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An off-lattice Metropolis Monte Carlo algorithm with reptation is used to find the average fractional ionization a as a function of pH for a generic ionizable linear polyelectrolyte in a salt solution. The polyelectrolyte is treated as a threefold rotational isomeric state model polymer; each unit can bear a negative charge or not with intrinsic ionization constant pK a. Debye-Huckel screening is assumed between the charges. For computational convenience, the dielectric constant of the polymer is taken to be that of the solvent. The number of units Nwas either 50 or 100. Monte Carlo results were collected for various Debye screening lengths at six combinations of number of chain units N, bond angle (J, and Manning parameter when fully charged, So. For four of the combinations, So was 1 to take partial account of counterion condensation. These runs had Nand (J of 50 and 1°, 50 and 70°, 100 and 1°, and 100 and 70°. The fifth combination had N = 50, (J = 70°, and So = 2.85. The sixth had N = 50, (J = 27.34°, and So = 0.72, for comparison with data for hyaluronate. The Monte Carlo results are compared to third nearest-neighbor linear Ising type calculations and to simple mean field theories in a. Mean field theory in a worked very well in the (nearly rodlike) (J = 1° cases using the known distance between units. Mean field theory in a using an estimate for the distance between units based on the ideas of electrostatic persistence length and excluded volume worked equally well for the (J = 1° cases and moderately well for the (J = 70° cases. The free energy and entropy per simulated chain were calculated by thermodynamic integration of the Monte Carlo results for a as a function of pH.

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.

An automatic, continuous, online monitoring technique was used to follow the polymerization of acrylamide under a variety of temperature and initiator conditions, without chromatographic columns. The technique furnishes, as a function of time, the weight-average polyacrylamide mass M w, the monomer conversion, reduced viscosity, and certain measures of polydispersity. After a complex initial phase following initiator addition, wherein impurities competed with monomer for free radicals, monomer conversion followed a first-order decay during most of the subsequent reaction. For fixed monomer concentration, at every point in conversion beyond very early points, M w was proportional to the inverse square root of the initiator concentration. Furthermore, the monomer decay time also scales in the same way, and M w vs conversion is linear during most of the conversion, with a negative slope. Hence, the overall reaction scheme falls within the quasi-steady state approximation (QSSA) of ideal polymerization kinetics. The rate constant for initiator decay, as well as the ratio of propagation rate constant squared to termination rate constant were determined. The activation energy for the potassium persulfate initiator decomposition was also determined. Deviations from the ideal kinetics at early and late conversion are rationalized by existing models. Using a technique for determining instantaneous polydispersity from the derivative of M w, it was possible to follow the evolution of the polydispersity for the polyacrylamide reactions.