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SYNOPSISNucleating agents increase the impact strength, tensile strength, and tensile elasticity modulus of semicrystalline polymers. Nucleating agents also decrease product cycle times, resulting in a cost savings per product unit. We have synthesized and tested 15 compounds as nucleators for polypropylene. Of these, trinaphthylidene sorbitol, tri (4-methyl-1-naphthylidene) sorbitol, tri-(4-methoxy-1-naphthylidene) sorbitol, and dibenzylidene xylitol are efficient nucleators of polypropylene. Trinaphthylidene sorbitol ( t n s ) has two major diastereomers: The "S" diastereomer yields a faster crystallization rate for polypropylene than does the commercial nucleator dibenzylidene sorbitol ( Millad 3905 ) . Crystallization rates are 208 and 88, respectively ( t & min-' X 1000). The " R " diastereomer, however, is a poor nucleator and interferes with the nucleating activity of the "S" diastereomer. A 52/48 mixture of diastereomers does not nucleate polypropylene, even at twice the concentration. This is the first time that the importance of stereochemistry has been demonstrated in the nucleating action.

An X-ray crystallographic study on 4"-0-(4-iodobenzoyl)megalomicin A has led to the revision of the structures of the megalomicins and the XK-41 antibiotics. Crystals are orthorhombic, space groupP2,2,2, with a = 12.669(2), b = 19.501 (6), c = 25.741 (9) A, and Z = 4. The structure was solved by the heavy-atom technique, and 1 812 observed reflections led to a final R of 0.095. The novel amino-sugar previously thought to be D-rhodosamine has been shown to have the L-configuration and is therefore renamed L-megosamine. It has also been shown to be glycosidically attached to the tertiary 6-hydroxy group. The 13C n.m.r. and circular dichroism (c.d.) parameters of these macrolides are described. The syntheses of methyl aand P-D-rhodosaminide, methyl aand P-D-megosaminide, methyl a-and 6-L-megosaminide, methyl a-and (3-D-angolosaminide, and methyl 2,3,6-trideoxy-3-(dimethylamino) -a-D-xylo-hexopyranoside are described and their conformations and 13C n.m.r. parameters are discussed. Methyl a-D-and -L-amicetoside, methyl a-D-and -L-cineruloside and other model 4-oxopyranosides and pyrans have been synthesized. Their c.d. properties have been determined and they have been shown to exhibit Anti-Octant behaviour.

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