Polymer Chemistry Blog

In this context,  Chiefari and co-workers reported a convenient synthetic method for the systematic preparation of quasi-diblock copolymer libraries utilizing a sequential reversible addition–fragmentation chain transfer (RAFT) polymerization strategy. This approach used a commercially available parallel synthesizer, which allowed the unattended and fully automated synthesis of these libraries in a short period of time. The materials obtained in this investigation have shown properties very similar to those expected in “pure” diblock copolymers as determined by differential scanning calorimetry. The described method can be a useful and less expensive alternative for the rapid preparation and screening of block copolymer libraries.

In this context,  Sprakel and co-workers approached these contradictory constraints through the synthesis of well-defined thermoresponsive surfactants based on di(ethylene glycol)methacrylate and poly(ethylene glycol)methacrylate using Atom Transfer Radical Polymerization. The surfactants showed a Lower Critical Solution Temperature (LCST) of approximately 34°C, independent of molecular weight, which is ascertained by both Differential Scanning Calorimetry as well as Dynamic Light Scattering. Below the LCST, the surfactants stabilized the emulsions for at least four months. Above this temperature the hydrophilic block collapsed and coalescence between the emulsion droplets occurred; this led to demixing of the sample within several minutes. The authors revealed the mechanism for the temperature-triggered coalescence by measurements of the temperature-dependent interfacial tension and by studying the interfacial morphology of surfactant-covered emulsion droplets.

In this context,  Markova et al. intended to use the synthetic advantages of acyclic diene metathesis (ADMET) polymerization (which offers a synthetic route to strictly linear polyethylenes functionalized at precise intervals) for the formation of new membrane materials for low temperature fuel cells. Well-defined, precise poly(vinylbenzyl phosphonic acid) (PVBPA)-containing-polyolefins were obtained for the first time by a combination of ADMET and atom transfer radical polymerization (ATRP), yielding a set of well-defined graft copolymers composed of polyethylene (PE) “backbone” and PDEVBP brushes, precisely placed on every 21st carbon. Quantitative deprotection of the phosphonates led to the corresponding polymer bonded phosphonic acids. The PA-containing electrolytes exhibited sufficient thermal properties with a high mobility for proton conduction. Moreover, the enhancement of the proton conductivity properties compared to the existing phosphonic acid containing block copolymer structures, the improved properties in the high temperature operating regime and the conductivity range  make them interesting membrane materials for future studies.

In their study, Yan and co-workers  reported a facile and effective strategy for the preparation of plastic pH indicator strips and the characterization of their pH sensitivity. They focused their attention on poly(ionic liquids) (PILs) due to their excellent ion exchange capability, enabling the preparation of PILs with a variety of counteranions by polymerization of only one IL monomer and followed by anion-exchange reactions. The pH-sensitive strips were prepared via the cross-linking of imidazolium type IL monomers with acrylonitrile and followed by anion-exchange with sulfonated anionic dyes which bear their negative charge in a wide pH range. The resultant pH indicator strips exhibited enhanced pH-responsive colour changes and robust pH-response reversibility in both aqueous and organic solutions.

In this view, Huang and co-workers reported on the design and the synthesis of a novel supramolecular polymer constructed from two heteroditopic monomers driven by the combination of crown ether-based and charge-transfer molecular recognition. High molecular weight supramolecular polymers were formed by complexation between crown ethers and secondary ammonium salts, and paraquat derivatives and pyrene derivatives, respectively. This kind of supramolecular polymer exhibited the ability to construct nanofibers via electrospinning technology.

In oder to develop materials with recognition properties, Shahgaldian used cyclodextrins (CDs) for their known ability to include hydrophobic drugs into their cavity. Nevertheless, as the range of molecules known to form inclusion complexes with CDs is fairly broad, one can expect that the produced polymers will exhibit a lack of selectivity. With this in mind, 51 water-insoluble cyclodextrin-based polyurethanes were synthesized using a high-throughput approach. The selective molecular recognition properties of the produced polyurethanes were investigated by measuring their capability to bind ten selected compounds from aqueous solutions. Interestingly, the results indicated that the influence of different CDs on the selective molecular recognition properties was fairly limited. It was demonstrated that the selective molecular recognition properties can be suitably designed and optimized by tuning their compositions and successfully applied for selective binding of targets under purely aqueous conditions.

In this context, Claverie and co-workers reported a functional polymer with chemically switchable crystallinity. Linear polyethylenes containing pendant diacetone acrylamide groups were prepared using Pd phosphine sulfonate catalysts. These polymers are easily cross-linked upon reaction with hydrazine, and the cross-links can be cleaved by ozonolysis to regenerate the original polymer. The cross-linked polymer, once heated above the melting point, becomes permanently amorphous, as the crosslinks prevent the chains from packing. Crystallinity can only be recovered with the cleavage of the cross-links. Thus, the polymeric material exhibits two states (crystalline and amorphous) which are triggered upon action of simple chemicals. This study thus offers a proof of principle that crystallinity responds to the action of a chemical stimulus.

In this context, Lefay and co-workers reported an efficient CS modification method based on nitroxide-mediated polymerization (NMP) under heterogeneous conditions. After introduction of acrylamide and/or acrylate functions onto the CS backbone followed by intermolecular 1,2 radical addition of the BlocBuilder alkoxyamine, methyl methacrylate in the presence of a small amount of acrylonitrile or sodium 4-styrenesulfonate was successfully polymerized by NMP under the SG1 nitroxide control. Analyses revealed that 20-30 wt% of synthetic polymers were grafted onto the CS backbone, yielding a hybrid material with potential applications such as a biocompatibilizer.

In this study, Coulembier and co-workers have demonstrated that the preparation of giant regioregular poly(3-hexylthiophene) (P3HT) cyclics is possible with a simple but unperfected aldol reaction from a pre-formed telechelic P3HT. The four-step synthetic strategy is based on a non-metallic aldol cyclization of a designed Luscombe-type regioregular P3HT. AFM analyses highlight that linear and macrocyclic P3HTs give different self-assembled nanostructures. Interestingly, the tubular assembly of the macrocyclic P3HT, with an estimated diameter of 5 nm, could be exploited to incorporate nano-sized structures such as carbon nanotubes or fullerenes, with potential application as a compatibilizer for bulk heterojunction photovoltaic diodes for instance.