To perform on-line monitoring of the absolute weight-averaged mass, Mw, of the polymers produced in a polymerization reaction, refractometer (RI), ultraviolet absorbance (UV), and time-dependent static light scattering (TDSLS) detectors were placed in series, and a diluted stream of reactant solution was made to flow through them. The technique allows rapid determination of time-dependent reaction "signatures" and end-product masses. Hence the effects of changing reaction conditions such as reactant concentrations, temperature, and initiators can be quickly assessed. Such a technique is expected to be of wide utility in characterizing polymerization reactions, both on the laboratory scale, where new polymers are synthesized and conditions optimized, as well as on the industrial scale, where on-line quality control can be performed. For stepwise reactions, the RI and TDSLS detectors are sufficient for determination of M w, whereas for free radical reactions, the polymer concentration must be measured in order to obtain the traditionally defined Mw (i.e. without monomer taken into consideration). The latter was achieved for poly(vinyl pyrrolidinone) polymerization by measuring the monomer concentration with the UV detector. As a further measure of characterization, a single capillary viscometer was also placed in series with the other instruments. This allowed the reduced viscosity to be monitored simultaneously.

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Analysis of a variety of properties of supramolecular aggregates in aqueous urea supports an explanation for the urea effect that differs from traditional explanations based on the direct mechanism of urea−water solvation or the indirect mechanism via rupture of the three-dimensional (3-D) structure of water. The urea-induced effects investigated are increases in amphiphile critical micelle concentrations, ionization degrees (α), and aggregation numbers; decreases in percolation thresholds of reversed micelles; expansion of minimum areas of monolayers; increases in the radii of gyration of polyelectrolytes; changes in morphologies of sodium bis-2-ethylhexylsulfosuccinate thin films on glass substrates; and direct evidence for urea-induced reduction in ion pairing. All of these effects are attributed to an urea-induced enhancement of the hydrophilic properties of water that results in more strongly solvated polar groups and ions and a reduction in ion pair formation. The implications of this analysis for urea effects on protein 3-D structure are briefly highlighted.

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Direct and indirect mechanisms have been used to explain the effect of urea on surfactant aggregates. By studying formation properties, anion selectivities, and stabilities of cationic and zwitterionic micelles and of cationic vesicles, we confirm previous evidence in favor of the direct mechanism (Langmuir 1995, 11, 1715). Differential fluorescence suppression of 2,3-N-butylnaphthalimide by Br- and Cl- is used to investigate in a short time scale (nanoseconds) effects of urea on ion binding and exchange in micelles and vesicles. Enhanced degree of dissociation and decreased anion selectivity of the surfactant aggregates are observed. Micellar catalysis of the unimolecular decarboxylation of 3-carboxy-6-nitrobenzoxazol studied to investigate the effect of the additive on a long range (minutes) also shows a reduced anion selectivity. Formation properties of the thermodynamically stable (cmc) and nonstable aggregates (hydrodynamic radii and molecular weight) are measured to obtain parameters for analysis. Addition of urea caused increase in the cmc and led to increase in vesicles molecular weight and hydrodynamic radii. These results support preferential headgroup solvation in the aggregates (direct mechanism) by urea resulting in the loss, or size reduction, of the interfacial region for counterion specificity (size, polarizability, and other non-Coulombic terms) to manifest.

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