James C. Stevens - Advancements To Chemistry

Advancements To Chemistry

Stevens is known primarily for the discovery and commercialization of a number of significant families of polymers in widespread commercial use today. This discovery can be found in many forms of consumer products including plastic wine corks; shoe and sneaker insoles; casual plastic footwear (such as Crocs); automobile parts (dashboards, bumpers, hoses, gaskets); food wraps and films like poultry bags; synthetic EPDM rubber, hot melt adhesives and more.

Stevens discovered and led the implementation of many families of new single site catalysts, cocatalysts, and new polymers. His ground-breaking discovery of constrained geometry catalysts (see Constrained geometry complex), single-site catalysts for olefin polymerization, today accounts for the production of over 2 billion pounds of polymers per year. In addition, the exquisite control over molecular structure imparted by these discoveries allows the production of an unprecedented breadth of polymers covering a wide array of applications. In a series of elegant studies, Stevens and his coworkers were able to demonstrate that these catalysts had an unusual ability to incorporate long-chain branches into polyethylene, leading to a new class of highly processable ethylene copolymers (US Patent 5,272,236 (and others)).

Olefin polymerization catalysis is important because polyolefins are the largest volume thermoplastics produced worldwide. Catalyst structure controls polymer microstructure, which ultimately determines macromolecular properties and applications. Ziegler and Natta won the Nobel Prize for the original discoveries in olefin polymerization catalysis. These catalysts are poorly understood, possess a range of activities within a particular batch of catalyst and are limited in terms of precise control of polymer architecture. Homogeneous, molecular-based or “single site” olefin polymerization catalysts have their genesis in the 1950’s, with the early discoveries of Breslow and Newberg of Group 4 metallocenes activated with aluminum alkyls. The discoveries of MAO and fluorinated aryl borate cocatalysts reenergized this field, leading to the promise of precise control of molecular architecture for these commercially important polymers.

Stevens was among the first to recognize the potential of combinatorial chemistry and high-throughput screening in the discovery of olefin polymerization catalysts. Stevens’ work here led to an amazing hafnium-based catalyst family (few experts would have believed a hafnium complex would have the needed activity) that enables the polymerization of propylene to isotactic polymers and copolymers in a high temperature solution process. In a series of papers and patents starting in 2002, Stevens, along with colleagues and collaborators, disclosed new catalysts which are non-conventional, counter-intuitive, subtle, and have an unprecedented stereoselectivity along with remarkable high temperature performance. This discovery has led to another family of new propene-based polyolefins and a process for the large-scale production of new thermoplastic and elastomeric materials. The resulting polymers have been commercialized under the VERSIFY tradename.

His group developed a “chain-shuttling” processes in which polyolefin chains are rapidly exchanged between two single-site catalytic centers to create, catalytically for the first time, olefin block copolymers with thousands of polymer chains produced per catalyst molecule. This remarkable advance was described in a Science paper and is the basis for the successful INFUSE polymer line.

Stevens invented or contributed significantly to the commercialization of a large number of commercial products, including AFFINITY* polyolefin Plastomers, ENGAGE polyolefin elastomers, ELITE enhanced polyethylene resins, NORDEL-MG EPDM rubber, NORDEL-IP elastomers, Dow XLA-fibers, INDEX ethylene/styrene copolymers, VERSIFY propylene copolymers, and INFUSE Olefin Block Copolymers. He is an inventor on 87 issued US patents, numerous foreign patents, has 18 publications, and is the editor or author of two books.