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The thermoresponsive nature of aqueous solutions of poly(N‐isopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo‐SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo‐SALS data suggest that this is due to a fragmentation of the aggregates followed by re‐aggregation at even higher temperatures. Although the 6‐arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point., How many arms? Aqueous solutions of poly(N‐isopropylacrylamide) (PNIPAAM) star polymers exhibit a complex thermosensitive behavior. Increasing the number of arms promotes aggregation below the cloud point. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Some of the samples exhibits fragmentation of the aggregates at temperatures above the cloud point, followed by re‐aggregation at even higher temperatures.

Xanthate is a class of non-toxic, rapid, and eco-friendly rubber vulcanization accelerator, but it is seldom used in the rubber industry because of its poor thermostability and ease of decomposition. To overcome these drawbacks, silica supported sodium isobutyl xanthate (silica-s-SIBX) was prepared by chemically bonding SIBX onto the silica surface. After loading, the initial degradation temperature (T0), maximum degradation temperature (Tp), and final decomposition temperature (Tf) of silica-s-SIBX were increased by 85.8, 118.9, and 146.9 °C, respectively. Meanwhile, silica-s-SIBX could not only improve the dispersion of fillers in the rubber but also enhance the interfacial interaction between silica and the rubber matrix. Therefore, it may offer new scientific and technological opportunities for preparation of green additives in the rubber industry.

Condensation of DNA helices into hexagonally packed bundles and toroids represents an intriguing example of functional organization of biological macromolecules at the nanoscale. The condensation models are based on the unique polyelectrolyte features of DNA, however here we could reproduce a DNA-like condensation with supramolecular helices of small chiral molecules, thereby demonstrating that it is a more general phenomenon. We show that the bile salt sodium deoxycholate can form supramolecular helices upon interaction with oppositely charged polyelectrolytes of homopolymer or block copolymers. At higher order, a controlled hexagonal packing of the helices into DNA-like bundles and toroids could be accomplished. The results disclose unknown similarities between covalent and supramolecular non-covalent helical polyelectrolytes, which inspire visionary ideas of constructing supramolecular versions of biological macromolecules. As drug nanocarriers the polymer– bile salt superstructures would get advantage of a complex chirality at molecular and supramolecular levels, whose effect on the nanocarrier assisted drug efficiency is a still unexplored fascinating issue.

Antibiotic resistance is an emerging threat to public health. The development of a new generation of antimicrobial compounds is therefore currently required. Here we report a novel antimicrobial polymer of chitosan/polypropylene carbonate nanoparticles (CS/PPC NPs). These were designed and synthesized from readily available chitosan and a reactive oligomer polypropylene carbonate (PPC)-derived epoxy intermediate. By employing a simple and efficient functionalized strategy, a series of micelle-like chitosan-graft-polypropylene carbonate (CS-g-PPC) polymers and chitosan–polypropylene carbonate (CS–PPC) microgels were prepared by reacting mono-/bis-epoxy capped PPC with chitosan. The chemical structure, particle size, and surface charge of the newly synthesized polymers were characterized by infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. The antimicrobial activities of these nanoparticles were determined in both Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). Minimum inhibitory concentration (MIC), the nanoparticle concentration needed to completely inhibit the bacterial growth, was found at 128 μg mL−1 to 1024 μg mL−1, strongly depending both on the nature of the epoxy-imine network formed from the functional groups (mono- or bis-capped epoxy groups reacting with amine groups) and the feed ratio of the functional groups (-epoxy/-NH2) between the functionalized PPC and chitosan. No hemolysis was observed at concentrations well in excess of the effective bacteria-inhibiting concentrations. These findings provide a novel strategy to fabricate a new type of nanoantibiotic for antimicrobial applications.

Understanding self-assembly of amphiphilic copolymers in aqueous solution is an important issue in many areas, e.g., in order to tailor-make carriers for drugs and genes. We have synthesized modified versions of the copolymer of type PEO-PPO-PEO (Pluronic, F127), with short (PCL(5)) or long (PCL(11)) PCL blocks at both ends. Turbidity, dynamic light scattering (DLS), small angle neutron scattering (SANS), and rheology measurements were carried out on dilute aqueous solutions of these polymers to investigate their self-assembly behavior. The DLS results clearly show that both micellization and inter-micellization can be controlled by polymer concentration, temperature, and length of the PCL block. The interplay between unimers, micelles, and clusters of micelles could be monitored and the size and size distribution of the species were determined. The SANS data could be portrayed by a spherical core-shell model at all considered conditions of temperature and concentration for F127 and PCL(5) apart from F127 at the lowest temperature measured. The SANS data for PCL(11) were described by a spherical core-shell model at low temperatures, whereas at elevated temperatures asymmetric sub-structures appeared and a cylindrical core-shell model was employed in the analysis of the data. The appearance of pronounced correlation peaks at elevated temperatures signalizes marked intermicellar interactions. The shear viscosity data revealed a minor shear thinning effect, suggesting that the interchain structures are rather stable and not easily disrupted. The work shows that PCL-modification of Pluronic has a large influence on the self-assembly process and on the final structure of the assemblies.

