Recently, we have conducted a fine study dealing with the nucleation of the gamma-form in isotactic polypropylene (PP) under high pressure. To nucleate crystallization of PP three nucleating agents were used, namely alpha-nucleants (Hyperform HPN-20E, PTFE submicron particles [1]) and a beta-nucleant (calcium pimelate). The study utilized a ‘model’ PP (3250MR1, Atofina). During processing crystallization is non-isothermal, hence the study has focused on nucleation of the gamma form in PP under high pressure in isothermal conditions [2] as well as during cooling [3]. The present study focuses on a specific alpha-nucleant, 1,3:2,4-bis(3,4-dimethylbenzylidene sorbitol) or DMBS, named Millad 3988i (Milliken Chemical). As its homologues, neat PP and PP with 0.2 wt% of Millad were crystallized in a high-pressure cell [4], under pressure ranging from 50 to 300 MPa, with i) annealing at 200°C for 15 min or annealing at 200 MPa for 2 min, 15 min, 1h and 4h), and ii) during cooling at approx. 8 °C/min. Crystallinity, contents of crystallographic forms and spherulitic structure were then analysed. Compared to its homologues, nucleation of the gamma-form induced by Millad showed a different behavior. It was pressure-dependent for both isothermal and non-isothermal conditions. Millad increased crystallization temperature and reduced the grain size at 100 MPa, indicating intense nucleation. Under 200-300 MPa, large spherulites were embedded in fine-grain structure; most probably the large ones were nucleated as in neat PP while the small ones were nucleated later, when larger spherulites were growing, at lower temperature by Millad; crystallization temperature did not increase. So it means that high pressure cancelled the effect encountered at 100 MPa; this was not observed for Hyperform HPN-20E and PTFE submicron particles. Direct nucleation of gamma-form on the substrate can be envisaged as a possible mechanism [1] Masirek R, Piorkowska E (2010) Eur Polym J 46:1436-1445 [2] Sowinski P, Piorkowska E, Boyer SAE, Haudin JM, Zapala K (2015) Colloid Polym Sci 293:665-675 [3] Sowinski P, Piorkowska E, Boyer SAE, Haudin JM (to be published)