Location: JHE 326H
The use of two single-site catalysts to synthesize polymers with complex microstructures is a versatile way to make polyolefins with new properties. Dual metallocene systems have been used to produce polyolefins with bimodal distributions of molecular weight and chemical composition,[1,2] to maximize the formation of long chain branches in polyethylene, and to produce branched and linear olefin block copolymers.[4-7] Similar products can also be made with a single metallocene in two reactors operated in series at different conditions.
A detailed knowledge of the kinetics of polymerization is required in order to make polymers with the desired microstructure, since changes in polymerization temperature, monomer pressure, catalyst concentration and hydrogen concentration may have a marked impact on the properties of the final polymer. Therefore, a reliable kinetic model is one of the important requirements to implement this technology.
The use of dienes, in addition to ethylene and an a-olefin, opens up the possibility of creating chains with even more complex polymer microstructures because the pendant double bonds resulting from diene copolymerization can be used to create crosslinks among the chains.[8,9] In this presentation, we will show how the conditions during the solution polymerization of ethylene, a-olefin (1-butene and 1-octene) and 1,9-decadiene can be varied to create polymers with branched structures composed of three main components: a high-crystallinity and a low-crystallinity (or amorphous) domain, and a third component that results from the crosslinking of the two previous components (cross-product). These three components are easily detected by the Crystaf analysis of the polymers. We will also show that the polymerization kinetics of these systems can be well described with relatively simple mathematical models.
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