Efficient production of uniform nanometer‐sized polymer vesicles in stirred‐tank reactors

Polymer vesicles, so‐called polymersomes, gain more and more attention as potential carriers for medical and biotechnological applications. To put the production of these nanocompartments into action at an industrial scale, an efficient and scalable process has to be established. Moreover, being able to control the resulting particle size distribution (PSD) is vital. In this work, the amphiphilic triblock copolymer poly(2‐methyloxazoline)₁₅–poly(dimethylsiloxane)₆₈–poly(2‐methyloxazoline)₁₅ is formed into polymersomes in miniaturized stirred‐tank reactors. Varying flow conditions have a huge impact on the resulting PSD. Dynamic light scattering measurements show that driving a S‐shaped stirrer at 4000 rpm in unbaffled reactors leads to a monomodal PSD with a low polydispersity index (PDI<0.2). Vesicles with a mean diameter of 200 nm are achieved within less than 1 h in a single production step. The robustness of the established process is shown by producing uniform polymersomes at different temperatures and varying pH and buffer molarities. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43274.     

Mechanical control of foaming in stirred‐tank reactors

The foam‐breaking characteristics of rotating‐disk mechanical foam‐breakers (MFRDs) fitted to stirred‐tank reactors (STRs) containing various foaming liquids were evaluated. The critical disk rotational speed, N_c, required for foam‐breaking and the liquid hold‐up, ?_L, in ascending foam reflected, respectively, the foam‐breaking behaviour of MFRDs and the foaming behaviour of STRs. Empirical equations for the prediction of N_c and ?_L, which can be applied independently of the type, concentration and temperature of foaming liquid, were obtained. The foam‐breaking power, P_kc, of MFRDs was also clarified in relation to the level of ?_L which is related to the difficulty or ease of mechanical foam‐breaking. © 2001 Society of Chemical Industry     

Long‐range‐ordered,hexagonally packed nanoporous membranes from degradable‐block‐containing diblock copolymer film templates

Polystyrene (PS)‐b‐polylactide (PLA) diblock copolymers with different molecular weights and fractions were synthesized through a combination of living anionic polymerization and controlled ring‐opening polymerization. Then, the PS–PLA films were guided to phase‐separate by self‐assembly into different morphologies through casting solvent selection, solvent evaporation, and thermal and solvent‐field regulation. Finally, perpendicularly oriented PS–PLA films were used as precursors for PS membranes with an ordered periodic nanoporous structure; this was achieved by the selective etching of the segregated PLA domains dispersed in a continuous matrix of PS. Testing techniques, including IR, ¹H‐NMR, gel permeation chromatography, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were used to determine the chemical structure of the PS–PLA copolymer and its film morphology. AFM images of the self‐assembled PS‐PLA films indicate that vertical tapers of the PLA domains were generated among PS continuum when either toluene or tetrahydrofuran was used as the annealing solvent. The SEM images certified that the chemical etching of the PLA component from the self‐assembled PS–PLA films led to a long‐range‐ordered array of hexagonally packed nanoporous membranes with a diameter about 500 nm and a center‐to‐center distance of 1700 nm. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39638.     

A general template for synthesis of hollow microsphere with well‐defined structure

Using chitooligosaccharides (COS) as the backbones and polycaprolactones (PCL) as the branches, a novel type of amphiphilic graft copolymers with a large amount of free ? OH and ? NH₂ groups remained on the COS backbones was synthesized. The obtained Chitooligosaccharide‐graft‐poly(ε‐caprolactone)(COS‐g‐PCL) was self‐assembled into giant vesicles which served as templates for the preparation of hollow spheres of a series of metals(Au, Ag, Cu, Pt, and Pd). The method involved the initial mixing of COS‐g‐PCL and metal‐containing groups or metal ions to generate corresponding complex, followed by adding the selective solvent of water to induce the self‐assembly of the graft copolymers into giant vesicles; Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. In addition, hybrid hollow spheres with fluorescent quantum dots and silica hollow spheres were also prepared by slightly modified procedures. A preliminary study on the trinitrotoluene sensor of CdS/vesicle hybrid hollow spheres revealed a considerable sensitivity, which exemplifies the distinct properties imparted by the hybrid hollow structure. All of the results demonstrate that the giant vesicles self‐assembled from COS‐g‐PCL could be utilized as effective templates for the synthesis of various hollow spheres. Using Chitooligosaccharide‐graft‐poly(ε‐caprolactone) vesicles as general templates, the hollow spheres of a series of metals such as Au, Ag, Cu, and Pt were produced. The method involved the initial absorption of metal ions from solution into the functional surface layer of the graft copolymer giant vesicles. Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Application of the biodegradable diblock copolymer poly(L‐lactide)‐block‐poly(L‐cysteine): Drug delivery and protein conjugation

