The emulsion polymerization of styrene is initiated by persulfate fragments. Therefore, there is at least one SO₄^-· at the end of each polymer chain. Then, we tried to know how many SO₄^-·groups exist on the surface of an emulsion particle by means of the electrophoretic methods. In preparation of these emulsions, Tween 80 and ammonium persulfate (APS) were used as the emulsifier and the initiator, respectively. The obtained results were the following: 1) In the case of sulphuric acid buffer solution, of which ionic strength 0.04, the particles prepared with APS indicated electophoretic mobility, but ones prepared with hydrogen peroxide and azobisisobutyronitrile did not indicate the mobility. 2) In the hydrogen chloride buffer solution, of which ionic strength 0.01, the density of surface charges, (D), of the particle (APS particle) prepared with APS is nearly equal to D of the particle with redox catalyst, and D of APS particle was not influenced by the ionic strength and pH. 3) D increased as the concentration of Tween 80 decreased. 4) On the surface of these emulsion particles, there is a half of the total SO₄^-·groups in the particles.
From the results obtained above, it was evident that the surface charges of styrene-acrylic acid copolymer emulsion reported in Part III of this series consisted of -COO- of acrylic acid, 55%, CH₃COO- of acetic acid added as buffer solution 20%, and other ions, 24.5%, which may be considered as SO₄^-·from APS, respectively.

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15 kinds of pigments on the market have been tested to study the influence of pigments upon thermal degradation of polypropylene. The result indicates that the effects of pigments are so remarkable that careful attention is necessary in practical use. Furthermore, the degradation effect was studied in the same way for various metals and their chlorides and oxides, and it was concluded that this effect could be explained by considering the catalytic effects of metals contained in pigments since both results, mentioned above, had a correlation between them. Furthermore, the interactions between pigments and various kind of stabilizers were studied.

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The influence of pigments, dispersed in polypropylene, upon its degradation by ultra-violet ray was studied. The result has shown a remarkable influence of the pigments and suggested the necessity of precaution in their applications. From a further study of the influence of various metalic chlorides, oxides and metal itself and study of screening effects of various pigment contained in polypropylene, it was concluded that the influence upon degradation could not be explained merely by the screening effect unless the catalytic action, in detail of which was reported in previous report, of metals contained in the pigments is taken into consideration.

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Our study of influence of pigments on thermal degradation of polyacetal resin showed that most of all pigments have tendencies to accelerate the degradation.
This effect of acceleration was proved to be caused by both factors, the metallic components in pigments and the pH value of pigments, which was expected to have influence upon the hydrolysis at ether bond. Therefore the pigments containing copper, lead and zink etc, or the pigments having the strong acidity have remarkable influences for acceleration of thermal degradation upon polyacetal resin.

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Molecular weights and their distributions of polycarbonate, prepared by the phosgenation process, were measured after melting. When the polymer was melted at the temperature lower than 320°C, the molecular weights decreased, showing some limiting values, and the shape of molecular weight distribution curves became somewhat sharper ones. The result could be explained as the influence of the amount of low molecular weight fractions.
The phenomenon of the Flory's “Random reorganization of molecular weight distribution”, was observed.

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The photo- and thermal-degradation of polycarbonate in air and vacuum have been investigated using infrared, ultraviolet, mass-spectrograph and X-ray diffractometer. It has been concluded that cross linking is developed in polycarbonate by irradiation with ultraviolet rays. The carbonate group is broken down at high temperature, liberating large quantity of carbone dioxide. Hydroxyl group increases in both photo- and thermal- degradation.

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Polyvinyl alcohol (PVA) was acetalized with acetaldehyde in water or a water-dioxane mixture using N/200 sulphuric acid or hydrochloric acid as a catalyst. The rate of acetalyzation was almost independent of polymer concentration (0.05-0.20 base mol/l). The rate of deacetalization of partially acetalized PVA was also investigated in a wate r-dioxane mixture using N/100 sulphuric acid as a catalyst, and it was found that addition of PVA to the reaction mixture decreased the reaction rate. These results are provoking contrast tothose obtained by Smets and Petit. Rate of saponification of partially acetylated PVA in water or a water-dioxane mixture with N/200 hydrochloric acid was almost indep endent of polymer concentration and of addition of PVA. Some discussions were given for the results.

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