pH‐responsive polymer core–shell nanospheres for drug delivery

Stimuli‐responsive polymer nanoparticles are playing an increasingly more important role in drug delivery applications. However, limited knowledge has been accumulated about processes which use stimuli‐responsive polymer nanospheres (matrix nanoparticles whose entire mass is solid) to carry and deliver hydrophobic therapeutics in aqueous solution. In this research, pyrene was selected as a model hydrophobic drug and a pyrene‐loaded core‐shell structured nanosphere named poly(DEAEMA)‐poly(PEGMA) was designed as a drug carrier where DEAEMA and PEGMA represent 2‐(diethylamino)ethyl methacrylate and poly(ethylene glycol) methacrylate, respectively. The pyrene‐loaded core‐shell nanospheres were prepared via an in situ two‐step semibatch emulsion polymerization method. The particle size of the core‐shell nanosphere can be well controlled through adjusting the level of surfactant used in the polymerization where an average particle diameter of below 100 nm was readily achieved. The surfactant was removed via a dialysis operation after polymerization. Egg lecithin vesicles (liposome) were prepared to mimic the membrane of a cell and to receive the released pyrene from the nanosphere carriers. The in vitro release profiles of pyrene toward different pH liposome vesicles were recorded as a function of time at 37 °C. It was found that release of pyrene from the core‐shell polymer matrix can be triggered by a change in the environmental pH. In particular the pyrene‐loaded nanospheres are capable of responding to a narrow window of pH change from pH = 5, 6, to 7 and can achieve a significant pyrene release of above 80% within 90 h. The rate of release increased with a decrease in pH. A first‐order kinetic model was proposed to describe the rate of release with respect to the concentration of pyrene in the polymer matrix. The first‐order rate constant of release k was thus determined as 0.049 h^?1 for pH = 5; 0.043 h^?1 for pH = 6; and 0.035 h^?1 for pH = 7 at 37 °C. The release of pyrene was considered to follow a diffusion‐controlled mechanism. The synthesis and encapsulation process developed herein provides a new approach to prepare smart nanoparticles for efficient delivery of hydrophobic drugs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4440–4450     

Self‐Assembled Fluorodendrimers Combine the Features of Lipid and Polymeric Vectors in Gene Delivery

An ideal vector in gene therapy should exhibit high serum stability, excellent biocompatibility, a desired transfection efficacy and permeability into targeted tissues. Here, we describe a class of low‐molecular‐weight fluorodendrimers for efficient gene delivery. These materials self‐assemble into uniform nanospheres and allow for efficient transfection at low charge ratios and very low DNA doses with minimal cytotoxicity. Our results demonstrate that these vectors combine the features of synthetic gene vectors such as liposomes and cationic polymers and present promising potential for clinical gene therapy.     

Fabrication of Reduction‐Sensitive Amphiphilic Cyclic Brush Copolymer for Controlled Drug Release

The cyclic brush polymers, due to the unique topological structure, have shown in the previous studies higher delivery efficacy than the bottlebrush analogues as carriers for drug and gene transfer. However, to the best of knowledge, the preparation of reduction‐sensitive cyclic brush polymers for drug delivery applications remains unexplored. For this purpose, a reduction‐sensitive amphiphilic cyclic brush copolymer, poly(2‐hydroxyethyl methacrylate‐g‐poly(ε‐caprolactone)‐disulfide link‐poly(oligoethyleneglycol methacrylate)) (P(HEMA‐g‐PCL‐SS‐POEGMA)) with reducible block junctions bridging the hydrophobic PCL middle layer and the hydrophilic POEGMA outer corona is designed and synthesized successfully in this study via a “grafting from” approach using sequential ring‐opening polymerization (ROP) and atom transfer free radical polymerization (ATRP) from a cyclic multimacroinitiator PHEMA. The resulting self‐assembled unimolecular core–shell–corona (CSC) micelles show sufficient salt stability and efficient destabilization in the intracellular reducing environment for a promoted drug release toward a greater therapeutic efficacy relative to the reduction‐insensitive analogues. The overall results demonstrate the reducible cyclic brush copolymers developed herein provides an elegant solution to the tradeoff between extracellular stability and intracellular high therapeutic efficacy toward efficient anticancer drug delivery.     

