/mol) connected to blocks of PDMAEMA⁺ cations in the DP_n = 5–20 range (where DP is the number‐average degree of polymerization). The overall synthetic strategy for the preparation of these block cationomers had four steps: (1) synthesis by living cationic polymerization of mono‐ and diallyltelechelic polyisobutylenes, (2) end‐group transformation to obtain PIBs fitted with termini capable of mediating the atom transfer radical polymerization (ATRP) of DMAEMA, (3) ATRP of DMAEMA, and (4) quaternization of PDMAEMA to PDMAEMA ⁺I^? by CH₃I. Scheme 1 shows the microarchitecture and outlines the synthesis route. Kinetic and model experiments provided guidance for developing convenient synthesis methods. The microarchitecture of PIB–PDMAEMA di‐ and triblocks and the corresponding block cationomers were confirmed by ¹H NMR and FTIR spectroscopy and solubility studies. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3679–3691, 2002     

An insight into the schizophrenic self‐assembly of thermo and proton sensitive graphene oxide grafted block copolymer

In order to study the self‐assembly of block copolymer grafted from graphene oxide (GO) by the fluorescence of GO, poly(ε‐caprolactone) (PCL)‐block‐poly(dimethyl aminoethyl methacrylate) (PDMAEMA) is grafted from its surface using consecutive ring opening (ROP) and atom transfer radical polymerization (ATRP). GO‐g‐(PCL₁₃‐b‐PDMAEMA₁₁₇) (GPCLD) at pH 9.2 exhibits cloud point (T_c) at 32 °C. At pH 9.2 HRTEM images indicate schizophrenic morphology from vesicle at 26 °C to annular ring at 30 °C followed by giant size aggregation at 38 °C. But the reference block copolymer (PCL₁₄‐b‐PDMAEMA₁₂₆, PCLD), synthesized using benzyl alcohol as ROP initiator, exhibits only core–shell morphology whose size increases with rising temperature at pH 9.2. GPCLD solution exhibits good photoluminescence (PL) property arising from GO at pH 9.2 and PL‐intensity increases abruptly during phase transition. Both T_c and size of GPCLD assembly can be reversibly tuned by CO₂ and N₂ gas purging. ¹H NMR spectra exhibit a gradual shift of resonance peaks of the protons on CO₂ bubbling. Thus at pH 9.2 and at 38 °C the GPCLD acts as a good CO₂ sensor. Additionally, the GPCLD vesicle can load hydrophobic guest molecules which can be released by triggering with CO₂. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3878–3887     

Novel Amphiphilic Block Copolymers for the Formation of Stimuli-Responsive Non-Lamellar Lipid Nanoparticles

Non-lamellar lyotropic liquid crystalline (LLC) lipid nanoparticles contain internal multidimensional nanostructures such as the inverse bicontinuous cubic and the inverse hexagonal mesophases, which can respond to external stimuli and have the potential of controlling drug release. To date, the internal LLC mesophase responsiveness of these lipid nanoparticles is largely achieved by adding ionizable small molecules to the parent lipid such as monoolein (MO), the mixture of which is then dispersed into nanoparticle suspensions by commercially available poly(ethylene oxide)–poly(propylene oxide) block copolymers. In this study, the Reversible Addition-Fragmentation chain Transfer (RAFT) technique was used to synthesize a series of novel amphiphilic block copolymers (ABCs) containing a hydrophilic poly(ethylene glycol) (PEG) block, a hydrophobic block and one or two responsive blocks, i.e., poly(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl acrylate) (PTBA) and/or poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA). High throughput small angle X-ray scattering studies demonstrated that the synthesized ABCs could simultaneously stabilize a range of LLC MO nanoparticles (vesicles, cubosomes, hexosomes, inverse micelles) and provide internal particle nanostructure responsiveness to changes of hydrogen peroxide (H₂O₂) concentrations, pH and temperature. It was found that the novel functional ABCs can substitute for the commercial polymer stabilizer and the ionizable additive in the formation of next generation non-lamellar lipid nanoparticles. These novel formulations have the potential to control drug release in the tumor microenvironment with endogenous H₂O₂ and acidic pH conditions.     

