Combining RAFT Radical Polymerization and Click/Highly Efficient Coupling Chemistries: A Powerful Strategy for the Preparation of Novel Materials

This paper highlights the powerful combination of reversible addition–fragmentation chain transfer (RAFT) radical polymerization and various click/coupling chemistries. This is not an exhaustive review but rather an overview demonstrating the impressive possibilities that the “marriage” of these two synthetic approaches offers in modern macromolecular design and synthesis.

     

All‐Conjugated,Rod‐Rod Block Copolymers‐Generation and Self‐Assembly Properties

Based on their rigid‐rod structure all‐conjugated, rod‐rod block copolymers show a preferred tendency to self‐assemble into low‐curvature vesicular or lamellar nanostructures independent from their specific chemical structure and composition. This unique and attractive behaviour is clearly illustrated in a few examples of such all‐conjugated block copolymers. The resulting nanostructured heteromaterials may find applications in electronic devices or artificial membranes.

     

Polymerization of Aniline by Auric Acid: Formation of Gold Decorated Polyaniline Nanoballs

Summary: We report a new method for the preparation of polyaniline nanoballs by using HAuCl₄ as an oxidizing agent. During the reaction, aniline is oxidized and forms polyaniline whilst the hydrogen tetrachloroaurate is reduced and forms gold nanoparticles. These gold nanoparticles are found to decorate the nanoballs.

The resultant precipitate and corresponding TEM image of the gold‐nanoparticle covered polyaniline nanoball.     

A Density Functional Theory Study of Secondary Reactions in n‐Butyl Acrylate Free Radical Polymerization

In this work, secondary reactions involved in the free radical polymerization of butyl acrylate are investigated using quantum chemistry. First, various backbiting reactions are studied by adopting a simplified molecular model suitable for treating long polymer chains. The predicted reaction kinetics suggest the possibility of a radical migration along the poly(butyl acrylate) (PBA) chain as a consequence of subsequent j:j + 4 hydrogen abstractions, which are characterized by a low activation energy. Moreover, branching propagation and β‐scission reactions originating from mid‐chain radicals are investigated using a complete PBA model composed of five monomer units. The reaction kinetics involving short‐branch radicals are also examined, and a novel backbiting step leading to the formation of short branches is proposed.

     

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.     

Complexation of Syndiotactic Polystyrene with 12‐Crown‐4

Solid‐state complexation of syndiotactic polystyrene (sPS) with a crown ether compound, 1,4,7,10‐tetraoxa‐cyclododecane (12‐crown‐4), took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted with a plasticizing agent. The new guest 12‐crown‐4 molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of host sPS helices. X‐ray diffraction and thermogravimetric investigations showed that sPS/12‐crown‐4 complex had a clathrate complex structure which contained four 12‐crown‐4 molecules per unit cell. IR and Raman data suggested that 12‐crown‐4 took a C_i‐type conformation in the sPS complex phase.

     

Carbon Nanotubes as a Ligand in Cp2ZrCl2‐Based Ethylene Polymerization

Summary: We report a simple method for tuning catalytic property of a metallocene‐based catalyst, Cp₂ZrCl₂, for ethylene polymerization by the direct adsorption of Cp₂ZrCl₂ onto multi‐walled carbon nanotubes (MWCNTs). The direct interactions between MWCNTs and the Cp rings of Cp₂ZrCl₂ controlled the polymerization behaviors, and we could generate polyethylene with an extremely high molecular weight ( = 1 000 000) at 30 °C and under 1 atm of ethylene gas.

Preparation of Cp₂ZrCl₂‐MWCNT.     

Phantom Chain Simulations of Realistically Sized Polymer‐Based Nanocomposites

Summary: Phantom chain MC simulations have been performed for realistically sized systems of polymer chains filled with solid nanoparticles. The results of the simulations and simple theoretical considerations are used to rationalize a number of parameters relevant to the characterization of these systems. Even when the average number of nanoparticles in contact with a chain is very small (much less than unity), the nanoparticles are nodes of highly interconnected transient networks bridged by the polymer chains.

     

Fabrication of Thermo‐Responsive Hybrid Hydrogels by In‐Situ Mineralization and Self‐Assembly of Microgel Particles

Summary: An in‐situ mineralization process in the presence of thermo‐responsive microgels leads to the formation of well‐defined hybrid materials. Experimental data suggest that control of the mineralization process in the presence of the microgels offers the possibility to obtain sub‐micrometer‐sized hybrid particles or macroscopic hybrid hydrogels. The rapid formation of CaCO₃ crystals in the microgel structure favors the preparation of the hybrid particles wherein inorganic crystals cover the shell layer of the microgel. The slow formation of CaCO₃ crystals leads to the simultaneous self‐assembly of the microgel particles on the bottom of the reaction vessel, and the formation of a physical network. It has been demonstrated that hybrid hydrogel materials with different calcium carbonate contents and temperature‐dependent swelling‐deswelling properties can be prepared.

Formation of a hybrid hydrogel by the vapor diffusion method.     

Alternating Poly(Pt‐salphen)‐(p‐phenyleneethynylene) as Phosphorescent Conjugated Linear‐Rod and Coilable Sensory Materials

Phosphorescent conjugated polymers consisting of alternating p‐phenylene‐ethynylene and ‘para‐’ or ‘meta‐type’ Pt(II)‐salphen luminophore units have been synthesized. Side‐arms bearing different substituents (n‐alkoxy and acetylated‐sugar) have afforded contrasting emission properties that are attributed to the polymer conformation, extent of π‐stacking interactions and differences in chemical structure. Intriguing selectivity in luminescent sensing of metal ions has been observed.

     

Dry Spinning Based Spinneret Based Tunable Engineered Parameters (STEP) Technique for Controlled and Aligned Deposition of Polymeric Nanofibers

Polymeric nanofibers are finding increasing number of applications and hold the potential to revolutionize diverse fields such as tissue engineering, smart textiles, sensors, and actuators. Aligning and producing high aspect ratio fiber arrays (length/diameter > 2 000) in the sub‐micron and nanoscale diameters has been challenging due to fragility of polymeric materials, thus making it difficult to deposit them as one dimensional structures functionally interfaced with other systems. Here, we present a pseudo dry spinning technique which allows precise control on fiber diameters and further allows deposition of fiber arrays in aligned configurations. Control on fiber diameters ranging from 50–500 nm and having lengths of several millimeters is achieved by altering the polymeric solution concentration. In the dilute and semi‐dilute unentangled concentration domain droplets or beaded fibers are observed to form. Smooth uniform diameter fibers are observed to form at the onset of semi‐dilute entangled concentration regime. For a given molecular weight, the increase in fiber diameter with increasing solution concentration is attributed to both the increase in the entanglement density and the decrease in the radius of gyration of solvated polymer molecules. Using this technique polymeric fiber arrays in single and multiple layers are demonstrated which can be used towards developing strong textiles, biological scaffolds, and sensor networks.

     

Interconversion of Planar Networks and Vesicles Triggered by Temperature

Dumbbell‐shaped amphiphiles based on an elongated rod segment can self‐assemble into planar networks with in‐plane hexagonally ordered pores in aqueous solution. On increasing temperature, the 2D networks change into hollow capsules passing through the closed sheets as an intermediate structure due to a LCST behavior of the oligoether dendritic exterior. The primary driving force for this interesting feature seems to originate from a consequence of the energy balance between hydrophobic interactions of anisotropic rod segments and alkyl chains, and repulsive interactions between dissimilar blocks. This dynamic structural variation triggered by external stimuli in a self‐assembling system can provide a useful strategy to create smart supramolecular materials and biomimetic systems.