Increasing Block Length Research Articles

Densely Sulfophenylated Segmented Copoly(arylene ether sulfone) Proton Exchange Membranes

Segmented copoly(arylene ether sulfone) membranes having densely sulfonated pendent phenyl blocks were synthesized by the coupling reaction of phenoxide-terminated oligomers with bis(4-hydroxyphenyl) sulfone and decafluorobiphenyl (DFBP), followed by postpolymerization sulfonation of the blocks containing pendent phenyl substituents. The coupling reaction was conducted at relatively low temperature by utilizing highly reactive DFBP to prevent any possible trans-etherification that would randomize the hydrophilic–hydrophobic sequences. Segmented copolymer molecular weights were reasonably high, as determined by viscosity measurements. Postsulfonation occurred selectively on the pendent phenyl substituent to yield hydrophilic blocks that were highly sulfonated in regular sequence on the linked phenyl rings. The resulting polymers gave transparent, flexible, and tough membranes by solution casting. Morphological observation by transmission electron microscopy (TEM) and atomic force microscopy (AFM) showed that the high local concentration and regular sequence of pendent sulfonic acid groups within the hydrophilic blocks enhanced nanophase separation between the hydrophobic and hydrophilic blocks. A comparison of copolymers with similar ion exchange capacities (IECs) indicated that proton conductivity and water uptake were strongly influenced by the hydrophilic block sequence lengths. Proton conductivity and water uptake increased with increasing block length, even at low relative humidity (RH). The ionomer membrane with X20Y20 (X and Y refer to the number of hydrophilic and hydrophobic repeat units, respectively) and 1.82 mequiv/g of IEC had a proton conductivity of 3.6 × 10–2 S/cm at 80 °C and 50% RH, which is comparable to that of perfluorinated ionomer (Nafion) membrane (4.0 × 10–2 S/cm).

Micelle formation of polystyrene-block-poly(4-tert-butoxystyrene) in hexane

A new type of hexane-soluble polymeric surfactant based on poly(4-tert-butoxystyrene) (PtBSt) was prepared by the nitroxide-mediated living radical polymerization, and their self-assemblies in hexane were explored. Polystyrene-block-PtBSt diblock copolymers with six different PtBSt block lengths were obtained by the sequential living radical polymerization of styrene followed by 4-tert-butoxystyrene using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator; Mn(PtBSt block) = 13,500, 21,700, 26,600, 47,500, 91,300, and 108,000 at the constant length of the PSt block (Mn = 12,900). Dynamic light-scattering studies demonstrated that the copolymers self-assembled into monodispersed spherical micelles in hexane. The hydrodynamic diameter of the micelles increased with an increase in the PtBSt block length. The micellar size also increased as the copolymer concentration increased. However, the size decreased as a result of the increasing temperature due to a decrease in the aggregation number. The 1H NMR analysis confirmed that the copolymers formed micelles with PSt cores.

Exponential error rates in multiple state discrimination on a quantum spin chain

We consider decision problems on finite sets of hypotheses represented by pairwise different shift-invariant states on a quantum spin chain. The decision in favor of one of the hypotheses is based on outcomes of generalized measurements performed on local states on blocks of finite size. We assume the existence of the mean quantum Chernoff distances of any pair of states from the given set and refer to the minimum of them as the mean generalized quantum Chernoff distance. We establish that this minimum specifies an asymptotic bound on the exponential rate of decay of the averaged probability of rejecting the true state in increasing block size, if the mean quantum Chernoff distance of any pair of the hypothetic states is achievable as an asymptotic error exponent in the corresponding binary problem. This assumption is, in particular, fulfilled by shift-invariant product states (independent and identically distributed states). Further, we provide a constructive proof for the existence of a sequence of quantum tests in increasing block length with an error exponent which equals, up to a factor, the mean generalized quantum Chernoff distance. The factor depends on the configuration of the hypothetic states with respect to the binary quantum Chernoff distances. It can be arbitrary close to 1 and is never less than 1/m for m being the number of different pairs of states.