Synthesis and supramolecular self‐assembly of thermosensitive amphiphilic star copolymers based on a hyperbranched polyether core

A novel amphiphilic thermosensitive star copolymer with a hydrophobic hyperbranched poly (3‐ethyl‐3‐(hydroxymethyl)oxetane) (HBPO) core and many hydrophilic poly(2‐(dimethylamino) ethyl methacrylate) (PDMAEMA) arms was synthesized and used as the precursor for the aqueous solution self‐assembly. All the copolymers directly aggregated into core–shell unimolecular micelles (around 10 nm) and size‐controllable large multimolecular micelles (around 100 nm) in water at room temperature, according to pyrene probe fluorescence spectrometry and ¹H NMR, TEM, and DLS measurements. The star copolymers also underwent sharp, thermosensitive phase transitions at a lower critical solution temperature (LCST), which were proved to be originated from the secondary aggregation of the large micelles driven by increasing hydrophobic interaction due to the dehydration of PDMAEMA shells on heating. A quantitative variable temperature NMR analysis method was designed by using potassium hydrogen phthalate as an external standard and displayed great potential to evaluate the LCST transition at the molecular level. The drug loading and temperature‐dependent release properties of HBPO‐star‐PDMAEMA micelles were also investigated by using indomethacin as a model drug. The indomethacin‐loaded micelles displayed a rapid drug release at a temperature around LCST. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 668–681, 2008     

Synthesis and drug release properties of novel pH- and temperature-sensitive copolymers based on a hyperbranched polyether core

Multi-arm star amphiphilic hyperbranched copolymers with poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) shell and hyperbranched poly(3-ethyl-3-(hydroxymethyl)oxetane) (HBPO) core were synthesized by reversible addition?Cfragmentation chain transfer method. The hyperbranched copolymers were further modified by succinic anhydride (SUC) to obtain the novel pH- and thermosensitive hyperbranched copolymer HBPO-star-PDMAEMAs-SUC. The composition and morphology of synthesized copolymers were investigated by ¹H NMR, dynamic light scattering, and transmission electron microscopy. These copolymers exhibited phase transitions in response to pH and temperature. The pH-dependent release properties of the drug-loaded micelles were also investigated using indomethacin (IND) as a model drug. The IND-loaded micelles displayed a rapid drug release at an alkaline pH.     

Amphiphilic diblock,triblock, and star block copolymers by living radical polymerization: Synthesis and aggregation behavior

Copper(I)‐mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n‐butyl methacrylate) [P(n‐BMA)] and poly[(2‐dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n‐BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2‐bromo‐2‐methylpropionic acid 4‐methoxyphenyl ester, 1,4‐(2′‐bromo‐2′‐methyl‐propionate)benzene, and 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow‐polydispersity polymers for which the number‐average molecular weight increased fairly linearly with time with good first‐order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2‐dimethylamino)ethyl methacrylate to obtain well‐defined [P(n‐BMA)_x‐b‐PDMAEMA_y]_z diblock (15,900; polydispersity index = 1.60), triblock (23,200; polydispersity index = 1.24), and star block copolymers (50,700; polydispersity index = 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac = 3.22–7.13 × 10^?3 g L^?1) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 439–450, 2002; DOI 10.1002/pola.10122     

Rosette‐Shaped Calcite Structures at Surfaces: Mechanistic Implications for CaCO3 Crystallization

Biomineralization is believed to be achieved by the intimate cooperation of soluble macromolecules and an insoluble matrix at the specific inorganic–organic interface. It has been reported that positively charged matrices play an important role in controlling the structure of CaCO₃ at surfaces, although detailed mechanisms remain unclear. In this work, we studied the transformation from amorphous CaCO₃ to calcite crystals on surfaces by using thin films of poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) and its quaternized form. The positively charged PDMAEMA film was found to possess unique properties for CaCO₃ crystallization: individually separated, single calcite crystals were formed on the PDMAEMA film in the absence of poly(acrylic acid) (PAA), while circularly fused calcite crystals were formed in the presence of PAA. The circularly fused (rosette‐shaped) calcite crystals could be changed from a completely packed rosette to a ring‐shaped, hollow structure by tuning the crystallization conditions. A number of factors, such as reaction time, amount of (NH₄)₂CO₃, concentration of PAA, and charge of matrix‐films, were varied systematically, and we now propose a mechanism based on these observations.     

Mussel‐Inspired Photografting on Colloidal Spheres: A Generalized Self‐Template Route to Stimuli‐Responsive Hollow Spheres for Controlled Pesticide Release

A thermo‐controlled pesticide release system composed of poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) thin film grafted polydopamine (PDA) (PDMAEMA‐g‐PDA) microcapsules is reported. SiO₂ microparticles are used as a template to prepare PDA‐coated SiO₂ microparticles. The thermally‐responsive PDMAEMA thin films are grafted on PDA surfaces using a metal‐free surface‐initiated photopolymerization approach without adding any photo­initiator or photosensitizer under UV light irradiation. The subsequent acid etching yields PDMAEMA‐g‐PDA hollow microcapsules. PDMAEMA‐g‐PDA microcapsules exhibit well‐controlled release of avermectin (Av). The results show that the loading ability of PDMAEMA‐g‐PDA microcapsules of Av is up to 52.7% (w/w). The release kinetics of Av demonstrate that Av@PDMAEMA‐g‐PDA microcapsules exhibit temperature‐controlled release performance. This work is significant for controlled release systems. This simple design is expected to be used in various applications, such as in controlled drug release and agriculture‐related fields.

