Design,synthesis and properties of molecular composites of rod-like polymers

Processing and performance of fiber reinforced polymers suffer from problems related to the heterogeneous nature of the composites. The strong impact of the nature of the interface between fibers and matrix adds to the complication of the field. Consequently many attempts have been made to reduce the cross-section of the reinforcing fibers to molecular dimensions and to increase the compatibility between the rod-like molecules or bundles of molecules and the isotropic matrix of ordinary flexible polymers. All such attempts have failed, mainly for reasons of thermodynamics which predict immiscibility of rods and coils on the molecular level. A possibility to create structures in which molecular rods are embedded in a continuous matrix of flexible chain segments exists nevertheless.¹ Rod-like backbone structures decorated with a skin of flexible side chains of moderate length in terms of the number of carbon atoms (typically C₆ - C₁₈-side chains) have been synthesized and tested for the spontaneous formation of molecular composites. Some of the materials built along this principle can be processed by solution casting or even melt extrusion. The academically more interesting materials can be built up layerwise by a modified Langmuir-Blodgett technique. The latter process gives rise to monodomain textures which allow for straight-forward testing of the mechanical properties by optical means (Brillouin-spectroscopy) and by piezoquartz-techniques. Hairy-rod macromolecules can also be synthesized which contain crosslinkable side chains. Thus, after formation of layered, oriented structures, these can be crosslinked photochemically or by curing. The result is a network, which is unidirectionally reinforced by the rod-like macromolecules. These novel types of networks can serve as membranes by which size exclusion is achieved via control of the distance between adjacent backbone molecules in the matrix. Recent synthetic advances in the field have concentrated on hairy-rod macromolecules based on cellulose alkyl ethers and on derivatives of poly-(p-phenylene). The latter materials serve as examples of systems which can be processed by casting and extrusion processes. Due to their excellent thermal stability relevant data on the rheological and mechanical-dynamical data have become available. These data serve to document the unique behavior of the hairy-rod macromolecules as bulk materials.     

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.     

Studies on triazine dye-enzyme interaction by means of affinity partitioning

Affinity partitioning in aqueous two-phase systems composed of dextran and polyethylene glycol the latter being partially replaced by dye-substituted polymer was evaluated for the study of enzyme-dye interaction. The method was found excellently suited for the recognition of any interaction between a certain enzyme and triazine dyes by determining the actual partition coefficient, K. Two enzymes, intestinal alkaline phosphatase and yeast phosphofructokinase, were studied. Alkaline phosphatase binds more or less specifically to various triazine dyes. A number of substrates but also inorganic phosphate, NAD⁺ and selected chromophores are competing agents in enzyme-dye interaction whereas hydrophobic and uncompetitive inhibitors fail to compete with the dye. Thus, information on the chemical nature of the dye-enzyme interaction was obtained. Affinity partitioning turned out also appropriate to study the structural dynamics of enzymes. This was exemplified on the specific interaction of phosphofructokinase with a number of triazine dyes. A change of the allosteric properties of the enzyme in respect to ATP-inhibition and its reversibility was indicated by a corresponding alteration of the partition coefficient. The results are discussed in terms of a conformational change of the enzyme.