Nanostructure and Shape Control in Polymer‐Ceramic Hybrids from Poly(ethylene oxide)‐block‐Poly(hexyl methacrylate) and Aluminosilicates Derived from Them

Summary: The present study describes the use of poly(ethylene oxide)‐block‐poly(hexyl methacrylate) diblock copolymers (PEO‐b‐PHMA) as structure‐directing agents for the synthesis of nanostructured polymer‐inorganic hybrid materials from (3‐glycidylpropyl)trimethoxysilane and aluminium sec‐butoxide as precursors and organic, volatile solvents. Four different morphologies, i.e., inorganic spheres, cylinders, lamellae, and organic cylinders in an inorganic matrix, are obtained confirmed by a combination of small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). The composites are further characterized by differential scanning calorimetry (DSC) and solid‐state ¹³C, ²⁹Si, and ²⁷Al NMR. It is demonstrated that the change in the hydrophobic block from polyisoprene (PI) to poly(hexyl methacrylate) (PHMA) has no significant effect on the local structure of the inorganic rich phase. By the dissolution of the composites rich in poly(hexyl methacrylate), nano‐particles of different shapes, i.e., spheres, cylinders, and lamellae, are obtained as demonstrated by atomic force microscopy (AFM) and TEM. Finally, calcination of composites with the inverse hexagonal structure at elevated temperatures up to 600 °C results in nanostructured aluminosilicates that retain their structure as evidenced through a combination of SAXS and TEM. The study opens pathways towards tailoring filler‐matrix interactions in model nanocomposites and builds the bases for the preparation of composites from multiblock copolymers with polyisoprene (PI), poly(ethylene oxide) (PEO), and poly(hexyl methacrylate) (PHMA) as building blocks.

Bright field TEM micrograph of composite T55/1 with inverse hexagonal morphology after calcination.     

Hyperbranched Poly[bis(alkylene)pyridinium]s

3,5‐Bis(bromomethyl)pyridine hydrobromide and 3,5‐bis(bromobutyl)pyridine hydrobromide were synthesized from commercially available 3,5‐lutidine. The poly(N‐alkylation) of these monomers readily yielded new hyperbranched polyelectrolytes. The progress of reaction was followed by ¹H NMR. A second‐order kinetic scheme fits the experimental data. Rate constants and activation parameters were determined, showing the higher reactivity of 3,5‐bis(bromomethyl)pyridine hydrobromide. This was explained by the electron‐attractive effect of pyridinium groups on the ? CH₂Br end groups. The structures of the hyperbranched poly[3,5‐bis(alkylene)pyridinium]s were investigated by ¹H and ¹³C NMR spectroscopy and a preliminary study of their properties is reported.

     

Interaction Between Polymer Chains Covalently Fixed to Single‐Walled Carbon Nanotubes

Summary: A single‐walled carbon nanotube (SWNT), which had been oxidized with a mixture of nitric acid and sulfuric acid to afford polar groups at its ends, was incubated with an azo‐type macroinitiator carrying dextran (DEX), poly(ethylene glycol) (PEG) or poly(N‐vinylpyrrolidone) (PVPy) chains at 70 °C. Similarly, the oxidized SWNT was incubated with 2,2′‐azoisobutyronitrile and acrylic acid (HAA) or N‐vinylpyrrolidone at 70 °C. Due to the large radical trapping ability of SWNT, the polymer chains corresponding to the cloven macroinitiator (PEG, DEX or PVPy) and the propagating polymer chains (poly(acrylic acid) (HPAA) or PVPy) were covalently fixed to the surface of the SWNTs. The hydrophilic polymer‐modified SWNTs could be stably dispersed in water. Furthermore, the SWNTs modified with PEG and DEX sedimented in the presence of free DEX and PEG, respectively, whereas there was no precipitation of the PEG‐ and DEX‐modified SWNTs in the presence of the same kind of free polymer. This seemed to be related to the phase separation phenomena in water soluble DEX and PEG systems induced by the repulsive interaction between PEG and DEX molecules. However, the mixture of two kinds of polymer‐modified SWNTs (PEG‐SWNT and DEX‐SWNT) did not show noticeable phase separation, probably due to steric hindrance for the efficient repulsive polymer‐polymer interaction by fixation to the gigantic SWNTs. Furthermore, upon mixing the dispersions of HPAA‐SWNT and PEG‐SWNT or PVPy‐SWNT, the turbidity of the dispersions gradually increased, while no increase in turbidity of the dispersion mixture was observed in the presence of dimethyl sulfoxide, indicating hydrogen bonding between the HPAA and PEG or PVPy chains on the surface of the SWNTs. The modification methods examined in this work would be promising to give various functions to SWNT.