In situ polymerization and morphology of polypyrrole obtained in water‐soluble polymer templates

Several water‐soluble polymers were used as templates for the in situ polymerization of pyrrole to determine their effect on the generation of nanosized polypyrrole (PPy) particles. The polymers used include: polyvinyl alcohol (PVA), polyethylene oxide (PEO), poly(vinyl butyral), polystyrene sulfonic acid, poly(ethylene‐alt‐maleic anhydride) (PEMA), poly(octadecene‐alt‐maleic anhydride), poly(N‐vinyl pyrrolidone), poly(vinyl butyral‐co‐vinyl alcohol‐co‐vinyl acetate), poly(N‐isopropyl acrylamide), poly(ethylene oxide‐block‐propylene oxide), hydroxypropyl methyl cellulose, and guar gum. The oxidative polymerization of pyrrole was carried out with FeCl₃ as an oxidant. The morphology of PPy particles obtained after drying the resulting aqueous dispersions was examined by optical microscopy, and selected samples were further analyzed via atomic force microscopy. Among the template polymers, PVA was the most efficient in generating stable dispersions of PPy nanospheres in water, followed by PEO and PEMA. The average size of PPy nanospheres was in the range of 160 nm and found to depend on the molecular weight and concentration of PVA. Model reactions and kinetics of the polymerization reaction of pyrrole in PVA were carried out by hydrogen ¹H NMR spectroscopy using ammonium persulfate as an oxidant. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Electro‐Controlled Living Cationic Polymerization

Cationic polymerizations have long been industrialized; however, stimulus‐regulated cationic polymerization remains to be developed. An electrochemically controlled living cationic polymerization is presented for the first time. In the presence of external potential and organic‐based electrocatalyst, a series of monomers can be polymerized under a cationic chain‐transfer mechanism. The resulting polymers exhibit well‐defined molecular mass, narrow dispersity, and good chain‐end fidelity. By controlling the external potential to switch the electrocatalyst between its oxidized and reduced states, ON/OFF polymerization can be achieved. This method is a versatile way to a large range of monomers, including vinyl ether‐type and p‐substituted styrene‐type monomers. Given the sustainability feature and broad interest of electrochemical synthetic techniques, we envisaged that this method would lead a new direction of external regulated living ionic polymerization.     

Monomer Protonation‐Dependent Surface Polymerization to Achieve One‐Step Grafting Cross‐Linked Poly(4‐Vinylpyridine) Onto Core–Shell Fe3O4@SiO2 Nanoparticles

Functional polymer‐grafting silica nanoparticles hold great promise in diverse applications such as molecule recognition, drug delivery, and heterogeneous catalysis due to high density and uniform distribution of functional groups and their tunable spatial distance. However, conventional grafting methods from monomers mainly consist of one or more extra surface modification steps and a subsequent surface polymerization step. A monomer protonation‐dependent surface polymerization strategy is proposed to achieve one‐step uniform surface grafting of cross‐linked poly(4‐vinylpyridine) (P4VP) onto core–shell Fe₃O₄@SiO₂ nanostructures. At an approximate pH, partially protonated 4VP sites in aqueous solution can be strongly adsorbed onto deprotonated silanol groups ( Si O⁻) onto Fe₃O₄@SiO₂ nanospheres to ensure prior polymerization of these protonated 4VP sites exclusively onto Fe₃O₄@SiO₂ nanoparticles and subsequent polymerization of other 4VP and divinylbenzene monomers harvested by these protonated 4VP monomers onto Fe₃O₄@SiO₂ nanoparticles, thereby achieving direct grafting of cross‐linked P4VP macromolecules onto Fe₃O₄@SiO₂ nanoparticles.     

New Design of Thiol‐Responsive Degradable Polylactide‐Based Block Copolymer Micelles

A new design to synthesize thiol‐responsive degradable polylactide (PLA)‐based micelles having a disulfide linkage in the middle of triblock copolymers is reported. They were synthesized by a new method that centers on the use of a disulfide‐labeled diol as an initiator for ring‐opening polymerization, followed by controlled radical polymerization. These well‐controlled copolymers with monomodal and narrow molecular weight distribution (M _w/M _n < 1.15) self‐assembled to form aqueous micellar aggregates with disulfide‐containing PLA cores, which is not toxic to cells. Central disulfide linkages were cleaved in response to thiols; such thiol‐triggered degradation enhanced the release of encapsulated anticancer drugs.     