A novel approach to self‐assembled and shell‐crosslinked (SCL) micelles from the diblock copolymer poly(L ‐lactide)‐block‐poly(L ‐cysteine) to be used as drug and protein delivery carriers is described. Rifampicin was used as a model drug. The drug‐loaded SCL micelles were obtained by self‐assembly of the copolymer in the presence of the drug in aqueous media. Their morphology and size were studied with dynamic light scattering and field emission scanning electron microscopy. The rifampicin loading capacity and encapsulation efficiency were studied with ultraviolet–visible spectrophotometry. The drug‐release rate in vitro depended on the oxidizing and reducing environment. Moreover, a straightforward approach to the conjugation of the copolymer with bovine serum albumin (BSA) was developed, and a gel electrophoresis test demonstrated that this conjugated BSA could be reversibly released from the copolymer substrate under reducing conditions. In conclusion, this L ‐cysteine copolymer can be used in drug delivery and in protein fixation and recovery. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparison between the self‐assembling behaviors of PLLA‐PEO‐PLLA triblock copolymers and PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers

Poly(L ‐lactic acids) (PLLAs) were grafted to both ends of poly(ethylene oxide) (PEO) to produce biocompatible amphiphilic PLLA‐PEO‐PLLA triblock copolymers. The self‐assembling behaviors of two PLLA‐PEO‐PLLA copolymers in aqueous solutions were examined by Dynamic Light Scattering and Transmission Electron Microscopic techniques. PLLA‐PEO‐PLLA formed spherical micelles, whereas PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers were reported to produce vesicles. It is believed that the PPO segment within the PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers has a dominant role in the formation of vesicles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Atomic force microscopy study of self‐assembly behaviors of hydrophobic poly(n‐butyl methacrylate)‐block‐polydimethylsiloxane‐block‐poly(n‐butyl methacrylate) ABA triblock copolymers

Poly(n‐butyl methacrylate)‐block‐polydimethylsiloxane‐block‐poly(n‐butyl methacrylate) (PBMA‐block‐PDMS‐block‐PBMA) ABA triblock copolymers were synthesized successfully via atom‐transfer radical polymerization using PDMS as macroinitiator. The effects of PDMS content and substrate nature on self‐assembly behaviors of PBMA‐block‐PDMS‐block‐PBMAs were systematically studied using atomic force microscopy. Two series of triblock copolymers with different molecular weights and compositions, i.e. PBMA‐block‐PDMSA12‐block‐PBMAs and PBMA‐block‐PDMSA21‐block‐PBMAs, were used, where the latter were of a higher PDMS content than the former. On silicon wafer, it was found that only spherical structures formed after annealing films spin‐coated from chloroform solutions of PBMA‐block‐PDMSA12‐block‐PBMAs. In contrast, films of PBMA‐block‐PDMSA21‐block‐PBMAs formed semi‐continuous structures. On mica wafer, it was found that ordered cylindrical pores formed after annealing films spin‐coated from chloroform solutions of PBMA‐block‐PDMSA12‐block‐PBMAs. In contrast, films of PBMA‐block‐PDMSA21‐block‐PBMAs formed isolated cylinders or worm‐like morphologies. Copyright © 2011 Society of Chemical Industry     

Construct biomimetic giant vesicles via self‐assembly of poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L‐lactide)

The poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D ,L ‐lactide) (PMPC‐b‐PLA) was specially designed to develop biomimetic giant vesicles (GVs) and giant large compound vesicles via a simple spontaneous assemble in aqueous solution. The weight fraction of the hydrophilic PMPC block (f_PC) was proved to play an important role in the size and morphology control of the self‐assembled aggregates. The GVs with controlled micrometer size and biomimetic PMPC corona have great potential as artificial cell models. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Self‐assembling amphiphilic PEGylated block copolymers obtained through RAFT polymerization for drug‐delivery applications