Susceptible processes of radical trap on SWNT surface.     

Friction and Mechanical Properties of Highly Filled Polybenzoxazine Composites: Nanosilica Particle Size and Surface Treatment

Frictional and mechanical properties of highly filled polybenzoxazine [poly(BA‐a)] composites which are influenced by nanosilica contents, particle sizes, and surface treatments are investigated. The coefficient of friction and wear resistance, storage moduli, and microhardness of the nanosilica‐filled poly(BA‐a) composites systematically increase with an increase of nanosilica content, while those values of the nanocomposites are improved with decreasing particle sizes at the equivalent nanosilica content. The modulus can be predicted by the Kerner model with the maximum packing fraction, while the microhardness of the nanocomposites is in agreement with the Halpin–Tsai model. The nanocomposites fabricated with untreated nanosilica particles exhibit higher frictional and mechanical properties when compared with the surface‐treated nanocomposites at the equivalent particle sizes. The interfacial interactions via covalent bond formation between the nanosilica and the poly(BA‐a) are determinative factors for the nanocomposite properties. Highly filled nanosilica‐poly(BA‐a) composites can be employed in various applications where wear‐resistance plays an important role.     

Self‐Healing Metallo‐Supramolecular Amphiphilic Polymer Conetworks

The current challenge in self‐healing materials resides in the design of materials which exhibit improved mechanical properties and self‐healing ability. The design of phase‐separated nanostructures combining hard and soft phases represents an attractive approach to overcome this limitation. Amphiphilic polymer conetworks are nanostructured materials with robust mechanical properties, which can be tailored by tuning the polymer composition and chemical functionality. This article highlights the design of phase‐separated nanostructured polymers from metallo‐supramolecular amphiphilic polymer conetworks, and their application for self‐healing surfaces. The synthesis of poly(N‐(pyridin‐4‐yl)acrylamide)‐l‐polydimethylsiloxane polymer conetworks from the poly(pentafluorophenyl acrylate)‐l‐polydimethylsiloxane activated ester is presented. Loading of ZnCl₂ salt into the phase‐separated polymer conetwork strengthens the network by cross‐linking the poly(N‐(pyridin‐4‐yl)acrylamide) phases, while offering reversible interactions needed for self‐healing ability.     

Complexation Behavior of Cu2+ in the Presence of Iminodiacetic Acid and Poly(ethyleneimine)

Summary: Multicomponent aqueous systems containing Cu²⁺ as metal ion, iminodiacetic acid (IDAA) as a low‐molecular‐weight chelating molecule, and branched poly(ethyleneimine) (BPEI) as a polychelatogen are analyzed at different pH by UV‐Vis spectroscopy and diafiltration. It was found that at pH 4, saturation of BPEI with Cu²⁺ takes place at a Cu²⁺:BPEI ratio of 1:5.7, probably indicating a stoichiometry for the complex of 1:4. At the same conditions the Cu²⁺‐IDAA complex has a stoichiometry of 1:1. The ability of BPEI to bind the metal ion is higher than that of IDAA in mixtures of both chelating molecules. Lowering the pH between 2 and 3.5, protonation of BPEI allows increasing the amounts of Cu²⁺‐IDAA complex so that Cu²⁺ is transferred from the polychelatogen to IDAA. Good correlations are found comparing the results obtained by diafiltration and by UV‐Vis spectroscopy. Moreover, diafiltration results indicate that in the absence of Cu²⁺, IDAA interacts with BPEI with apparent dissociation constants of 2.88 at pH 2.7 and 0.96 at pH 4. These interactions may be responsible for the appearance of an apparent dissociation constant of 3.60 for the interactions between BPEI and the Cu²⁺‐IDAA complex at pH 4.

