Fifty years after the Nobel Prize was awarded to Ziegler and Natta, the transition-metal catalyzed polymerization of olefins remains one of the most important reactions conducted on the industrial scale and the subject of industrial as well as academic research. This introductory article will provide a short historical review of the discovery of catalyzed olefin polymerization by Ziegler, Natta, and others and its development in the years following the Nobel Prize, as well as giving insight into Ziegler-Natta polymerization for the nonspecialist.

The future of polyolefin-based materials and the opportunities for further research and development in Ziegler-Natta catalysis are discussed. Thorough control of polymer microstructure and architecture ensured by modern olefin polymerization catalysts and processes warrants further progress in fundamental and applied research for many years to come.

The success of polyolefins is governed to a large extent by the development of robust and versatile catalysts offering excellent morphology control. This review highlights the major evolution steps made in the polyolefin catalyst systems in terms of productivity and possibilities to control the molecular architecture of both polypropylene and polyethylene. Starting from the initial TiCl3-types, the continuous improvement of the Ziegler-Natta catalysts in terms of performance and cost is the major factor behind their wide market penetration. On the other hand, metallocene and the other “single-site” catalysts enable an unprecedented fine-tuning of chain microstructure by ligand design. In this article, special emphasis is placed on the influence of catalyst type on polymer structure characteristics such as molecular weight distribution, stereoregularity, and comonomer distribution and, ultimately, on the end-use properties of polyolefins. It is the excellent balance among price, performance, and processability that will further strengthen the position of polyolefins as a dominant class of materials in the polymer industry.

The state of Phillips Cr/silica catalyst technology is discussed in this article, including recent advances in the science and also economic and environmental challenges to its continued viability. Although these catalysts have often been described as “mature,” many new innovations have been introduced in the past decade that reduce cost, improve quality, and expand the range of products that can be made. Polymers having unusually high, and low, levels of long-chain branching have been introduced. Several advances in the control of the short-chain branch distribution have also been made. Ways to lower the catalyst costs have been successfully implemented, such that Phillips-type catalysts are still the least expensive in the industry. Finally, new chromium-containing hybrid catalysts have been made that marry attributes from single-site and conventional Cr oxide catalysts.

Although aliphatic polyketones built from carbon monoxide and olefins have not yet found widespread application in industry and everyday life, this material has great potential, as its properties can be tuned, almost boundlessly, to desired traits or values. For example, the melting temperature and the phase transition temperatures can be varied largely, therefore making it possible to design a polymeric material with adjustable properties. Regardless of its feasibility for replacing common commodity polymers such as polypropylene or polyethylene in some special utilization areas, we want to highlight some aspects for the great potential of aliphatic polyketones as a functional material in drug delivery, bioengineering, optical devices, and other applications.

Highly active metallocenes and other single site catalysts as well as Grubbs and Schrock metathesis catalytic systems have opened up the possibility to polymerize cycloolefins or to copolymerize them with ethene or propene. The polymers obtained show exciting structures and properties. Cycloolefins such as cyclopentene, cyclooctene, norbornene, and their substituted derivatives are incorporated into the polymer chain either by double bonds or by ring-opening metathesis polymerization. Materials with elastomeric properties or tactic polymers with high glass transition temperatures and melting points are obtained with a wide range of microstructures. For example, cycloolefin copolymers and other homo- and copolymers of norbornene are of great academic and industrial interest because of their properties and applications in optoelectronics, lenses, and coatings.

Recent advances in polymerization of allyl and diallyl monomers catalyzed by homogeneous Ziegler-Natta catalysts are reviewed. Zirconocene catalysts are effective for copolymerization of ethylene or propylene with Al-masked allyl monomers, as well as homopolymerization of allylsilanes. Phosphine-sulfonate Pd complexes promote the copolymerization of ethylene with various polar allyl monomers, in the absence of a masking agent. Late transition metal catalysts promote stereoselective cyclopolymerization of diallyl monomers having various polar functional groups. The cyclopolymerization of alkyl-substituted diallyl monomers by Pd diimine complexes affords the polymer having alternating oligomethylene and trans-1,2-cyclopentene groups.

Poly(ethylene glycol) (PEG) hydrogels represent a versatile material scaffold for culturing cells in two or three dimensions with the advantages of limited protein fouling and cytocompatible polymerization to enable cell encapsulation. By using light-based chemistries for gelation and for incorporating biomolecules into the network, dynamic niches can be created that facilitate the study of how cells respond to user-dictated or cell-dictated changes in environmental signals. Specifically, we demonstrate integration of a photo-cleavable molecule into network cross-links and into pendant functional groups to construct gels with biophysical and biochemical properties that are spatiotemporally tunable with light. Complementary to this approach, an enzymatically cleavable peptide sequence can be introduced within hydrogel networks, in this case through photoinitiated addition reactions between thiol-containing biomacromolecules and ene-containing synthetic polymers, to enable cellular remodeling of their surrounding hydrogel microenvironment. With such tunable material platforms, researchers can employ a systematic approach for 3D cell culture experiments, spatially and temporally modulating physical properties (e.g., stiffness) as well as biological signals (e.g., adhesive ligands) to study cell behavior in response to environmental stimuli. Collectively, these material systems suggest routes for new experimentation to study and manipulate cellular functions in four dimensions.