Grafting modification and properties of polypropylene with pentaerythritol tetra-acrylate

The α-β transition of isotactic polypropylene (PP) under stress hasn’t received much attention although it may cause deterioration of mechanical properties. PP was modified by grafting polyfunctional monomer, pentaerythritol tetra-acrylate (PETeA) carried out in a Haake mixer at 180 °C in the presence of 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane peroxide (DDHP) to enhance the melt strength and suppress formation of β crystal and α-β transition. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-rays diffraction (XRD), polarized optical microscopy (POM) and melt flow index (MFI) were used to characterize the microstructure and properties of the grafted PPs. The FTIR spectra and transient torque results indicated that the acrylic polymers were grafted onto the polypropylene chains. The grafted polypropylenes gave both high crystallization and melting temperatures, and lowered the spherulite dimensions, and increased the melt strength. The grafted branching polyacrylics retarded segmental chain movement during processing and seemed to recover the depression in fatigue experiment to some extent. This work will be benefit to the extensional processing and especially provide the information on the fatigue stability of crystal structure of isotactic polypropylene during the engineering application.