The effect of the steric structure of the original polyvinyl alcohol on the rate of hydrolysis of polyvinyl acetal derived therefrom has been investigated. As the syndiotactic content of the original polyvinyl alcohol increased, the acetal derived therefrom became more easily hydrolyzable. Confirmation on the model compound led to the same conclusion; acetal derived from dl-type pentane-2,4-diol (corresponds to the syndiotactic portion) hydrolyzed more easily than that from the meso-type diol (corresponds to the isotactic portion). These results are entirely consistent with that expected from the conformational view.

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SynopsisUltraviolet-induced crossliking of the film of polyvinyl alcohol with different degrees of polymerization was investigated in air a t 25°C. in the presence of sodium benzoate as a sensitizer.In the absence of the sensitizer, no crossliing occurred. The gel content increased with irradiation time, and tended to a limiting value, depending on the initial sensitizer concentration. The final gel content increased as a function of the initial amount of sodium benzoate. A plot of solubility ( S + AS'/^) against the reciprocal of the concentration of sensitizer converted gives a straight line in each caae. The number of crosslinks is directly related to the number of sensitizer molecules destroyed. The crosslinking occurred predominantly, and main-chain scission was negligible. This result is in marked contrast to the effect of ionizing radiation, since the ionizing radiation causes only degradation under the identical conditions. This ultraviolet method waa applied successfully to the crosslinking of water-soluble cellulose derivatives, such as methyl cellulose and sodium carboxymethyl cellulose.Crossliing is always accompanied by photolysie of the sensitizer.

By measurement of peak areas in the dioxymethylene region of high‐resolution NMR spectra of partly formalized poly(vinyl alcohol), PVA, the relationship between tacticity of PVA, rate of formalization reaction, and stereochemical configuration of poly(vinyl formal) was studied. Formation of cis‐formal at an isotactic part of a PVA chain is faster than that of trans‐formal at a syndiotactic part. When the reaction is allowed to continue for a long period, the migration of formal rings from syndiotactic to isotactic portions is observed. Partition of formal rings in partly formalized PVA into cis and trans types is discussed in connection with the tacticity of original PVA and degree of formalization. The rate‐determining step of acetalization reaction is also discussed.

Effects of aliphatic esters, aldehydes and some impurities, as monovinyl and divinyl acetylene which exist normally in vinyl acetate, on the polymerization of vinyl acetate were studied. Esters and saturated aldehydes such as methyl acetate, ethyl acetate, isopropyl acetate and dimethyl oxalate etc., and acetaldehyde and butyraldehyde act only as transfer agent and the values of the transfer constants on these substances were determined. Unsaturated aldehyde such as crotonaldehyde and also benzaldehyde, and monovinyl and divinyl acetylene act as retarder. The several reaction constants relating the retarding effect were obtained. ZUSAMMENFASSUNG:Es wurde der EinfluB von aliphatischen Estern, Aldehyden und Verunreinigungen, die imvinylacetat iiblicherweise vorhanden sindwie Monovinylacetylen und Divinylacetylen a d die Polymerisation von Vinylacetat untersucht. Ester und gesattigte aliphatische Aldehyde, wie z. B. Methylacetat, Athylacetat, Isopropylacetat, Dimethyloxalat usw., Acetaldehyd und Butyraldehyd, wirken nur als ubertrager. Ihre tfbertragungskonstanten wurden bestimmt. Ungesattigte Aldehyde, wie Crotonaldehyd, aber auch Benzaldehyd, ferner Mono-und Divinylacetylen wirken als Verzogerer. Die Polymerisationsgeschwindigkeit von Vinylacetat in Gegenwdrt solcher Verzogerer wurde nach der Gleichung von KICE analysicrt, und die verschiedenen Geschwindigkeitskonstanten wprden bestimmt. *) This report is a summarization of several of the author' papers which appear in the 1) I. SAKURADA and R. INOUE, Chem. High Polymers (Japan) 7 (1950) 211. Industrially pure vinyl acetate, made by the KURASAIKI RAYON COMPANY, was used in all tests. The monomer was washed with aqueous NaHSO, and water. It was then dried and rectified. The fraction boiling at 72.5"C. was partially polymerized, and the unpoly-5) A. J. BUSELLI, M. K. LINDEMANN, and C. E. BLADES, J. Polymer Sci. 28 (1958) 485. 6) T. OHSUGI, Chem. High Polymers [Japan] 6 (1949) 460. 7) 0. L. WHEELER, S. L. ERNST, and R. N. CROZIER, J. Polymer Sci. 8 (1952) 409. 8 ) 0. L. WHEELER, E. LAVIN, and R. N. CROZIER, J. Polymer Sci. 9 (1952) 157. 9) M. YANO and M. MATSUMOTO, J. chem. SOC. Japan; Ind. Chem. Sect. (Kogyo Kagaku

Studies of the steric structures of poly(vinyl alcohol), as deduced from studies of the structures of its esters, particularly poly(vinyl formate) are described. Two types of tactic poly(vinyl formate) crystallize with different structures, corresponding to their different molecular structures. Therefore, the type of molecular stereoregularity in poly(vinyl formate) samples can be deduced from an examination of the crystals produced by a given crystallization treatment. From the results of the study of the poly(vinyl formate) crystals, some conclusions can be drawn concerning the steric structure of poly(vinyl alcohol). Crystallizabilities of other tactic poly(vinyl esters) have also been investigated.

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