Polyurethanes with Pendant Hydroxyl Groups: Synthesis and Characterization

Communication: Phenoxycarbonyloxymethyl ethylene carbonate 4 was synthesized from glycerol carbonate and phenyl chloroformate. Polyurethanes with pendant hydroxyl groups were obtained from polycondensation reactions of this AA* monomer with diamines. These polymers contain primary as well as secondary hydroxyl groups. The obtained polyurethanes are amorphous materials. The glass transition temperature decreases with increasing number of methylene groups between the urethane groups.

As the number of methylene groups increases between the urethane groups, the glass transition temperature of the polymer decreases.     

On the β Transition in High Density Polyethylene: the Effect of Transcrystallinity

Summary: Transcrystallinity in UHMWPE fiber‐reinforced HDPE composites promotes a significant β transition that is untypical of high‐density polyethylene. Surface profiling by atomic force microscopy identifies two distinct morphologies in the composite without a boundary phase between them, which coincide with the transcrystalline layer and with the bulk spherulitic matrix. As a result, the claim that attributes this transition to loose chain folds at the lamella surface is favored.

Atomic force microscopy scan of the transcrystalline layer above the fiber with the impression of the fiber in the center.     

Covalently Scaffolded Inter‐π‐System Orientations in π‐Conjugated Polymers and Small Molecule Models

Organic π‐conjugated polymers have emerged as one of the most fascinating classes of materials as they have found utility in a host of plastic electronics technologies. The distance between π‐systems and their relative orientation dictate energy/charge transfer, conductivity, and photophysical properties of these materials in bulk. This Feature Article discusses π‐conjugated polymers and model compounds in which specific inter‐π‐system interactions are covalently enforced and the effect that the scaffolding has on optoelectronic properties.

     

Surface Fixing Effect of Vacuum Evaporated Particles on Polyethylene Single Crystals

Summary: The recrystallization behavior of high density polyethylene (HDPE) single crystals with vacuum evaporated metal chromium or carbon on their surface has been investigated by transmission electron microscopy (TEM) and electron diffraction (ED) techniques. The results indicate that the particle‐coated HDPE single crystals can retain their single crystal structure after complete melting and subsequent recrystallization, with the heat‐treated temperature as high as 200 °C. This phenomenon is attributed to a surface fixing effect of vacuum evaporated Cr or carbon on the single crystals.

A bright‐field electron micrograph and the corresponding electron diffraction pattern of recrystallized Cr‐coated HDPE single crystals.     

Efficient Usage of Thiocarbonates for Both the Production and the Biofunctionalization of Polymers

End group modification of polymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization was accomplished by conversion of trithiocarbonate into reactive functions able to conjugate easily with biomolecules or bioactive functionality. Polymers were prepared by RAFT, and subsequent aminolysis led to sulfhydryl‐terminated polymers that reacted in situ with an excess of dithiopyridyl disulfide to yield pyridyl disulfide‐terminated macromolecules or in the presence of ene to yield functional polymers. In the first route, the pyridyl disulfide end groups allowed coupling with oligonucleotide and peptide. The second approach exploited thiol–ene chemistry to couple polymers and model compounds such as carbohydrate and biotin with high yield.

     

pH‐Responsive Self‐Assembly by Molecular Recognition on a Macroscopic Scale

Macroscopic pH‐responsive self‐assembly is successfully constructed by polyacrylamide(pAAm)‐based gels carrying dansyl (Dns) and β‐cyclodextrin (βCD) residues, which are represented as Dns‐gel and βCD‐gel, respectively. Dns‐gel and βCD‐gel assemble together at pH ≥ 4.0, but disassemble at pH ≤ 3.0. The adhesion strengths for pairs of Dns‐gel/βCD‐gel increase with increasing pH. The fluorescence study on the model system of pAAm modified with 1 mol% Dns moieties (pAAm/Dns) reveals that Dns residues are protonated at a lower pH, which results in the reduction in binding constant (K) for Dns residues and βCD.

     

Design of Soluble Hyperbranched Polythiophenes with Tailor‐Made Optoelectronic Properties

Hyperbranched polythiophenes were prepared via a simple one‐pot synthesis approach based on oxidative coupling of branched conjugated monomers. Only small variations in the building unit and architecture lead to large differences of absorption and photoluminescence properties. Interestingly, soluble hyperbranched polythiophenes with relatively small molecular weights show enhanced absorption at low and high wavelengths compared to linear analogues, such as poly(3‐hexyl thiophenes) with high molecular weights. With this versatile approach we present a method to design tailor made, functional materials with potential applications in optoelectronics.

     

Preparation of Highly Transparent and Thermally Stable Films of α‐Cyclodextrin/Polymer Inclusion Complexes

Films of an α‐cyclodextrin/poly(ε‐caprolactone) inclusion complex have been successfully prepared and show high transparency and heat resistance in comparison to the pure polymer film. The physical properties, such as transparency, mechanical properties, and thermal stability, of the α‐CD‐PCL‐IC films are found to depend on the α‐cyclodextrin‐to‐polymer stoichiometry.

     

Nitroxide‐Mediated Polymerization of Styrene in a Continuous Tubular Reactor

Summary: Nitroxide‐mediated polymerization of styrene in a continuous tubular reactor has been demonstrated for the first time. The polymerization kinetics in the tubular reactor are similar to those in a batch reactor. The number average molecular weight increases linearly with conversion, and chain extension experiments were successful, indicating that the living nature of the polymerization is maintained in the tubular reactor.

Evolution of molecular weight as measured by GPC for chain‐extended latex in continuous tubular reactor.     

Synthesis of Biotinylated Aldehyde Polymers for Biomolecule Conjugation

Biotinylated polymers with side‐chain aldehydes were prepared for use as multifunctional scaffolds. Two different biotin‐containing chain transfer agents (CTAs) and an aldehyde‐containing monomer, 6‐oxohexyl acrylate (6OHA), are synthesized. Poly(ethylene glycol) methyl ether acrylate (PEGA) and 6OHA are copolymerized by reversible addition‐fragmentation chain transfer (RAFT) polymerization in the presence of the biotinylated CTAs. The resulting polymers are analyzed by GPC and¹H NMR spectroscopy. The polymer end groups contained a disulfide bond, which could be readily reduced in solution to remove the biotin. Reactivity of the aldehyde side chains is demonstrated by oxime and hydrazone formation at the polymer side chains, and conjugate formation of fluorescently labeled polymers with streptavidin is investigated by gel electrophoresis.

     

Transparent and Conductive Polyethylene Oxide Film by the Introduction of Individualized Single‐Walled Carbon Nanotubes

It is demonstrated that an optically transparent and electrically conductive polyethylene oxide (PEO) film is fabricated by the introduction of individualized single‐walled carbon nanotubes (SWNTs). The incorporated SWNTs in the PEO film sustain their intrinsic electronic and optical properties and, in addition, the intrinsic properties of the polymer matrix are retained. The individualized SWNTs with smaller diameter provide high transmittance as well as good electrical conductivity in PEO films.