A novel linear cationic ABCBA pentablock terpolymer composed of a positively charged poly (3-acrylamidopropyl) trimethyl ammonium chloride)) (PAMPTMA (+)) block at both ends and two thermoresponsive poly ( N -isopropylacrylamide) (PNIPAAM) blocks separated by a hydrophilic poly(ethylene glycol) (PEG) block was synthesized via a “one-pot” atom transfer radical polymerization procedure (ATRP). The chemical composition of the pentablock terpolymer was confirmed by nuclear magnetic resonance (NMR) and asymmetric flow field-flow fractionation (AFFFF). Depending on the polymer concentration in aqueous solution, this terpolymer forms unimers and self-assembled structures at elevated temperatures. The effect of concentration and temperature-induced self-assembling behavior of the pentablock terpolymer in aqueous solution was examined by using turbidimetry, shear viscosity, rheo-small angle light scattering (rheo-SALS), dynamic light scattering (DLS), and small angle neutron scattering (SANS). The turbidity measurements demonstrated that the formation of intermicellar structures and compaction of the complexes are function of both polymer concentration and temperature. The viscosity and rheo-SALS experiments elucidated the intricate interplay between building-up and breaking-up of interchain complexes under the influence of shear flow. The DLS experiments show the coexistence of small entities and interchain complexes at low temperatures and the evolution of large intermicellar structures at higher temperatures. At the highest temperatures, compaction of the complexes occurred. The results from SANS revealed significant temperature-induced changes of the copolymer structure on a semi-local dimensional scale.

The properties of synthesized diblock poly(N-isopropylacrylamide)-poly((3-acrylamidopropyl)trimethylammonium chloride) and triblock methoxy-poly(ethylene glycol)-poly(N-isopropylacrylamide)-poly((3-acrylamidopropyl)trimethylammonium chloride) cationic copolymers at the silica/aqueous interface are investigated using quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Moreover, dynamic light scattering is employed to assess the copolymers in terms of the hydrodynamic size and interchain aggregation. Although viscoelastic Voigt modeling of the QCM-D data suggests a comparable layer thickness for the copolymers on the silica surface, the AFM imaging and colloidal probe measurements reveal significant differences in surface coverage and thickness of the layers, which are discussed and compared with respect to the stabilization effect by the hydrophilic poly(ethylene glycol) block.

We tested the efficiency of 2 different antibiotics, rifampicin and oxolinic acid, against an established infection caused by fish pathogen Francisella noatunensis ssp. orientalis (F.n.o.) in zebrafish. The drugs were tested in the free form as well as encapsulated into biodegradable nanoparticles, either polylactic-co-glycolic acid (PLGA) nanoparticles or nanostructured lipid carriers. The most promising therapies were PLGA-rifampicin nanoparticles and free oxolinic acid; the PLGA nanoparticles significantly delayed embryo mortality while free oxolinic acid prevented it. Encapsulation of rifampicin in both PLGA and nanostructured lipid carriers enhanced its efficiency against F.n.o. infection relative to the free drug. We propose that the zebrafish model is a robust, rapid system for initial testing of different treatments of bacterial diseases important for aquaculture.

Reinforcing agents and accelerators are the most important auxiliaries for rubber industry. In this paper, ceric ammonium nitrate (CAN), for the first time, worked as a catalyst for hydroxyl groups in silica to prepare silica grafted sodium xanthate (SSX), which was used as an in-situ modified multifunctional rubber additive in this work. Compared with sodium isobutyl xanthate (SIBX), SSX has enhanced the initial and final degradation temperatures, achieving the improvement of 103 °C and 277 °C, respectively. Notably, owing to the powerful interaction between each component, SSX can be homogeneously dispersed in the natural rubber (NR) matrix in contrast to the seriously aggregated silica. Meanwhile, NR/SSX composites exhibited superior curing properties and showed an increase of 29.1% and 33.4% in the tensile strength and tear strength, respectively, compared to that of traditional 2-mercaptobenzothiazole (MBT) system. Since high-performance rubber composites can be obtained by introducing SSX, we believe that this work can provide a novel and facile approach to prepare natural silicate minerals-based vulcanization accelerators.

We report on the effect of different stimuli-responsive polymer shells on Fe@Au core-shell nanoparticles (NPs) with respect to thermoresponse as well as loading and release characteristics. The hybrid NP systems were investigated using a wide array of characterization techniques including dynamic light scattering, electrophoretic mobility, UV-visible spectroscopy, and scanning transmission electron microscopy. Three different polymeric shells were selected for loading and release of l-dopa: thiolated polyethylene glycol (PEG), poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAAM_AAc) microgel crosslinked with N,N′-methylenebis(acrylamide) (BIS), and finally concomitant PEG and PNIPAAM_AAc microgel (Fe@Au_PEG_Microgel). All three shells were found to exhibit high loading (∼10%) and encapsulation efficiencies up to 100 μg l-dopa/mg. Although the loading efficiencies are comparable for the three systems, Fe@Au_PEG_Microgel has the highest release (87%) at elevated temperature and acidic conditions. The attenuated release from the PEG-based systems can be attributed to stronger dipole-dipole interactions between the carboxyl group of PEG and the amino group of l-dopa.

The thermal responsive behavior of adsorbed layers of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAAM) and poly((3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA(+)) with γ-cyclodextrin (γ-CD) at the solid/liquid interface has been investigated using three in situ techniques: null ellipsometry, quartz–crystal microbalance with dissipation monitoring, and neutron reflectometry. The measurements provided information about the adsorbed amounts, the layer thickness, hydration and viscoelastic properties, and the interfacial structure and composition. The copolymers adsorb to silica with the cationic PAMPTMA(+) blocks sitting as anchors in a flat conformation and the PNIPAAM chains extending into the solution. The copolymer system alone exhibits reversible collapse above the lower critical solution temperature of PNIPAAM. The addition of γ-CD to pre-adsorbed copolymer layers results in a highly extended conformation as well as some loss of copolymer from the surface, which we discuss in terms of the formation of surface-invoked lateral steric repulsion of formed inclusion complexes. © 2017, The Author(s).

