The morphological behavior of PS‐containing diblock copolymer blends is reported. Three sets of PS/PLA and PS/PEO blends are prepared and evaluated by SAXS, WAXS, DSC, and DMA. No macrophase separation is observed, and the formation of PLA/PEO composite cylinders is identified by SAXS for all compositions. The PLA and PEO segments in these blends have been found to be miscible and the crystallization of the confined PEO is suppressed in the ordered nanostructures. The domain spacing, diameter of composite cylinders, and order/disorder transition temperature could be tuned by varying the blend composition in the binary blends.
Segmented block copolymers comprised of flexible PEO segments and monodisperse crystallizable bisestertetraamide segments have been synthesized. The influence of the terephthalic units in the soft phase on the transitions and the thermal mechanical and elastic properties are studied. The presence of terephthalic units in the copolymer increases the glass transition temperature of the soft phase by ≈5 °C. The low‐temperature flexibility of the copolymers is improved because of the lower crystallinity and melting temperature of PEO. With the use of terephthalic‐extended PEO segments, segmented block copolymers with low moduli (G' < 15 MPa) and good elastic properties could be obtained.
Blends of poly(ethylene oxide) (PEO) and novolac‐type phenolic resin were investigated for potential use as a crystallizable switching component for shape‐memory polymer systems with adjustable switching temperature. High‐molecular‐weight PEO and novolac blends with low novolac content were studied. Dynamic and isothermal DSC studies indicated a significant decrease in the crystallization temperature as a result of incorporation of novolac. We investigated the spherulitic morphology using a cross‐polarized optical microscopy and found a decrease in size and regularity of the spherulites with increasing novolac content. The rheological and mechanical properties corroborated the existence of strong interactions through H‐bonding in the amorphous phase.
We synthesized xanthene‐based oligothiophene‐layered polymers containing bithiophenes, terthiophenes, quaterthiophenes and quinquethiophenes by the Suzuki‐Miyaura coupling reaction. The polymers were characterized by various spectroscopic and electrochemical methods. They were well soluble in common organic solvents and thermally stable. Effective π‐π interactions among the layered oligothiophene units in the polymer backbone were not observed in the ground state as well as in the excited state. A possible application of the polymers in opto‐electronic devices such as hole transporting materials is expected.
The isothermal crystallization kinetics of PEO and PE blocks within various triblock terpolymers were studied by DSC. The effect of the geometry of the microdomains was analyzed by studying different compositions of PE‐b‐PS‐b‐PEO triblock terpolymers. The crystallization rate decreased for decreasing block content for both crystallizable blocks. The effect of the microdomain geometry, confinement or chain tethering on the crystallization of PEO was extensively studied by comparing pairs of triblock terpolymers with differences either in the nature (crystalline, glassy, amorphous) or in the location of the other blocks in the terpolymer.
We introduce and discuss the recently developed concept of electrostatic self‐assembly for the formation of nanoscale assemblies in solution. As opposed to many approaches to self‐assembly relying on amphiphilicity, the driving force here is electrostatics plus secondary interaction such as stacking of aromatic molecule parts: Polyelectrolyte dendrimers can be linked with multiply charged aromatic dye molecules as “structural counterions” yielding 100 nm scale aggregates of narrow size distribution and different shapes. We discuss competing interaction forces and the potential of this approach to lead to versatile and functional supramolecular structures.
We report the first study of using CPE to disrupt block copolymer micelles containing an organic chromophore. Micelles formed by an amphiphilic diblock copolymer composed of PEO and PCMA are electrochemically active in aqueous electrolyte solution, displaying an irreversible oxidation process of coumarin at a potential of about 1.75 V. CPE of the micellar solution at the fixed oxidation potential allows a large amount of coumarin moieties inside the hydrophobic micelle core to be electrochemically oxidized, resulting in the transformation of small polymer micelles (ca. 38 nm) onto larger aggregates (ca. 1 µm). This study demonstrates that electrochemical redox reactions can be explored as a means to disrupt block copolymer micelles that contain a light‐sensitive organic chromophore such as coumarin.