In this work, ring‐opening polymerization and reversible addition‐fragmentation chain transfer polymerization (RAFT) have been employed for the production of block copolymers where the backbone is brushed with poly(ethylene glycol) (PEG) and polyester chains. Because of their amphiphilic properties, they are able to self‐assemble in water, forming micelles. Molecular dynamics simulations have been accomplished to study the behavior of the copolymer single chain in water, and the self‐assembly properties have been characterized and correlated to the copolymer structure in terms of critical micellar concentration and particle size. As a proof of their flexibility, these materials have been employed for the production of polymer–lipid hybrid nanoparticles with tunable dimensions (from 120 to 260 nm) adopted for the controlled release of anticancer compounds (paclitaxel and curcumin). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43084.     

Copolymer‐induced silk‐based hydrogel with porous and nanofibrous structure

A novel physical blend method was developed to accelerate the self‐assembly process of silk fibroin (SF) solution into porous and nanofibrous hydrogel by temperature‐sensitive copolymer. Silk‐based hydrogel was firstly achieved through blending SF solution with copolymer aqueous solution and then removed the copolymer from blend solution by heat treatment (50°C) after 24 h hydrogelation. Copolymer molecules would interact with SF molecules resulting in reduction of copolymer micelles, which further affect the hydrogelation of SF solutions. Copolymers could be separated from blend solution by heat treatment under an acceptable temperature (50°C), especially the copolymer₂. Fourier transform infrared (FTIR) and X‐ray diffraction showed the blending of copolymer significantly accelerated the self‐assembly of SF into physically crosslinked β‐sheet crystals at room temperature which led to the sol‐gel transition. Results from DTA and X‐ray diffraction showed that the effect of copolymer on crystalline structure of SF in silk‐based hydrogel was very weak. SF molecules transformed from distributed globular nanoparticles to nanofilaments clustered during hydrogelation, resulting in the porous and nanofibrous structure of silk‐based hydrogel. Furthermore, silk‐based hydrogel was prepared in aqueous solution avoiding organic solvents and harsh processing conditions, suggesting that this silk‐based hydrogel could be a potential candidate scaffold for biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Water‐dispersible porous polyisoprene‐block‐poly(acrylic acid) microspheres

Two polyisoprene‐block‐poly(tert‐butyl acrylate) (PI‐b‐PtBA) samples and a poly(tert‐butyl acrylate) (PtBA) homopolymer (hPtBA) were prepared by anionic polymerization and characterized by light scattering, size exclusion chromatography, and NMR. The tert‐butyl groups were removed from one of the diblocks to yield amphiphilic polyisoprene‐block‐poly(acrylic acid) (PI‐b‐PAA). PI‐b‐PAA was then used as the surfactant to disperse dichloromethane containing PI‐b‐PtBA and hPtBA at different weight ratios as oil droplets in water. Solid microspheres containing segregated polyisoprene (PI) and PtBA/hPtBA domains were obtained after dichloromethane evaporation. Permanent microspheres were obtained after PI domain crosslinking with sulfur monochloride. Porous microspheres were produced after the hydrolysis of PtBA and the extraction of the homopoly(acrylic acid) chains. The shape and connectivity of the poly(acrylic acid)‐lined pores were tuned by changes in the PtBA/hPtBA content in the precursor microspheres. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2785–2793, 2003     

Highly efficient electrically conductive networks in carbon‐black‐filled ternary blends through the formation of thermodynamically induced self‐assembled hierarchical structures

Highly efficient electrical conductive networks were constructed in carbon‐black (CB)‐filled polyoxymethylene (POM)–thermoplastic polyurethane (TPU)–polyamide 6 (PA6) ternary blends through the formation of a hierarchical structure composed of a minor PA6 phase as droplets inside one major phase (TPU) and CB particles localized at the TPU–PA6 interface by thermodynamically induced self‐assembly. The hierarchical structure was thermodynamically predicted on the basis of the minimization of total interfacial energies and confirmed by electron microscopy. The degrees of the TPU phase continuity before and after the addition of PA6 were determined by solvent‐extraction experiments. The percolation threshold of CB decreased by 50% compared to that in the POM–TPU binary blend because of the more efficient formation of a CB conductive network through CB‐covered PA6 domains inside the TPU phase. The hierarchical structure not only increased the electrical conductivity of the composites but also improved their thermal stability in comparison with the simple structure formed by the homogeneously dispersed CB particles in POM. The method reported in this article can offer possibilities for improving the comprehensive properties of the conductive composites and the widening of their applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45877.     

