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Dendritic polymers are highly branched polymer structures, with complex, secondary architectures and well-defined spatial location of functional groups. Due to their unique physical and chemical features, applications in areas such as targeted drug-delivery, macromolecular carriers, catalysis, sensors, light harvesting, surface engineering and biomimetic materials have been proposed. However, only a few dendritic materials have been exploited commercially due to time consuming syntheses and the generation of significant waste/presence of unreacted starting materials. This tutorial review describes traditional synthesis of dendritic materials as well as recent advances in synthetic strategies, for example the use of Click chemistry, as a tool to efficiently obtain complex, functional dendritic structures.

A fourth wheel: Two sets of bifunctional AB(2)C dendrimers having internal acetylene/azides and external hydroxy groups were constructed utilizing benign synthetic protocols. An in situ postfunctionalization strategy was successfully carried out to illustrate the chemoselective nature of these dendrimers. The dendrimers were also transformed into dendritic nanoparticles or utilized as dendritic crosslinkers for the fabrication hydrogels.

Cationic polymerization of diethyleneglycoldivinyl ether was thermally induced by diphenyliodonium, alkylbenzylsulfonium, and phenacyltetramethylenesulfonium salts. The reactivity was enhanced by using free radical sources in combination with diphenyliodonium or phenacyltetramethylenesulfonium salts. Even at low onium salt concentrations extremely reactive formulations could be obtained, e.g., the polymerization was complete within 1 minute at 100°C when using the most reactive salts. Polymerizations were induced at temperatures ranging from 50 to 180°C. The Counterion, Supplied by the onium salts, strongly influenced the appearance of the resulting crosslinked polymer: salts containing SbF−6 usually gave highly discolored samples due to the large heat evolution during polymerization whereas polymerization with PF−6 proceeded smoother resulting in transparent, uncolored polymers. The purity of the monomer greatly affected the initiation by the diphenyliodonium and phenacyltetramethylenesulfonium salts. Adventitious radical sources, e. g., hydroperoxides on oxidized monomer, lowered the activation temperature but also led to poor storage stability of these formulations.

The effects of allyl ethers in coating resins have been studied in relation to different systems. The details that have been investigated are: the reactions between allyl ethers-styrene-cobalt salt ...

Procedures are presented for the synthesis of a series of dicarbonate oligomers with either methacrylate or p-vinylphenoxy end-groups as polymerizable units. In addition, the synthesis route is given for a novel precursor of p-vinylphenoxy-type carbonates, namely, p-nitrophenyl 3-p-vinylphenoxypropyl carbonate. Polymerization of the new oligomers was studied by differential scanning calorimetry (DSC). The bis(p-vinylphenoxy) dicarbonates were polymerized by thermally induced cationic polymerization, and the corresponding dimethacrylates by free-radically initiated photopolymerization.

Five novel photocrosslinkable oligomers were evaluated with regard to polymerization and acid-catalysed degradation. The oligomers include either a methacrylate or p-vinylphenoxy unit as the polymerizable moiety. A carbonate functionality susceptible to acid-catalysed degradation is also incorporated. This work shows that it is possible to formulate an oligomer-based photo-curable coating which can be polymerized to an insoluble matrix. In the case of the styrene-type dicarbonates, no pure coatings can be studied at room temperature, and at elevated temperatures cationic polymerization competes with degradation. They can, however, be degraded to soluble products at reasonable temperatures if the system is exposed to a strong acid catalyst.

Liquid crystalline vinyl ethers have been bulk polymerized cationically in the mesophase using onium salts for thermal initiation. High molecular mass polymers (Mn≤83 000) with a narrow molecular mass distribution (around 2) were produced at very high temperatures (≤120°C). Apparently the polymerization system stabilizes the propagating cation and thus reduces chain transfer reactions that are determining the molecular mass. Possible reasons for this stabilization are e.g. influence of the mesophase of the formed polymer, interfacial polymerization, and nucleophilic stabilization by nucleophiles present in the monomer or produced by the initiators.

The effect of allyl ethers on the free radical polymerization of styrene has been studied with respect to chain transfer, copolymerization, and conversion. The studies have been performed in an ine ...

Etude par DSC et microscopie optique de 2 polymeres a base de bis(hydroxy-4 phenoxy) p-xylene et comportant un groupe espaceur respectivement 9 et 11 methylene. La transition est controlee par nucleation et suit l'equation generale d'Aurami. Un processus de rearrangement de la mesophase smectique sans nucleation et suivant l'equation d'Aurami est aussi observe

Greffage radiochimique de methacrylate de glycidyle sur des films de LDPE puis accrochage de PEG aux groupes epoxy; la surface des films obtenus est constituee a 95% de PEG qui inhibent l'adsorption de transferrine humaine sur le film. L'heparine greffee en surface du copolymere inhibe la coagulation sanguine. Des anticorps de lapin diriges contre la proteine urinaire de la souris sont fixes a la surface d'un polystyrene greffe de methacrylate de glycidyle et modifie par un hydrazide

A chemoselective and layered growth approach has been developed for the synthesis of dendrimers, combining Click chemistry with traditional esterification/etherification reactions, without the need for activation steps and with excellent overall yields.

