Linear infrared dichroism by a double modulation technique

In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio.     

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, characterization, and controlled aggregation of biotemplated polystyrene nanodisks

Cross-linked polystyrene nanodisks were prepared by controlled polymerization of styrene and divinylbenzene in the interior of bicelles, discoidal lipid aggregates. Aggregation behavior of polymer nanodisks was studied in water, organic solvents, and solid phase. Nanodisks form stable dispersions in aqueous solutions of surfactants, such as sodium dodecyl sulfate (SDS). Varying SDS/nanodisk ratio allowed us to control the size of nanodisk aggregates. Nanodisks are readily solubilized in nonpolar organic solvents, such as toluene and carbon tetrachloride, to yield stable monodisperse suspensions. These findings open opportunities for creating nanodisk-based nanocomposite materials. Stable nanodisk suspension in toluene enabled small angle neutron scattering (SANS) measurements. SANS data confirmed the nanodisk diameter and allowed accurate measurement of nanodisk thickness (19.5 ± 1.0 Å). In solid phase, nanodisks aggregate in sub-micron platelets.