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

A novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) wa s 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 stru cture of the spherulites fibrillae. Thin films of iPP/uPP-g-PS blends conta ining 2, 5, and 10% (wt/wt) of graft copolymer were prepared by o-dichlorob enzene casting, according to the method we used previously to obtain sample s of iPP/atactic polystyrene/uPP-g-PS ternary blends (D'Orazio et al. J App l Polym Sci 1997, 65, 1539; D'Orazio et al. J Appl Polym Sci, 1999, 72, 142 9). The variation of tan delta with temperature and differential scanning c alorimetry thermograms showed respectively that, regardless of blend compos ition, 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, bo th dimension and number per unit area of the amorphous interspherulitic con tact regions decreased. The long period values of the IPP phase, calculated from the peak position of Lorentz-corrected desmeared small angle X-ray sc attering profiles, increased markedly with increasing uPP-g-PS content; suc h an increase was due to an increase of both average crystalline lamellar t hickness and interlamellar amorphous phase. (C) 2000 John Wiley & Sons, Inc .