Effects of the addition of a graft copolymer of propylene with styrene on thermal behavior, crystallization, and morphology of isotactic polypropylene

Abstract

A novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) was added to isotactic polypropylene (iPP) to investigate the state of mixing between uPP-g-PS and iPP phase and effects of the uPP-g-PS addition on iPP intrinsic phase structure, i.e., on iPP spherulitic texture and inner structure of the spherulites fibrillae. Thin films of iPP/uPP-g-PS blends containing 2, 5, and 10% (wt/wt) of graft copolymer were prepared by o-dichlorobenzene casting, according to the method we used previously to obtain samples of iPP/atactic polystyrene/uPP-g-PS ternary blends (D'Orazio et al. J Appl Polym Sci 1997, 65, 1539; D'Orazio et al. J Appl Polym Sci, 1999, 72, 1429). The variation of tan δ with temperature and differential scanning calorimetry thermograms showed respectively that, regardless of blend composition, a single glass transition temperature and a single apparent melting temperature were found for the iPP phase in the iPP/uPP-g-PS binary systems. Optical microscopy investigation revealed that, with increasing uPP-g-PS content, iPP spherulites become more open and coarse. On the other hand, both dimension and number per unit area of the amorphous interspherulitic contact regions decreased. The long period values of the iPP phase, calculated from the peak position of Lorentz-corrected desmeared small angle X-ray scattering profiles, increased markedly with increasing uPP-g-PS content; such an increase was due to an increase of both average crystalline lamellar thickness and interlamellar amorphous phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 553–565, 2000