Maleation of polypropylene and EPDM through reactive extrusion using the Alder Ene reaction

Abstract

An investigation into the site-specific functionalization of several polymers within a co-rotating intermeshing twin screw extruder was initiated. The Alder Ene reaction between maleic anhydride and the inherentdbouble bond of polypropylene and EPDM, was chosen for the high temperature environment of the extruder to accomplish the desired reaction. In order to improve the incorporation of maleic anhydride into the polymer, several Lewis acids were employed as catalysts in the reaction. The high temperature application of Lewis acid into the reaction was a unique contribution of this thesis. The primary Lewis acid examined in this work was stannous chloride dihydrate, along with aluminum chloride and ruthenium chloride hydrate. The reactions were carried out in a round bottom flask, a batch reactor, a bath mixer, a single screw extruder and a co-rotating intermeshing twin screw extruder. Characterization of the maleated products by FT-IR, ^1H NMR, DSC, and GPC was used to differentiate between site-specific attachment and free radical grafting of the functionality. Polyisobutylene was used to carry out preliminary studies on the high temperature application of Lewis acids int he Alder Ene reaction. A low molecular weight polypropylene wax (Polypol-19) was chosen as a model material to study the kinetics of the reaction and identify reaction parameters useful for reaction optimization purposes. The preparation of a vinylidene-rich polypropylene for the reaction in the extruder, via 8-scission has been shown to be an effective route, with thermal degradation favoured over peroxide-initiated degradation due to the reduced presence of carbonyl functionalities in the polymer. Both methods of degradation due to the reduced presence of carbonyl functionalities in the polymer. Both methods of degradation have been shown to produce greater than one site of unsaturation per chain, demonstrating their advantage over commercial polymerization for producing an effective ene species in this work. Finally, EPDM was examined as a material with a high vinyl content useful for the reaction, that was also highly viscous making it more suited for reactive extrusion.

The degree of functionalization was determined by infrared analysis, though an alternative method, explored with EPDM, also showed a direct correlation between the level of maleation and the mechanical properties of an ionic network formed by neutralizing the maleated rubber. Temperature and maleic anhydride concentration were found to be the most significant factors for this Alder Ene reaction. Increased temperature and maleic anhydride reactant concentration were found to improve the extent of reaction. Significant isomerization and maleic anhydride homopolymerization side reactions have been observed in the batch reactor, beyond 230*C, indicating the presence of an optimal limit though this is likely to differ int he extruder.

The Lewis acid, which was employed as a solid or mixed in phase with molten maleic anhydride, improved succinyl anhydride incorporation with reduced acid concentration. Among the Lewis acids examined aluminum chloride gave rise to the greatest improvement of succinyl anhydride incorporation, at least into the rubber. Ruthenium chloride was found to improve the extent of reaction in Polypol-19, degraded polypropylene and EPDM. Employing the Lewis acid in phase with the reactant (maleic anhydride) was shown to lead to higher conversion. Based on an observed "induction period" in the conversion-time plots, the formation of the Lewis acid-anhydride enophile for the reaction was relatively slow with respect to the duration of the reaction. However, when the acid was employed as a solid creating a heterogeneous reaction (omitting the limited solubility of maleic anhydride within the examined polymers), the rate of formation of the acid-anhydride enophile was probably too low to observe an induction period. Unlike the homogeneous catalyst system, the applicability of second order kinetics to the heterogeneous catalyzed system provides immediate evidence of this phenomenon. In general, even in the absence of catalyst, the application of a second-order kinetic model to the measured succinyl anhydride results, was not valid over the entire temperature range studied due to side reactions, particularly vinylidene isomerization and homo-polymerization of maleic anhydride. The rheological results from the maleated EPDM series offered interesting results. In the absence of a Lewis acid catalyst in the reaction, the elasticity of the rubber increased with increasing degree of succinyl functionalization. Likely, these polar groups were introducing intermolecular bonds with sufficient strengths to produce rheological behaviour similar to cross-linking.