Ordered hexagonal arrays of isoporous films prepared from poly(9,9'-dihexylfluorene) and polystyrene grafted silica nanoparticles (Si-graft-PS) are presented. These close packed arrays were formed in areas of many square millimeters. The pore size varied from 2.9 - 8.5 mu m, depending on the concentration of Si-graft-PS and the processing conditions. Solid state photoluminescence resulted in a significant red shift of up to 30 nm in these films compared to conventional processing techniques. These differences are attributed to induced aggregation of the polymers caused by polymer- solvent interactions. Interfacial properties were investigated, and it was found that hydrophobic surfaces (contact angles of up to 129 degrees) were prepared because of high surface roughness. These ordered porous polymer films may find use in microelectronic and bio- and/or chemical sensor applications.

In this study, ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and L-lactide (L-LA) has been performed from cellulose fibers. The hydroxyl groups on cellulose act as initiators in the polymerization, and the polymers are covalently bonded to the cellulose fiber. As an attempt to introduce more available hydroxyl groups on the surface, and thereby obtain higher grafting efficiency in the ROP of epsilon-CL and L-LA, unmodified paper was modified with xyloglucan-bis(methylol)-2-methylpropanamide (XG-bis-MPA) and 2,2-bis(methylol)propionic acid (bis-MPA), respectively. The grafted substrates were characterized via Fourier transform infrared spectroscopy (FTIR), contact angle measurement, atomic force microscopy, and enzymatic degradation. The results showed a successful grafting of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) from the cellulose fiber surfaces. Furthermore, the results showed an improved grafting efficiency after activation of the cellulose surface with bis-MPA, and showed that the amount of grafted polymer could be controlled by the ratio of added free initiator to monomer.

Highly ordered hexagonal arrays of isoporous films prepared from poly(9,9'-dihexylfluorene) and polystyrene-grafted silica nanoparticles (Si-graft-PS) are presented. These close-packed arrays were formed in areas of many square millimeters. The pore size varied from 3.6 to 8.5 microm, depending on the concentration of Si-graft-PS and the processing conditions. Solid-state photoluminescence resulted in a significant red shift of up to 30 nm in these films compared to that in conventional processing techniques. These differences are attributed to enhanced aggregation of the polymers caused by polymer-solvent interactions. These highly ordered polymer films may find use in microelectronic and biological and/or chemical sensor applications.

Hyperbranched, aliphatic polyesters of theoretically calculated molar masses 1 200–44 300 (2–7 generations) were synthesized in the molten state from 2, 2-bis(hydroxymethyl)propionic acid (bis-MPA) (repeating unit of ABx-type) and 2-ethyl-2-(hydroxymethyl)-1, 3-propanediol (TMP) (core molecule) using acid catalysis. The synthetic procedure was a pseudo-one-step divergent reaction. The degree of branching was found to be near 80 %. A study has also been made with respect to the rheological properties of the hyperbranched aliphatic polyesters. The polymers exhibit an almost newtonian behaviour in the molten state. They also exhibit a lower increase in viscosity with molecular weight than linear polymers. The surface functionality is shown to greatly affect the viscosity of the polymers.

There is significant interest for polymers in electronics and/or opto-electronics. This is due to the fact that polymeric materials are relatively easy to give certain properties. From a processing point of view polymers are also advantageous over inorganic materials.

In the protection against lasers, optical power limiting (OPL) is an area of interest. We have explored the effect of using dendritic molecules, based on bis-MPA (2,2-bis(methylol)-propionic acid), as encapsulants of porphyrine and thiophene dyes having OPL-properties. Preliminary results indicate that the OPL-effect of the porphyrine is increased approximately by a factor 2 if the porphyrine is decorated with dendritic wedges. This is thought to be a result of isolation of the dye leading to extended lifetimes for the excited states, increasing the probability for multi-photon absorption. For the thiophenes no OPL-effect was observed. This was probably due to the small size of the dendrons (first generation).

First to fourth generation dendritic substituents based on 2,2-bis(hydroxymethyl)propionic acid and (1R,2S,5R)-menthoxyacetic acid were attached to 2-(hydroxymethyl)pyridinooxazoline and bis[4-(hydroxymethyl)oxazoline] compounds. The new ligands obtained were assessed in palladium-catalyzed allylic alkylations. The first type of ligands exhibited enantioselectivity similar to that of a benzoyl ester derivative, whereas the latter type of ligands afforded products with higher selectivity than the analogous benzoyl ester. The activity of the dendritic catalysts decreased with increasing generation.