In the present study, aqueous solutions of a thermo-responsive negatively charged triblock copolymer methoxy-poly(ethylene glycol)- block -poly( N -isopropylacrylamide)- block -poly(2-succinic acid-propyloxyl methacrylate) (MPEG 45 - b -PNIPAAM 48 - b -PSAPMA 10 ), have been characterized in the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) surfactant, at a constant concentration of polymer and various levels of surfactant addition. For this purpose, dynamic light scattering (DLS) was used to probe the effect of the ionic surfactants on the size of the block copolymer species, and small-angle neutron scattering (SANS) was applied as a complementary technique to probe the structure on a mesoscopic length scale. The results obtained revealed that the addition of a surfactant to the copolymer solution leads to a decrease of the particle size, due to electrostatic repulsions and solubilization of the hydrophobic microdomains. By zeta potential analysis it was shown that the charge density of the surfactant-coated polymer moieties increases with increasing surfactant concentration. The turbidities of the polymer–surfactant mixtures were measured using a cloud point analyzer. Our data revealed that the behavior not only depends on the surfactant concentration, but it is also affected in some cases by temperature. In addition, cytotoxicity studies were carried out on mouse fibroblasts cells NIH–3T3 to evaluate the potential of the systems as drug delivery carriers. Results showed that the cytotoxicity of the polymer changes with surfactant addition, rising as the concentration of SDS increases but falling off with increasing DTAB concentration.

The self-assembly of two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (pNIPAAM) has been investigated. The effect of the mixing ratio and total polymer concentrations on the self-assembly of the components and on the phase stability of the mixtures was studied by dynamic light scattering, electrophoretic mobility, and turbidimetry measurements in water at 20 °C. The effect of the competing electrostatic and hydrophobic interactions on the nanostructure of negatively charged electrostatically self-assembled micelles bearing a pNIPAAM corona was investigated by small-angle X-ray scattering (SAXS). The electrostatic and hydrophobic interactions were controlled independently by tuning the ionic strength (from pure water to 50 mM NaCl) and the temperature (20-50 °C) of the investigated mixtures. The SAXS data could be fitted by a spherical micelle model, which has a smoothly decaying radial profile and a Gaussian star term that describes the internal structure of the micellar structures and possible attractive interactions between the polymer chains. At high temperature, a cluster structure factor was included for describing the formation of bulky clusters of the formed micelles. At low temperature and ionic strength, the formation of micelles with a coacervate core and hydrated pNIPAAM shell was observed. The structural evolution of the self-assembled micelles with increasing ionic strength and temperature could be followed, and finally at high ionic strength and temperature, the formation of inverted micelles with a hydrophobic core and polyelectrolyte shell could be identified.

Temperature-induced gelation of amphiphilic copolymers in aqueous media has attracted a great deal of interest in recent years. We have investigated phase behavior, gelation, rheology, and structure of modified versions of the water-soluble copolymer of type PEO-PPO-PEO (Pluronic, F127) with short (PCL(5)) or long (PCL(11)) poly(caprolactone) blocks at both ends. By visual inspection of the studied semidilute and concentrated polymer samples at various temperatures, gelation and phase separation could be mapped and the length of the PCL blocks had a strong impact on the observed features. By using oscillatory shear experiments, the gel points of the systems were determined and an interesting anomaly of the complex viscosity was observed at high frequencies where the moieties were kinetically arrested. This irregularity was strengthened for the PCL(11) copolymer and this was ascribed to bridging of the micelles due to the long PCL blocks. The mesoscopic structure of the systems was studied by using small angle neutron scattering. The position and amplitude of the observed correlation peak, which discloses vital intermicellar correlations in the scattering function depends on temperature, concentration, and the length of the PCL blocks. Frequently the scattering function could be portrayed by a spherical core-shell micelle model with hard sphere interaction between them. The estimated aggregation number (Nagg) was substantially affected by the PCL content of the polymer and a significant influence of polymer concentration and temperature on the value of Nagg was found.

A novel eco-friendly vulcanization accelerator, starch supported sodium isobutyl xanthate (SSX) has been synthesized firstly. The modification of starch using sodium isobutyl xanthate (SIBX) has improved the thermal stability significantly, and the vulcanization process of natural rubber (NR) could be accelerated by SSX at 145 ℃ accordingly. More importantly, SSX can be dispersed into NR matrix uniformly along with the strong interfacial interaction between SSX and NR, as evidenced by the constrained rubber chains around SSX surface. In addition, mechanical properties of the obtained NR have been enhanced remarkably, showing a 22.4 % increase in tensile strength when compared with traditional vulcanization accelerator. Laying on the fact that a novel vulcanization accelerator has been fabricated successfully using SIBX functionalized starch, new strategies for the preparation of green vulcanization accelerators and the functional application of biopolymers can be provided.

Therapeutic nanoparticles (NPs) have great potential to deliver drugs against human diseases. Encapsulation of drugs in NPs protects them from being metabolized, while they are delivered specifically to a target site, thereby reducing toxicity and other side-effects. However, non-specific tissue accumulation of NPs, for example in macrophages, especially in the spleen and liver is a general problem with many NPs being developed for cancer therapy. To address the problem of non-specific tissue accumulation of NPs we describe the development of the zebrafish embryo as a transparent vertebrate system for characterization of NPs against cancer. We show that injection of human cancer cells results in tumor-like structures, and that subsequently injected fluorescent NPs, either made of polystyrene or liposomes can be imaged in real-time. NP biodistribution and general in vivo properties can be easily monitored in embryos having selective fluorescent labeling of specific tissues. We demonstrate in vitro, by using optical tweezer micromanipulation, microscopy and flow cytometry that polyethylene glycol (PEG) coating of NPs decreases the level of adhesion of NPs to macrophages, and also to cancer cells. In vivo in zebrafish embryos, PEG coating resulted in longer NP circulation times, decreased macrophage uptake, and reduced adhesion to the endothelium. Importantly, liposomes were observed to accumulate passively and selectively in tumor-like structures comprised of human cancer cells. These results show that zebrafish embryo is a powerful system for microscopy-based screening of NPs on the route to preclinical testing.

