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24-Methylcholesta-5,E-22-dien-3/3-ol (C2s AS,~2-sterol) was separated from the unsaponifiable matters of the following eight seed oils of Brassica species: Brassica campestris (candle I and II and torch), B. napus (tower and midas), B. juncea (brown and oriental mustards), and B. alba (yellow mustard). The configuration at C-24 methyl group of the respective sterols was evaluated by ~3C NMR spectroscopy. All the C2s As,22-sterols in the Brassica seed oils were found to contain the C-24 epimer of brassicasterol, trans-22-dehydrocampesterol, in the range of ca. 10-30%.

SynopsisThe alternating copolymer was prepared from butadiene (BD) and acrylonitrile (AN) with ethylaluminum dichloride as a complexing agent and with vanadyl chloride as a cocatalyst, and was investigated to explain effects of composition and sequence distribution on the physical properties, especially the viscoelastic properties and the ultimate mechanical properties. In the unvulcariixed state, the viscoelastic properties of the alternating rubber is not essentially different from the random one, except for a slight difference in the relaxation spectra. However, the vulcanized rubbers show different shift factors.The latter depends upon the glass transition temperature (To). Since the alternating copolymer possesses a T , lower than the random one, the nature of the alternating eopolymer corresponds to that of the random copolymer having an AN content of 40%. The difference in dynamic properties can be expressed with the different shift factors. In the isofree-volume state or a t the temperature T , + 25"C, the rubbers having various acrylonitrile contents and various degrees of alternation exhibit almost the same dynamic properties. However, the strain a t break of the alternating rubber is higher than that of the random one. The temperature of maximum strain increases with increasing degree of alternation. The alternating rubber shows higher stress a t break than the random one. The stiffness of the chain of the alternating copolymer is smaller than the random copolymer; in other words, the niolecular chain of the former is more flexible than the latter. It can be said that the alternating copolymer is an excellent rubber having high tensile strength and elongation a t break.

synopsisAs a model for the vulcanizates of block copolymers, mixtures of polyisoprene and polyethylene vulcanized both with a peroxide and with sulfur were investigated by stress birefringence. It was found that the polyethylene dispersion showed a reinforcing effect only in the peroxide vulcanizates. On the other hand, the stress birefringence was decreased with increased polyethylene content except at high polyethylene content.In the latter case, the slope of the line in the birefringence-stress plot was almost equal to that for the pure polyisoprene vulcanizate at high stress levels. However, at lower stresses significant optical creep was observed, i.e., the stresa increased without birefringence. Such an optical creep as this exists also in styrene-butadiene block copolymer. These facts are interpreted by the assumption that polyethylene dispersion, when it is linked chemically with polyisoprene matrix, acts as a reinforcing agent by forming physical crosslinks similar to the hard domains in block copolymers. Such physical crosslinks can slip during elongation, resulting in the observed optical creep. These phenomena disappear at the elevated temperature. -INTRODUCTIONIn the preceding paper' on the properties of a styrene-butadiene block copolymer, an optical creep (i.e., stress increase without increased birefringence) was observed in the early stage of elongation. This phenomenon was interpreted by the assumption that the hard polystyrene domains acted as crosslinks, although some slippage in these domains may take place on stretching. In similar vulcanized block copolymers, two kinds of crosslinks occur, i.e., chemical crosslinks with sulfur and physical ones produced by the polystyrene domains. The stress birefringence of the latter is lower than that of the former, because the deformation of block copolymer involves not only the orientation of polybutadiene matrix, but also the slippage of polystyrene blocks. At higher temperatures such physical crosslinks become ineffective and under these conditions the stress birefringence increases to a high value characteristic of pure polybutadiene vulcanizates. In this paper we wish to describe a stress birefringence experiment carried out on a blend of polyisoprene rubber and polyethylene dispersion, which is regarded as a model of block copolymer composed of a soft matrix and hard * Present address: Japan