Melt functionalization of polypropylene with methyl esters of itaconic acid
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Polypropylene (pp) was functionalized in the melt phase by grafting with itaconic acid derivatives. 2,5-dimethyl-2,5-bis(tert-buthyl-peroxy) hexane (lupersol 101) was used as radical initiator. A Brabender Plasticorder was used for all the experiments. The optimum conditions for the grafting reaction were 190 degreesC, 75 rpm and 6 min. The itaconic acid derivatives used in this work were mono- and dimethyl esters. When dimethyl itaconate (DMI) was used as functional polar monomer, a maximum of 1.5% of grafting was reached. A similar value was found for grafting of monomethyl itaconate (MMI) where a maximum of 1.6% by weight of this monomer was incorporated in pp. The existence of grafted MMI and/or DMI in pp was confirmed by FT-IR spectroscopy. Carbonyl absorption bands from either MMI and/or DMI were observed in the FT-IR spectrum of the modified pp. The percentage of grafting attained was also followed by FT-IR analysis, where the amount of monomer incorporated in pp was estimated from a calibration curve established for the monomers used in this work. A systematic study of the reaction variables allowed the optimization of the grafting process. It was found that the percentage of grafting attained depends on the initial concentration of both monomer and initiator used in the reaction. Some properties of the modified pps were evaluated by employing dilute solution viscosity and differential scanning calorimetric (DSC) measurements. It was found that the molecular weight of the grafted polymer decreased with increasing percentage of grafting. DSC measurements indicated that functionalized pp samples have slightly higher crystallinity but show the same melting temperature as pp.