In vitro degradability and stability of hydrophobically modified pH‐sensitive micelles using MPEG‐grafted poly(β‐amino ester) for efficient encapsulation of paclitaxel

Methoxypoly(ethylene glycol)‐grafted poly(β‐amino ester) was synthesized for the fabrication of pH‐sensitive micelles, and these micelles were modified with deoxycholic acid to facilitate the hydrophobic interaction between the micellar core and paclitaxel. The micelle properties were studied by dynamic light scattering and fluorescence spectrometry. An in vitro degradation study showed that the synthesized polymers degraded hydrolytically within 24 h under physiological conditions. The stability of paclitaxel‐loaded pH‐sensitive micelles was evaluated in vitro. The introduced deoxycholic acid more stabilized the micelles at pH 7.4 compared to the micelles without modification. But the pH‐sensitive region of the micelles was lowered from pH 6.8 to pH 5.8. These results indicate that pH‐sensitive micelles with improved stability have great potential as hydrophobic drug carriers for tumor targeting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Performance characteristics of mechanical foam‐breakers fitted to a stirred‐tank reactor

In a stirred‐tank reactor (STR), a comparison of the performance of mechanical foam‐breakers: a six‐blade turbine (F‐B), a six‐blade vaned disk (V‐D), a two‐blade paddle (T‐P), a conical rotor (C‐R), a fluid‐impact dispersion apparatus (FIDA) and a rotating disk mechanical foam‐breaker (MFRD) was carried out using defined foaming media. The foam‐breaking ranges (relative to the gas superficial velocity, U_g) of the T‐P, C‐R and FIDA were inferior to that of the F‐B, V‐D and MFRD. The power consumption, P_kc, for foam‐breaking in the MFRD was the lowest among the F‐B, V‐D and MFRD. Operation of the F‐B and V‐D in the STR caused a considerable amount of liquid droplets from the collapsed foam to be entrained with the exhaust air. © 2002 Society of Chemical Industry     

Self‐assembled structures in polystyrene‐block‐polyisoprene‐blend‐polystyrene and polystyrene‐block‐poly(methyl methacrylate)‐blend‐polystyrene or ‐blend‐poly(methyl methacrylate) in the strong segregation regime

This study deals with the investigation of microphase‐separated morphology and phase behaviour in blends of polystyrene‐block‐polyisoprene with homopolystyrene and blends of polystyrene‐block‐poly(methyl methacrylate) with homopoly(methyl methacrylate) or homopolystyrene in the strong segregation regime using small‐angle X‐ray scattering and transmission electron microscopy as a function of composition, molecular weight of homopolymers, r_M and temperature. Parameter r_M = M_H/M_C (where M_H is the molecular weight of homopolymer and M_C that of the corresponding block copolymer) was selected to encompass behaviour of the chains denoted as a ‘wet brush’ (i.e. r_M < 1). The relative domain spacing D/D_o increases in the regime 0 < r_M?1 with increasing concentration of homopolymer w_P and increasing r_M but depends on the specific implemented morphology. We tested a new approximate D/D_o versus w_P relation in the strong segregation regime using block copolymers of high molecular weights. It is shown that the parameters r_M and χ^3/2N determine the slope of the D/D_o versus w_P relation in the strong segregation regime and the new approximation generally matches the experimental data better than the approximations used so far. Copyright © 2010 Society of Chemical Industry     

Effect of block composition on the morphology,hydration, and transport properties of sulfonated PS‐b‐PEGPEM‐b‐PS

