Functionalized Polyolefins Produced by Post-Metallocenes; High Added Value Materials, but Can They Be Produced Efficiently?

Abstract

Randomly functionalized polyolefins produced by catalysis have received increasing attention owing to their welldefined molecular structures, uniform distribution, and variety in types of functionalities. Herein, we investigate the scalability of the production of hydroxyl-functionalized propylene copolymers via a high temperature solution polymerization process using aluminum trialkyls as passivating agents. Initially, we evaluated the impact of (i) the type of passivating agent (triethylaluminum versus triisobutylaluminum) and (ii) the distance between the hydroxyl and olefin functionality within the functionalized comonomer on the catalytic activity and the functional comonomer incorporation efficiency. Both the functional comonomer's chain length and the type of trialkylaluminum passivating agent have a profound effect on the incorporation efficiency. Subsequently, deeper insight into the origin of the catalyst poisoning by trialkylaluminum-passivated hydroxyl-functionalized comonomers reveals that catalyst deactivation solely happens after incorporation of the functional comonomer and not by coordination of the oxygen of the functional comonomers present in the reaction system. During recycling of dialkylaluminum alkenolates by means of distillation, the occurrence of carbo-and/or hydroalumination side reactions were noticed, triggered by the presence of dialkylaluminum hydrides formed by thermolysis of excess aluminum trialkyls. Exchanging aluminum trialkyls by dialkylaluminum alkoxides as scavengers solved this problem. Modeling studies revealed the impact of the higher nuclearity of trialkylaluminum-passivated hydroxyl-functionalized comonomers on their incorporation efficiency. Addition of a saturated alcohol significantly improved the incorporation efficiency of the functional comonomer, thus bringing the scalability (i.e., enhance the productivity and cost-efficiency) of the copolymerization process a step closer.