The micellization behavior of a temperature and pH responsive pentablock terpolymer, poly(2-(N,N-diethylamino)ethylmethacrylate)-block-poly(N-isopropylacrylamide)-block-poly(ethylene glycol)-block-poly(N-isopropylacrylamide)-block-poly(2-(N,N-diethylamino)ethylmethacrylate, abbreviated as PDEAEMAx-b-PNIPAAMy-b-PEGz-b-PNIPAAMy-b-PDEAEMAx, was studied. Two variants of the polymer, with difference in block lengths, were examined using light scattering and small angle neutron scattering (SANS) as the main tools, with the aim of following nanostructural changes in the system with varying temperature and pH. With a sufficiently long PDEAEMA block, micelles of overall sizes around 50 nm and with a PDEAEMA-rich corona are formed at room temperature and at low pH. A change to a system with a PDEAEMA-rich core can be obtained via a jump in pH from 3 to 9. An increase in temperature will, at low pH, lead to formation of micelles also for the polymer with a short PDEAEMA block, with a transition around 42 °C. If the temperature increase is instead performed at pH 9, the transition to compact PDEAEMA-core micelles occurs at a slightly lower temperature (39 °C). This difference is attributed to the increased hydrophobic character for a system with deprotonated PDEAEMA-blocks.

We present a systematic investigation of a novel series of star polymers consisting of arms made up from poly(N-isopropylacrylamide)-b-poly(2-acrylamido-2-methylpropanesulfonate) (PNIPAAM-block-PAMPS) block copolymers. The polymers were synthesized as a 3-arm and 2-arm (i.e., a tetrablock copolymer) using a “core-first” method and a sequential atomic transfer radical polymerization (ATRP) protocol. Using asymmetric flow field-flow fractionation (AFFFF), Zetasizer, and small-angle X-ray scattering (SAXS), the phase behavior and nanostructure of the system in dilute solutions are studied in detail. While AFFFF equipped with a light scattering and refractive index detectors provides distribution of molecular weight and overall sizes in solution, we use SAXS combined with theoretical modeling to elucidate the inter- and intramolecular interactions of the star polymers. In particular, by employing a detailed model for a star-diblock copolymer assuming Gaussian chain statistics, we extract the chain conformatio...

The behavior of a range of different stimuli-responsive star poly(N-isopropylacrylamide) (PNIPAAM) polymers in water was investigated using small-angle X-ray scattering (SAXS). The samples of 1, 2, and 5 wt % PNIPAAM stars with 2, 3, 4, and 6 arms were measured at seven temperatures ranging from 15 to 36 °C, which covers the known lower critical solution temperature (LCST) for linear PNIPAAM. The data were fitted with a Gaussian star form factor, and interactions were accounted for by a random-phase approximation (RPA) expression. A clear LCST was observed at ∼32 °C for the four polymers in agreement with turbidity data on the same polymers. The molecular weight was calculated from the forward scattering, which showed reasonable agreement with the values expected from the synthesis and characterization. From the fits the root-mean-square radius of gyration ⟨Rg2⟩1/2 and the second virial coefficient A2 were obtained and compared with the literature.

The association properties of aqueous solutions of the anionic thermo-responsive triblock terpolymer n-octadecyl-poly(ethylene glycol)-block-poly(N-isopropyl acrylamide)-block-poly(2-acrylamido-2-methyl-1-propanesulfonic sodium), abbreviated as C18-PEG10-b-PNIPAAM54-b-PAMPS10, have been studied as a function of temperature and salinity. This polymer exhibits a lower critical solution temperature (LCST) owing to its PNIPAAM block, and the presence of charges at the end of the chain influences the interaction properties. The effect of ionic strength was examined in detail by means of turbidimetry, zeta-sizer, dynamic light scattering, densitometry, and small angle neutron scattering (SANS). A temperature increase was seen to promote the formation of large aggregates in this system, with a strong dependency on the ionic strength of the solution. Increasing the ionic strength was found to give a large and controllable decrease in the cloud point (CP) due to screening of the electrostatic interactions. The hydrodynamic radius was found to drop significantly upon the addition of salt. At temperatures above CP, the intermicellar clusters observed by dynamic light scattering were found to contract. Furthermore, zeta-potential measurements demonstrated that charges were forced out towards the surface of the micellar structures with increasing temperature due to the strong dehydration effect of the associating PNIPAAM blocks.

Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two-dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D H-1 NMR NOESY), dynamic light scattering, and small angle X-ray scattering measurements. Well-defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D H-1 NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1457-1469

Thermoresponsive amphiphilic biodegradable block copolymers of the type poly(e-caprolactone-co-lactide)-poly(ethylene glycol)-poly(e-caprolactone-co-lactide) (PCLA-PEGm-PCLA) have great potential for various biomedical applications. In the present study, we have surveyed the effects of PEG spacer length (m = 1000 and 1500), temperature, and polymer concentration on the self-assembling process to form supramolecular structures in aqueous solutions of the PCLA-PEGm-PCLA copolymer. This copolymer has a lower critical solution temperature, and the cloud point depends on both concentration and PEG length. Thermoreversible hydrogels are formed in the semidilute regime; the gel windows in the phase diagrams can be tuned by the concentration and length of the PEG spacer. The rheological properties of both dilute and semidilute samples were characterized; especially the sol-to-gel transition was examined. Small-angle neutron scattering (SANS) experiments reveal fundamental structural differences between the two co...

