SynopsisA semicontinuous emulsion process was used to polymerize vinyl acetate. The parameters studied were the rate of addition of the various ingredients. The polymerization evolution was followed as samples were taken a t regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography (GPC). Our study showed that the total surface of the particles is an important factor, that the reaction mechanism follows Krackeler's and Wessling's theory, and that the Smith-Ewart ideal case does not apply here.

The mechanism of thermal degradation of poly(vinyl chloride) has been studied by pyrolysis up to 400°C in a thermobalance under four kinds of dynamic atmospheres: helium, oxygen, air, and hydrogen chloride. The gaseous product from the thermobalance was analyzed for hydrogen chloride by the argentometric determination of chloride ions by using Mohr's method. An attempt was made to analyze for other gases in the product stream by chromatography with the use of a glass column, but failed due to the accumulation irreversibly of hydrogen chloride on the column. The molecular weights of the samples were determined by measurements of viscosities at 25°C in cyclohexanone; their molecular weight distributions were studied by fractionation and gelpermeation chromatography (GPC). From the thermograms, the mechanism of degradation in different heating atmospheres, the rate, the heat effect, the energy of activation, and the order of decomposition were deduced.

Isothermal emulsion polymerization at 60°C of styrene in a batch reactor were studied by using sodium lauryl sulfate as surfactant and potassium persulfate as initiator source. The concentrations of surfactant and initiator were varied during the runs. The polymerization evolution was followed as samples were taken at regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization, as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography. Our study showed that fresh nucleation takes place even at high conversion, causing a continuous shifting toward broadening of particle size distribution. Contrary to the theory of Smith and Ewart, which assumes a constant number of particles during interval II of the polymerization reaction, our digital simulation of the reaction presents better experimental results with a variable number of particles, and indicates that the Hui–Hamielec model for termination constant kt as function of conversion is not applicable under our working conditions.

The thermal degradation of poly(vinyl acetate) was investigated under dynamic atmosphere of helium up to 400 ~ with a thermobalance. The volatile products were analyzed by a gas chromatograph.Acetic acid proved to be the main component of the volatile products (90 to 95 ~). Kinetic measurements of numerous samples obtained showed that the rates and orders of the degradation were different for all the samples and depended on their internal structures (the polydispersity). This is contrary to data published by A. Servotte et al. [1] and agreed with N. Grassie [2,3].This dependence of the degradation on the internal structures of the samples is latter verified by a probabilistic approach.In recent years, the degradation of a number of poly (vinyl) compounds has been studied. On the thermal degradation of poly (vinyl acetate), important works have been published by N. Grassie [2. 3] and A. Servotte et al. [1].Existing techniques for studying the thermal degradation of polymeric materials are either very time consuming or very qualitative especially when the degradation reaction is complex.A method that gives rapid, yet quantitative results for the parameters of thetmal degradation of polymeric material is by thermobalance which combines DTA, TG and DTG. Moreover, the heating atmosphere can be controlled and changed quite easily.There is no shortage of publications presenting DTA curves for a wide range of polymeric materials. This might possibly give the impression that the DTA curve, for a plastic is unique and characteristic i.e. is a "finger-print" which can serve for identification when compared with curves for known materials.In fact, this is not so, the DTA curve itself, is not necessarily reproducible since the thermal degradation of polymeric material depends -beside many factorson the internal structure of the sample used.In this paper, poly (vinyl acetate) is degraded up to 400 ~ in a thermobalance, under the inert dynamic atmosphere of helium. The heating temperature is programmed linearly at 10~The results, obtained by the analytical scheme concurrently developed for deter-