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

Abstract

ABSTRACT:The free-radical grafting of the multimonomer system of pentaerythritol triacrylate (PETA) and styrene (St) onto polypropylene (PP) in the melt state was studied 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 promoted 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 mechanism was that St reacted with the PP macroradicals to form more stable St macroradicals, and thus b scission was limited. 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 bform crystals. The presence of ungrafted PETA increased the crystallization and melting temperatures of PP; however, the PETA-grafted samples showed higher crystallization and melting temperatures than physically blended samples.

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