     

Biodegradable amphiphilic block copolymers containing functionalized PEO blocks: Controlled synthesis and biomedical potentials

A series of controllable amphiphilic block copolymers composed of poly(ethylene oxide) (PEO) as the hydrophilic block and poly(?-caprolactone) (PCL) as the hydrophobic block with the amino terminal group at the end of the PEO chain (PCL-b-PEO-NH₂) were synthesized. Based on the further reaction of reactive amino groups, diblock copolymers with functional carboxyl groups (PCL-b-PEO-COOH) and functional compounds RGD (PCL-b-PEO-RGD) as well as the triblock copolymers with thermosensitive PNIPAAm blocks (PCL-b-PEO-b-PNIPAAM) were synthesized. The well-controlled structures of these copolymers with functional groups and blocks were characterized by gel permeation chromatography (GPC) and ¹H NMR spectroscopy. These copolymers with functionalized hydrophilic blocks were fabricated into microspheres for the examination of biofunctions via cell culture experiments and in vitro drug release. The results indicated the significance of introducing functional groups (e.g., NH₂, COOH and RGD) into the end of the hydrophilic block of amphiphilic block copolymers for biomedical potentials in tissue engineering and controlled drug release.     

Crystallization and stereocomplexation behavior of poly(D‐ and L‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) block copolymers

The thermal properties, crystallization, and morphology of amphiphilic poly(D ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PDLA‐b‐PDMAEMA) and poly (L ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were studied and compared to those of the corresponding poly(lactide) homopolymers. Additionally, stereocomplexation of these copolymers was studied. The crystallization kinetics of the PLA blocks was retarded by the presence of the PDMAEMA block. The studied copolymers were found to be miscible in the melt and the glassy state. The Avrami theory was able to predict the entire crystallization range of the PLA isothermal overall crystallization. The melting points of PLDA/PLLA and PLA/PLA‐b‐PDMAEMA stereocomplexes were higher than those formed by copolymer mixtures. This indicates that the PDMAEMA block is influencing the stability of the stereocomplex structures. For the low molecular weight samples, the stereocomplexes particles exhibited a conventional disk‐shape structure and, for high molecular weight samples, the particles displayed unusual star‐like shape morphology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1397–1409, 2011     

Study on novel hydrogels based on thermosensitive PNIPAAm with pH sensitive PDMAEMA grafts

A series of novel hydrogels based on poly(N-isopropylacrylamide) (PNIPAAm) with pendant poly(N-(2-(dimethylamino) ethyl)-methacrylamide) (PDMAEMA) grafts were designed and synthesized. The influence of the pendant PDMAEMA grafts on the properties of the resulted hydrogels was examined in terms of morphology observed by scanning electron microscopy (SEM), thermal property characterized by differential scanning calorimetry (DSC) and shrinking/swelling kinetics upon external temperature changes. In comparison with the conventional PNIPAAm hydrogels, resulting hydrogels presented favorable pH sensitivity as well as improved thermosensitive properties, including enlarged water containing capability at room temperature and faster shrinking/swelling rate upon heating. In addition, fish DNA, used as a model drug, was loaded into the hydrogels, and the controlled release behavior of the drug-loaded hydrogels at different temperatures (22 and 37 °C) was further studied.     

Synthesis of double‐hydrophilic block copolymers via combination of oxyanion‐initiated polymerization and polymer reaction for fabricating magnetic target gene carrier

In this work, we have synthesized a polycation and a polyanion via a combination of oxyanion‐initiated polymerization and polymer reaction, and then developed a novel approach to prepare a controlled magnetic target gene carrier with magnetic Fe₃O₄ nanoparticles as core and poly(ethylene glycol) (PEG) segment as corona via layer‐by‐layer (LbL) assembly and shell‐crosslinking. Magnetic nanoparticles (MNPs) were first modified by poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) via radical polymerization. The resulting MNPs were used to compact deoxyribonucleic acid (DNA) through LbL assembly, involving four steps: ( 1 ) the binding of DNA to the polycation PDMAEMA on the surface of MNPs; ( 2 ) the produced particles in Step 1 with negative charge interacting with additional polycation ethoxy group end‐capped PDMAEMA (EtO‐PDMAEMA) homopolymer, leading to a positive charge surface; ( 3 ) using carboxyl group (‐COO^‐) of poly(methacrylic acid) (PMAA) in a diblock copolymer (MePEG2000‐b‐PMAA_SH) as polyanion, which has partial mercapto groups (‐SH) in PMAA segment, to interact with the particles produced in Step 2; ( 4 ) the shell of the composite nanoparticle was crosslinked by oxidizing the ‐SH groups of the MePEG2000‐b‐PMAA_SH to form disulfide linkage (S? S). All the processes of LbL assembly were investigated by agarose gel retardation assay and zeta potential measurements. The in vitro cytotoxicity analysis proves that polyions/DNA MNPs have excellent properties and potential applications as gene carriers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Physicochemical characterization and drug release properties of PDMAEMA/OSA Semi‐IPN hydrogels with microporous structure

