Polypropylene-POSS Nanocomposites: Morphology and Crystallization Behaviour Mariano Pracella, * 1 Donatella Chionna, 1 Alberto Fina, 2 Daniela Tabuani, 2 Alberto Frache, 2 Giovanni Camino 2 Summary: Nanocomposites of isotactic polypropylene (PP) with polyhedral oligo- meric silsesquioxanes (POSS) [RSiO 1,5 ] 8 having different alkyl substituents (R ¼ methyl, isobutyl, isooctyl) were obtained by melt blending and analysed with electron microscopy, optical microscopy and DSC calorimetry. The influence of POSS structure on the morphological characteristics, the crystallization and melting behaviour of PP/POSS composites was investigated with varying the filler amount. The crystallization kinetics of the composites from the melt, examined both in isothermal and non-isothermal conditions, demonstrated that the nucleation activity of the examined POSS can be related to the length of alkyl substituents which, depending on the loading amount, affect the filler dispersion in the PP matrix and the growth of polymer crystals. Keywords: crystallization; morphology; nanocomposites; polypropylene; POSS Introduction In the field of inorganic-organic composite materials, many research interests are oriented to polyhedral oligomeric silses- quioxane (POSS) based materials, both as organic-inorganic hybrids and as poly- mer nanocomposites. POSS are a family of compounds with general formula (RSiO 1,5 ) p where R is hydrogen or an organic group (alkyl, aryl or any of their derivatives), and are characterized by a size in the range 1–3 nm and by high chemical versatility and capability to form nanos- tructures with tailored dimensionality. [1] The dispersion of POSS nanoparticles in polymeric matrices - such as polyacrylates, polyesters, polyimides, polystyrene and its copolymers - allows to obtain advanced composite materials with high thermal, mechanical and oxidative performances. [2] The compatibility of these materials is expected to be markedly enhanced due to the possibility of modifying the chemical/ physical interactions at polymer-filler inter- face through introduction of functional groups on the POSS molecules. The final properties of polymeric com- posites are strictly dependent on the morphology generated during their process- ing when the filler may act as nucleating agent and affect the crystallization beha- viour and the supermolecular structure. Therefore, the study of the phase transi- tions phenomena and polymer-filler inter- actions is crucial for the control of the processing conditions and the optimization of the end-product properties. Although the crystallization kinetics of plain polyolefins have been extensively examined, little research has been so far carried out on the crystallization processes and supermolecular organisation of poly- olefin/POSS nanocomposites. [3,4] The preparation and characterization of PP nanocomposites containing various alkyl substituted POSS (Figure 1) was recently reported by some of the authors. [5] Macromol. Symp. 2006, 234, 59–67 DOI: 10.1002/masy.200650209 59 1 Istituto per i Materiali Compositi e Biomedici, CNR, Sezione di Pisa, Via Diotisalvi 2, Pisa 56126, Italy (INSTM member) Fax: 0039-050-511266 E-mail: pracella@ing.unipi.it 2 Centro di Cultura per l’Ingegneria delle Materie Plastiche – Politecnico di Torino, V.le Michel 5, Alessandria 15100, Italy (INSTM member) ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim