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A novel technique is described for the investigation of polyanions by direct polyelectrolyte titration. In connection with a specially developed phototitrator, an extremely high sensitivity can be reached using 3,640nene bromide as cationic titrant and eriochrome black T as metachromatic indicator for end-point detection. This enables both the determination of charge densities for polymer characterization as well as the detection of polymers in aqueous solution down to trace concentrations of 10 pg/L. Monovalent salt ions do not interfere with the titration up to concentrations of about 0,l mol/L. Potential interference of divalent metal ions can be prevented by adding ethylenediaminetetraacetic acid (EDTA) as chelating agent. The applicability of the method was proved by measuring charge densities of poly(sodium acrylate) (NaPAA) in the concentration range of 0,Ol to 10 mg/L and of poly(potassiurn vinyl sulfate) (KPVS). As expected, the charge density of NaPAA decreases with a pH decrease from 11 to 7, whereas the charge density of KPVS is independent of pH.

Water sorption was determined and dynamic‐mechanical measurements made on dry and water‐containing systems. Different types of surface treatments of the glass fiber were studied. Immobilization of polymer chains in the interphase is determined by the nature of the curing system, annealing conditions, and surface treatment of glass fibers. Penetrating water can be found at three kinds of locations in the composite; water in the interphase has different properties than water in the polymer matrix and in microvoids. This fact can be used as a microscopic probe in epoxy‐containing composites. Water content depends on the density of polar groups and the density of the network. At higher temperatures water causes crazes, at lower it mainly acts as a plasticizer. Water in crazes does not affect the glass transition temperature Tg, but it decreases (tan δ) and weakens the material. As long as water mainly goes into swelling, energy transfer between the resin and the matrix is not affected. The reinforcement then works as it should. The results demonstrate the importance of interphase properties on the behavior of the composite.

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