Crystallization and thermal behaviour of isotactic Polypropylene blended with an alicyclic random co-oligomer.

A fully saturated, alicyclic hydrocarbon resin (IST) was blended with isotactic polypropylene (iPP). IST is a random co-oligomer of low average molecular weight obtained by oligomerization of indene, ?-methyl styrene and vinyl toluene, followed by hydrogenation. The crystallization and thermal behaviour of iPP/IST blends were analyzed by microscopy and differential scanning calorimetry (DSC). The influence of blend composition on the spherulite growth rate and on the overall crystallization rate suggests that the two components form a miscible blend in the amorphous phase, as confirmed by the following observations: All blends show a single glass transition temperature (Tg); its value, depending on composition, lies between the iPP and IST Tg values (-14°C and 82°C, respectively), and is in good agreement with the theoretical values calculated by the Fox equation. The equilibrium melting temperature calculated for pure iPP was equal to 187°C; this value decreases with blending to 175°C for the iPP/IST 50/50 (w/w) blend. The ?12 parameter of the iPP/IST system was equal to -0.435, the negative value should suggest that the two components can form a compatible mixture which is thermodynamically stable above the equilibrium melting temperature.