Hyperbranched polyvinylsulfides have been prepared through a facile, metal-free, radical induced “A₂+B₃” thiol-yne polymerization of 1,3,5-tris(naphthalylethynyl) benzene and 1,4-dithiolbenzene with three different input ratios. The resulting polymers exhibit excellent optical properties like high transparency and very high refractive index (RI) of up to 1.7839, combined with high thermal stability (T_d5% up to 420 °C) and excellent solution processability. These properties make them ideal candidates as high RI polymeric materials (HRIP) in connection with light out-coupling schemes for organic light-emitting diodes (OLEDs). A series of hyperbranched HRIPs with varying monomer compositions have been compared in their optical properties. Finally, phosphorescent monochrome OLEDs are fabricated on top of HRIP layers to test the compatibility of HRIPs with state-of-the-art OLEDs. The results show that the HRIPs do not deteriorate the performance of the OLEDs while maintaining external quantum efficiencies of over 20% for phosphorescent red OLEDs. These results open a pathway toward alternative, low-cost, and scalable out-coupling concepts through refractive index matching of the OLED materials and the HRIPs presented.

For better understanding and improving the non-covalent interactions of dendritic core–shell, we evaluated the interactions of hyperbranched poly(ethylene imine) (PEI) decorated with various oligosaccharide shells with water-soluble B vitamins, an estradiol derivative and pantoprazole. Depending on the different properties of the analyte molecules, dendritic core–shell glyco architectures showed (very) weak, moderate and strong interactions with the analyte molecules. Thus, ionic interactions are the strongest driving force for the formation of host–guest complexes. The core–shell glyco architecture is a necessary prerequisite for stable analyte/PEI complexes; the pure hyperbranched PEI did not show any sufficiently strong interactions with neutral, cationic or anionic analytes under the shear forces applied during ultrafiltration of pure aqueous solution without an adjusted pH. Thus, only robust non-covalent interactions between analytes and the dendritic polyamine scaffold of the glycopolymer structure survive this separation step and allow isolation of stable host–guest complexes in aqueous solution.

Two phase separating block copolymers with photolabile protected amino groups in one block have been synthesized through RAFT polymerization followed by efficient click modification. Techniques like NMR, GPC, and DSC were applied for the characterization of these functional materials. The block copolymers were used for the preparation of thin films where they assemble to form distinct nanostructures as detected by AFM analysis.

Nitrile-ligated copper(II) and zinc(II) complexes comprising (fluoroalkoxy)aluminates as weakly coordinating anions (WCAs) have been synthesized and applied for the polymerization of isobutylene at room temperature (30°C). The polymers obtained are in the low and moderate molecular weight range and show characteristics of the highly reactive polyisobutylene. Results indicate that the fluoroalkoxy aluminate WCAs have even a higher tolerance toward water in IB polymerization than the earlier tested perfluoroborate WCAs. Studies showed that water plays an important role in the polymerization process, which indicates a polymerization mechanism similar to a proton-initiated carbocation polymerization. The role of the WCAs and their importance for the room-temperature polymerization process was re-examined, and the effect of the addition of proton and electron donors including proton traps (2,6-di-tert-butyl-4-methylpyridine or DTBP) was studied in detail. The polymerization reaction seems to be dominated by transfer reactions that lead to the high content of exo double bonds while propagation proceeds via conventional cationic polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile-ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups—the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Here, we report on the first example of crosslinking (CL) hyperbranched polyphenylene (hb–PPh) with a small molecule crosslinker 1,3,5-tris(azidomethyl)benzene (TAMB). It was successfully shown that CL of the hb–PPh/TAMB (9:1) film is possible either thermally or photochemically making use of fundamentally different reaction mechanisms. Starting from a model reaction to prove the feasibility of the thermal CL reaction, we went on to check both the thermal and the photochemical crosslinkability of micrometer thick films. IR spectroscopy was furthermore used to confirm the CL process. Finally, the thin film morphology of the films before and after CL was investigated by AFM, revealing that the surface morphology was unaffected by the CL processes.

For using successful (ultra)thin dendritic macromolecule films in (bio)sensing and microfluidic devices and for obtaining reproducible film properties, alteration effects arising from precoatings have to be avoided. Here, oligosaccharide-modified hyperbranched poly(ethylene imine)s (PEI-OS) were used to fabricate very thin PEI-OS films (15–20 nm in dry state), cross-linked with citric acid under condensation, and vacuum condition. However, no reactive precoating is necessary to obtain stable films, which allows very simple film preparation and avoids alteration of the PEIS-OS film properties arising from precoating. Several methods [(in situ) ellipsometry, AFM, XPS, (in situ) ATR-IR, streaming potential measurements] were applied to characterize homogeneity, surface morphology, and stability of these PEI-OS films between pH 2 and pH 10, but also the low protein adsorption behavior.

