Iodine relative weight

Dmitri Mendeleyev (1834-1907), a Russian scientist and creator of the modern periodic table, discovered that if elements were lined up according to atomic weights and arranged in rows of 2, 8, 18, and 32, atoms with similar chemical and physical properties appeared in the same column. However, there were some exceptions. Argon and potassium were out of place. So were iodine and tellurium. Mendeleyev thought his relative weights were incorrect. 

The polymerization of 1,3,3-trimethyl-2,7-dioxabicyclo[2.2.1 Jheptane 35 was carried out in methylene chloride, toluene, and 1-nitropropane at temperatures between —78 and 0 °C32l Boron trifluoride etherate, triethyloxonium tetrafluoro-borate, antimony pentachloride, and iodine were used as initiators. Irrespective of the solvents and initiators employed, the products obtained at 0 °C were white powders with melting points of 50—55 °C, while those obtained at tower temperatures were sirups. The number average molecular weight of the unfractionated products ranged from 400 to 600. The molecular weight distribution of the oligomers prepared at 0 °C was broad, in contrast to the relatively narrow distribution of those obtained at -40 °C. 

Figure 26 shows a typical GPC elution curve of the ethanol insoluble polymers obtained at 0 °C, (b), together with the GPC curve of the original iodine-terminated polypropylene, (a). Curve b clearly shifted toward higher molecular weights relative to curve a, but retained a narrow molecular weight distribution (Mw/Mn = 1.14), indicative of the formation of a propylene-THF diblock copolymer. The 13C NMR spectrum of the block copolymer is shown in Fig. 27. 

Relative to the initiator/activator mechanism shown in Scheme 5, it is interesting to compare vinyl ether polymerizations initiated with the HI/I2 system and with iodine alone. The former system provides living polymers of controlled molecular weights and very narrow MWD [58], whereas the latter has been known for more than a century but fails to give such controlled polymerizations (cf., Sections IV.A) [49,55]. In the iodine-mediated polymerization, iodine serves as both the initiator and activator one molecule of iodine first slowly adds across the vinyl ether double bond to give an adduct. The a-carbon-iodine bond is activated by another molecule of iodine [34,95]. Thus, both systems would in fact form the identical growing chain end [ CH2CH(OR)+.I3 ], and the ob-... 

Solid iodine (I) chloride is usually obtained as the a-form, the melting point of which has been reportedas 27.2°. A /3-modification (m.p. 13.9°) has also been described. Values for its boiling point vary from 94.7 to 102°, because of decomposition into chlorine and iodine. This tendency toward decomposition and the relatively low melting point have hindered the accurate determination of sample weights. In current practice, crystalline iodine (I) chloride... 

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