We report on optical transmission properties and results of optical waveguide characterization of flourinated hyperbranched polymers and dendrimers (details on chemical synthesis were reported recently [1]). The polymers and dendrimers allow the introduction of additional functionality, such as cross-linking and refractive index tuneability. The dendrimers having a similar bulk structure as the hyperbranched polymer were also shown to house lanthanide cations for optical amplifying application. The fluorinated bulk structure results in a low contribution from vibration overtones in the absorption spectra in the NIR/IR region (800 - 2200 nm). The refractive index of the fundamental fluorinated hyperbranched polymer was found to be tuneable between ca 1.45 and 1.65 by incorporating various substituents. Optical losses were measured to be below ca 0.5 dB/cm at 1550 nm.

Metal complexes of chiral oxazoline derivatives immobilized on soluble as well as insoluble supports serve as versatile asymmetric catalysts in a variety of applications. In a few cases recovery and reuse of the chiral ligands have been achieved.

In this work, photo-induced thiol–ene coupling (TEC) was used to produce well-defined poly(ethylene glycol) (PEG)-based hydrogels. PEGs of four different molecular weights (2k, 6k, 10k, and 20k) were functionalized with G1-allyl dendrons using anhydride chemistry to produce tetra-functional TEC crosslinkable PEGs. The tetra-functional PEGs were subsequently crosslinked with a tri-functional thiol in ethanol to form hydrogels. The synthesized hydrogels were characterized with respect to swelling behaviour, rheological properties and hydrolytic degradation. It was found that the molecular weight of the PEG chain greatly influences the final properties of the hydrogel, where a higher molecular weight of PEG gives an increased weight swelling ratio from 240% for PEG-2k hydrogels to 1400% for PEG-20k hydrogels, as well as decreased elastic moduli, with Young's moduli ranging from 106 MPa to 6 MPa, for PEG-2k and PEG-20k hydrogels, respectively. It was also found that the hydrolytic stability in alkaline conditions (pH 10) decreased when the molecular weight of PEG in the hydrogels increased.

We report the preparation and characterization of novel isotropic polymer slab waveguides made by photochemical crosslinking, and their integration with a ferroelectric liquid crystal in an integra ...

A binary mixture of ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The FLCs possess two important functionalities: a chromophore with a high hyperpolarizability $\beta$ and photoreactive groups. The smectic liquid crystal is aligned in layers parallel to the glass plates in a sandwich geometry. This alignment offers several advantages, such as that moderate electric fields are sufficient to achieve a high degree of polar order. The arrangement was then permanently fixed by photopolymerization which yielded a polar network possessing a high thermal and mechanical stability which did not show any sign of degradation within the monitored period of several months. The linear and nonlinear optical properties have been measured and all four independent components of the nonlinear susceptibility tensor $\bar d$ have been determined. The off-resonant $d$-coefficients are remarkably high and comparable to those of the best known inorganic materials. The alignment led to an inherent channel waveguide for p-polarized light without additional preparation steps. The photopolymerization did not induce scattering sites in the waveguide and the normalized losses were less than 2 dB/cm. The material offers a great potential for the design of nonlinear optical devices such as frequency doublers of low power laser diodes., Comment: LaTeX2e article, 15 pages, 10 figures, 11 EPS files, submitted to Physical Review E

M-line measurements have been performed on thin films of pyroelectric liquid crystalline polymers (PLCP), in order to determine the magnitude and anisotropy of the refractive index. The films, polymerized under various conditions, are based on materials exhibiting a chiral smectic C phase. The results of the measurements were analyzed and compared with a new numerical method to model the optical properties of anisotropic multilayered thin films. In the model, which is an extension of the analytical approach of Berreman, the eigenmodes and boundary conditions of refracted light waves are handled and solved by numerical matrix manipulations. Model calculations of total reflection measurements for various multi-layered systems were used to investigate the effect of ITO and polyimide aligning layers to the apparent effective index of m-lines.

A facile methodology for the fabrication of functional crosslinked three dimensional (3D) networks has herein been explored via the benign and UV initiated thiol–ene coupling (TEC) chemistry. The careful selection of monomers or polymers and their feed ratio resulted in straightforward design of organic, inorganic and hydrogel networks with readily available alkenes or thiol functional groups. All crosslinked networks were fabricated within 1 second of UV exposure at wavelengths of 320–390 nm and generally exhibited excellent gel fractions around 90%. By introducing off-stoichiometric thiol and ene (OSTE) monomer feed ratios the window of mechanical properties could be manipulated. For the organic triazine system, the Young's modulus was altered from 780 MPa at an equimolar monomer ratio to soft 106 kPa for 2.5 equiv. with excess of thiol compared to enes. Postfunctionalizations with hydrophilic polyethylene glycols or acrylic acid and hydrophobic heneicosafluorododecyl acrylate were explored for the manipulation of functional networks. In this case, the rigid networks with excess of thiols were used as model substrates of which the initial contact angle (CA) of 60° was decreased to 43° by the introduction of acrylic acid and increased to 140° by successful attachment of fluorinated molecules. Finally, amalgamating micropatterning strategy with simple postfunctionalizations of hydrophobic groups resulted in superhydrophobic rigid surfaces with a CA of 173°.

