Modification des propriétés du polypropylène par mise en oeuvre réactive / Modification of polypropylene properties by reactive processing
(2006)
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- Abstract
- (en) This work is part of a project supported by the Walloon Region, and it was performed in collaboration between the Chimie Organique et Médicinale (CHOM), Chimie Structurale et des Mécanismes Réactionnels (CSTR), and Chimie et Physique des Hauts Polymères (POLY) laboratories. Its object is the modification of the isotactic polypropylene (PP) properties by reactive processing, and more especially the control of PP crystallinity by means of a brominated additive (N-bromosuccinimide) in presence of a free radical initiator at high temperatures (between 180 and 260°C). The main objective of this study is to identify and to control the modifications induced in the products, which implies a fine understanding of the chemical mechanisms occuring during the PP reactive processing. This knowledge would allow us, subsequently, to substitute another additive for the N-bromosuccinimide (which yields toxic and polluting by-products), in order to achieve a better applicability of both the process and the products. The strategy relies on a double approach : on one side, on a study of the various parameters affecting the reaction on the polymer, and on the other side on the synthesis of a model compound of PP : 2,4,6,8,10-pentamethylundecane (PMU). By means of reactive extrusion of the polymer, we obtained controlled crystallinity PP's (from semi-crystalline to amorphous), including some with an elastomeric behaviour. Studies carried out mainly by thermal analysis and nuclear magnetic resonance allowed us to correlate these macroscopic properties to an isotactic/atactic stereoblock microstructure (epimerization of the PP tertiary carbons), combined with the presence of long chain branchings (recombination of macroradicals). Moreover, we highlighted the various parameters that are able to influence the yield of the epimerization reaction. Even if the informations arising from these studies allowed us to propose the main mechanisms involved in the PP modification, only a mechanistic study carried out on a model compound would give us access to the characterization methods required for the confirmation of these mechanisms. We undertook, subsequently, the synthesis of a propene oligomer. The PMU synthesis, as stated in the litterature, revealed itself more difficult than initially foreseen, mainly due to a lack of reproducibility concerning the key step. Therefore we established a new synthesis pathway for the PMU (as a mixture of stereoisomers) with a global yield of 45% over 7 steps (multigram scale). Moreover, this pathway gave us access to 6-hydroxymethyl-2,4,8,10-tetramethylundecane and 6-p-toluenesulfonyloxymethyl-2,4,8,10-tetramethylundecane, for which chromatographic techniques allowed a separation of the diastereoisomers. The transposition of these experiments on a larger scale would allow us to obtain the (4R,6s,8S)-PMU for future mechanistic studies relative to the epimerization reaction of initially isotactic PP.
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Henry, G. (2006). Modification des propriétés du polypropylène par mise en oeuvre réactive / Modification of polypropylene properties by reactive processing. https://hdl.handle.net/2078.5/129831