Styrene‐assisted melt free‐radical grafting of pentaerythritol triacrylate onto polypropylene and its crystallization behavior

The free-radical grafting of the multimono- mer system of pentaerythritol triacrylate (PETA) and sty- rene (St) onto polypropylene (PP) in the melt state was stud- ied by reactive extrusion. The effects of the St and initiator concentrations on the grafting reaction were investigated by means of the melt flow rate, gel permeation chromatography (GPC), and Fourier transform infrared spectroscopy. The results showed that the use of St as a comonomer could effectively depress the degradation of PP and enhance the grafting degree of PETA. Increasing the peroxide level pro- moted the degradation of PP and reduced the grafting degree of PETA. When the molar ratio of St to PETA was 3 : 1, the GPC data showed that the molecular weight of the grafted PP sample was almost equal to or a little higher than that of virgin PP, suggesting that almost no chain scission occurred. In the presence of St, the dominant grafting mech- anism was that St reacted with the PP macroradicals to form more stable St macroradicals, and thus b scission was lim- ited. Then, St macroradicals reacted with PETA to form PETA-grafted PP. X-ray diffraction results showed that the grafted chains not only had a good nucleating effect on PP crystallization but also might induce the formation of b- form crystals. The presence of ungrafted PETA increased the crystallization and melting temperatures of PP; how- ever, the PETA-grafted samples showed higher crystalliza- tion and melting temperatures than physically blended samples. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 1737-1743, 2008