Oligomerization of L-leucine N-carboxyanhydride under different reaction conditions and investigation of the resulting poly-L-leucines as the catalyst of the Julia-Colonna asymmetric epoxidation of benzalacetophenones supports the original speculation that a α-helical structure of the catalyst is important for high asymmetric induction. -(TAKAGI, R.; BEGUM, S.; SIRAKI, A.; YONESHIGE, A.; KOYAMA, K.-I.; OHKATA*, K.; Heterocycles 64 (2004) 129-141; Dep. Chem., Grad. Sch. Sci., Hiroshima Univ., Higashi-Hiroshima 739, Japan; Eng.) -Mais 25-100

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Our previousreveal that compounds containing a donor nitrogen atom can play a significant role in the polymerization of vinyl monomers initiated by a charge-transfer mechanism. A number of different catalysts have been found to be effective and they are all Lewis acids. However, a mechanism of the reaction in the presence of Lewis acid is very obscure. Amines are very effective donors for chargetransfer initiation, but Lewis acids such as Fe3+ and Cu2+ cannot be used in the presence of amines since they are precipitated.The present communication contains the results of the polymerization of methyl methacrylate (MMA) in dimethylsulfoxide (DMSO) in the presence of carbon tetrachloride (CC14), malononitrile CH2(N)2, and hexakis(dimethylsulfoxide)iron(III)perchlorate [Fe(DMSO)6] (c104)3 (A) at 60°C. It is an attempt to elucidate the mechanism of such chargetransfer-initiated polymerization reactions. EXPERIMENTAL MaterialsMMA? DMSO" and CC14,4 and chloroform were purified as in literature. The complex [Fe(DMSO)6] (A) was prepared as b e f~r e .~ PolymerizationThe rates of polymerization were determined dilatometrically as before.1° Molecular Weight DeterminationMolecular weights were determined using a vapor-pressure osmometer (Corona/Wescan model 232A). The polymer was precipitated from the reaction mixtures with methanol, washed with methanol and dried. The following relation, as detailed in the manual of Wescan 2328 model, was used AV = KClm where AV, is the observed voltage change, m is the solute molecular weight, and K is the calibration factor. The calibration was done with benzil. RESULTS AND DISCUSSIONThe rates of polymerization of MMA were recorded at 60 "C by adding different amounts of malononitrile (MN) to a constant composition of MMA, CCb, and A in DMSO. Experimentally it was found that the polymerization of MMA in this system required the presence of all the three components MN, A, and CCl,. Polymerization rate (Fig. 1) attained its maximum value when the mole ratio of [MN] to [A] was 3:1, when the concentration of other components were kept constant. However, beyond this ratio a d e c r e h rate was observed.We propose the following reaction scheme for this system in light of charge-transfer-initiated polymerization reaction.

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