Conformations of Highly Charged Dendronized Polymers in Aqueous Solutions of Varying Ionic Strength

Conformations of two linear, charged dendronized polymers in aqueous solutions of different ionic strengths have been studied by light scattering. Both polymers have a polyacrylic core. The repeating unit of the first of the polymers studied contains a residue of aspartic acid bound to a carboxylic group of the core by an amide group as a first‐generation dendron, whereas the second polymer contains second‐generation dendrons constructed of three molecules of aspartic acid. The dendritic polymers adopt different conformations depending on the generation. Polymers with first‐generation dendrons are flexible and their conformation is sensitive to salt. The polymers with dendrons of the second generation adopt a semi‐flexible rod conformation. Their conformation is not sensitive to salt but is determined by the bulkiness of the dendrons.

Polyacrylic polymers having a residue of aspartic acid as a first‐generation dendron ( P1 ), and having a second‐generation dendron on the basis of aspartic acid ( P2 ).     

Cylindrical Polypeptide Brushes

Summary: Cylindrical brushes with poly(L ‐lysine) and poly(L ‐glutamate) side chains were prepared by “grafting through” and “grafting from” techniques. Grafting from is shown to be more successful for the synthesis of cylindrical brushes with high molar mass main and side chains.

AFM height image of polypeptide brushes with protected polylysine side chains spin‐cast from HFIP solution.     

Acyclic Triene Metathesis Oligo‐ and Polymerization of High Oleic Sun Flower Oil

High oleic sunflower oil, a renewable raw material consisting of triglycerides with internal C?C‐double bonds, was polymerized via acyclic triene metathesis (ATMET) to highly branched and functionalized polyesters. If the Hoveyda–Grubbs second generation catalyst was used and methyl acrylate was introduced as a chain stopper, the molecular weight of the obtained polymers could be tuned by varying the ratio of the triglyceride and methyl acrylate. Using the first generation Grubbs catalyst for the polymerization of high oleic sunflower oil, no cross‐linking was observed, even without the use of a chain stopper. The resulting branched materials were characterized by GPC, ¹H and ¹³C NMR, and ESI‐MS.

     

Metathetic Selective Degradation of Polyisoprene: Low‐Molecular‐Weight Telechelic Oligomer Obtained from Both Synthetic and Natural Rubber

Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.

Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene.     

Biomacromolecules and Bio‐Related Macromolecules

The present article briefly reviews research developments in the area of biomacromolecules and bio‐related macromolecules, whose research papers have been published for several decades preferably in the Macromolecular Journals. The area covers the important classes of macromolecules, polysaccharides (cellulose, amylose, chitin, etc.), polyesters (poly(lactic acid), poly(hydroxyalkanoate)s, etc.), and phenolic polymers (lignin, urushi, etc.). These polymers and their derivatives are very important for scientific interests as well as for industrial applications. Their synthesis, structure, reactions, and properties are mainly mentioned, and important topics of the target polymers are selected and mostly chronologically reviewed.

     

Photo‐Crosslinked Side‐Chain Liquid‐Crystalline Elastomers for Microsystems

Photo‐crosslinkable side‐chain liquid‐crystalline polymers (LCPs) containing photoreactive benzophenone cores are synthesized in order to obtain their corresponding side‐chain liquid‐crystalline elastomers (LCEs). This strategic synthesis allows thin elastomeric films and their integration into microsystems for actuators and micromachines to be obtained. As an example of this principle, a gripper was developed. The position of its arms can be changed by applying voltages from 1.5 to 3.5 V at different rates. Small changes in the liquid‐crystalline elastomer film cause strains of up to 150% in the microdevice and the capacity to move up to 400 times its own mass due to the nematic‐to‐isotropic transformation.

     

Linear Terpyridine‐Ruthenium(II) Poly(ethylene glycol) Coordination Polymers

In the present contribution, we synthesized linear coordination polymers based on oligo(ethylene glycol)s as well as poly(ethylene glycol)s and terpyridine ruthenium(II) complexes. The reaction conditions, e.g., solvent, concentration, were varied to obtain well‐soluble, high molecular weight polymers. The resulting compounds were characterized by UV‐vis and NMR spectroscopy. The viscosity of the materials was also investigated with and without salt addition. Finally, the polymers were characterized with DSC and AFM. AFM revealed a lamellar morphology.

     

Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous‐Flow Microreactor

The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol^?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.

     

Narrowly Distributed Surfactant‐Free Polystyrene Latex with a Water‐Soluble Comonomer

Summary: The surfactant‐free synthesis of latex polymers of styrene and sodium styrenesulfonate (NaSS) was investigated. The development of size and size distribution of the particles was studied by photo‐correlation spectroscopy (PCS) and transmission electronic microscopy (TEM). The effects of NaSS concentration and the order of addition of reactants were examined in detail. The results showed that the particle size decreases with an increase in the styrene sulfonate concentration. The polydispersity index can be reduced by mixing NaSS with styrene homogeneously before adding initiator, but this leads to a slightly larger mean particle size.

TEM image of surfactant‐free polystyrene latex made by the modified method.     

Are Electrografted Polymers Chemisorbed or Physisorbed onto their Substrate?

Summary: AFM‐based single‐molecule force spectroscopy was used to evaluate the mechanical strength of the link between a polymer and the substrate onto which the polymer is electrografted. Poly(N‐succinimidyl acrylate) was electrografted onto gold substrates and brought into contact with an aminothiol‐functionalized AFM tip. Bridging of single polymer chains resulting from the strong coupling between the activated esters on the polymer and amine groups on the tip was investigated. We found that the link between the polymer and the gold substrate can withstand a force far beyond the force characteristic for physisorption on gold.

     

Novel Poly(butylene succinate)‐Based Ionomers with Sulfonated Succinate Units: Synthesis,Morphology, and the Unique Nucleation Effect on Crystallization

Summary: Poly(butylene succinate) (PBS) and PBS‐based ionomers (PBSi's) with 0.3 and 1.2 mol‐% of sodium sulfonated succinate unit were synthesized. The existence of ionic aggregates in the ionomer matrices was indicated by melt viscosity and glass transition data. It seems that the ionic aggregates have two opposing roles in crystallization: one is the induction of nucleation and the other is the interference with lamellar growth. Because of these two contrary effects, the crystallization behavior of the ionomers exhibited measurably different cooling rate‐dependencies than that of the parent PBS. The rate varied distinctly with ionic content.

Spherulitic morphologies of PBS and PBSi's measured with polarizing optical microscopy.     

Self‐Assembly of Dendritic Macromolecules Based on the Ionic Interaction of Linear Chain Polyelectrolyte Cores with Oppositely Charged Focal Ionogenic Groups of Dendrons

Summary: A new principle for the design of dendritic macromolecules – the ionic binding of linear chain polyelectrolyte with oppositely charged focal ionogenic groups of dendrons – has been developed. The majority of the dendritic ionic complexes (DICs) are prepared with poly(styrenesulfonic acid) (PSS) as a polymeric core and L ‐aspartic acid dendrons of different generations. Two series of DICs were prepared using PSS and aspartic dendrons bearing terminal (located at the external periphery) methoxycarbonyl and hexyloxycarbonyl groups (C1‐n and C6‐n respectively where n is the generation number). Ionic binding of about 100% was found for dendrons of Generation 1–3. The solubility of the DICs was examined and the DICs prepared were studied by IR spectroscopy, ¹H NMR and viscometry.

Dendritic ionic complexes prepared using poly(styrenesulfonic acid) acid and aspartic dendrons bearing terminal methoxycarbonyl and hexyloxycarbonyl groups.     

Synthesis and Characterization of Conducting Copolymers of (S)‐2‐Methylbutyl‐2‐(3‐thienyl)acetate with Pyrrole and Thiophene

Polymerization of methylbutyl‐2‐(3‐thienyl)acetate (MBTA) was achieved by constant current electrolysis at low temperature. Subsequently, the syntheses of block copolymers of polyMBTA were accomplished in the presence of either pyrrole or thiophene by constant potential electrolysis. Moreover, the copolymer of MBTA with thiophene was obtained with constant potential electrolysis.

The synthesis of monomer MBTA.     

Novel Polymerization of Fluorinated 2‐Vinylcyclopropane in Aqueous Solution via Cyclodextrin Complexes

We report on the first examples of the free radical polymerization of a fluorinated 2‐vinylcyclopropane 1 and its copolymerization with an alkyl 2‐vinylcyclopropane 2 in aqueous solution via their host‐guest complexation with a random methylated β‐cyclodextrin (RAMEB) using a water‐soluble initiator (VA50). Upon polymerization, the dethreaded cyclodextrin remained in water solution, whereas the water‐insoluble polymer precipitated out and was isolated. The polymers prepared exhibited mesophase behavior over a wide range of temperature. Both T_g and T_i of the copolymers increased linearly with the amount of fluorinated co‐units.

Complexation of fluorinated vinylcyclopropane 1 with RAMEB and polymerization in water solution.     

