Low‐Cost,Thermoresponsive Wettability of Surfaces: Poly(N‐isopropylacrylamide)/Polystyrene Composite Films Prepared by Electrospinning

Low‐cost, responsive poly(N‐isopropylacrylamide)/polystyrene composite films were prepared by a facile electrospinning technique. The surface structures and wettabilities of the composite films are tunable by simply controlling the concentration of polymer. With a proper proportion of each polymer, the wettability of the surface can be switched between superhydrophilicity and superhydrophobicity when the temperature is changed from 20 °C to 50 °C. The combination of a stimuli‐responsive polymer with micro/nanostructures on the surface of the composite film contributes to this unique surface property.

     

Step‐Growth Radical Addition‐Coupling Polymerization (RACP) for Synthesis of Alternating Copolymers

We report a new type of step‐growth radical addition‐coupling polymerization (RACP) involving consecutive addition of carbon‐centered radical derived from α,α′‐dibromo dibasic ester to NO double bond of C‐nitroso compound followed by cross‐coupling of carbon‐centered radical and in situ formed nitroxyl radical, which produces alternating copolymers with high molecular weight and unimodal molecular weight distribution from saturated and unsaturated monomers.

     

Ring Opening Polymerization of Lactide under Solvent‐Free Conditions Catalyzed by a Chlorotitanium Calix[4]arene Complex

A novel chlorotitanium calix[4]arene complex was synthesized and tested, without activator, as catalyst for the polymerization of L ‐ and rac‐lactide under solvent‐free conditions. The catalyst displayed high activity, which depended on the monomer‐to‐catalyst molar ratio, and led to highly isotactic PLLA. Despite concomitant transesterification during the polymerization, polylactide formation was well‐controlled, the molar mass distribution indexes remaining in the restricted range of 1.2–1.4.

     

Diffusion Through Membranes of the Polyelectrolyte Complex of Chitosan and Alginate

The swelling of membranes of the polyelectrolyte complex (PEC) between chitosan and alginate shows a similar pattern to that of other PECs. However, if the swelled membranes are dried, a second swelling process is seen which exhibits Fickian behavior. The apparent activation energy was estimated to be 32.8 kJ · mol^?1. The release rate of model solutes was highly dependent on their molecular weight and the pH of the medium.

Arrhenius type plot of the temperature dependence of the apparent diffusion coefficients for the membrane of the polyelectrolyte complex between chitosan and alginate in water.     

Spontaneous Birefringence in Layer‐by‐Layer Films of Chitosan and Azo Dye Sunset Yellow

Layer‐by‐layer (LBL) films consisting of layers of the azo dye Sunset Yellow alternated with chitosan display spontaneous birefringence, which is attributed to the film anisotropy imparted by the LBL method. This is unusual for azobenzene‐containing materials as they normally form films with randomly oriented molecules, presenting birefringence only due to photoinduced isomerization cycles. Spontaneous birefringence does not appear in cast films, but occurs for LBL films obtained under various experimental conditions.

Chemical structures of (a) Sunset Yellow and (b) chitosan.     

Synthesis and Unusual Swelling Behavior of Combined Cationic/Non‐Ionic Hydrogels Based on Chitosan

Hydrogel‐forming copolymers based on chitosan grafted with different amounts of polyacrylamide were synthesized and its swelling capacity determined in distilled water, sodium chloride solutions, as well as in buffer solutions at pH 1.2 and 8.0. The resulting products are highly efficient as hydrogel‐forming materials with swelling at equilibrium going approximately from 300 to 3 000 times the volume of the dry solid polymer in all the investigated media. The products, different to usual hydrogels, swells considerably more and quickly in electrolyte‐containing solutions compared to in distilled water. This has been attributed to their structure that contains non‐ionic polyacrylamide macromolecules grafted onto the trunk polymer chitosan, which is cationic in nature. In‐vitro drug‐release behavior of formulations containing grafted copolymers have been tested using theophylline as a water‐soluble drug and the results were compared with similar formulations containing unmodified chitosan. It was found that tablets based on formulations containing grafted chitosan show higher erosion and swelling compared with those of the matrix based on unmodified chitosan, leading to a higher fraction of theophylline released. It can be concluded that formulations based on the synthesized copolymers are potentially useful for fluid absorbency and as prolonged drug‐release matrices.

The swelling of one of the hydrogels studied here.     

Dual Aggregation Behavior of Porphyrin‐Cored Thiophene Dendrimers

Two porphyrin‐cored thiophene dendrimers T(3T)P and T(7T)P have been successfully synthesized and characterized by UV‐vis and fluorescence measurements. The self‐assembly of these two water‐insoluble free base porphyrins to form both intrinsic H‐ and J‐aggregates has been reported for the first time. This intrinsic behavior is in contrast to the use of surfactants, dyes, and metal ions to induce aggregation behavior on most porphyrin systems. This work emphasizes the importance of controlling the size, solvent, and extent of conjugation of polythiophene dendron groups in porphyrin systems. These materials may yet be applied to polythiophene or porphyrin blend system in energy conversion devices with the light‐harvesting properties of the polythiophene dendrons.