The effect of distribution of monomer moiety on the pH response and mechanicalproperties of poly(acrylonitrile-co-acrylic acid) copolymers

The pH response and mechanical properties of copolymer-based hydrogels such aspoly(acrylonitrile-co-acrylic acid) are usually attributed to their chemical composition. In thisstudy, it has been shown that the architecture of the polymer chains, i.e. the distribution ofcomonomers in the macromolecules, also plays a major role in controlling these properties.A series of four poly(acrylonitrile-co-acrylic acids) with fixed composition (i.e. ∼30 mol% acrylic acid moieties) were synthesized, where the block lengths of both AN(acrylonitrile) and AAc (acrylic acid) moieties in the copolymers were varied by controllingthe feeding pattern of the monomers during free radical copolymerization. Thesecopolymers were then converted into fine fibers of the same dimensions. The monomerdistribution in the four copolymers was estimated using quantitative carbon 13C nuclear magnetic resonance (NMR) and related to the mechanical and pH responseproperties of the resultant fibers. The pH response of the fibers with similar compositionincreased dramatically as the block length of the AAc moiety was increased, while themechanical properties increased as a direct function of the block length of the AN moieties.The fiber’s response at pH 10 in terms of the change in length increased by∼four times while its responserate increased by ∼50 times with the increase in block length of the AAc moiety. On theother hand, the tensile properties and retractive stress increased by∼four times with the increase in the block length of the AN moiety.

Synthesis and characterization of multiblock copolymers based on hydrophilic disulfonated poly(arylene ether sulfone) and hydrophobic partially fluorinated poly(arylene ether ketone) for fuel cell applications

AbstractSulfonated fluorinated multiblock copolymers based on high performance polymers were synthesized and evaluated for use as proton exchange membranes (PEMs). The multiblock copolymers consist of fully disulfonated poly(arylene ether sulfone) and partially fluorinated poly(arylene ether ketone) as hydrophilic and hydrophobic segments, respectively. Synthesis of the multiblock copolymers was achieved by a condensation coupling reaction between controlled molecular weight hydrophilic and hydrophobic oligomers. The coupling reaction could be conducted at relatively low temperatures (e.g., 105 °C) by utilizing highly reactive hexafluorobenzene (HFB) as a linkage group. The low coupling reaction temperature could prevent a possible trans‐etherification, which can randomize the hydrophilic‐hydrophobic sequences. Tough ductile membranes were prepared by solution casting and their membrane properties were evaluated. With similar ion exchange capacities (IECs), proton conductivity and water uptake were strongly influenced by the hydrophilic and hydrophobic block sequence lengths. Conductivity and water uptake increased with increasing block length by developing nanophase separated morphologies. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments revealed that the connectivity of the hydrophilic segments was enhanced by increasing the block length. The systematic synthesis and characterization of the copolymers are reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 214–222, 2010

Synthesis, surface and aggregation properties of a series of amphiphilic dendritic copolymers

With 3.0 G polyamidoamine (PAMAM) as initiator and poly (propylene oxide) (PPO)–poly (ethylene oxide) (PEO) blocks as branches, a new class of amphiphilic copolymers were synthesized. The critical micelle concentration (CMC) and γ CMC (surface tension at CMC) values were determined by surface tension measurement, and the result showed that they both decrease with the increase of amphiphilic branch length. The turbidity properties were investigated and it was found that the cloud point (CP) temperature decreases as the PEO block length increases. Freeze-fracture transmission electron microscopy (FF-TEM) results exhibited spherical shape of aggregates with the most probable distribution size of around 100 nm, which agrees with the results of the dynamic light scattering (DLS). Moreover, the relationship between PPO block length and the activity and CP properties was discussed.