Ring‐Opening Polymerization of Prodrugs: A Versatile Approach to Prepare Well‐Defined Drug‐Loaded Nanoparticles

The synthesis of polymer–drug conjugates from prodrug monomers consisting of a cyclic polymerizable group that is appended to a drug through a cleavable linker is achieved by organocatalyzed ring‐opening polymerization. The monomers polymerize into well‐defined polymer prodrugs that are designed to self‐assemble into nanoparticles and release the drug in response to a physiologically relevant stimulus. This method is compatible with structurally diverse drugs and allows different drugs to be copolymerized with quantitative conversion of the monomers. The drug loading can be controlled by adjusting the monomer(s)/initiator feed ratio and drug release can be encoded into the polymer by the choice of linker. Initiating these monomers from a poly(ethylene glycol) macroinitiator results in amphiphilic diblock copolymers that spontaneously self‐assemble into micelles with a long plasma circulation, which is useful for systemic therapy.     

Charge‐transfer piperazine‐containing polymeric systems via ring‐opening metathesis polymerization

This article describes the synthesis of piperazine‐containing homopolymer systems via ring‐opening metathesis polymerization (ROMP). These systems were subsequently used as electron donors in the formation of charge‐transfer (CT) complexes. Using exo‐N‐(6‐bromohexyl)‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxamide as a starting material, monomers were synthesized to act as electron donors. The amine group at the “open” end of the piperazine was either left open or alkylated with various alkyl groups. The monomers' ability to act as electron donors and their polymerization rates were studied. After initial photometric titration studies using 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) as an electron acceptor proved that these monomers would act as electron donors, they were subsequently polymerized into homopolymers via ROMP. The experimental results showed that a methanol:chloroform mixed solvent system enhanced the rate of polymerization over a single solvent (chloroform) system. Studies also showed that the alkylated piperazine‐containing monomer had a faster rate of polymerization than the secondary piperazine monomer. These monomers were used to make piperazine‐containing homopolymers via ROMP and the resulting polymers, like the monomers, also functioned as electron donors. Potential functions of these polymers include electronics, solar cells, optical systems, and biological applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5034–5043, 2009     

Regioselective Ring‐Opening Polymerization of a Polyhydroxycarboxylic Acid for the Synthesis of a Nanoscale Carrier Material with pH‐Dependent Stability and Sustained Drug Release

Synthetic polyesters are usually composed of monohydroxycarboxylic acids to avoid the problem of regioselectivity during ring‐opening polymerization. In contrast, the linear polyester BICpoly contains four secondary OH groups and is nevertheless esterified regioselectively at only one of these positions. Neither the synthesis of the tricyclic monomers nor the ring‐opening polymerization requires protecting groups, making BICpoly an attractive novel and biocompatible polymer. BICpoly nanoparticles can be loaded with low‐molecular weight drugs or coated onto surfaces as thin films. The release of loaded compounds makes BICpoly an attractive depot for drug release, as shown herein by loading BICpoly with dyes or the cytostatic drug doxorubicin. BICpoly is distinguishable from other polymers by its characteristic pH‐dependent degradation.     

Solvent‐free ring‐opening polymerization of cyclohexene oxide catalyzed by palladium chloride

In this study, we have for the first time demonstrated that palladium chloride (PdCl₂) is an efficient catalyst for ring‐opening polymerization of cyclohexene oxide in a solvent‐free condition. The polymerization product was in atactic structure, and reaction conditions, such as reaction temperature, time, and catalyst amount, showed effects on polymerization conversion yield, turnover number, and number‐average molecular weight of the resulting poly(cyclohexene oxide). PdCl₂ catalysis follows a cationic ring‐opening mechanism. The polymerization result is highly determined by the chemical structure of the monomers.     