The binding of Cu²⁺ to branched poly(ethyleneimine) and iminodiacetic acid in water.     

UV Laser Deposition of SiS/Poly(thiacarbosilane) Composites and their Conversion to SiO/Poly(thiacarbosiloxane) Composites

ArF laser irradiation of gaseous mixtures of carbon disulfide and silane allows efficient deposition of Si? S bond‐containing poly(thiacarbosilanes) incorporating SiS bodies. These SiS/poly(thiacarbosilane) composites are the first example of silicon sulfide/polymer composites. Composite formation is analyzed by GC/MS analysis of volatile products and the structure of the composite as determined by electron microscopy and FT‐IR spectra. The composites undergo reaction with air moisture and methanol vapor, evolve H₂S and evolve to nano‐sized poly(thiacarbosiloxane)s and poly(methoxythiacarbosiloxane)s.

     

Ordered Nanostructures of Carbon Nanotube–Polymer Composites from Lyotropic Liquid Crystal Templating

A series of polymer nanocomposites containing single‐walled carbon nanotubes (SWNTs) are prepared from polymerizable quaternary ammonium surfactants using photo‐polymerization and investigated by means of polarized optical microscopy, small‐angle X‐ray scattering, and rheological measurements. The surfactant monomers with various alkyl chains of nonpolar tails form lyotropic liquid crystalline (LLC) mesophases in aqueous medium with hexagonal packing of cylindrical micelles. The physical adsorption of nonpolar tails of surfactants on the surface of SWNTs results in de‐bundled nanotubes. The LLC phase diagram is investigated as functions of alkyl chain length, concentration, temperature, and SWNTs. As such, addition of SWNTs does not change the hexagonal mesophases but enhances the order–disorder transition temperatures and alters the rheological behaviors. After photo‐polymerization, the microstructures of hexagonal packing are changed while addition of SWNTs does not disrupt the resulting microstructures. The polymerized composites are consistent with both lamellar and gyroid nanostructures and a possible model is proposed to interpret the observed phenomenon. Under the shear flow, the defect‐free monodomain structures are obtained in the LLC phase and subsequently locked in the solid film after polymerization.     

Poly(amine‐amide‐imide)s Bearing Pendent N‐Carbazolylphenyl Moieties: Synthesis and Electrochromic Properties

Summary: A series of novel poly(amine‐amide‐imide)s with pendent N‐carbazolylphenyl units that have inherent viscosities of 0.45–0.66 dL · g⁻¹ are prepared from various aromatic bis(trimellitimide)s and the new carbazole‐based aromatic diamine, 4,4′‐diamino‐4″‐N‐carbazolyltriphenylamine, by direct polycondensation. All the polymers are readily soluble in polar organic solvents. Flexible, amorphous, and deep reddish films of poly(amine‐amide‐imide)s can be obtained by solution casting, and have useful levels of thermal stability associated with high glass transition temperatures (307–343 °C), 10% weight‐loss temperatures in excess of 500 °C, and char yields at 800 °C in nitrogen higher than 65%. These polymers exhibit a maximum UV‐vis absorption at 300 nm with a fluorescence emission maxima around 449–454 nm in N‐methyl‐2‐pyrrolidinone solution. The hole‐transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine‐amide‐imide) films cast onto an indium tin oxide‐coated glass substrate exhibit a reversible oxidation at 0.84 V and irreversible oxidation redox couples at 1.27 V versus Ag/AgCl in acetonitrile solution, and reveal good stability of electrochromic characteristics, with a color change from yellowish to green at applied potentials ranging from 0.00 to 0.95 V.

Structure and properties of PAI‐2M (bottom left: cyclic voltammetry; bottom right: potential‐step absorptometry).     