The development of a facile method for the fabrication of breath figure (BF) films from hydrophobic polymers is gaining significant importance for their accessibility as templates in fields ranging from electronics and cell culturing to sensing and catalysis. By introducing polyester-based dendritic linkers, a library of micrometre sized honeycomb structures was successfully fabricated from amphiphilic linear–dendritic–linear hybrids comprising hydrophobic PCL or PLA and hydrophilic PEG blocks. From the array of produced films, the incorporation of a third generation dendritic linker was found to generate well-ordered honeycomb films in the several hundreds of micrometre range. This one component approach minimizes the number of unknown parameters and represents a fully reliable methodology for the fabrication of functional BFs from challenging and biocompatible polymers.

The interfacial properties of solution-processed conjugated polymer films are investigated. Their surface roughness was controlled by varying the humidity during the film deposition and mechanical exfoliation. A superhydrophobic film was obtained from a rough film of a partially fluorinated conjugated polymer. These films would be beneficial towards robust organic electronic devices.

Die Chemoselektivitat der Klick-Chemie wurde fur die Synthese einer neuen Gruppe difunktioneller AB2C-Dendrimere mit Acetylen/Azidgruppen im Innern und Hydroxygruppen an der Peripherie genutzt. M. Malkoch et al. stellen in der Zuschrift auf S. 2160 ff. einen einfachen Zugang zu zwei Gerusttypen vor. Die Nutzlichkeit der AB2C-Dendrimere wurde durch ihren Einsatz zur nachtraglichen Eintopffunktionalisierung, bei der Entwicklung dendritischer Nanopartikel und zur Bildung von Hydrogelen illustriert.

Dendrimers up to the fourth generation (G1–G4) were successfully synthesized via the efficient copper catalyzed 1,3-dipolar cycloaddition between primary alkynes and azides (CuAAC), also referred to as a click reaction. The synthetic protocol involved the preparation of presynthesized dendron wedges that subsequently were attached to a tetra-valent alkyne functional cyclen core. These constructed structures integrated stable triazole groups “intra-locked” between the cyclen and dendron wedges. The incorporation of a lanthanide metal ion, europium, into the interior of all cyclen dendrimers was monitored by FT-IR. Interestingly, the photophysical results showed that the proximate triazole not only acts as a stable linker but also as a sensitizers, transferring its singlet–singlet excitation in the ultraviolet region (270–290 nm) to the partially filled luminescent lanthanide 4f shell. An increase of luminescence decay time from the lanthanide 5D0 → 7F2 emission was observed with increasing dendrimer size, indicating that the shielding effect of the dendron wedges is important for the relaxation of the photo-excitation and energy transfer. To the best of our knowledge, this is the first time a set of dendron wedges have successfully been attached to a cyclen metal ion cage via the versatile click reaction. Furthermore, the produced triazoles intra-locked in close proximity to the macrocycle core elucidated an interesting photophysical function.

The absolute absorption spectra of low-loss optical waveguides, together with their intrinsic and extrinsic scatterings, were measured in the near infrared. Photothermal deflection spectroscopy was used to measure the full absorption spectra of a series of fluorinated cross-linked polymers. Assignment of —CH3,—CH2—, and —OH overtones as well as of combinations of overtones were made by use of the theory of anharmonic vibrations based on a Morse potential for local modes. Details of the molecular potential are given. The total attenuation in slab waveguides made with these polymers was measured by a prism-coupling technique and compared with the absolute absorption. Losses that are due to the material itself and those that are due to the processing are quantified.

2- Iso -propylthioxanthone (ITX) and N -methyldiethanolamine (MDEOA) were used as the initiating system to study the photo-chemical stability of photo-cured coatings. Primary yellowing is caused by photo-products from initiator residues. This yellowing decreases during storage in darkness. Permanent yellowing is caused by photo-degradation of the resin used. This photo-degradation is sensitized by ITX. Photo-curing in the presence of oxygen leads to a rapid surface oxidation. Photo-oxidation studies with ESCA, infra-red reflection and transmission spectroscopy show that the oxidation occurs mainly in a thin surface layer. In a surface layer ∼ 10 nm thick, oxidation is almost complete after 24–48 hours' ageing.