A polarographic study of propene-maleic anhydride copolymers

The polarographic behaviour of hydrolyzed propene-maleic anhydride copolymers in the interval pH 2.0–11.0 has been investigated by differential pulse polarography in aqueous lithium chloride solution at 25°C. In dependence on the pH-value, one, two or three signals, belonging to the acid groups in the copolymer, appear in the polarograms. Three apparent polarographic acid constants have been determined graphically from the changes in the half-wave potential of the separate peaks in correlation with pH.     

Reaction behaviour of monomeric β-ketoesters, 4. Polymer network formation by Michael reaction of multifunctional acetoacetates with multifunctional acrylates

Based on the Michael reaction of multifunctional acetoacetates with multiacrylates, in the presence or absence of dimethacrylates, tailor made matrix materials can be prepared. This can be achieved in a one- or two-step process. The Michael addition (first step) can be followed by radiation curing of excessive acrylate (second step).     

Molar mass determination by end group analysis - amino group determination in aliphatic and partially aromatic polyamides with 1-fluoro-2,4-dinitrobenzene in benzyl alcohol

End group analysis is the most important absolute method of obtaining number-average molar mass values for polymers of the step-growth polymerization type. A great number of methods are available which primarily differ in the detection of the end group concerned. Special chemical methods based on the formation of covalent derivatives of the end groups (e.g. introduction of UV/VIS chromophores) are important if there is a need to demonstrate, with the aid of gel permeation chromatography, that damage to the polymer (e.g. onset of cross-linking) has occurred. In the case of fibre-forming polycondensation products, the applicability of end group analysis is often restricted by the lack of suitable reagents and solvents. This is also true of the determination of amino end groups in polyamides by means of 1-fluoro-2,4-dinitrobenzene, as is already contained in the German Standards specification (DIN 54 274) - albeit only for polyamide 6 and 6,6. This contribution describes a modified version of the 1-fluoro-2,4-dinitrobenzene method. The analytical principle and practical procedure correspond to those of DIN 54 274, but the solvent used for the reaction with the reagent is benzyl alcohol, and that for the photometric evaluation is 1,1,1,3,3,3-hexafluoro-2-propanol. The scope of the method is thus increased. Examples of applications for this method are commercial products based on aliphatic polyamides (6; 11; 12; 6,6; 6, 12), partially aromatic polyamides (2,4,4-trimethylhexamethylenediamine, terephthalic acid; copolyamides with bis-(4-aminocyclohexyl)propane(2), isophthalic acid, ω-aminododecanoic acid) and multicomponent systems with the abovementioned polyamides (bicomponent fibres, blends). It is shown that large differences may arise between the value determined by titration and the actual amino end group content. In addition, the presence of secondary amino groups can be demonstrated in polyamides of the Trogamid T type.     

Synthesis and Hydrogen-Bond Patterns of Aryl-Group Substituted Silanediols and -triols from Alkoxy- and Chlorosilanes

Organosilanols typically show a high condensation tendency and only exist as stable isolable molecules under very specific steric and electronic conditions at the silicon atom. In the present work, various novel representatives of this class of compounds were synthesized by hydrolysis of alkoxy- or chlorosilanes. Phenyl, 1-naphthyl, and 9-phenanthrenyl substituents at the silicon atom were applied to systematically study the influence of the aromatic substituents on the structure and reactivity of the compounds. Chemical shifts in ²⁹Si NMR spectroscopy in solution, correlated well with the expected electronic situation induced by the substitution pattern on the Si atom. ¹H NMR studies allowed the detection of strong intermolecular hydrogen bonds. Single-crystal X-ray structures of the alkoxides and the chlorosilanes are dominated by π-π interactions of the aromatic systems, which are substituted by strong hydrogen bonding interactions representing various structural motifs in the respective silanol structures.     

Exciton‐Vibrational Couplings in Homo‐ and Heterodimer Stacks of Perylene Bisimide Dyes within Cyclophanes: Studies on Absorption Properties and Theoretical Analysis

The optical properties of a series of three cyclophanes comprising either identical or different perylene bisimide (PBI) chromophores were studied by UV/Vis absorption spectroscopy and their distinctive spectral features were analyzed. All the investigated cyclophanes show significantly different absorption features with respect to the corresponding constituent PBI monomers indicating strong coupling interactions between the PBI units within the cyclophanes. DFT calculations suggest a π‐stacked arrangement of the PBI units at close van der Waals distance in the cyclophanes with rotational displacement. Simulations of the absorption spectra based on time‐dependent quantum mechanics properly reproduced the experimental spectra, revealing exciton‐vibrational coupling between the chromophores both in homo‐ and heterodimer stacks. The PBI cyclophane comprising two different PBI chromophores represents the first example of a PBI heterodimer stack for which the exciton coupling has been investigated. The quantum dynamics analysis reveals that exciton coupling in heteroaggregates is indeed of similar strength as for homoaggregates.