Mechanisms of Moisture Sorption in Barrier Polymers Used in Food Packaging: Amorphous Polyamide vs. High‐Barrier Ethylene‐Vinyl Alcohol Copolymer Studied by Vibrational Spectroscopy

The nature of the association between sorbed water and two high‐barrier hydrophilic polymers used in oxygen‐sensitive food packaging, and exhibiting opposite oxygen barrier behavior in the presence of moisture, has been studied by FT‐Raman and FT‐Infrared spectroscopy. The polymers considered in this work were an ethylene‐vinyl alcohol copolymer with superior oxygen barrier properties (32 mol‐% of ethylene EVOH) and an amorphous polyamide (aPA). The results revealed that for the latter glassy amorphous polymer, water molecules associate with the C?O and N? H groups of the ca. 10% “free” amide moieties, being the excess sorbed water self‐associated in clusters; thus, moisture sorption does not appear to disrupt the originally present hydrogen‐bonded amide groups. This “unusual” behavior leads to an overall increase in the extension of the hydrogen‐bonding, which may help explain the lower oxygen permeability displayed by the aPA with increasing relative humidity on the basis of the known free‐volume competing mechanism. Differently, water sorption appears to progressively disrupt the strong polymer self‐association present in the very efficient high‐barrier semicrystalline EVOH material by hydrogen‐bonding to hydroxyl groups, hence leading to the well‐known highly plasticized rubbery structure with much lower intermolecular cohesion and oxygen barrier.

FT‐IR spectra of severely dried, dry (dotted), and water‐equilibrated (thicker line) aPA in the range 2 600–3 800 cm^?1.     

Ethylene‐co‐Norbornene Copolymers Grafted Carbon Nanotube Composites by In Situ Polymerization

Vinyl functionalized multiwalled carbon nanotubes (MWCNT‐vinyl) are synthesized and used as monomers to prepare poly(ethylene‐co‐norbornene)‐grafted carbon nanotube composites by in situ polymerization with [Ti(η⁵‐C₅Me₅)(N?C^tBu₂)Cl₂] activated with methylalumoxane (MAO). The glass transition temperatures (T_g) of grafted MWCNT composites are more than 30 °C higher than those of copolymers. This difference is rationalized by the immobilization of the copolymer chain to the MWCNT surface by a covalent bond. The Young's modulus is shown to increase by more than 200% compared to poly(ethylene‐co‐norbornene) by incorporating 3.4 wt% functionalized MWCNT.     

Solid‐State Electrochromic Devices via Ionic Self‐Assembled Multilayers (ISAM) of a Polyviologen

A PV was synthesized by polymerization of N,N′‐bis(δ‐aminopropyl)‐4,4′‐bipyridinium bromide hydrobromide (APD) and isophthaloyl chloride (ISP). The PV was completely soluble in water as well as in organic solvents. The spectroelectrochemical and EC properties of the resulting ionic self‐assembled multilayers of PV/poly‐(2‐acrylamido‐2‐methylpropanesulfonic acid) (PAMPs) were examined by cyclic voltammetry, FT‐IR spectroscopy, UV‐vis spectroscopy, optical switching and current density measurements. Solid state devices made of PV films sandwiched with PANI as a counter electrode have switching times of 100–250 ms. 40 Bilayer films of PV/PAMPs show high contrast (ΔT = 61%) in 0.1 M NaClO₄ liquid electrolyte solution and CE as high as 57 cm² · C^?1, one of the highest reported so far for any bipyridinium salt system.

     

Energy Consumption for the Desalination of Salt Water Using Polyelectrolyte Hydrogels as the Separation Agent

The energy consumption for a novel desalination approach using charged hydrogels under externally applied pressure is experimentally measured and calculated. The salt separation is based on a partial rejection of mobile salt ions caused by the fixed charges inside the polyelectrolyte network. Self‐synthesized and commercial poly(acrylic acid) hydrogels are used to study the desalination performance in reference to sodium chloride solutions within the concentration range of 0.1–35 g L⁻¹. The influence of various synthetic parameters, such as the degree of crosslinking (DC) and the size and shape of the particles, is investigated. Furthermore, the effect of process parameters including the amount of the feed solution, the applied pressure profile, and the swelling time of the hydrogel is discussed. The best energy estimation found so far, is 8.9 kWh m⁻³ fresh water if a poly(acrylic acid) with a DC of 5 mol% is used in an infinite large salt bath.     

