Maleic anhydride has been homopolymerized, contrary to accepted beliefs. Polymerization of either molten or dissolved monomer was initiated with the use of gammaradiation and free‐radical initiators. An anhydride having [η] = 0.146 dl./g. in acetophenone had a molecular weight of 23,100 (free acid), DP = 199, by the light‐scattering method. The carboxyl group propinquity is responsible for peculiar behavior of aqueous solutions of salts of the poly‐acid.

S31tween Flory's and Hermans' equations cannot be made a t this time as a result of this work. The wide rurrent discussions on the theory of network ~t r u c t u r e s~-~ indicate that a rigorous analysis of this very complex problem must await further experimental data on numerous other polymer systems.

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The polymerization of vinyl monomers has been inhibited or retarded by many substances including quinoid, hydroquinoid, and nitrophenolic compounds; the terms "inhibition" and "retardation" are differentiated in this article according to the definitions given by Foord (27). A comparison is made of the behavior of these compounds, particularly the nitrophenolic compounds, as polymerization retarders, studying the effect of temperatures and chelation upon their relative efficiency. The temperature effect is important in the selection of an inhibitor (or retarder) because a compound suitable to prevent polymerization of a monomer at room temperature and at low concentration during storage does not necessarily prevent polymerization during distillation. This fact is especially true when hydroquinoid compounds are compared with nitrophenolic compounds, and/or sulfur is compared with phenolic compounds. Apparently, an inhibitor (or retarder) has a certain operable temperature range, and a higher temperature destroys the inhibitor by its reaction with a growing polymer chain, or by thermal decomposition. Therefore, the stabilizing effect produced by chelation would be important in the inhibition of monomer at higher temperatures. EXPERIMENTAL Apparatus. The polymerization bath and the constant temperature water bath were identical, consisting of a borosilicate glass battery jar 12 inches high and 12 inches in diameter, set