A new poly(2‐(dimethylamino) ethyl methacrylate)/oxidized sodium alginate (PDMAEMA) semi‐interpenetrating network (Semi‐IPN) hydrogel with microporous structure was prepared by using PDMAEMA microgels as an additive during the polymerization/crosslinking process. The interior morphology characterized by scanning electron microscopy showed the Semi‐IPN hydrogels have different pore sizes by changing the amount of microgels. The hydrogels were also characterized by using Fourier transform infrared and DSC. The swelling behaviors of hydrogels indicated that the hydrogels have excellent pH and temperature sensitivity. Bovine serum albumin was entrapped in the hydrogels and the in vitro drug release profiles were established in different buffer solutions at various temperatures. The release behaviors of the model drug were dependent on the pore size of the hydrogels and environmental temperature/pH, which suggested that these materials have potential application as intelligent drug carriers. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparations and properties of a tunable void with shell thickness SiO2@SiO2 core–shell structures via activators generated by electron transfer for atom transfer radical polymerization

Core–shell structure nanoparticles are attracting considerable attention because of their applications in drug delivery, catalysis carrier, and nanomedicine. In this study, SiO₂@SiO₂ core–shell structure with tunable void and shell thickness was successfully prepared for the first time using SiO₂-poly(buty acrylate) (PBA)-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) (SiO₂-PBA-b-PDMAEMA) as the template and tetraethoxysilane (TEOS) as the silica source. An amphiphilic copolymer PBA-b-PDMAEMA was first grafted onto the SiO₂ nanosphere surface through activators regenerated by electron transfer for atom transfer radical polymerization. TEOS was hydrolyzed along with the PDMAEMA chain through hydrogen bonding, and the core–shell structure of SiO₂@SiO₂ was obtained through calcination to remove the copolymer. The gradient hydrophilicity of the PBA-b-PDMAEMA copolymer template facilitated the hydrolysis of TEOS molecules along the PDMAEMA to PBA segments, thereby tuning the voids between the SiO₂ core and SiO₂ shell, as well as the SiO₂ shell thickness. The voids were about 10–15 nm and the shell thicknesses were about 4–11 nm when adding different amounts of DMAEMA monomer. SiO₂@SiO₂ core–shell structures with tunable void and shell thickness were employed as supports for the loading and release of doxorubicin hydrochloride (DOX) in PBS (pH 4.0). The samples demonstrated good loading capacity and controlled release rate of DOX.     

Thermal and pH‐sensitive gold nanoparticles from H‐shaped block copolymers of (PNIPAM/PDMAEMA)‐b‐PEG‐b‐(PNIPAM/PDMAEMA)

Well‐defined H‐shaped pentablock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM), poly(N,N‐dimethylaminoethylacrylamide) (PDMAEMA), and poly(ethylene glycol) (PEG) with the chain architecture of (A/B)‐b‐C‐b‐(A/B) were synthesized by the combination of single‐electron‐transfer living radical polymerization, atom‐transfer radical polymerization, and click chemistry. Single‐electron‐transfer living radical polymerization of NIPAM using α,ω azide‐capped PEG macroinitiator resulted in PNIPAM‐b‐PEG‐b‐PNIPAM with azide groups at the block joints. Atom‐transfer radical polymerization of DMAEMA initiated by propargyl 2‐chloropropionate gave out α‐capped alkyne‐PDMAEMA. The H‐shaped copolymers were finally obtained by the click reaction between PNIPAM‐b‐PEG‐b‐PNIPAM and alkyne‐PDMAEMA. These copolymers were used to prepare stable colloidal gold nanoparticles (GNPs) in aqueous solution without any external reducing agent. The formation of GNPs was affected by the length of PDMAEMA block, the feed ratio of the copolymer to HAuCl₄, and the pH value. The surface plasmon absorbance of these obtained GNPs also exhibited pH and thermal dependence because of the existence of PNIAPM and PDAMEMA blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010