Solid Polymer Electrolytes Based on Copolymers of Cyclic Carbonate Acrylate and n‐Butylacrylate

Solid polymer electrolytes (SPEs) are prepared by mixing poly(2‐oxo‐1,3‐dioxolan‐4‐yl)methyl acrylate‐random‐n‐butylacrylate) [P(cyCA‐r‐nBA)] statistical copolymers with bis(trifluoromethane)sulfonimide lithium salt. The P(cyCA‐r‐nBA) copolymers are synthesized by reversible addition‐fragmentation chain transfer polymerization and different molar masses as well as copolymer composition are targeted in order to study the influence of the molecular parameters on the thermal, mechanical, and electrochemical properties of the SPEs obtained after mixing the copolymers with lithium salts. In the investigated experimental window, it is shown that the thermal and mechanical properties of the SPEs mainly depend on the composition of the copolymer and are poorly influenced by the molar mass. In sharp contrast, the ionic conductivities are more deeply influenced by the molar mass than by the composition of the copolymers. In this respect ionic conductivity values ranging from 4.2 × 10^?6 S cm^?1 for the lower molar mass sample to 8 × 10^?8 S cm^?1 for the higher molar mass one are measured at room temperature for the investigated SPEs.     

Premature degradation of poly(α-hydroxyesters) during thermal processing of Bioglass®-containing composites

Bioactive, biodegradable composites are increasingly being explored as bone replacement materials and as scaffolds for tissue engineering. Their properties are not only dependent on the properties of the filler and matrix, but are also determined by their interaction. This study investigated the effect on poly(d,l-lactide) (PDLLA) matrix when processed at high-temperatures in the presence of Bioglass^® particulate filler. Composites with different filler contents were compounded at elevated temperatures by co-extrusion followed by compression moulding and compared with composites of similar composition prepared by thermally induced phase separation (TIPS), a low-temperature processing route. It was found that the inclusion of Bioglass^® in PDLLA under elevated temperatures resulted in the degradation of the matrix, leading to a reduction in the mechanical properties of the composites and in the molecular weight of the matrix. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy showed the presence of a peak at 1600 cm^?1 in the composite material, particularly when processed at elevated temperatures, whereas no peak at this wavelength was discernible for the pure PDLLA. Furthermore, time-based ATR-FTIR spectra taken at elevated temperatures on the TIPS-processed composites showed an increase in the intensity of the peak at 1600 cm^?1 and a concomitant reduction of the CO stretch peak at 1745 cm^?1 with time. This suggested the formation of a carboxylate salt by-products as a consequence of a reaction at the interface between the Bioglass^® filler and the PDLLA matrix. Therefore, the results confirmed that this degradation was not solely due to shear effects during the extrusion process. This work thereby supports the assertion that, in the presence of Bioglass^® filler particles, poly(α-hydroxyester)-based composites should not be processed at elevated temperatures.     

Functionalization of Shortened Single‐Walled Carbon Nanotubes with Poly(p‐dioxanone) by “Grafting‐From” Approach

Summary: It has been a real challenge to form carbon nanotube (CNT)/polymer composites where CNTs are well‐dispersed in the polymer matrix and the interactions between CNTs and polymers are effectively strong. In this paper, we applied surface‐initiated, ring‐opening polymerization (SI‐ROP) of p‐dioxanone (PDX) to shortened single‐walled carbon nanotubes (s‐SWCNTs) and successfully formed s‐SWCNT/PPDX composites (see Figure). Due to intimate interactions between s‐SWCNTs and PPDX, we observed dramatic changes in PPDX properties upon the formation of the composites: 10%‐weight‐loss‐temperature of PPDX increased by 20 °C (measured by thermogravimetric analysis) and the patterns of T_g and T_m were greatly altered. We did not observe any noticeable peaks from the composite up to 120 °C in differential scanning calorimetry (DSC), while DSC data of PPDX itself showed T_g and T_m at ?13.4 and 103 °C respectively.

Schematic representation of the procedure for formation of s‐SWCNT/PPDX composites.     