A Context Quantization Approach to Universal Denoising

We revisit the problem of denoising a discrete-time, continuous-amplitude signal corrupted by a known memoryless channel. By modifying our earlier approach to the problem, we obtain a scheme that is much more tractable than the original one and at the same time retains the universal optimality properties. The universality refers to the fact that the proposed denoiser asymptotically (with increasing block length of the data) achieves the performance of an optimum denoiser that has full knowledge of the distribution of a source generating the underlying clean sequence; the only restriction being that the distribution is stationary. The optimality, in a sense we will make precise, of the denoiser also holds in the case where the underlying clean sequence is unknown and deterministic and the only source of randomness is in the noise. The schemes involve a simple preprocessing step of quantizing the noisy symbols to generate quantized contexts. The quantized context value corresponding to each sequence component is then used to partition the unquantized symbols into subsequences. A universal symbol-by-symbol denoiser (for unquantized sequences) is then separately employed on each of the subsequences. We identify a rate at which the context length and quantization resolution should be increased so that the resulting scheme is universal. The proposed family of schemes is computationally attractive with an upper bound on complexity which is independent of the context length and the quantization resolution. Initial experimentation seems to indicate that these schemes are not only superior from a computational viewpoint, but also achieve better denoising in practice.

Self-Assembling Properties of Well-Defined Poly(ethylene oxide)-b-poly(ethyl acrylate) Diblock Copolymers

Poly(ethylene oxide)-b-poly(ethyl acrylate) amphiphilic diblock copolymers were synthesized by atom transfer radical polymerization (ATRP). The controlled character of the polymerization was confirmed by kinetic studies, evolution of number-average molecular weight and polydispersity index with conversion. Various block copolymers with different PEA/PEO molar ratio were synthesized and their self-assembling properties in aqueous medium were studied by fluorescence measurements, static light scattering (SLS), and dynamic light scattering (DLS). The critical micelle concentrations (CMC) were determined by pyrene fluorescence analysis. The CMC was shown to decrease as the hydrophobic (PEA) block length increases. SLS and DLS allowed the determination of the aggregation numbers (Nagg) and hydrodynamic radii (Rh) of the core−shell micelles formed in water. Both Nagg and Rh exhibit a monotonic increase as a function of the PEA block length. TEM and cryo-TEM micrographs of the micelles showed spherical objects w...

On Defining a Simple Empirical Relationship to Predict the Pore Size of Mesoporous Silicas Prepared from PEO-b-PS Diblock Copolymers

Mesoporous silicas with large and accessible pores have been successfully synthesized using laboratory-made poly(ethylene oxide)-b-polystyrene (PEO-b-PS) copolymers as templates. The PEO-b-PS copolymers were synthesized using living/controlled radical polymerization. The porous structure (mesopore size, size distribution, and microporous volume) was characterized using small-angle X-ray scattering, electron transmission microscopy, and nitrogen sorption measurements. In this study, we have investigated the dependence of the mesoporosity on both the PS and PEO blocks length using two series of PEO-b-PS copolymers with a constant degree of polymerization of the PEO block for each series (NPEO = 114 and NPEO = 232). It was found that the mesopore size increases and the microporous volume decreases as the PS block length (NPS) increases. The PEO block participates to both the micropore and mesopore formation. By fitting these experimental data, a simple empirical relationship between the pore radius and the length of the both PS block (NPS) and PEO block (NPEO) is found RP (nm) = 0.36.NPEO0.19NPS0.5. This relationship is in agreement for both low- and high-molecular-weight copolymers and can be easily be used to fine-tune the mesopore size of silica materials, in a large range (from 4 to 22 nm), when using PEO-b-PS copolymers as templates. Furthermore, the influence of the synthesis temperature (between 25 and 60 °C) on the porous structure was also investigated and it was found that by increasing the synthesis temperature, the mesopore diameters remain relatively constant; however, the pore entrances increase in size, leading to more open pore structures.

