Peter Ernst Froehling

The use of dendrimers to modify the dyeing behaviour of reactive dyes on cotton

Cotton fabric which had been pretreated with a dendrimer displayed markedly enhanced colour strength with reactive dyes, even when dyeing had been carried out in the absence of both electrolyte and alkali. Competitive dyeing of untreated and dendrimer pretreated cotton suggests that the dendrimers offer the potential for differential-dyeing patterning possibilities. When non-competitively dyed, dendrimer pretreatment also enhances colour strength.

New synthetic routes to poly (isothianaphthene) I. Reaction of phthalic anhydride and phthalide with phosphorus pentasulfide

Abstract A new route for the formation of the low bandgap polymer poly(isothianaphthene) is presented. The route comprises the reaction of phthalic anhydride or phthalide with phosphorus pentasulfide at elevated temperatures ( T ⩾ 120 °C), and leads to the formation of poly(isothianaphthene) in one single step. The product obtained was analysed by elemental analysis, IR, Raman and solid state NMR spectroscopy. Chemical doping and dedoping of the material were investigated, and the maximum conductivity obtained was 10 S cm −1 by doping with NOSbF 6 . Both doped and undoped samples of poly(isothianaphthene) prepared by this new route were thermally very stable in air or in an inert helium atmosphere as shown by thermogravimetric analysis. Furthermore, the conductivity of a doped sample remained unchanged up to 250 °C in air. Preliminary results showed that the reaction with phosphorus pentasulfide can also be used to obtain nitrogen analogues of poly(isothianaphthene).

Synthesis and properties of a new, branched polyhydridocarbosilane as a precursor for silicon carbide

Polymerization of Cl2Si(CH3)CH2Cl with Mg in THF, followed by reduction with LiAlH4, gave a polycarbosilane with Si-H groups and branches at the Si atoms. The polymer could be cross-linked thermally at 150°C. Pyrolysis of the cross-linked material gave SiC with a yield of 70%.

Positional and compositional heterogeneity of partially modified poly(propyleneimine) dendrimers

The partial end group modification of dendrimers leads to two types of heterogeneity in the products structure: compositional heterogeneity (distribution of degree of substitution) and positional heterogeneity (spatial distribution of the substituents over the dendrimer molecule). Poly(propyleneimine) dendrimers were partially modified by direct amidation at 150°C with stearic acid. The compositional distribution (analysed by HPLC and ES-MS) follows a random pattern, governed by a binomial distribution. The positional distribution can be expressed as the distribution of dyads AA (two unreacted end groups), AB (one unreacted. one reacted) and BB (both reacted), where a dyad consists of two end groups originating at a common final branching point in the dendrimer. 13 C NMR and a Cu(II) complexation titration were used for determining the dyad distribution. Lower generations of dendrimers give a random distribution of dyads. In higher generations a marked preference for single substitution of dyads was found, possibly caused by intramolecular interactions or steric hindrance.

New synthetic routes to poly(isothianaphthene). II. Mechanistic aspects of the reactions of phthalic anhydride and phthalide with phosphorus pentasulfide

The results of some mechanistic studies on the formation of poly(isothianaphthene) from phthalic anhydride and phthalide by reaction with phosphorus pentasulfide (P4S10) are described. Based on the observed intermediates during the polymerization and their reactivity, it is proposed that both reactions occur by a sequence of substitution (thionation), isomerization, and polymerization reactions. P4S10 is the most efficient reagent for the conversion of phthalic anhydride and phthalide, and Lawessons Reagent (a commonly used thionating reagent) gives less satisfactory results. It is suggested that P4S10 assists the rate-determining step. Oxygen-containing monomers do not polymerize in the absence of a thionating reagent under the conditions for the synthesis of PITN, thereby keeping the incorporation of oxygen into the polymeric backbone to a minimum.

New synthetic routes to poly(isothianaphthene): III. Polymerization of dithiophthalide and 1,1,3,3-tetrachlorothiophthalan

Abstract In this paper, the polymerization of sulfur-containing precursor molecules to poly(isothianaphthene) (PITN) is described. Most attention has been devoted to the polymerization of dithiophthalide, as other useful precursors were synthetically less accessible. The thermal polymerization of dithiophthalide leads to the formation of undoped PITN, which had a conductivity in the order of 10 −4 S cm −1 . The insoluble polymer was characterized by IR, Raman and solid state NMR spectroscopy, and elemental analysis. The polymerization proceeds by simply heating the precursor without the presence of any added reagent or solvent and is the first non-oxidative route to PITN.

Blends of Fatty-Acid-Modified Dendrimers With Polyolefins

Blends were made by solution and melt-mixing fatty-acid-modified dendrimers with various polyolefins. Small-angle neutron scattering (SANS) was used to determine the miscibility of the blends. Poly(propylene imine) (PPI) dendrimers G1, G3, and G5 [DAB-dendr-(NH2)y] with y = 4, 16, and 64, were reacted with stearic acid or stearic acid-d35 forming amide bonds. The modified dendrimers were then blended with high-density polyethylene (HDPE), high-density polyethylene-d4 (HDPE-d4), low-density polyethylene (LDPE), amorphous polypropylene (PP), or an ethylene–butylene copolymer (E-co-B). Limiting power law behavior shows that all of the blends are immiscible. It is likely that the dendrimers form a second phase, being finely dispersed, but thermodynamically immiscible.