SELF-ORGANIZATION AND POLYOLEFIN NUCLEATION EFFICACY OF 1,3 2,4-DI-P-METHYLBENZYLIDENE SORBITOL/

Recent studies have demonstrated that addition of a small quantity of dibenzylidene sorbitol (DBS) to a molten polymer may result in a physi cal gel if conditions permit the DBS molecules to self-organize into a three-dimensional network composed of highly connected nanofibrils. I f the polymer crystallizes, DBS may also serve as a nucleating agent, promoting the formation of spherulites, especially in commercially imp ortant polyolefins such as polypropylene. We examine the thermal and m echanical properties, as well as the morphological characteristics, of an isotactic polypropylene copolymer with 3 wt % ethylene upon additi on of less than 1 wt % of 1,3:2,4-di-p-methylbenzylidene sorbitol(MDBS ). From dynamic rheological measurements, pronounced complex viscosity increases, attributed to MDBS nanofibril network formation, are obser ved at concentration-dependent temperatures above the melting point of the nucleated copolymer. Transmission electron micrographs of RuO4-st ained sections confirm the existence of MDBS nanofibrils measuring on the order of 10 nm in diameter and, at higher concentrations, fibrilla r bundles measuring up to about 200 nm across and several microns in l ength. The addition of MDBS at different concentrations is also found to promote increases in optical clarity, yield strength, tensile stren gth, and ultimate elongation of modified copolymer formulations. (C) 1 997 John Wiley & Sons, Inc.