Morphological investigations of disulfonated poly(arylene ether sulfone)- b-naphthalene dianhydride-based polyimide multiblock copolymers as potential high temperature proton exchange membranes

A major goal of current proton exchange membrane fuel cell research involves developing high temperature membranes that can operate at ∼120 °C and low humidities. Multiblock copolymers synthesized from 100% disulfonated poly(arylene ether sulfone) (BPSH100) and naphthalene polyimide (PI) oligomers may be an alternative. The high temperature behavior of BPSH100–PI multiblock copolymers was evaluated in terms of morphology and water retention and compared to that of BPSH-based random copolymers, Nafion 112, and new recast Nafion (NRE211). Atomic force microscopy (AFM) performed at elevated temperatures with a hot stage demonstrated that at block lengths of ∼15 kg/mol the multiblock copolymers displayed no morphological changes up to 120 °C or even higher. Water desorption was observed to decrease with increasing block length. The copolymers exhibited little to no water loss during a 200 °C isotherm in contrast to random BPSH copolymers and Nafion. A BPSH100–PI multiblock copolymer with large block length appears to have morphological stability and retain water (likely strongly bound) at temperatures exceeding 120 °C, suggesting its candidacy as a high temperature PEM.

Y‐shaped poly(ethylene glycol) and poly(trimethylene carbonate) amphiphilic copolymer: Synthesis and for drug delivery

AbstractNew Y‐shaped (AB2‐type) amphiphilic copolymers of poly(ethylene glycol) (PEG) with poly(trimethylene carbonate) (PTMC), PEG‐b‐(PTMC)2, were successfully synthesized by the ring‐opening polymerization (ROP) of TMC with bishydroxy‐modified monomethoxy‐PEG (mPEG). First, a bishydroxy functional ROP initiator was synthesized by esterification of acryloyl bromide with mPEG, followed by Michael addition using excess diethanolamine. A series of Y‐shaped amphiphilic PEG‐(PTMC)2 block copolymers were obtained via ROP of TMC using this PEG with bishydroxyl end groups as macroinitiator and ZnEt2 as catalyst. The amphiphilic block copolymers with different compositions were characterized by gel permeation chromatography (GPC) and 1H NMR, and their molecular weight was measured by GPC. The results showed that the molecular weight of Y‐shaped copolymers increased with the increase of the molar ratio of TMC to mPEG‐(OH)2 initiator in feed while the PEG chain length was kept constant. The Y‐shaped copolymer mPEG‐(PTMC)2 could self‐assemble into micelles in aqueous medium and the critical micelle concentration values of the micelles decrease with increase in hydrophobic PTMC block length of mPEG‐(PTMC)2. The in vitro cytotoxicity and controlled drug release properties of the Y‐shaped amphiphilic block copolymers were also investigated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8131–8140, 2008

Effects of polystyrene- b-poly(aminomethyl styrene)s as stabilizers on dispersion polymerization of styrene in alcoholic media

The effects of polystyrene- b-poly(aminomethyl styrene) (PS n - b-PAMS m ) stabilizers on the particle size ( D n ) and size distribution (PSD) in dispersion polymerization of styrene were investigated. The block copolymers, PS n - b-PAMS m , were prepared as follows: (i) atom transfer radical polymerization (ATRP) of styrene (PS-Br), (ii) ATRP of vinylbenzylphthalimide with the PS-Br (PS- b-PVBP), and (iii) treatment of the PS- b-PVBP with hydrazine. When the dispersion polymerization of styrene proceeded at 60 °C in ethanol with PS 19- b-PAMS 130 stabilizer, spherical polystyrene particles with D n = 0.91 μm (PSD = 1.01) were obtained. The particle size was strongly affected by the copolymer composition. With an increase in PAMS block length from m = 54 to 100 in PS 17- b-PAMS m , particle diameter became smaller from 1.55 to 0.91 μm. On the other hand, an increase in the length from m = 20 to 82 in PS 34- b-PAMS m s caused an increase in particle size from 0.35 to 0.70 μm. Titration of the particles suggests that 14–81% of stabilizers used in the polymerization system were attached on the polystyrene particle surfaces, depending on the composition of the block copolymers. Thus, for the dispersion polymerization of styrene, PS n - b-PAMS m block copolymers have both functions as a stabilizer during polymerization and surface-modification sites of polystyrene particles.

