Abstract
The catalytic emulsion polymerization of ethylene has been a long-lasting technical challenge as current techniques still suffer some limitations. Here we report an alternative strategy for the production of semi-crystalline polyethylene latex. Our methodology consists of encapsulating a catalyst precursor within micelles composed of an amphiphilic block copolymer. These micelles act as nanoreactors for the polymerization of ethylene in water. Phosphinosulfonate palladium complexes were used to demonstrate the success of our approach as they were found to be active for hours when encapsulated in micelles. Despite this long stability, the activity of the catalysts in micelles remains significantly lower than in organic solvent, suggesting some catalyst inhibition. The inhibition strength of the different chemicals present in the micelle were determined and compared. The combination of the small volume of the micelles, and the coordination of PEG appear to be the culprits for the low activity observed in micelles.
Highlights
The catalytic emulsion polymerization of ethylene has been a long-lasting technical challenge as current techniques still suffer some limitations
We focus our investigation on a family of phosphinosulfonate palladium catalysts because these catalysts were shown to exhibit high activity in organic solvent and to be mostly inactive in miniemulsion or as a water-soluble catalyst[39,59,60]
turn over (TO) frequency = 204,000 h−1 (Table 1, entry 1), three separate miniemulsion polymerizations with this catalyst precursor and a polymerization in water initiated by a water-soluble catalyst precursor resulted in TO frequency of less than 50 h−1 (Table 1, entries 2 and 3)
Summary
The catalytic emulsion polymerization of ethylene has been a long-lasting technical challenge as current techniques still suffer some limitations. The improved catalyst lifetime provided a most impressive turn over (TO) frequency of 4000 h−1 after 24 h of reaction time Despite this enhancement in productivity and stability, the activity in the aqueous medium remained lower than in organic solvent for the same catalyst (TO ~ 49,800 after 1 h)[24]. Miniemulsion polymerization has been applied to the polymerization of olefins in aqueous medium[26,27,28,29,30,31,32,33,34,35,36,37] In this process, an organic soluble catalyst is dissolved in a highly hydrophobic organic solvent mixture that is dispersed in nanometer-sized droplets by sonication[38]. The difficulty to match the activity achieved in organic solvent with these emulsion polymerization methods motivated us to develop an alternative strategy for the catalytic polymerization of ethylene in aqueous medium
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