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ABSTRACT:The effect of the monomethyl ether of hydroquinone (MEHQ) on the polymerization of acrylic acid was studied. The rate of polymerization was quantified at various levels of MEHQ by use of an in situ NMR technique. While oxygen functions as an inhibitor in acrylic acid polymerizations, MEHQ was shown to function as a retarder. The decrease in the rate of polymerization allowed the calculation of an inhibition constant for this system. MEHQ was found to remain in the polymerizing mixture throughout the course of the reaction, significantly reducing the rate of polymerization, but not reducing the molecular weight of the polymer. The data are consistent with direct reaction of MEHQ with initiator fragments, but not termination of growing chains. Superabsorbent polyacrylic acid gels were prepared and the properties measured.

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The kinetics of the electron transfer from phenanthrenequinone dianion 2Na+) to the parent quinone (PQ) was investigated. The reaction produces a paramagnetic "red" species (PQ. -,Na+) which dimerizes in a subsequent slower step into a diamagnetic "green" species (D2-,2Na+). The results are described by the equations (PQ*-,2Na+) + ( P Q 2(PQ. -,Na+) ("red"), k = 2-3 x 106 M-1 sec-1; and 2(PQ. -,Na+) ("red)" e (D2-,2Na+) ("green"), k N lo4 M -] sec-I. However, the free PQ. -ions do not dimerize. The spectra of all the pertinent species were examined and fully recorded. The green species further agglomerate forming (D2 -,2Na+)2, etc., which are spectrally indistinguishable from (D2-,2Na+). The thermodynamics of the reversible dimerization and tetramerization was studied quantitatively. The nature of the dimer was discussed and a tentative structure for it was proposed. The acenaphthenequinone system behaves similarly, its comprehensive study being prevented by technical reasons. The "blue" species, described recently by some investigators and believed to be the acenaphthenequinone dianion (ACQ2-), probably is the diamagnetic dimer of ACQ. -,Na+. The genuine spectrum of ACQ*-,2Na+ was recorded and shown to be unmistakably different from that of the blue species.imerization of ion pairs, or their association into D still larger aggregates, is a well-known phenomenon caused by the Coulombic attractions. Such forces, we believe, may facilitate the formation of T-T bonds between suitable partners and yield associates having properties fundamentally different from those of the electrostatically bonded dimers of ion pairs. The salts of radical ions derived from phenanthrenequinone (PQ) and acenaphthenequinone (ACQ) seem to form such T-T bonded dimers. Experimental Section9,lGPhenanthrenequinone and 9,lGacenaphthenequinone were acquired commercially and purified by crystallization and vacuum sublimation. The solutions of quinones were prepared on a highvacuum line, and their concentrations were determined spectrophotometrically. Solutions of phenanthrenequinone were found to be light sensitive, their yellow color rapidly disappearing on exposure to daylight. Therefore, they had to be stored and handled in darkness. ResultsOn contact with sodium mirror the quinones are reduced, the reaction being completed after a day or two. Titration with HC1 of samples withdrawn after completion of the reduction demonstrated that 2 equiv of sodium reacted with each mole of quinone, Le., dianions of the quinones were produced. The reduction of phenanthrenequinone by magnesium mirror in T H P led to a product possessing only 1 equiv of base/mol of quinone. Apparently, no dianion of quinone is formed with Mg. The dianions are diamagnetic, but paramagnetic species are formed on the addition of the respective quinones.Reactions Involving Phenanthrenequinone (PQ). The optical spectra of PQ and of its dianion (PQ2-,2Na+) are shown in Figure 1. Their shape is not affected either by dilution or by variation of temperature. Addition of a slight e...

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