Synthesis and characterization of poly(arylene ether sulfone)-b-polybenzimidazole copolymers for high temperature low humidity proton exchange membrane fuel cells

Multiblock copolymers based on poly(arylene ether sulfone) and polybenzimidazole (PBI) with different block lengths were synthesized by coupling carboxyl functional aromatic poly(arylene ethers) with ortho diamino functional PBI oligomers in NMP, selectively doped with phosphoric acid, and evaluated as a high temperature proton exchange membrane (PEM). Transparent and ductile membranes were produced by solvent casting from DMAc. From dynamic mechanical analysis (DMA), the neat copolymer membranes showed two distinct glass transition temperatures which implies the existence of a nanostructured morphology in the membranes. These two nanophases became more distinct with increasing block length. The membranes were immersed in various concentrations of phosphoric acid solution to produce the proton conductivity. The doping level increased with increasing concentration of the acid solution and a maximum doping level of 12 was achieved when 14.6M phosphoric acid solution was used. The acid doped membranes showed significantly reduced swelling behavior compared to a control conventional phosphoric acid doped PBI homopolymer system which appears to be related to the selective sorption into the PBI phase. The ionic conductivity of the doped samples at 200°C afforded up to 47mS/cm without external humidification. The protonic conductivity was found to increase with block length at a given doping level, reflecting the sharpness of the nanophase separation and the effect was even more prominent at a low doping level of 6–7. It is suggested that the phosphoric acid doped multiblock copolymer system would be a strong candidate for high temperature and low relative humidity PEM applications such as those required for stationary power.

Self-Assembly Behavior of pH- and Thermosensitive Amphiphilic Triblock Copolymers in Solution: Experimental Studies and Self-Consistent Field Theory Simulations

We investigated, both experimentally and theoretically, the self-assembly behaviors of pH- and thermosensitive poly(L-glutamic acid)- b-poly(propylene oxide)-b-poly(L-glutamic acid) (PLGA-b-PPO-b-PLGA) triblock copolymers in aqueous solution by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), circular dichroism (CD), and self-consistent field theory (SCFT) simulations. Vesicles were observed when the hydrophilic PLGA block length is shorter or the pH value of solution is lower. The vesicles were found to transform to spherical micelles when the PLGA block length increases or its conformation changes from helix to coil with increasing the pH value. In addition, increasing temperature gives rise to a decrease in the size of aggregates, which is related to the dehydration of the PPO segments at higher temperatures. The SCFT simulation results show that the vesicles transform to the spherical micelles with increasing the fraction or statistical length of A block in model ABA triblock copolymer, which corresponds to the increase in the PLGA length or its conformation change from helix to coil in experiments, respectively. The SCFT calculations also provide chain distribution information in the aggregates. On the basis of both experimental and SCFT results, the mechanism of the structure change of the PLGA- b-PPO- b-PLGA aggregates was proposed.

Hydrophilic–hydrophobic multiblock copolymers based on poly(arylene ether sulfone)s as novel proton exchange membranes – Part B

There has been growing evidence, both experimental and theoretical, that block copolymer systems with well-defined sulfonated regions may provide enhanced proton transport, especially at low relative humidity. We have recently demonstrated a novel way to make hydrocarbon hydrophobic–hydrophilic block copolymers. While the chemical structure and chemical compositions are very similar to random copolymers, the microstructure and the morphology are very different. The self-diffusion coefficients of water, as measured by Pulse Gradient Stimulated Echo (PGSE) NMR techniques, have indicated a significant improvement in water transport after reaching a particular block length. At that block length (10kg/mol:10kg/mol), the multiblocks display better proton conductivity under partially hydrated conditions than the random copolymers. The presence of increased free water content in the multiblocks with increasing block lengths was confirmed by states of water analysis. A significant change in the distribution of three types of water was also observed compared to the random copolymers. This paper will discuss the structure–property relationships of these multiblock copolymers for potential application as proton exchange membranes.