Hydrophobically modified hydroxyethylcellulose (HM-HEC) of different hydrophobicity has been used to stabilize pluronic gels against dissolution in an aqueous environment. While pluronic by itself dissolves within 1–2 days, the addition of HM-HEC can stabilize part of the gels from dissolving for a period of at least six months. A larger fraction of the gel remains undissolved when utilizing high HM-HEC concentrations and when the degree of hydrophobic modification is increased. The stabilization against fast dissolution makes these systems interesting for drug delivery purposes. The effect of HM-HEC addition on rheological properties of pluronic gels has also been examined. For a low pluronic concentration, the addition of HM-HEC increases the viscosity of the sample, shifts the gel transition to a lower temperature, and reduces the deviscosification of the pluronic gels at high temperatures. When the pluronic concentration is increased, the addition of HM-HEC only affects the sample viscosity at low tem...

Based on a parent diblock copolymer of poly(styrene)-b-poly(methacrylic acid), PS-b-PMAA, linear-b-amphiphilic comb (L-b-AC) ionic supramolecules [Soft Matter 2013, 9, 1540-1555] are synthesized in which the poly(methacrylate) backbone of the ionic supramolecular AC-block is neutralized by alkyl (Cn; n = 8, 12, and 16) trimethylammonium counterions (i.e., side chains) at various ion (pair) fractions X [i.e., counterion/side-chain grafting density; X = number of alkyl counterions (i.e., side chains) per acidic group of the parent PMAA block] these L-b-AC ionic supramolecules exhibit a spherical-in-lamellar hierarchical self-assembly. For these systems, (1) the effective Flory-Huggins interaction parameter between L- and AC-blocks chi'(Cn/x) was extracted, and (2) analysis of the lamellar microdomains showed that when there is an increase in X, alkyl counterion (i.e., side chain) length l(sc), or both, there is an increase in both the average interfacial area per block junction Sigma and the thickness of the microlayer of the AC-block d(Ac).

The release of the opioid antagonist naltrexone from neutral poly(N-isopropylacrylamide) (PNIPAAM)microgels and negatively charged PNIPAAM microgels containing acrylic acid groups (PNIPAAM-co-PAA) has been studied at various microgel and drug concentrations. The release curves were found to be well represented by the Weibull equation. The release rates were observed to be dependent on the microgel concentration. At most conditions, the release from the charged microgels was slower than for the neutral microgels. In addition, the charged microgels exhibited a release lag time, which was dependent on the microgel concentration. No significant lag time could be observed for the neutral microgels. Increasing the naltrexone concentration did not significantly affect the release rates from the neutral microgels, but the release from the charged microgels became faster. The microgels did not exhibit any significant cytotoxic effect on HeLa cells at the tested concentrations. Norwegian Research Council

A series of N-alkyl/aryl carbazole 3,6-substituted arylene trifluorovinyl ether (TFVE) monomers were synthesized in high purity and yield from a concise four-step synthesis using carbazole as a starting material. Condensate-free, step-growth chain extension of the monomers afforded perfluorocyclobutyl (PFCB) arylene ether homo- and copolymers as solution processable, optically transparent blue-light emissive materials. Arylene TFVE monomers and conversion to PFCB arylene ether polymers were structurally elucidated and purity confirmed by high resolution mass spectroscopy, NMR (1H, 13C, and 19F) spectroscopy, gel permeation chromatography, and attenuated total reflectance Fourier transform infrared analysis. Thermal analysis by differential scanning calorimetry and thermogravimetric analysis revealed glass transition temperatures >150 °C and onset of decomposition in nitrogen >410 °C with 40 wt % char yield up to 900 °C. Optical and electrochemical studies included solution (tetrahydrofuran) and solid state (spin cast thin film) UV–vis/fluorescence spectroscopy and cyclic voltammetry which showed structure dependence of these blue emissive systems on the nature of the N-alkyl/aryl carbazole substitution in either homo- or copolymer configurations. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 552–560

The adsorption of a series of four poly(N-isopropylacrylamide)-based copolymers composed of a hydrophilic block of methoxy poly(ethylene glycol) (MPEG) with a variable length and a PNIPAAM block of fixed size (MPEG n -b-PNIPAAM71) onto flat and spherical citrate-coated gold surfaces has been investigated. The adsorption onto planar surfaces was studied by means of the quartz crystal microbalance with dissipation monitoring, whereas polymer adsorption onto gold nanoparticles was examined using dynamic light scattering and visible spectroscopy. Experiments were performed with two different concentrations of polymer in bulk solution, namely 0.05 and 0.0005 wt%. The influence of the MPEG length on the thickness of the adsorbed layer on the nanoparticles, and the adsorbed mass onto the planar surfaces were recorded at different temperatures.