     

An All‐ROMP Route to Graft Copolymers

A new versatile synthesis strategy for macromonomers has been developed that uses the living ring‐opening metathesis polymerization (ROMP) with commercial Grubbs first generation ruthenium initiators. Homopolymers as well as diblock copolymers were end‐functionalized with norbornene derivatives to serve as macromonomers. The graft copolymerization of the macromonomers was also carried out employing ROMP. Well‐defined and highly functional graft copolymers are accessible by this new synthetic route.

     

Controlled Chemical Modifications of Chitosan. Characterization and Investigation of Original Properties

The main techniques developed to characterize chitosan are recalled. The interaction of chitosan with oppositely charged surfactants was investigated giving very important surface activity effects. A few chemical modifications are described and the new properties obtained are mentioned: alkylation gives amphiphilic polymers having interesting thickening behavior; grafting cyclodextrin (chit‐CD) gives a polymer able to include hydrophobic molecules; grafting adamantane gives an amphiphilic polymer able to specifically interact with chit‐CD forming a temporary network with gel‐like behavior.

The viscosities of adamantane‐chitosan, cyclodextrin‐chitosan, and unmodified chitosan solutions studied here.     

Significant Improvement of the Processability of Ladder‐Type Polymers by Using Aqueous Colloidal Dispersions

Summary: It has been shown that stable aqueous dispersions of nanoparticles of the rigid‐rod ladder‐type polymer poly(benzo‐bisimidazobenzo‐phenanthroline) (BBL) can be prepared in order to facilitate BBL processing. The obtained dispersions have a controllable particle size in the range between 50 and 150 nm and, consequently, the deposition of layers by spin‐coating or drop‐casting is realized. The resultant films exhibit a particulate structure and their morphology has been characterized by means of SEM and AFM. Upon investigation of the BBL dispersions in organic field‐effect transistors an ambipolar charge carrier transport has been observed, which presumably is related to the presence of mobile ions.

SEM image of a drop‐cast film of the BBL nanoparticles.     

Monte Carlo Simulation of Controlled/Living Radical Polymerization in Emulsified Systems

A new MC simulation method is proposed for the controlled/living radical polymerization in a dispersed medium, assuming an ideal miniemulsion system. This tool is used to consider the effects of particle size on the polymerization rates and the molecular weight distributions. For NMP, the polymerization kinetics are basically governed by two conflicting factors, (i) the confined space effect that promotes the coupling reaction between a radical and a trapping agent and (ii) the isolation effect of radicals into different particles that suppresses the overall frequency of bimolecular termination. For RAFT polymerization, a significant rate enhancement by reducing the particle size could be observed only for the systems with fast fragmentation of adduct radicals.

     

Morphologies of Diblock Copolymer/Homopolymer Blend Films

Summary: Using bond length fluctuation and cavity diffusion algorithm, the morphologies of diblock copolymer/homopolymer blend films, AB/C and AB/A, confined between two hard walls are studied via Monte Carlo (MC) simulation on a cubic lattice. For the AB/C film, the C homopolymer is supposed to be more compatible with the A block than with the B block, while A and B are mutually incompatible. Effects of the composition of the diblock copolymer/homopolymer mixture, the symmetry of the diblock copolymer chain, the film thickness and the selective wall field on morphologies are studied in detail. Furthermore, the simulated results are compared with that of corresponding ABA and ABC triblock copolymer thin films. Comparisons with experiments and SCF theory also show good agreement. The results indicate that both the AB/C and AB/A can be used to prepare porous AB diblock copolymer membranes, the size of the pore channel can be controlled by the volume fraction of homopolymer C or homopolymer A.

Morphology of A₆B₁₄/C₁₀ polymer blend film.     

Aggregation Behavior of Homo‐PS/PS‐b‐P2VP Blends at the Air/Water Interface

The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.

     

Synthesis and Evaluation of Novel Proton Exchange Membranes Containing the Semisquaric Acid Group

We focus our attention here on semisquaric acid, which is known to show high acidity, as a new proton dissociating group for proton exchange membranes (PEMs). The introduction of a squaric acid group into aromatic polymers was conducted by the reaction of lithiated aromatic polymers and diisopropoxy squarate, followed by treatment with hydrochloric acid. A resulting polyphenylsulfone membrane with the squaric acid group introduced (PPSf‐SQ, IEC = 4.1 meq·g⁻¹) showed proton conductivity of 1.0 × 10⁻¹ S·cm⁻¹ at 80 °C under 95% relative humidity, which indicates that the semisquaric acid has the potential to become an alternative proton‐conducting group for PEMs.