Synergistic interaction of epoxides and N‐vinylcarbazole during photoinitiated cationic polymerization

A kinetic study was conducted of the independent photoinitiated cationic polymerization of a number of epoxide monomers and mixtures of these monomers with N‐vinylcarbazole. The results show that these two different classes of monomers undergo complex synergistic interactions with one another during polymerization. It was demonstrated that N‐vinylcarbazole as well as other carbazoles are efficient photosensitizers for the photolysis of both diaryliodonium and triarylsulfonium salt photoinitiators. In the presence of large amounts of N‐vinylcarbazole, the rates of the cationic ring‐opening photopolymerization of epoxides are markedly accelerated. This effect has been ascribed to a photoinitiated free‐radical chain reaction that results in the oxidation of monomeric and polymeric N‐vinylcarbazole radicals by the onium salt photoinitiators to generate cations. These cations can initiate the ring‐opening polymerization of the epoxides, leading to the production of copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3697–3709, 2000     

Disulfide‐centered star‐shaped polypeptide‐PEO block copolymers for reduction‐triggered drug release

Disulfide‐centered star‐shaped poly(ε‐benzyloxycarbonyl‐l ‐lysine)‐b‐poly(ethylene oxide) block copolymers (i.e., A₂B₄ type Cy‐PZlys‐b‐PEO) were synthesized by the combination of ring‐opening polymerization and thiol‐yne chemistry. Their molecular structures and physical properties were characterized in detail by FTIR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscope. Despite mainly exhibiting an α‐helix conformation, the inner PZlys blocks within copolymers greatly prohibited the crystallinity of the outer PEO blocks and presented a liquid crystal phase transition behavior in solid state. These block copolymers Cy‐PZlys‐b‐PEO self‐assembled into nearly spherical micelles in aqueous solution, which had a hydrophobic disulfide‐centered PZlys core surrounded by a hydrophilic PEO corona. As monitored by means of DLS and TEM, these micelles were progressively reduced to smaller micelles in 10 mM 1,4‐dithiothreitol at 37 °C and finally became ones with a half size, demonstrating a reduction‐sensitivity. Despite a good drug‐loading property, the DOX‐loaded micelles of Cy‐PZlys‐b‐PEO exhibited a reduction‐triggered drug release profile with an improved burst‐release behavior compared with the linear counterpart. Importantly, this work provides a versatile strategy for the synthesis of the disulfide‐centered star‐shaped polypeptide block copolymers potential for intracellular glutathione‐triggered drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2000–2010     

Photoresponsive Cross‐linked Polymeric Particles for Phototriggered Burst Release

We synthesized a series of cross‐linked photoresponsive polymeric particles with photolabile monomers and cross‐linkers through miniemulsion polymerization. These particles are quite stable in dark, while light irradiation caused the breakage of particles and the efficient release of encapsulated contents up to 95% based on Nile red fluorescence. Photoswitches of particle systems were confirmed by fluorescence spectroscopy, SEM and colorimetry. Particle uptake and triggered release in RAW264.7 cells were confirmed by fluorescein diacetate loaded particles.     

Controlled Synthesis of N‐Doped Carbon Nanospheres with Tailored Mesopores through Self‐Assembly of Colloidal Silica

Limited strategies have been established to prepare monodisperse mesoporous carbon nanospheres (MCNs) with tailored pore sizes. In this work, a method is reported to synthesize MCNs by combining polymerization of aniline with co‐assembly of colloidal silica nanoparticles. The controlled self‐assembly behavior of colloidal silica enables the formation of uniform composite nanospheres and convenient modulation over mesopores. After carbonization and removal of sacrificial templates, the resultant MCNs possess tunable mesopores (7–42 nm) and spherical diameters (90–300 nm), as well as high surface area (785–1117 m² g^?1), large pore volume (1.46–2.01 cm³ g^?1) and abundant nitrogen moieties (5.54–8.73 at %). When serving as metal‐free electrocatalysts for the oxygen reduction reaction (ORR), MCNs with an optimum pore size of 22 nm, compared to those with 7 and 42 nm, exhibit the best ORR performance in alkaline medium.     