This work discusses the effect of block composition on the properties of proton conducting polymer membranes. A homopolymer and two block copolymers were synthesized using atom transfer radical polymerization. The homopolymer poly(ethylene glycol phenyl ether methacrylate) (PEGPEM) was used as a bifunctional macroinitiator. Polystyrene (PS), was added to both sides of PEGPEM (A) with two different percentages of PS (B) (i.e., 18 and 31%). These copolymers, BAB 18, BAB 31 and the homopolymer A, were completely sulfonated (SA, SBAB 18 and SBAB 31). The resulting polymers produced different water absorption values and transport properties for direct methanol fuel cell (DMFC) applications. The nanostructure and morphology of the casted membranes were studied using small‐angle X‐ray scattering and atomic force microscopy. The results revealed that all six membranes exhibited a disordered phase‐segregated morphology, which changed on sulfonation into small‐interconnected ionic domains. Normalized DMFC selectivities (proton conductivity over methanol permeability divided by the respective values for Nafion^®) were calculated and ranged from 1.16 (SBAB 31) to 15.30 (BAB 18), indicating that the performance of these materials can be comparable or better than Nafion^®. Transport property results also suggest that chemistry (block nature and composition), morphology and water content play a critical role in the transport mechanism of protons and methanol. For example, the percentage of B in BAB 18 provides shorter interstitial ionic distances and sufficient water content to produce high proton conductivity, while maintaining low methanol permeability in a multi‐ionic proton exchange membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44343.     

Preparation and self‐assembly of poly(diglycidyl maleate‐co‐stearyl methacrylate)

Poly(diglycidyl maleate‐co‐stearyl methacrylate) (P(DGMA‐co‐SMA)) with reactive epoxy groups was synthesized by reaction of poly(maleic anhydride‐co‐stearyl methacrylate) (P(MA‐co‐SMA)) and epichlorohydrin. The effect of precipitant on self‐assembly behaviors of the resultant copolymer was investigated. It was found that vesicles and nanotubule liked aggregates can be obtained through self‐assembly of P(DGMA‐co‐SMA) in THF solution using CH₃CH₂OH (EtOH) as precipitant while spheral aggregates can be obtained using H₂O as precipitant. The mechanism of the self‐assembly behavior was discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Self‐assembled nanoblends of functional polystyrene and a reactive aramid: Morphological and thermomechanical profile

Various blends composed of pure polystyrene (PS) and modified PS [amino‐functionalized polystyrene (PS–NH₂)] were prepared with a new aromatic polyamide obtained through the polycondensation of 1,5‐diaminonaphthalene and 1,4‐phenylenediamine with isophthaloyl chloride. The variation in the morphological and thermophysical profiles in the two blend systems with aramid loading were investigated. The amine functionality introduced to PS enhanced its compatibility with the polyamide because of the formation of an aramid‐graft‐PS copolymer. The grafting, hydrogen bonding, and phenylene‐ring (π–π) stacking between the chains of the two components finally nurtured self‐assembled nanostructured blends. A strong compatibilizing effect was observed for the 50, 60, and 70 wt % aramid blends, where an exceptionally inimitable cocontinuous self‐assembled morphology was formed by PS–NH₂/aramid. Significant developments in the morphology along with thermal and mechanical stability were observed for the reactive PS/aramid system. The most favorable mechanical and thermal data supported by the finest nanostructure were observed with 70 wt % polyamide addition. Future prospects may involve the formation of nanotemplates and nanostructured membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39954.     

Modification of SPPESK proton exchange membranes through layer‐by‐layer self‐assembly

Sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) composite membranes are fabricated through electrostatic layer‐by‐layer (LbL) self‐assembly method with chitosan (CS) and phosphotungstic acid (PWA) to enhance the proton conductivity and stability. The results demonstrate that LbL self‐assembly has different effects on the SPPESK membrane substrates with different sulfonation degrees (DSs). It elevates proton conductivity of the SPPESK membrane of lower DS and enhances swelling stability of the SPPESK membrane of higher DS. For instance, at 80°C, proton conductivity of the SPPESK0.74/(CS/PWA)₁ membrane (lower DS) increases by 16%–96.49 mS cm^?1, and swelling ratio of the SPPESK1.01/(CS/PWA)₃ membrane (higher DS) decreases from 58 to 29%. Attribute to the electrostatic interaction and ion cross‐linking networks, permeability of the SPPESK0.74/(CS/PWA)₃ membrane and the SPPESK1.01/(CS/PWA)₅ membrane are reduced by 45 and 30%, respectively. The results indicate that the LbL self‐assembly has broadened the available DS range for fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42867.