The kinetics of the emulsion polymerization of butyl acrylate at 20 "C in Smith-Ewart interval 111 were investigated using a redox initiator system peroxodisulfatebisulfite-copper. The aim of this work was to obtain more basic knowledge about the kinetic behavior of the butyl acrylate system. Monomer conversion into polymer was based on gravimetrically calibrated online densitometry. The experimentally obtained conversion versus time curves for these seeded reactions were fitted by a linear regression procedure (slope and intercept) as well as by a nonlinear regression procedure based upon zero-one kinetics. The conclusion is that the emulsion polymerization of butyl acrylate may reflect zero-one kinetics up to a particle size of approximately 130 nm. The rate coefficients for entry and exit can be obtained fairly accurately with the slope and intercept procedure and with the nonlinear regression method if the propagation rate coefficient is accurately known. However, this is not the case. Therefore the development of universal procedures for obtaining the propagation rate coefficients is essential, since this parameter is of paramount importance in all further model calculations concerning emulsion polymerization.x exp [-20 f 2 x 1 O~/ R T ] (40 "C --7 0~x 2 ) k = 107.4*0.4 P Acta Polymer., 47,441-449 (1996) 0 VCH Verlagsgesellschafi mbH, D-69451 Weinheim, 1996

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Knowledge of local monomer concentrations in the case of heterogeneous polymerizations is extremely important, since these local concentrations determine the kinetics of the reactions. In this paper two techniques to determine the local concentrations are reported. The first technique makes use of the well known pulsed initiation method, which is fiequently used nowadays Íirr the experimental determination of the propagation rate constant (k"). The second technique is applied Íbr the determination of monomer concentrations in vesicle bilayer structures.

A new kinetic model is proposed for the accumulation of poly(3-hydroxybutyrate) (PHB) in Alcaligenes eutrophus. The model developed is closely related to the descriptive model of Harkins for the emulsion polymerization process. The PHB accumulation is discussed in terms of polymerization events such as initiation, propagation and termination, taking into account the heterogeneous nature of the system. Experimental results on the PHB accumulation in Alcaligenes eutrophus can be described in both a quantitative and qualitative manner by the model. Further, it is shown that the decrease in the rate of polymerization during the PHB accumulation can be explained by coalescence of the granules. The decrease of the molecular weight of the polymer formed during the accumulation process can be fully explained in terms of the kinetic mechanisms of progapation and chain transfer, and the effect of granule size on these. 0 1995, Huthig &

SY NOPSlSPhysisorption of nitrogen at one specific pressure is used to determine the specific surface area of a flocculated polystyrene latex by applying BET theory. Assuming that a flocculated sample of polymer latex is composed of distinct spherical latex particles (i.e., there is no coagulation of particles), the volume-surface-average diameter can be calculated. The resulting diameters are compared to sizes obtained using a disc centrifuge sedimentometer, which fractionizes the particles by sedimentation. The diameters from both techniques were in good agreement, showing that physisorption of nitrogen, which is a simple technique, can be used to determine sizes of flocculated latex particles. This agreement also shows that the flocculation of the polystyrene latex produced separate nonporous spherical particles. When flocculation of a latex is done above its glass transition temperature, coagulation will occur. While other particle sizing techniques can produce particle size distributions, the physisorption of nitrogen only gives the volume-surface-average diameter. However, one advantage of the physisorption of nitrogen is that it covers a broad range of particle sizes compared to most other techniques.