Synthesis and characterization of tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers via RAFT polymerization

A new bipyridine‐functionalized dithioester was synthesized and further used as a RAFT agent in RAFT polymerization of styrene and N‐isopropylacrylamide. Kinetics analysis indicates that it is an efficient chain transfer agent for RAFT polymerization of the two monomers which produce polystyrene and poly(N‐isopropylacrylamide) polymers with predetermined molecular weights and low polydispersities in addition to the end functionality of bipyridine. The bipyridine end‐functionalized polymers were further used as macroligands for the preparation of star‐shaped metallopolymers. Hydrophobic polystyrene macroligand combined with hydrophiphilic poly(N‐isopropylacrylamide) was complexed with ruthenium ions to produce amphiphilic ruthenium‐cored star‐shaped metallopolymers. The structures of these synthesized metallopolymers were further elucidated by UV–vis, fluorescence, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) as well as NMR techniques. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4225–4239, 2007     

TiO2 Nanospheres: A Facile Size‐Tunable Synthesis and Effective Light‐Harvesting Layer for Dye‐Sensitized Solar Cells

A facile route to synthesize amorphous TiO₂ nanospheres by a controlled oxidation and hydrolysis process without any structure‐directing agents or templates is presented. The size of the amorphous TiO₂ nanospheres can be easily turned from 20 to 1500 nm by adjusting either the Ti species or ethanol content in the reaction solution. The phase structure of nanospheres can be controlled by hydrothermal treatment. The TiO₂ nanospheres show excellent size‐dependent light‐scattering effects and can be structured into a light‐harvesting layer for dye‐sensitized solar cells with a quite high power conversion efficiency of 9.25 %.     

Dual‐templates molecularly imprinted monolithic columns for the evaluation of serotonin and histamine in CEC

To extend the application of molecularly imprinted polymers, the dual‐templates molecularly imprinted monolithic columns were developed in a capillary format. Two templates serotonin and histamine were simultaneously imprinted using two different functional monomers such as methacrylic acid (MAA) and methylenesuccinic acid (MSA) in a mixture of ethylene glycol dimethacrylate (EDMA) as a cross‐linker and AIBN as polymerization initiator dissolved in DMF as porogen. The resulting molecular imprinted polymers (MIPs) were characterized based on their performance in the CEC separation of two imprinted templates. The optimization parameters such as pH, ACN composition, and concentration of the eluent were varied to achieve best resolution and efficiency for CEC separation of templates with each MIP column. It was found that the MIP monolith column fabricated using MSA offered better resolution and separation efficiency compared to column fabricated with MAA. This work utilized the dual‐templates imprinting approach successfully and broadens the scope of multi‐templates imprinting capabilities in capillary format in CEC application.     

Side‐chain ferrocene‐containing (meth)acrylate polymers: Synthesis and properties

A comprehensive investigation on the synthesis and properties of a series of ferrocene‐containing (meth)acrylate monomers and their polymers that differ in the linkers between the ferrocene unit and the backbone was carried out. The side‐chain ferrocene‐containing polymers were prepared via atom transfer radical polymerization. The kinetic studies indicated that polymerization of most monomers followed a “controlled”/living manner. The polymerization rates were affected by the vinyl monomer structures and decreased with an increase of the linker length. Methacrylate polymerization was much faster than acrylate polymerization. The optical absorption of monomers and polymers was affected by the linkers. Thermal properties of these polymers can be tuned by controlling the length of the linker between the ferrocene unit and the backbone. By increasing the length of the linker, the glass transition temperature ranged from over 100 to ?20 °C. Electrochemical properties of both monomers and polymers were characterized. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Fabrication of poly(aniline‐co‐pyrrole) hollow nanospheres with Triton X‐100 micelles as templates

A one‐step route has been reported for the fabrication of poly(aniline‐co‐pyrrole) (PACP) copolymer hollow nanospheres via the oxidation polymerization of a mixture of aniline and pyrrole in the presence of Triton X‐100. It was found that the variations in polymerization conditions, such as the concentrations of Triton X‐100 and comonomers, and [pyrrole]/[aniline] molar ratios, could change the size and uniformity of copolymer hollow nanospheres. The result of DLS has attested the presence of the spherical Triton X‐100 micelles swelled by the comonomers in reaction system, and such micelles might play template for the formation of hollow nanospheres, followed by developing a possible formation mechanism. The chemical structures and crystallinity of products were characterized by FTIR, UV–visible, ¹H NMR spectra, and XRD patterns, respectively, to prove the copolymer chemical structures of hollow nanospheres. The thermal‐stability and solubility of PACP were improved compared with homopolymers (polyaniline and pyrrole). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3563–3572, 2008