We report new measurements of the shear viscosity and of the mass density as functions of temperature at the composition of the upper critical solution point for a mixture of polystyrene in diethyl malonate. The viscosity measurements have a precision of 0.04-0.4% and are over a temperature range of 91 K. The viscosity increases by an order of magnitude from the highest temperature to near the critical temperature. However, the analysis of the data is complicated by strong effects of shear near the critical temperature and by our lack of understanding of the behavior of the noncritical background viscosity of a polymer solution. We are unable to construct a function to describe the shear viscosity as a function of temperature. The mass density of this mixture is simply linear over the same temperature range.

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We have measured the apparent critical exponent y characterizing the divergence of the viscosity η∝(T−Tc)−y near the liquid–liquid critical point of the mixture polystyrene in diethyl malonate. The data span the range in reduced temperature of 10−4<(T−Tc)/Tc<10−1. The sample was prepared from the same materials used by Gruner et al. in their capillary viscometer [Macromolecules 23, 510 (1990)]; however our torsion oscillator viscometer had a shear rate 80 times lower. This increased the range of reduced temperatures where shear effects could be neglected. In spite of the large reduction in shear rate and the different viscometry technique, the parameters fitted to our data and those of Gruner et al. are in agreement. For this polymer solution, y is in the range 0.028±0.003, close to recent results for two other polymer solutions measured in capillary viscometers. However, it is significantly smaller than the exponent for pure fluids (0.041± 0.001) and simple binary mixtures (0.042±0.002). It appears that polymer solutions are in a dynamic universality class different from that of simpler fluids.

We consider the polymerization of α-methylstyrene, initiated by sodium naphthalide in the solvent tetrahydrofuran on time scales that permit full thermodynamic equilibrium between the monomer and the polymer. We present new measurements as a function of temperature of the mass density, the shear viscosity, and the liquid–vapor surface tension, and we compare the data to theoretical expectations when the polymerization is viewed as a phase transition. The mass density is well described by either mean field or nonmean field theories. The shear viscosity increases as the average degree of polymerization (DP) increases, but the exponent 3.4 is not reached, presumably because the DP is too small. The surface tension increases as the DP increases, indicating depletion of the polymer from the surface.

We have designed a simple, low cost automatic optoelectronic meniscus sensor for a capillary tube viscometer with a timing resolution of 0.01 s. The sensor is specifically designed for use with critical composition binary liquids, which undergo a change in fluid opacity as a function of temperature. The sensor works over the temperature range −65°–150 °C.