Three new low‐bandgap copolymers containing 3,6‐linked carbazole units are synthesized and characterized using a combination of spectroscopic and electrochemical techniques and DFT calculations. The electron‐withdrawing effect of the BTD units leads to a significant decrease of the optical bandgap from 2.59 eV for PBTC to 1.81 eV for PCDTBT, whereas pendant octyl chains on the thiophene ring lead to an increase of the gap to 2.05 eV for PCDOTBT due to steric hindrance. PBTC:PCBM photovoltaic devices exhibit a PCE of 0.35% with an EQE reaching 35% in the blue region of the solar spectrum whereas PCDTBT:PCBM blends are efficient over a wider spectral range due to the lower bandgap of PCDTBT.
Functionalization of polysulfones by using “Click” chemistry is described for the example of a small fluorescent analyte propargylpyrene. First, PSUs were converted to azido‐functionalized polymers by successive chloromethylation and azidation. Propargylpyrene was prepared independently as a fluorescent click component. Finally, the azido‐functionalized PSUs were coupled with propargylpyrene with high efficiency by copper‐catalyzed azide/alkyne click reactions. The final polymers and intermediates at various stages were characterized by 1H NMR, FT‐IR, GPC, UV‐Vis, and fluorescence spectroscopy techniques.
The originally synthesized hydrophobic hybrid polymer Bu4N+‐POM‐PS is tuned into a giant amphiphile composed of a hydrophilic H+‐POM head and a hydrophobic PS tail through protonation. Immediately, the hybrid amphiphiles self‐assemble into vesicles. A further annealing treatment induces an evolution from vesicles to tubular aggregates containing H+‐POM nanotubes wrapped with PS coronas. After this transformation, the tubular aggregates grow further and then arrange in a parallel manner to form domains. This interesting morphology evolution provides us an opportunity to understand the intriguing aggregation behavior of the hybrid amphiphiles and, meanwhile, to generate POM nanotubes which might be utilized to create nanomaterials for potential applications.
The RAFT polymerization of styrene in a solvent consisting of a water/alcohol mixture with different water contents is performed and the solvent effects on polymerization kinetics, polymer chain propagation, and polymer particle growth are evaluated. It is found that the solvent affects the RAFT polymerization kinetics greatly, and the apparent polymerization rate constant (Kpapp) increases with an increase in the water content of the water/alcohol mixture. In addition, RAFT polymerization in a water/alcohol mixture with a higher water content affords better control of the polydispersity index (PDI) of the synthesized polymers. Furthermore, the solvent also exerts a great influence on the growth of the polymer particles. Hollow particles are formed either at the initial polymerization with low monomer conversion or in the solvent with a low water content, whereas solid polymer particles are produced either at high monomer conversion or in the solvent with a high water content.
A series of hydrogels were prepared from cellulose and PVA in NaOH/urea aqueous solution using both physical and chemical crosslinking methods. The hydrogels were secure and biodegradable materials. Their structure and properties were characterized by FTIR spectroscopy, DSC, XRD and SEM. The results indicated that all of the cellulose/PVA hydrogels exhibited homogeneous porous structures and a certain miscibility. The swelling degree and water uptake of the chemical hydrogels were markedly higher than those of the physical hydrogel. This work demonstrates two novel methods to prepare cellulose/PVA hydrogels with different functional properties via a green process.
A novel synthetic strategy towards monodisperse, sequence‐defined polymers is presented. This technique was applied for the synthesis of a set of polymer carriers for DNA delivery combining monodisperse, sequence‐defined PAA segments with PEO blocks. These precision polymers are sequentially assembled from a library of building blocks, enabling programmed interactions and functions by sequence‐specific positioning of different functionalities. Due to the absence of chemical and molecular‐weight distributions in the multifunctional segments, exact correlation of the monomer sequence and (bio)properties is attainable. This is demonstrated by the interactions with plasmid DNA, investigating the dsDNA complexation and condensation properties in dependence of the monomer sequence.
