The formation of a nanostructured interpenetrating polymer network (IPN) via electropolymerization is described. The electro‐copolymerization of alternate layer‐by‐layer (LbL) self‐assembled polyelectrolytes with thiophene and carbazole pendant monomers was demonstrated facilitating IPN formation of π‐conjugated polymers or conjugated polymer network (CPN) films. UV–Vis spectroscopy, QCM, and ellipsometry confirmed linear nanostructured LbL film growth. Electrochemical crosslinking by cyclic voltammetry (CV) manifested highly regular peak current increases with successive cycles. A quantitative correlation of the LbL layer number with the cathodic charge and scan rate was observed. Electrochemical impedance analysis confirmed CPN film formation and the change in capacitance behavior.
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.
Blends of linear and core‐crosslinked star (CCS) polymers are prepared. The relaxation and thermal properties of the blends are determined using conventional and modulated‐temperature DSC and modulated‐temperature thermomechanometry. Addition of CCS polymers increase the glass transition temperature while decreasing the enthalpy and the linear coefficient of thermal expansion, suggesting that the hyperbranched polymers restrict matrix chain motions. Isothermal annealing increased the Tg and ΔH and decreased sub‐Tgα due to the reduced free volume and mobility within the polymer films. Volume relaxation during annealing is observed using mT‐TM, while a stretched‐exponential function is utilised to interpret the data.
The photo‐polymerization of amphiphilic monomers, two isomers of N,O‐diacylated serine (AM and EM), has been studied. Self‐assembling properties of the monomers were characterized in aqueous media by NMR and fluorescence techniques. These data show that both can form micellar structures by forming hydrophobic cores from both of the polymerizable and alkyl groups. Photo‐polymerizations of AM and EM were performed in their micellar and solution states. In the micellar states, polymerizations proceeded rapidly and reached almost complete conversion within 1 h, while those in DMSO solutions did not. Comparing the polymers obtained, we concluded that EM was more useful for further applications mainly because of the solubility of the resulting polymer. Based on DLS data, the resulting EM‐polymer micelle had a diameter of ca. 20 nm, about ten times larger than the original micelle. Furthermore, preliminary experiments indicated that the micellar state polymerization of EM afforded an encapsulation of pyrene in a stable hydrophobic domain.
A new technology to measure the kinetics of bulk radical polymerization is presented. This technology is easy to connect with all systems using irradiation light, including Raman and IR measurement setups. The curing kinetics of commercially available offset printing dyes (acrylic esters) with initiators have been studied in situ in real‐time by light transmission. The setup consists of a slightly modified diode array UV–Vis spectrometer with a dual purpose xenon arc flash lamp light source. The lateral dependency (irradiation dosage) of the change in the transmitted light has the potential to be interesting for scientific and industrial applications. In addition, options for kinetics studies and quantum efficiencies are introduced to expand the possibilities of studying the polymerization processes.
Monodomains of smectic C liquid crystalline elastomers were prepared by controlled stretching of a polydomain thin film. Specimens were prepared from this film for stress–strain study. A Poisson's ratio of zero was found at small strains for uniaxial stretching perpendicular to the director. For uniaxial strain parallel to the director, Poisson's ratios of approximately 0.4–0.5 were found (by extrapolation) for very small strains. A modulus anisotropy of 8 was found for stretching parallel versus perpendicular to the director.
Among the stimuli responsive polymers, thermally active polymers have attracted great attention because of the accessible and effective characteristics of thermal stimulation. Nanomaterials with their unique properties could serve as “nanoantennas” and “nanoheaters” for harvesting external energy such as electrical, optical, and magnetic, and then convert them into useful thermal energy. With a uniform mixture of the nanomaterials, an external stimulus which has no impact on the thermally responsive polymers could effectively induce the mechanical actuation of polymer nanocomposites. Hence, the trend article aims to present a brief overview of recent progress on the externally induced thermal actuation of polymer nanocomposites as well as provide a summary of the thermal actuation mechanisms. Examples are introduced to highlight the influence of embedded nanomaterials during the actuation progress.
New polyhydrazides and poly(amidehydrazide)s bearing redox‐active carbazole and triphenylamine units were prepared. The resulting poly(1,3,4‐oxdiazole)s and poly(amide‐1,3,4‐oxadiazole)s had high glass‐transition temperatures (288–330 °C) and high thermal stability. The dilute solutions of all the hydrazide and oxadiazole polymers showed a weak–medium photoluminescence with emission maxima around 474–506 nm. The polymer films revealed two well‐defined and reversible redox couples upon electrochemical oxidation, together with interesting electrochromic behaviors. They showed enhanced redox‐stability and electrochromic performance. CV of the oxadiazole polymers also showed reduction processes due to the formation of radical anions of the oxadiazole units.
An alanine‐based peptide doped with charged lysines with a sequence of (AKA3KA)2 (AK2) was selected from the crosslinking regions of the natural elastin as a starting point for the fabrication of chemically diverse and structurally complex peptide/polymer hybrid hydrogels. At low peptide concentration, Pluronic F127 (F127) micelles are capable of increasing the peptide helicity and stabilizing it against thermal denaturation. At higher peptide concentration in basic media, the AK2 peptide developed a substantial amount of β‐sheet structure. The self‐assembled nanoscale structures were covalently interlocked. The crosslinked hybrid hydrogels were viscoelastic, exhibiting an elastic modulus of approximately 17 kPa and a loss tangent of 0.2.
