The study reported here investigates the effect of 1,3-phenylene dimaleimide (commonly known as BMI), a highly reactive coupling agent and interfacial modifier, on montmorillonite (MMT) platelet dispersion and interfacial properties of composites based on unmodified (Na-MMT) and organically modified montmorillonites (o-MMT) and polypropylene homopolymer. Whilst BMI was able to increase the interfacial adhesion in micro-composites based on Na-MMT, there was, predictably, no increase in the degree of platelet dispersion. As far as the o-MMTs (intercalated with octadecyl ammonium, bis(2-hydroxyethyl) tallow methyl ammonium and distearyl dimethyl ammonium chloride) were concerned, addition of BMI improved interfacial adhesion and the degree of platelet dispersion. The latter deduction was made primarily on the basis of WAXS data and was verified by gas barrier measurements on composite films, whilst the former deduction arose from tensile measurements and SEM imaging of fracture surfaces. It was, therefore, concluded that BMI acts as an effective dispersion aid and coupling agent for PPH/o-MMT composites. (c) Koninklijke Brill NV, Leiden, 2011