THE MECHANISM OF ACTION OF SUGAR ACETALS AS NUCLEATING-AGENTS FOR POLYPROPYLENE

We studied the nucleation of polypropylene via experimental measuremen ts and molecular modeling, and we propose that sugar acetal nucleators stabilize the helical form of polypropylene at the molecular level. T hrough FTIR techniques, we established that the nucleators dibenzylide ne sorbitol (DBS) and trinaphthylidene sorbitol are chemically stable in molten polypropylene. Using solid-state NMR, we determined that DBS is dispersed to particles 32 angstrom in diameter. These particles ar e three orders of magnitude smaller than the 1-10-mum size expected in the literature. DSC was employed to evaluate the nucleating ability o f our nucleators. Through molecular modeling, we demonstrated that nuc leating ability can be correlated with van der Waals attractions of th e individual nucleator molecules with the helical form of polypropylen e. A correlation was not seen when hydrogen bonded nucleator dimers we re used. The model correctly predicted that one TNS diastereomer nucle ates polypropylene and that the other diastereomer does not.