Nanoparticulate systems with an uncharged hydrophilic surface may have a great potential in mucosal drug delivery. In the present study liposomes were coated with hydrophobically modified hydroxyethyl cellulose (HM-HEC) to create a sterically stabilized liposomal system with an uncharged surface. The aim was to clarify the influence of the amount of hydrophobic modification of HEC and the length of the hydrophobic moiety, on the stability of the system and on the release properties. HM-HEC with different degrees of hydrophobic modification (1 and 2 mol%) and hydrophobic groups with different chain lengths (C8, C12, C16) were included in the study, as well as fluid phase and gel phase liposomes. Both types of liposomes were successfully coated with HM-HEC containing 1 mol% of hydrophobic groups, while 2 mol% did not work for the intended pharmaceutical applications. The polymer coated gel phase liposomes were stable (size, zeta potential, leakage) for 24 weeks at 4 °C, with no differences between the C8 and C16 HM-HEC coating. For the fluid phase liposomes a size increase was observed after 24 weeks at 4 °C for all formulations; the C8 HM-HEC coated liposomes increased the most. No differences in the leakage during storage at 4 °C or in the release at 35 °C were observed between the fluid phase formulations. To conclude; HM-HEC with a shorter hydrophobic chain length resulted in a less stable product for the fluid phase liposomes, while no influence of the chain length was observed for the gel phase liposomes (1 mol% HM).

By a selective complexation between different alkyltrimethylammonium amphiphiles (C8, C12 and C16) and three different diblock copolymer systems of poly(styrene)-b-poly(methacrylic acid) at various grafting densities X (X = number of alkyl chains per acidic group of the poly(methacrylic acid) PMAA block), a class of ionic supramolecules are successfully synthesized whose molecular architecture consists of a poly(styrene) PS block (Linear block) covalently connected to a strongly amphiphilic comb-like block (AmphComb block), i.e. Linear-b-AmphComb. In the melt state, these ionic supramolecules can show simultaneous microphase (between Linear and AmphComb blocks) and nanophase (within the AmphComb blocks) separations. This leads to the formation of various structure-in-structure two-scale hierarchical self-assemblies, including S-in-SLL, S-in-SBCC, S-in-C, S-in-L and C-in-L, where S, SLL, SBCC, C and L stand for spherical, spherical in liquid-like state, spherical in body-centered-cubic arrangement, cylindrical and lamellar, respectively. Synchrotron small angle X-ray scattering (SAXS) and crossed polarizers, together with SAXS modelling analysis, were used for a detailed structural study of the samples. The morphology of the microphase separated state was mapped out on ‘master’ microdomain morphology diagrams as a function of the volume fraction of the AmphComb blocks (ΦAmphComb) and the compositional window of each microdomain morphology was determined. It was observed that, (i) within samples based on the same parent diblock copolymer system, the occurrence of a specific microdomain morphology is only dependent on the value of ΦAmphComb, regardless of the grafting density X and the length of the alkyl side-chains, and (ii) microdomain morphological boundaries occur at ΦAmphComb values of ∼0.20 (SLL/C and SBCC/C) and ∼0.28 (C/L). Finally, the specific influences of the strongly amphiphilic nature of the AmphComb blocks on the observed morphological and hierarchical behaviours of our system are discussed. For reference, stoichiometric strongly amphiphilic comb-like (AmphComb) ionic supramolecules, based on complexation between a homopolymer of PMAA and the various alkyltrimethylammonium amphiphiles, were prepared, which nanophase separated into S (C8) or C (C12 and C16) domains.

New hybrid complexes composed by a thermoresponsive copolymer and gold nanoparticles (Rh = 22 nm) have been characterized by dynamic light scattering (DLS) and UV-visible spectroscopy. A cationic thermoresponsive triblock copolymer, methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide)-block-poly((3-acrylamidopropyl) trimethyl ammonium chloride), abbreviated as MPEG-b-PNIPAAM-b-PN(+), has been synthesized by atom transfer radical polymerization (ATRP). We have evaluated the thermal response at low concentrations of this triblock copolymer in bulk solution and the effect of concentration on the interaction between this thermosensitive copolymer and the gold nanoparticles (AuNPs) to form new hybrid complexes (60–1000 nm) at different temperatures. The thermosensitive nature of the copolymer causes both aggregation and contraction of the aggregates at elevated temperatures. The AuNPs were found to be separately embedded in the hybrid complexes. Interestingly, the AuNPs prevent macroscopic phase separation of the system at high temperatures.

The thermoresponsive amphiphilic block copolymer poly(d,l-lactic acid-co-glycolic acid)-block-poly(ethylene glycol)-block-poly(d,l-lactic acid-co-glycolic acid) (PLGA-PEGn-PLGA), which exhibits a reversible temperature-induced sol–gel transition at higher polymer concentrations in aqueous solution has attached a great deal of interest because of its potential in biomedical applications. In the present work, the length of the hydrophobic PLGA blocks is kept constant, whereas the length of the hydrophilic PEG block is altered and this variation has a pronounced impact on the phase behavior of the aqueous samples and the structure of the polymer. A short PEG block promotes gelation at a low temperature, whereas a longer PEG block shifts the gelation point to higher temperature. By using a combination of turbidity, rheology, and small angle neutron scattering (SANS) methods, the authors have revealed dramatic temperature effects. In dilute solution, the SANS experiments expose asymmetric ellipsoid structures for the copolymer with the short PEG-spacer, whereas spherical core–shell structure is observed for the polymer with long PEG-spacer. In the semidilute concentration regime, SANS measurements disclose similar profiles for the two copolymers. In a broad temperature interval, the transition from spherical core–shell micelles to cylindrical structure and packing of cylinders is observed.