Poly(styrene-r-propargyloxy styrene) with varying molecular weights is prepared by means of a nitroxide-mediated radical polymerization and a malonate is “clicked” to it. Fullerene C₆₀ is reacted under Bingel conditions with the polymer and can be covalently bound to its side chains. These polymers show good solubility in common organic solvents and intense studies are performed to determine the degree of substitution with fullerenes. A loading of around 15 to 20 wt% is detected by thermogravimetric analyses (TGA). These materials might be promising as the acceptor component for donor–acceptor block copolymers. Furthermore, new bromine- and organo-azide-functionalized methano fullerenes are prepared and characterized.

Amphiphilic graft copolymers with a thermosensitive PNiPAAm backbone and pH-sensitive hydrophilic poly(2-carboxyethyl-2-oxazoline) graft chains are synthesized. In aqueous solution, stable micelle-like aggregates are formed by increasing the temperature in the pH range 4.5–5.5. The micelles are crosslinked by electron-beam irradiation, yielding stable core–shell nanogels of about 100 nm diameter with reversible thermo- and pH-dependent swelling behavior. The temperature sensitivity is provided by a conformational change in the PNiPAAm core, whereas the thickness of the poly(2-carboxyethyl-2- oxazoline) corona depends on pH. The reversible bisensitivity of core-crosslinked nanogels is verified by DLS, while AFM measurements demonstrate the predicted core–shell structures of the aggregates.

Two phase separating block copolymers equipped with functional groups (acid and alkyne) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Thin films of these materials were prepared and examined with regard to surface morphology, surface composition, and film stability. Self-assembled structures with domain sizes of about 40 nm were detected through atomik force microscopy (AFM) analysis while X-ray photoelectron spectroscopy measurements revealed a balanced surface exposure of the two segregated phases. Thus, reactive groups being present in both phases are specifically provided within nanoscopic surface areas. The films showed good stability on exposure to various solvents but the self-organized surface patterns were only resistant toward ethanol. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

New hyperstar polymers (HSP) consisting of two different hyperbranched (hb) aromatic/aliphatic cores grafted with linear polymer arms were successfully synthesized. The hb cores were based on either hb poly(vinylbenzylchloride) synthesized by SCVP-ATRP or hb polyester from a polycondensation reaction. For the core-first approach, the hb cores have been modified to hb macroinitiators initiating either the cationic ring-opening polymerization of oxazolines (Oxa) or the atom transfer radical polymerization of alkylmethacrylates. For potential use as reactive binders in epoxy coatings the HSPs were equipped with a defined amount of OH-groups during arm growth via controlled block-copolymerization with nonfunctionalized and OH-functionalized monomers, either an oxazoline (OH)Oxa (2-[1-(hydroxymethyl)ethyl]-oxazoline) or a methacrylate HEMA (2-hydroxyethyl methacrylate). The amount of OH-groups could be well adjusted in this way. The hyperstars were comprehensively characterized with respect to chemical structure and molecule dimension. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2012

Summary: Polyisobutylene is an industrially important polymer which is conventionally prepared by polymerization at temperatures below 0 °C. The application of solvent ligated metal complexes associated with weakly coordinating counteranions (WCAs), however, allows the room temperature (30 °C) polymerization of isobutylene resulting in highly reactive polyisobutylene (HR-PIB) containing a high content of terminal double bonds. Recently described complexes include manganese (II), copper(II), molybdenum(III) and zink(II) complexes which were coordinated octahedrally with the boron and alumina based WCAs, each with its own advantages and traits.

Nitrile-ligated zinc(II) complexes incorporating aluminum-based weakly coordinating anions (WCAs) have been successfully prepared and fully characterized. An X-ray crystal structure proves both the octahedral symmetry of the zinc(II) cation having six nitrile ligands and the non-coordinating nature of the anion. Similar to complexes bearing boran-based WCAs, the compounds described here can be applied to polymerize isobutylene at room temperature resulting in polyisobutylene with a high content of exo double bonds.