Efficient design of block adaptive equalization and diversity combining for space-time block-coded single-carrier systems

In this paper, a weighted space-time block-coding (STBC)-like matrix-wise block adaptive frequency-domain equalization (WSB-FDE), which has a flexibility over the STBC-like matrix-wise block length as compared to a normalized least-mean-square (NLMS)-FDE and a recursive-least-square (RLS)-FDE, is proposed for the cyclic-prefixed STBC single-carrier systems equipped with a diversity combining. In the WSB-FDE, the STBC-like matrix-wise block is first formulated from received blocks. The correction terms of the equalizer coefficients in each block are then updated so as to minimize a weighted squared-norm of the a posteriori error vector for the formulated block. Moreover, a square-root adaptive algorithm based on an unitary Givens rotation is proposed to achieve the numerical stability and computational efficiency in update procedure of the WSB-FDE. The theoretic convergence and the steady-state excess mean-square error (EMSE) of the WSB-FDE are analyzed, where it is observed that the EMSE decreases as the STBC-like matrix-wise block length and the number of antenna increase. Finally, the performance evaluation shows in a typical urban (TU) channel that the bit-error-rate (BER) performance of the WSB-FDE is superior to that of the RLS-FDE as the STBC-like matrix-wise block length increases.

Synthesis, self‐assembly and recognition properties of biomimetic star‐shaped poly(ε‐caprolactone)‐b‐glycopolymer block copolymers

AbstractBiomimetic star‐shaped poly(ε‐caprolactone)‐b‐poly(gluconamidoethyl methacrylate) block copolymers (SPCL‐PGAMA) were synthesized from the atom transfer radical polymerization (ATRP) of unprotected GAMA glycomonomer using a tetra(2‐bromo‐2‐methylpropionyl)‐terminated star‐shaped poly(ε‐caprolactone) (SPCL‐Br) as a macroinitiator in NMP solution at room temperature. The block length of PGAMA glycopolymer within as‐synthesized SPCL‐PGAMA copolymers could be adjusted linearly by controlling the molar ratio of GAMA glycomonomer to SPCL‐Br macroinitiator, and the molecular weight distribution was reasonably narrow. The degree of crystallization of PCL block within copolymers decreased with the increasing block length ratio of outer PGAMA to inner PCL. Moreover, the self‐assembly properties of the SPCL‐PGAMA copolymers were investigated by NMR, UV‐vis, DLS, and TEM, respectively. The self‐assembled glucose‐installed aggregates changed from spherical micelles to worm‐like aggregates, then to vesicles with the decreasing weight fraction of hydrophilic PGAMA block. Furthermore, the biomolecular binding of SPCL‐PGAMA with Concanavalin A (Con A) was studied by means of UV‐vis, fluorescence spectroscopy, and DLS, which demonstrated that these SPCL‐PGAMA copolymers had specific recognition with Con A. Consequently, this will not only provide biomimetic star‐shaped SPCL‐PGAMA block copolymers for targeted drug delivery, but also improve the compatibility and drug release properties of PCL‐based biomaterials for hydrophilic peptide drugs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 817–829, 2008

Direct synthesis of mesoporous silica presenting large and tunable pores using BAB triblock copolymers: Influence of each copolymer block on the porous structure

