Reactive coupling of core-shell impact modifiers to polyamide matrices using styrene-maleic anhydride copolymers

Abstract

Core-shell impact modifiers have the advantage of a predetermined particle size; however, they must be appropriately dispersed in and coupled to the matrix polymer in order to be effective for toughening engineering plastics which are notch-sensitive. These functions can result from physical interaction of the shell material with the matrix or by chemical reaction. For the latter the most obvious route is to combine reactive moieties into the shell chains during fabrication by emulsion polymerization that subsequently react with the matrix during melt processing. An alternative is considered here for dispersing and coupling modifiers with shells based on poly(methyl methacrylate), PMMA, in a polyamide matrix. Certain styrene-maleic anhydride copolymers, SMA, are miscible with PMMA, yet through the maleic anhydride moiety these copolymers can react with polyamides during melt processing (via amine end groups). This concept leads to very tough blends based on nylon 6 but not to those based on nylon 6,6. Evidence for the proposed role of the SMA copolymer was demonstrated by transmission electron microscopy. Properties and morphology were examined for two different SMA copolymers, two core-shell impact modifiers (butadiene-based and acrylic-based rubber cores), various mixing protocols and component proportions. An attempt is made to explain the responses observed.