Poly(propylene) polymer nanocomposites containing graphene nanoplatelets (GnPs) with different loadings are fabricated via a facile ex‐situ solution approach. Improved thermal stability and higher crystallinity are observed in the PNCs. Both electrical conductivity and real permittivity increase with increasing GnP loading. Electrical conductivity percolation is observed at 12.0 wt% GnP. The rheological behavior of the PNC melts are also investigated. It is found that the modulus and viscosity are reduced at small GnP loadings and increased above a critical loading.
A versatile approach based on click chemistry to synthesize polyphosphazene glycopolymers is presented. The glucose‐substituted polyphosphazene was synthesized by nucleophilic substitution of poly(dichlorophosphazene) with propargylamine and the subsequent azide/alkyne “click” reaction of poly[di(propargylamine)phosphazene] (PDPAP) with azidosugar. The relative proportion of the glucose substituent can be easily controlled over a broad range by varying the amount of azidoglucose used in the azide/alkyne “click” reaction.
PEO‐based amphiphilic block copolymers that exhibit a pH responsive phase transition behavior are synthesized. The amphiphilic block copolymers show sharp phase transitions in the physiological pH (7.2) range of aqueous media. The block copolymers were efficient stabilizers for the preparation of superparamagnetic iron oxide nanoparticles in aqueous media. The resulting iron oxide nanoparticles in the size range of 5–30 nm showed a relatively good image on the basis of the results on their phantom test. All the materials were characterized by the combination of 1H NMR spectroscopy, size exclusion chromatography, UV/visible spectroscopic analysis, magnetization, transmission electron microscopy, electron diffraction, and X‐ray diffraction pattern analysis.
The controlled integration of sequence‐defined oligopeptides into synthetic polymers leads to peptide‐polymer conjugates with precisely defined, multifunctional peptide segments. These bioconjugates allow for the direct realization of bio‐inspired polymer science. Peptides combine self‐assembly properties with the potential to actively interact with biological systems. Hence conjugates can be exploited to program microstructure formation processes in polymeric materials by controlling secondary interactions between the peptide segments. Moreover, the programmable functionalities of the peptides can be used to tune specific interactions, e.g., between drugs and polymeric drug carriers or between inorganic crystal surfaces and polymeric crystal‐growth modifiers.
Kinetic investigations on the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline were conducted using acetyl chloride, acetyl bromide, and acetyl iodide as initiators. Various polymerization temperatures ranging from 80 to 220 °C were applied under microwave irradiation. The resulting polymerization mixtures were characterized with GC and GPC for the determination of monomer conversion and molecular weight distribution, respectively. Well defined polymers with narrow molecular weight distributions ( = 6 000 Dalton, PDI ≈ 1.10) were obtained with all three initiators.
New synthetic strategies for thiophene‐nickel(II)porphyrin hybrid molecules are described. Three principles—linear direct, linear spacer and lateral spacer connectivities—were realised and compared with respect to their electrochemical behaviour. Computational investigations by DFT methods confirm experimental data and explain cylic voltammetric oxidations. For the linear direct connectivity, the number of thiophene units per substituted position must be at least two, since the porphyrin core acts as conjugation breaker and hinders the formation of higher oligomers. Alternatively an ethynylene spacer can be introduced to increase conjugation and to optimise the conducting properties. The lateral spacer connection mode proved to be best suited to the electrochemical formation of hybrid compounds.
The Diels–Alder reaction of furan and maleimide is used to prepare reversibly cross‐linking polymer gels consisting of furan‐bearing polymer chains and bismaleimides. The roles of chain length, stoichiometry, and concentration on gelation kinetics and other properties are evaluated. Additionally, kinetics of the Diels–Alder reactions in the gelling system are compared with the kinetics of small molecule systems. By combining spectroscopic and rheological techniques, a mechanochemical analysis is performed.