A novel alternating copolymer of sulfonated poly(ether ether ketone‐benzimidazole)s (SPEEK‐BI) was synthesized by polycondensation of aromatic bisphenol containing benzimidazole and a mixture of sulfonated and non‐sulfonated difluorobenzophenones. By varying the amount of two difluorobenzophenones, the ratio of sulfonic acid unit to imidazole base was controlled straightforwardly. The polymer structure was characterized by 1H NMR and IR spectroscopy. Two different methods of ion exchange capacity measurement supported a strong inter‐ and intra‐molecular interaction between acid and base units, which resulted in an improved mechanical strength as well as avoiding phase separation. Tough membranes with good mechanical stability in hot water (80 °C) and alcohol were obtained by solution casting, which is potential for applications in polymer electrolyte membrane fuel cells and membranes for separation of liquids or gases.
A side chain polyrotaxane bearing photoresponsive and nonresponsive recognition sites, i.e., azobenzene (Azo) and heptamethylene (C7) moieties, respectively, linked with a long linker is synthesized. The photoregulated switching of the position of the rotor, i.e., α‐cyclodextrin (α‐CD), in the side chain polyrotaxane is demonstrated by two dimensional rotating frame Overhauser effect spectroscopy and circular dichroism spectroscopy: α‐CD includes the Azo moiety before UV irradiation, whereas α‐CD includes the C7 moiety after trans‐to‐cis photoisomerization of the Azo moieties.
The influence of the doping level in the formation of specific interactions between plasmid DNA and PEDOT is investigated using experimental assays and theoretical calculations. Electrochemical methods are used to prepare polymer samples with oxidation degrees ranging from 0.14 to 1.05 positive charges per repeating unit. A combination of experimental and theoretical results are used to propose a mechanism for the formation of DNA/conducting polymer complexes, which consists of the initial stabilization of the adducts through non‐specific interactions followed by small structural re‐arrangements that allow to be established specific hydrogen bonds involving the polar groups of the conducting polymer and selected DNA bases.
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.
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.
Clickable poly(ethylene glycol) (PEG) derivatives are used with two sequential aqueous two‐phase systems to produce microsphere‐based scaffolds for cell encapsulation. In the first step, sodium sulfate causes phase separation of the clickable PEG precursors and is followed by rapid geleation to form microspheres in the absence of organic solvent or surfactant. The microspheres are washed and then deswollen in dextran solutions in the presence of cells, producing tightly packed scaffolds that can be easily handled while also maintaining porosity. Endothelial cells included during microsphere scaffold formation show high viability. The clickable PEG‐microsphere‐based cell scaffolds open up new avenues for manipulating scaffold architecture as compared with simple bulk hydrogels.
Oriented films of miscible polymer blends of poly(vinylidene fluoride) and poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] were prepared using a flow‐orientation technique. The lamellar structure and crystal orientation depended upon composition and flow temperature (Tflow). An interlamellar exclusion structure was induced in the blend flow‐oriented below 150 °C, whereas an interlamellar inclusion structure was developed above 150 °C. The crystal orientation of PHBHV was affected by the lamellar structures because the PHBHV chains crystallized in the pre‐existing crystalline morphology of PVDF. Crystallization of PHBHV was markedly restricted at lower PHBHV contents.
This contribution describes the preparation and characterization of PEO/montmorillonite nanocomposite gels and films containing various lithium and sodium salts. The objective is to understand how the size and diffusion abilities of different ionic species added to these systems alter the crystallinity of the polymer, and affect the mechanical properties and ionic conductivities of the solid nanocomposites. The network strength of the polymer/clay dispersions influences decisively the crystallinity of the PEO chains and the final layered texture of the solid films. The characteristics of films were investigated using a combination of techniques, such as DSC, DMA, DEA, SEM, SAXS and XRD.
A novel tertiary amine and amino acid‐based “schizophrenic” pH‐responsive block copolymer, PDEA‐b‐PAP, has been synthesized by RAFT polymerization. By directly dissolving this copolymer in acid or basic aqueous solution block copolymer vesicles with switchable coronas and membranes were prepared. These novel assemblies were characterized using TEM, DLS, zeta potential, and SLS analysis.
Telechelic thiopolymers were explored towards formation of doubly‐bound (polymer loops) vs. singly‐bound (polymer brushes) chains on gold substrates. The conformation, adsorption kinetics, and viscoelastic properties of the α,ω‐dithiol and monothiol PS telechelics were investigated by means of XPS and QCM‐D techniques. The oxidation behavior of the free thiol proved to be important for distinguishing doubly‐bound vs. singly‐bound chains. The results show a critical dependence of $\overline {M} _{{\rm n}} $ on the ability to obtain polymer loops. Comparison with unperturbed dimensions obtained by scaling theory show that the loop is less stretched and occupies more lateral space than the brush. The results are important in demonstrating the different and perhaps superior properties of polymer loops vs. singly‐bound polymer brushes.
Nanoprecipitation of poly(methyl methacrylate) (PMMA) in the presence of water‐soluble core cross‐linked star (CCS) polymers is investigated. Slowly dropping water into DMF solutions containing PMMA and CCS polymers of varying compositions produces colloidally stable particles with CCS polymers being effectively incorporated. During the solvent‐shifting process, CCS polymers migrate to and concentrate at the particle surface to stabilize the formed particles, which is confirmed by X‐ray photoelectron spectroscopy, transmission electron microscopy, and contact angle measurements. This stabilizing effect is realized via the steric effect of the CCS polymers adsorbed at the particle surface.