     

Monte‐Carlo Study of Triblock Copolymer/Homopolymer Blend Films

The morphologies of triblock copolymer/homopolymer blend films confined between two neutral hard walls were studied via MC simulations on a simple cubic lattice. For ABA/A and ABA/B blend films, the effects of φ_h (the volume fraction of the homopolymer) and M_h/M_b (the ratio of the molecular mass of the homopolymer to that of the corresponding blocks) on the morphologies were investigated in detail. For both ABA/A and ABA/B blend films, a higher φ_h or M_h/M_b would result in stronger macrophase separation between the triblock copolymer and homopolymer. For ABA/C blend films, M_h/M_b hardly influences the morphologies of homopolymer domains regardless of whether the homopolymer C is more compatible with block A or with block B. Compared to AB/A and AB/C blend films, the morphologies of ABA/A (or ABA/B) and ABA/C blend films are much more irregular. The simulated results in this work show good consistency with experiments and other simulations.

     

Fabrication of Diverse Microcapsule Arrays of High Density and Good Stability

Microcapsule arrays attract a lot of interest due to their potential applications in sensing technology. A strategy for fabricating diverse microcapsule arrays through covalent linking is reported here. The self‐assembly of microcapsules was directed by using a poly(allylamine hydrochloride) (PAH)‐patterned template, which was created via microcontact printing. The microcapsules with PAH as the outermost layer were treated with glutaraldehyde and then covalently immobilized on the PAH regions, resulting in ordered microcapsule arrays. The arrays had a high density of capsules and the aggregate number in a pattern could be well controlled by adjusting the area of the PAH pattern. A single microcapsule array could be obtained if the diameter of the PAH region was smaller than that of the microcapsules. These covalently assembled arrays could survive through successive incubation in solutions of high ionic strength and extreme pHs. Such good stability ensures further treatments, such as chemical reactions and loading of functional substances.

     

Continuous Production of Functionalized Polymer Particles Employing the Phase Separation in Polymer Blend Films

This study reports a continuous prepartion of spherical or hemispherical polymer particles simply utilizing the phase separation in polymer blend films during the coating process. We took an advantage of the strong phase separation between a water‐soluble crystalline polymer as a matrix and hydrophobic polymers as minor components. We demonstrated the prepartion of water‐soluble polystyrene (PS) particles, nitrilotriacetic acid (NTA)‐functionalized PS particles for protein separation, and semiconducting poly(3‐hexylthiophene) (P3HT) particles. The sizes of the particles could be controlled by adjusting the film thickness and weight fraction of the minor component polymers in the blend film. It provides a simple facile way to prepare polymer particles in a continous process.

     

Effect of Chemical Crosslinking on the Swelling and Shrinking Properties of Thermal and pH‐Responsive Chitosan Hydrogels

The ability to form a gel through the physical or chemical crosslinking of chitosan has been well documented. In an attempt to mimic biological systems, thermal and pH‐sensitive chitosan cylindrical hydrogels were produced by a combination of physical and chemical crosslinking processes. To this end, chitosan hydrogels prepared from alkali chitin were molded in cylinders and, once washed, were further crosslinked with glutaraldehyde at stoichiometric ratios, R (= [? CH?O]/[? NH₂]), of 1.61 and 3.22 × 10^?2. Variation in swelling as a result of stepwise changes in temperature between 40 and 2 °C at pH values of 7.0, 7.6, and 8.0 revealed that the system responds in markedly different manners dependent upon the pH. At pH 7.0, cooling from 40 to 2 °C results in contraction of the gel network structure. While raising the temperature from 2 to 40 °C leads to a rapid swelling response (i.e., ca. a twofold increase in the amount of solvent uptake). Subsequent cooling to 2 °C is accompanied by a new contraction cycle. At pH ≥ 7.6 the temperature dependence of the swelling–contraction behavior is exactly the opposite of that observed at pH 7.0. Very similar trends were observed for the gels at both degrees of crosslinking. The swelling–shrinking behavior observed in gels of pH ≥ 7.6, is similar in kind to that of uncrosslinked gels and is interpreted in terms of a lower critical solution temperature (LCST) volume phase transition, driven by hydrophobic association, presumably involving residual acetyl groups in the chitin. The results at pH 7.0 suggest that the slight ionization of the ? NH groups leads to destruction of the hydrophobic hydration thus effectively reversing the negative thermal shrinking.

Evolution of the swelling ratio, S, as a function of time and temperature for crosslinked chitosan hydrogels. Circles represent S values recorded at pH 7.0 and triangles those at pH 7.6.     

Ethylene‐Norbornene Copolymerization by New Titanium Complexes Bearing Tridentate Ligands. Sidearm Effects on Catalytic Activity

The Ti complexes containing tridentate [O⁻NS^R] (R = Me, ⁱPr) ligands with alkylthio sidearms were prepared. The methylthio ether complex (R = Me shown in the Scheme) exhibits an excellent activity for copolymerization of ethylene with norbornene upon activation with MMAO, which is 10 times more active than the corresponding phenylthio one (R = Ph).