Self‐Healable and Conductive Double‐Network Hydrogels with Bioactive Properties

Nanocomposite hydrogels are a class of materials that are generally composed of hydrophilic polymers and nanofillers. They can have various important properties such as self‐healing, conductivity, toughness, bioactivity, facile processing ability, and this enables manifold practical applications. However, development of a single nanocomposite hydrogel with all of the properties of interest is yet to be realized. Here, a double‐network (DN) polymer hydrogel consisting of poly(vinyl alcohol)‐poly(sodium 4‐styrene sulfonate)‐poly(2‐aminoethylenemethacrylate) polymers (PVA‐P(NaSS)‐P(AEMA)) is reported. The obtained DN hydrogels containing copper ions, (PVA‐P(NaSS)‐P(AEMA)@Cu²⁺) hydrogel and copper nanoparticles (PVA‐P(NaSS)‐P(AEMA)@Cu) hydrogels, are found to exhibit self‐healing, conducting, high mechanical, bioactive, and wound healing properties. The fabricated hydrogel may potentially be applied in the biomedical and electronics sector.     

Self‐Assembly of Porphyrin‐Centered Amphiphilic Star Block Copolymer into Polymeric Vesicular Aggregates

Polymeric vesicular aggregates with spherical and tubular shapes were formed from the self‐assembly of a porphyrin‐centered amphiphilic star poly(oxazoline) [poly(phenyloxazoline)‐block‐poly(methyloxazoline)] in an DMF/water mixture containing excess DMF. The aggregates were evaluated by means of UV‐Vis, fluorescent, ¹H NMR spectroscopies, and optical microscopy. The driving force to induce the vesicular aggregates is the interactions between poly(phenyloxazoline) segments which were insoluble in DMF rich aqueous medium.

Polymeric vesicular aggregates with spherical and tubular shapes were formed from the self‐assembly of a porphyrin‐centered amphiphilic star poly(oxazoline) [poly(phenyloxazoline)‐block‐poly(methyloxazoline)] in an DMF/water mixture.     

Double Hydrophilic Poly(ethylene oxide)‐block‐Poly(dehydroalanine) Block Copolymers: Comparison of Two Different Synthetic Routes

Two different synthetic pathways give access to the amphiphilic block copolymer poly(ethylene oxide)‐block‐poly(tert‐butoxycarbonylaminomethylacrylate). In the first approach, two end‐functionalized segments are linked via click chemistry; and in the second approach, a poly(ethylene oxide) (PEO) based macroinitiator is chain extended via atom transfer radical polymerization (ATRP). In both cases the linking unit consists of an amide group, which is necessary to effectively deprotect the corresponding polymer precursor without cleavage of both segments. For this, amide‐containing ATRP initiators are employed and successful synthesis by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) analyses before comparing both pathways is demonstrated. After deprotection, a novel double hydrophilic block copolymer, poly(ethylene oxide)‐block‐poly(dehydroalanine), is obtained, which is investigated using SEC (aqueous and DMSO) and ¹H‐NMR spectroscopy. Containing a potentially zwitterionic PDha segment and a high density of both amino and carboxylic groups, pH‐dependent aggregation of the block copolymer is expected and is studied using dynamic light scattering, revealing interesting solution properties. The corresponding polymers are applied in various areas including drug delivery systems or in biomineralization.     

Systematic Investigation of a Novel Low‐Bandgap Terpolymer Library via Inkjet Printing: Influence of Ink Properties and Processing Conditions

The thin‐film properties of a polymer library consisting of novel conjugated low‐bandgap poly(diketopyrrolopyrrole‐co‐benzothiadiazole‐co‐fluorene) (poly(DPP‐co‐BTD‐co‐F)) polymers are investigated. The content of the monomer units in the copolymers is systematically varied. Structure–property relationships are obtained for the ink characteristics, the film formation qualities, and their optical properties. Toluene/o‐DCB in a ratio 90/10 and a concentration of 5 mg mL^?1 is found to be a suitable solvent system for all polymers. The polymer compositions and the choice of solvent have a significant influence on the film properties. Inkjet printing is shown to be a suitable technique for the preparation of thin‐film libraries that subsequently can be characterized by combinatorial screening tools.