CRYSTALLIZATION OF SYNDIOTACTIC POLY(PROPENE-CO-OCTENE)

The crystallisation behaviour of syndiotactic poly(propene-co-octene) (P-co-O)-X with octene contents, X, of 4, 15, 20, 40, and 67 wt% is st udied by light microscopy, atomic force microscopy (AFM), small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and differ ential scanning calorimetry (d.s.c.) The decrease of equilibrium melti ng points with increasing octene content is in agreement with theoreti cal values obtained from the copolymer melting equation of Flory. WAXS measurements show that (P-co-O)-4 forms at relatively low supercoolin gs the type III unit cell known from s-PP homopolymer. For higher supe rcoolings and for higher octene contents WAXS traces typical for the t ype II unit cell are observed exclusively. AFM and light microscopical investigations show that the crystalline morphology depends strongly on the octene content. Similar to s-PP homopolymer, (P-co-O)-4 isother mally crystallised at T-c = 132 degrees C forms single-crystal-like en tities and bundle-like morphologies. An important difference to s-PP h omopolymer is the absence of cracks and ripples in the single-crystal- like entities, that are typical for s-PP homopolymer. In contrast to s -PP, (P-co-O)-15 forms spherulites at higher crystallisation temperatu res and a granular morphology at lower crystallisation temperatures. A similar granular morphology in the nanometer range is also found for (P-co-O)-40. SAXS measurements show that (P-co-O)-15 isothermally crys tallised at 90 degrees C forms lamellae with a thickness of approximat ely 3.5 nm. In the SAXS trace of (P-co-O)-40 a long period cannot be o bserved. The large scattering at small scattering vectors can be relat ed to the granular morphology. (C) 1998 Elsevier Science Ltd. All righ ts reserved.