Pinacol rearrangement in the polymer backbone: Synthesis of novel reactive polymers with condensed benzopinacol units in the main chain and their complete rearrangement to poly(benzopinacolone)s

Novel reactive polymers with condensed benzopinacol moieties in the main chain were synthesized and their acid‐catalyzed pinacol rearrangement in the polymer backbone proceeded to afford poly(benzopinacolone)s quantitatively. Since the pinacol rearrangement shows an intramolecular mechanism, no crossover between the polymer chains was observed through the rearrangement. Although the number‐averaged molecular weights and their distributions were not changed, the optical and thermal properties of the poly(benzopinacolone)s were completely different from the parent poly(benzopinacolone)s.

     

Photodeformable Polymers: A New Kind of Promising Smart Material for Micro‐ and Nano‐Applications

Summary: Starting in the 1960s, several kinds of photodeformable polymers have been developed, such as monolayers, polymer gels, solid films and liquid‐crystalline elastomers with different photodeformation mechanisms. This field evolved slowly until recently when significant achievements have been made. Most recently, Lendlein and co‐workers have put forward another new concept – using photo‐crosslinking to prepare deformable polymers with various pre‐determined shapes (Nature 2005 , 434, 879). This highlight gives a general introduction into photodeformable polymers and brings forth future challenges.

A polymer film doped with SCAA molecules where (a) is the permanent shape, (b) is the temporary shape and (c) is the recovered shape.     

Fluorene‐Based Single‐Chain Copolymers for Color‐Stable White Light‐Emitting Diodes

Fluorene‐based single‐chain copolymers with a white light emitter consisting of a blue and an orange chromophore have been synthesized and their photophysical and electroluminescent properties are investigated. The experimental results suggest that only a relatively small fraction of the orange‐emitting units incorporated into the fluorene is needed to achieve efficient white light emission by controlled incomplete energy transfer. A device from a copolymer with 0.02% DDQ content showed the highest external quantum efficiency of 2.64% with a luminance efficiency of 4.06 cd · A^?1 with CIE coordinates (0.28, 0.24). The EL emissions are extremely stable over a wide range of current densities.

     

Semicontinuous Emulsion Polymerization of Butyl Methacrylate and 1, 3‐Butadiene in the Presence of Cyclodextrins and Cytocompatibility of Dicarboxylic Acid Telechelic Oligo(butyl Methacrylate)s Derived from Ozonolysis of the Latexes

Ozonolysis of unsaturated polymers produced useful telechelic oligomers that can form building blocks for networks and block copolymers. The unsaturated polymers can be prepared by semicontinuous emulsion polymerization with dienes, and here it is shown that the addition of cyclodextrins enhanced the incorporation of these comonomers. Both α‐ and β‐cyclodextrin provide copolymers with higher fractions of butadiene (BD) incorporated into the chain but α‐cyclodextrin had the highest levels of incorporation. Oxidative work up after ozonolysis produced latexes of carboxylic acid oligomers of different molar masses. A clear effect of polymer size on toxicity was observed with the oligomers with < 2 700 g · mol.^?1 proving to have similar cytotoxic effects to lactic acid. However, oligomers with above 2 700 g · mol.^?1 were cytocompatible and gave similar results to a polylactide control material.

     

Liquid‐Crystalline Colloidal Particles

Summary: Here we report about the synthesis of colloidal particles of nematic and smectic liquid‐crystalline polymers. For this purpose mesogen‐containing acrylate monomers were synthesized and polymerized in a special modification of a precipitation polymerization called dispersion polymerization. By variation of the polymerization conditions colloidal particles of different size and polydispersity could be obtained including very narrowly distributed samples in optimized batches. On azobenzene‐containing colloidal particles switching experiments with polarized light were performed. It could be observed that the nematic director of the mesogens within the colloidal particles can be rotated due to the photochemical trans‐cis‐isomerization of the azobenzene chromophores.

Microscope images of a monolayer of P3‐9 .     

Anisotropic Dimensional Swelling of Membranes of Ultrafine Hydrogel Fibers

Summary: Interconnecting fibrous membranes were generated by electrospinning an aqueous mixture of poly(acrylic acid) and poly(vinyl alcohol) at a 3.5 COOH/OH molar ratio. The membranes containing 200 to 500 nm diameter fibers were crosslinked by heat‐induced esterification and behaved like anionic hydrogels, i.e., they swelled significantly more at a pH above 4. The dimensional expansion of these fibrous membranes was far greater in their thickness than in their planar areas. The anisotropic dimensional expansion was associated with the spatial arrangement of fibers, i.e., much smaller inter‐fiber spaces along the thickness direction than in the planar directions. Crosslinking under constraint caused further fiber compaction in the thickness direction, leading to anisotropic and accordion‐like dimensional expansion upon swelling.

SEM image of the PAA/PVA membrane (C1) thermally crosslinked under high constraint.