The thermoresponsive poly(N-isopropylacrylamide) (PNIPAAM) and NIPAAM block copolymer derivatives are attractive for drug delivery applications as they contract reversibly at lower critical solution temperatures (LCST) close to physiological conditions. In order to investigate biomaterial-protein compatibility, we have studied the interaction between PNIPAAM copolymer films spread at the air-water surface and bovine serum albumin (BSA) injected below the precompressed polymer films, using the Langmuir technique coupled with Brewster angle microscopy (BAM). A PNIPAAM homopolymer was applied together with a number of PNIPAAM-based di- and triblock copolymers, to assess effects of e.g., charge and hydrophobicity on protein-polymer interactions. The nature and strength of protein-polymer interaction was found to be tunable, ranging from complex formation (PNIPAAM homopolymer) to mixed monolayers and electrostatic cross-linking, according to the nature of the co-monomer. Results show that intercalation versus adsorption can be controlled through polymer composition.

Effects of temperature on the association behavior in aqueous solutions of a series of charged thermoresponsive poly(N-isopropylacrylamide)-block-poly((3-acrylamidopropyl) trimethylammonium chloride) (abbreviated as PNIPAAM(n)-b-PAMPTMA(+)(20)) with different lengths of the PNIPAAM block (n = 24, 48, and 65) have been studied with the aid of turbidimetry, zeta sizer, and dynamic light scattering (DLS). The turbidity results show that the transition to high turbidity values is shifted to lower temperatures when the length of the PNIPAAM block increases. It was observed that the value of the cloud point (CP) dropped with increasing polymer concentration, enlarged length of the PNIPAAM block, and augmented salinity. It was found that the decay of the correlation function from DLS is bimodal at temperatures well below CP, where the fast mode represents the motion of the unimers and the slow mode the dynamics of micelles/intermicellar complexes. At higher temperatures, larger particles of the system grow at the expense of the smaller ones in the spirit of Ostwald ripening, and clusters with a narrow size distribution evolve at high temperatures. By adding salt (NaCl), enhanced aggregation occurs at elevated temperatures because of screening of Coulomb repulsions.

Effects of some sodium salts (NaCl, NaClO3, and NaSCN) in the Hofmeister series on deswelling and temperature-induced aggregation behavior of microgels of poly(N-isopropylacrylamide) (PNIPAAM) and PNIPAAM-co-PAA with attached poly(acrylic acid) moieties were investigated with the aid of turbidimetry and dynamic light scattering. Addition of salt in the concentration range 0.1–0.5 M generated aggregation of the PNIPAAM microgel particles at elevated temperatures, but it was no distinct difference between chaotropic and kosmotropic anions. In contrast, the flocculation behavior at high temperatures for PNIPAAM-co-PAA revealed a prominent influence of salinity and type of anion on the formation of aggregates. The aggregation transition was shifted to the highest temperature for the most chaotropic anion (SCN−), and the aggregation transition at the same salt concentration is consistent with the typical Hofmeister series. The turbidity results from the PNIPAAM-co-PAA microgels disclosed a two-step transition for the considered anions, and both a low and high temperature change in the turbidity data was observed. The high-temperature transition followed the Hofmeister series.

Upon conjugation of thermoresponsive polymers to nanomaterials such as gold nanoparticles (Aunps), whether and to what extent the properties of the polymer-coated Aunps differ from that of the free...

The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant hexadecyl trimethyl ammonium bromide with poly(N-isopropylacrylamide) (PNIPAAM) microgels with and without poly(acrylic acid) (PAA) was investigated by means of dynamic light scattering (DLS), zeta potential, and turbidimetry measurements. The DLS results show that the PNIPAAM microgels with PAA will contract when an anionic or cationic surfactant is added to the suspension, while the PNIPAAM microgels without PAA expand in the presence of an ionic surfactant. A collapse of the PNIPAAM microgels is observed when the temperature is increased. From the zeta potential measurements, it is observed that the charge density of PNIPAAM microgels in the presence of an ionic surfactant is significantly affected by temperature and the attachment of the negatively charged PAA groups. The turbidity measurements clearly indicate that the interaction between PNIPAAM and SDS is more pronounced than that of the cationic surfactant.

Time effects for the temperature-induced association complexes in solutions of the thermoresponsive poly(N-isopropylacrylamide)-block-poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (PNIPAAM(69)-b-PEG(23)-b-PNIPAAM(69)) copolymer that exhibit a lower critical solution temperature were studied by means of turbidimetry and dynamic light scattering (DLS). The DLS results clearly show that at temperatures below the cloud point (CP) unimers coexist with intermicellar structures, which contract as the CP is approached. At this stage, no time effect was detected. At temperatures above the CP, large association structures are formed, and these aggregates dominate the decay of the correlation functions. A novel time-dependent growth of the aggregates was observed over several hours. The growth of the clusters is strengthened as the temperature rises, and this feature is supported by the turbidity results and the reduced scattered intensity experiments. For a low polymer concentration, an initial growth of the clusters is observed, whereas at longer times the apparent hydrodynamic radius from DLS is virtually constant. The results from this work stress the importance to check possible time effects in solutions of thermosensitive copolymers as the cloud point is approached.

Temperature-induced interchain association and contraction of species in aqueous solutions of charged (MHEC(−)-g-PNIPAAM) and uncharged (MHEC-g-PNIPAAM) modified hydroxyethylcellulose-graft-poly(N-isopropylacrylamide) copolymer have been studied with the aid of turbidimetry and dynamic light scattering (DLS). It was shown that by attaching PNIPAAM chains to the backbone of a hydrophilic cellulose derivative, a strongly temperature-responsive copolymer could be prepared. The results show an intriguing interplay between interchain association and contraction of the multichain species. The transition zone for compression is narrow, and the compaction effect is promoted by a low polymer concentration and charges on the polymer moieties. The findings from DLS revealed two populations of species, namely molecularly dispersed molecules or small clusters and interchain complexes, which exhibit temperature-induced collapse. The magnitude of the cluster contraction can be modulated by changing the polymer concentration and charge density of the copolymer.