Mesoporous silicas with large and tunable (from 4 to 40 nm) accessible pores have been successfully synthesized using laboratory-made BAB (A: hydrophilic block, B: hydrophobic block) type triblock copolymers as templates. A direct synthesis is carried out in the absence of swelling agent and without any further treatment. The polystyrene- b–poly(ethylene oxide)- b–polystyrene (PS- b–PEO- b–PS) copolymers were synthesized using living/controlled radical polymerization. The porous structure (mesopore size, size distribution and microporous volume) was characterized using electron transmission microscopy and nitrogen sorption measurements. This study is focused on the control of the porous structure as a function of the hydrophobic PS block length and the hydrophilic block length (whilst keeping the other block length constant). It was found that when the PS block length increases: (i) the mesopore size increases linearly with PS block length which thus proffers a fine tuning of the pore diameter from 4 to 40 nm, (ii) the micropore volume decreases. When the PEO block length increases, (i) the mesopore size decreases (ii) the micropore volume increases. All these results were explained considering (i) that both PS and PEO block lengths have an influence on the degree of stretching of the PS chains, thus on the micellar core radius (ii) that the mesopore size is directly connected to the micellar core radius, i.e. that PEO chains do not directly participate to mesoporosity (due to its particular loop configuration) but only to microporosity.

Solubilisation of drugs in worm-like micelles of block copolymers of ethylene oxide and 1,2-butylene oxide in aqueous solution

Ethylene oxide and 1,2-butylene oxide were sequentially polymerised to form the diblock copolymer E 13B 10 (E = oxyethylene, B = oxybutylene, subscripts denote number-average block lengths in repeat units). Dynamic and static light scattering over the temperature range 10–30 °C demonstrated a transition from compact (spheroidal) micelles to larger, more elongated (worm-like) micelles with temperature increase above a critical onset temperature of about 20 °C. Determination of the solubilisation capacity for griseofulvin, carbamazepine and spironolactone of dilute micellar solutions of this copolymer, together with those of E 11B 8 and E 17B 12 block copolymers (which also show the sphere-to-worm transition), allowed investigation of the influence on solubilisation characteristics of hydrophobic block length and temperature. The extent of solubilisation at 25 °C of the poorly water-soluble drug spironolactone increased linearly with increase of hydrophobic block length, attributable to a concomitant increase in the proportion of worm-like micelles in solution.

Honeycomb structured porous films from amphiphilic block copolymers prepared via RAFT polymerization

The synthesis of polystyrene-block-poly(N,N-dimethylacrylamide) (PS-b-PDMA) via RAFT polymerization was investigated in detail. Two different RAFT agents – benzyl dithiobenzoate and 3-(benzylsulfanylthiocarbonylsufanyl) propionic acid, were employed to prepare polystyrene macroRAFT agents with molecular weights varying between 3000gmol−1 and 62,000gmol−1 and polydispersities between 1.1 and 1.4. Chain extensions with N,N-dimethylacrylamide (DMA) were carried out using a constant monomer to RAFT agent concentration ([DMA]/[RAFT]=500), to compare the rate of polymerization in dependency of the polystyrene chain length. A decreasing rate of polymerization with increasing block length was observed. Depending on the sizes of the first block and type of RAFT agents used, chain extension polymerization with DMA was found to be incomplete, leading to significant low molecular weight tailing in the GPC analyses. Block copolymers prepared using 3-(benzylsulfanylthiocarbonylsufanyl) propionic acid, followed the expected molecular weight evolutions with polydispersity indices of 1.2–1.4. In contrast, block copolymers using benzyl dithiobenzoate clearly showed bimodal molecular weight distributions, especially when the longest PS macroRAFT agent with a molecular weight of 38,000gmol−1 was employed. These amphiphilic block copolymers were used to fabricate honeycomb structured porous films using the breath figure technique. The regularity of the film was considerably influenced by the humidity of the environment, which could be controlled by the rate of the airflow or the humidity in the casting chamber. The interaction between the hydrophilic block copolymer and the humidity was found responsible for the delicate equilibrium during the casting process, which prevented high pores regularity at very low (below 50%) and at elevated (above 80%) humidity. The interactions of the hydrophilic block with the humidity were observed to superimpose an additional nano-scaled order onto the hexagonal micron-sized porous array. Pores, which are created by encapsulation of water droplets, were found to be more hydrophilic than the surface. Confocal microscopy studies were employed to locate hydrophilic blocks within the film using a fluorescence labeled PDMA polymer.