M.H.P. van Genderen

Polystyrene-dendrimer amphiphilic block copolymers with a generation-dependent aggregation.

A class of amphiphilic macromolecules has been synthesized by combining well-defined polystyrene (PS) with poly(propylene imine) dendrimers. Five different generations, from PS-dendr-NH2 up to PS-dendr-(NH2)32, were prepared in yields of 70 to 90 percent. Dynamic light scattering, conductivity measurements, and transmission electron microscopy show that in aqueous phases, PS-dendr-(NH2)32 forms spherical micelles, PS-dendr-(NH2)16 forms micellar rods, and PS-dendr-(NH2)8 forms vesicular structures. The lower generations of this class of macromolecules show inverted micellar behavior. The observed effect of amphiphile geometry on aggregation behavior is in qualitative agreement with the theory of Israelachvili et al. The amphiphiles presented here are similar in shape but different in size as compared with traditional surfactants, whereas they are similar in size but different in shape as compared with traditional block copolymers.

Chemistry : dendrimers set to self-destruct

The versatility of the branched macromolecules known as dendrimers is being exploited in various ways — explosively so, in the context of their application as potential drug-delivery systems.

Star-shaped poly(2,6-dimethyl-1,4-phenylene ether)

SummaryThe properties of star-shaped poly(2,6-dimethyl-1,4-phenylene ether) (PPE) as prepared by the redistribution of PPE and tyrosine-modified poly(propylene imine) dendrimers, are studied in solution and in 50/50 wt% blends with linear polystyrene. Star polymers with constant armlength but increasing number of arms show the same hydrodynamic volume as measured by Size Exclusion Chromatography (SEC), but decreasing hydrodynamic radius as measured by Dynamic Light Scattering (DLS). This is caused by the restricted mobility of the more densely packed chains at high numbers of arms, also leading to a decrease in intrinsic viscosities. These solution properties are also reflected in the miscibility behaviour in polymer blends. Star-shaped polymers with a high number of PPE arms (16,32 or 64 respectively) give inhomogeneous blends with linear polystyrene, in contrast to the miscible combination of linear polystyrene with linear PPE or starshaped polymers with a low number (4 or 8) of PPE arms.

Controlled Molecular Weight by the Precipitation Polymerization of 2,6-Dimethylphenol

Abstract Low molar mass poly(2,6-dimethyl-1,4-phenylene-ether)s (PPE) have been prepared by the precipitation polymerization of 2,6-dimethylphenol (DMP) under the action of a Cu(I)Cl/amine-catalyst and O2. The polymers prepared possess a rather narrow molecular weight distribution (D = 1.7−2.2), and the molecular weight can easily be controlled by adjusting the solvent mixture of 2-propanol and toluene. Molecular weights were determined using 1H-NMR spectroscopy, GPC, and FD-MS, and range from M n = 2700 to 7500 g/mol. No Mannich-basetype endgroups and no incorporation of DPQ (3,5,3′,5′-tetramethyl-4,4′-diphenoquinone) has been detected.

Enantioselective synthesis of (R)- and (S)-1-²H-1-octanol and their corresponding amines

Abstract Both enantiomers of 1-2H-1-octanol were obtained by the enzymatic reduction of deuterated octanal in the presence of alcohol dehydrogenases (ADH) (ADH-T or ADH-LB) as the biocatalyst in good yield, purity, and enantiomeric excess (>95%). The cofactor nicotinamide adenine dinucleotide phosphate was regenerated by the addition of isopropanol. To simplify the synthetic route, the direct reduction of octanal using the same enzymes and the same cofactor but adding deuterated isopropanol was evaluated. This provided a one-step procedure from a commercially available starting compound to both enantiomers of 1-2H-1-octanol in good yields (>80%) and good enantiomeric excess (∼97%). The (S)-alcohols were converted to their corresponding (R)-amines, which showed ees around 90%. GRAPHICAL ABSTRACT