In this article, we report a study of the adsorption of a charged thermoresponsive poly(N-isopropylacrylamide)-block-poly(3-acrylamidopropyl)trimethylammonium chloride) [abbreviated as PNIPAAM24-b-PAMPTMA(+)18] block copolymer onto gold nanoparticles by means of dynamic light scattering (DLS), zeta-potential measurements, cryo-TEM, rheology small-angle light scattering (rheo-SALS), and UV−visible absorbance spectroscopy. At low surface coverage, the cationic copolymer was found to mediate flocculation of the particles at elevated temperatures, whereas at higher polymer concentration, the gold particles were stabilized by the adsorbed copolymer layer. The DLS results showed that the adsorbed polymer was compressed prior to flocculation at elevated temperatures and that the flocs coexisted with single particles. The latter finding was confirmed by cryo-TEM. Rheo-SALS measurements revealed that shear flow disrupted the large flocs formed at higher temperatures. UV−visible absorbance measurements demonstrated...

The adsorption of two positively charged hydroxyethylcellulose derivatives with 7 and 60 mol % positively charged groups and a cationic, hydrophobically modified hydroxyethylcellulose containing 1 mol % hydrophobic groups and 7 mol % charged groups onto flat and spherical citrate-coated gold surfaces of different sizes has been investigated. The planar surfaces were studied by means of the quartz crystal microbalance with dissipation monitoring, whereas nanoparticle suspensions were examined using dynamic light scattering and UV-vis spectroscopy. Two different driving forces for adsorption have been evaluated: the electrostatic interaction between the positive charges on the polymers and the negatively charged gold surfaces and the affinity of the polymers for gold due to hydrophobic interactions. The comparison between the data obtained from curved and planar surfaces suggests a strong correlation between surface curvature and adlayer conformation in the formation of the hybrid polymer-gold nanoparticles. The influence of particle size on the amount of adsorbed polymer has been evaluated for the different polymers. The impact of the ionic strength on polymer adsorption has been explored, and the adsorbed polymer layer has been found to protect the gold nanoparticles from aggregation when salt is added to the solution. The addition of salt to a mixture of gold particles and a charged polymer can induce a thicker adsorbed layer at low salinity, and desorption was found at high levels of salt addition.

This review elucidates several aspects on the behavior of charged polysaccharides and mucin. Viscosification of dilute aqueous solutions of hyaluronan (HA) occurs in the course of time at low shear flow, whereas shear thinning as time evolves is found at moderate shear rates. Hydrogen bonds and electrostatic interaction play an important role for the emergence of these features. No time effect of the viscosity is observed for semidilute HA solutions. A degradation of HA is observed at low and high pH and this effect continues over long times, and it is only in the approximate interval 5

A bead-and-spring model has been used to simulate the behavior of thermoresponsive asymmetric diblock amphiphilic copolymers with aid of Monte Carlo simulations. The alteration of the thermodynamic conditions was mimicked by using a Lennard-Jones potential, which was related to the measured temperatures by comparison with experimental data for aqueous solutions of two sets of diblock copolymers, namely methoxypoly(ethylene glycol)-block-poly(N-isopropylacrylamide), one with different lengths of the hydrophilic block (MPEG(n)-b-PNIPAAM(71)) and one with varying lengths of the hydrophobic block (MPEG(57)-b-PNIPAAM(m)). The influence of the length of both the thermoresponsive and the hydrophilic block on the size and conformation of single molecules at various temperatures was studied by means of simulations. The temperature-induced contraction of the copolymer (MPEG(n)-b-PNIPAAM(71)) entities is only modestly affected by changing the length of the hydrophilic block, whereas for the MPEG(57)-b-PNIPAAM(m) copolymer both the transition temperature and the magnitude of the compression of the molecules are strongly influenced by the length of the thermosensitive block. When the MPEG chain fully covers the hydrophobic core, the copolymer moieties are stabilized, whereas poorly covered cores can promote interchain aggregation at elevated temperatures.

This paper reports turbidity, rheology, zeta potential, and rheo-small angle light scattering measurements on aqueous mixtures of oppositely charged and hydrophobically modified hydroxyethylcellulose derivatives (HM-HEC(−) and HM-HEC(+)) and mixtures of oppositely charged hydroxyethylcellulose (HEC(−) and HEC(+)). The experiments were restricted to the one-phase region, i.e., at mixing ratios before and after the two-phase area. The associative phase separation behavior usually observed when mixing oppositely charged polyelectrolytes was undetectable in the mixtures of the polyelectrolytes without attached hydrophobic groups. Upon modification of HEC by incorporation of pendant hydrophobic groups and by introducing charges of negative or positive sign (HM-HEC(−) and HM-HEC(+)), the mixtures showed phase separation over a certain mixing interval, revealing the existence of large polyelectrolyte complexes. The zero shear viscosity was strongly dependent on both the hydrophobicity of the polymers and the mixing ratio, increasing significantly with hydrophobic modification of polyelectrolytes. The strong enhancement of the turbidity and the viscosity drop as the two-phase area is approached suggest the formation of fragmented non-connected complexes. This work demonstrates that if the oppositely charged polyions have a hydrophilic character, it is not necessary that the attractive Coulombic forces induce insoluble polyelectrolyte complexes.