A facile way for the synthesis of hyperbranched poly(4-chloromethylstyrene) [P(4-CMS)] with adjustable molar mass by classic atom transfer radical polymerization (ATRP) and mechanistically similar procedures is presented. Subsequently, the chlorine functional groups have been modified to obtain polymers with different polarities. On the one hand, the polymer was end-capped with unpolar groups (e.g., methyl, phenol ether) to obtain chemically inert substances. On the other hand, more complex functional groups have been introduced through azide groups by 1,3-dipolar cycloaddition reaction (“click chemistry”). Furthermore, a method for the introduction of ester groups under mild conditions using cesium carboxylates is presented, which also allowed the preparation of so-called hyperstars by attaching COOH functionalized polystyrene chains onto the P(4-CMS) as core molecule. All these reactions were carried out in high or very high yields. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2224–2235, 2010

A series of s-triazine-based hyperbranched polyethers (HBPE) have been synthesized to obtain thermostability but flexible polymers by an interfacial polycondensation of different diols as A₂ and cyanuric chloride as B₃ monomers using A₂ + B₃ approach in the presence of a phase transfer catalyst. The polymerization reaction parameters are optimized, and the results indicate that the optimum conditions for the interfacial polycondensation are a 2:3 mole ratio of cyanuric chloride to diol using butanediol, benzyldimethylhexadecyl ammonium chloride as the catalyst, dichloromethane as the organic solvent, and a three-step procedure with keeping the reaction mixture at different low temperatures for 2h/2h/5h. Other techniques such as high-temperature solution, one-step polycondensation, and transesterification were also carried out to synthesize the HBPE but proved to be not suitable due to large number of side reactions. The synthesized polymers were characterized by FTIR, ¹H NMR, and ¹³C NMR spectroscopy, hydroxyl number determination, solution viscosity measurements, and GPC analysis. The thermal behavior of the hyperbranched polymer was investigated by thermogravimetric analysis and differential scanning calorimetry. All the results were compared with those from an analogous linear polyether, obtained from 2-methoxy-4,6-dichloro-s-triazine and butanediol by using the same polymerization technique. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3994–4004, 2010

Several functionalized block copolymers based on polystyrene with considerably different block polarities have been prepared using controlled radical polymerization techniques (NMRP, RAFT). The target polymers, having hydroxy, alkyne or amine functionalities in at least one block were characterized by techniques like NMR, GPC and DSC to verify structure, molar masses, molecular weight distributions and thermal properties. With the example of partly protected hydroxystyrene based block copolymers, regular structured film surfaces could be created and were shown to be converted into homogeneous polymer surfaces by applying heat as external trigger. With alkyne functionalized block copolymers, modifications with objects of varying sizes were carried out, employing the 1,3-dipolar cycloaddition of alkynes with azides. Once again, the “click approach” proved its high efficiency as the reactions proceeded completely even with objects of high steric demand. Studying the influence on the macromolecular architecture, we found a strong alteration of glass transition temperatures for the compared polymer materials, indicating a bracing of the chains due to steric hindrance between the bulky side objects.

To explore the possible applications of hyperbranched polymers for modifying linear polyamides, two hyperbranched aromatic polyesters characterized as high T_g polymers possessing phenolic end groups were used in melt mixing with partly aromatic polyamide and commercially available aliphatic polyamide-6, respectively. Different amounts of both hyperbranched polyesters (from 1 wt % up to 20 wt %) were added to the polyamides, and the influence of these hyperbranched polyesters on the properties of the polyamides was investigated. The hyperbranched polyester based on an AB₂ approach was found to be the most effective modifier. A significant increase of the glass transition temperature of the final blend was detected. However, a remarkable reduction of crystallinity as well as complex melt viscosity of those blends was also observed. The use of an A₂+B₃ hyperbranched polyester as melt modifier for the polyamides was less effective for changing the thermal properties, and the complex melt viscosity of the final material increased since heterogeneous blends were formed. In contrast to that, generally, the addition of the AB₂ hyperbranched polyester to the polyamides resulted in homogeneous blends with improved T_g and processability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3558–3572, 2009

Complexes with the general formula [M^II(NCCH₃)₆][TPFB]₂ [M = Cr, Fe, Co, Ni, Cu, Zn, (TPFB)^– = tetrakis(pentafluorophenyl)borate] were synthesized and characterized both in the solid state and in solution. According to the spectroscopic data, [TPFB] can be considered as a truly noncoordinating anion. The NCCH₃ ligands are lost if the samples are kept at room temperature for extended periods of time. Thermolysis leads to the loss of the NCCH₃ ligands and decomposition of the anion above 100 °C with the formation of MF₂. It has to be noted that distortion of the geometries of the Cu^II, Zn^II and Cr^II complexes occurs, as evidenced by infrared spectroscopy. The complexes can be easily prepared and obtained in high yields and are moderately sensitive to air. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)