Functionalization of polypropylene in solution through grafting with monomethyl itaconate.
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Polypropylene (PP) was functionalized in solution by grafting with monomethyl itaconate (MMI) by using xylene and decalin as solvents and 2,5-dimethyl-2,5-bis(tert-buthylperoxy)hexane (Lup. 101) as radical initiator. The existence of grafted MMI in PP was confirmed by FT-IR spectroscopy. Carbonyl absorption bands from MMI was observed in the FT-IR spectrum of the functionalized polypropylene. These absorption bands are absent in the FT-IR spectrum of the unmodified polypropylene. The percentage of grafted MMI was estimated by volumetric titration as well as FT-IR analysis. The amount of monomer incorporated in polypropylene by the latter method was determined from a FT-IR calibration curve established for this monomer. A systematic study of the reaction variables allowed the optimisation of the grafting process where a maximum of nearly 0.4% of grafting was achieved when xylene was used as solvent. When decalin was used as solvent, the percentage of grafting attained was lower. It was found that the percentage of grafting depends on the initial concentration of monomer and initiator as well as reaction time and reaction temperature. The grafted MMI was partially cyclized during the grafting reaction. This was attributed to the presence of the organic peroxide used as initiator for grafting reactions. It was also found that the molecular weight of the grafted polymer decreased with increasing initial concentration of the peroxide as was estimated by measuring the melt flow index (MFI) of modified polypropylene samples.