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.
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