Nahrain E. Kamber

Bio: Nahrain E. Kamber is an academic researcher from Stanford University. The author has contributed to research in topics: Ring-opening polymerization & Cycloaddition. The author has an hindex of 4, co-authored 6 publications receiving 1313 citations.

Organocatalytic ring-opening polymerization.

Abstract: Modern synthetic methods have revolutionized polymer chemistry through the development of new and powerful strategies for the controlled synthesis of complex polymer architectures. 1-5 Many of these developments were spawned by new classes of transition metal catalysts for the synthesis of new polyolefin microstructures, 5 the design of highly efficient families of “living” polymerization strategies for the synthesis of block, graft, and star polymers, 6-12 controlled methods for the synthesis of dendritic macromolecules, 3,13,14

N-Heterocyclic Carbenes for the Organocatalytic Ring-Opening Polymerization of ε-Caprolactone

Abstract: We report the synthesis of poly(e-caprolactone) utilizing N-heterocyclic carbene (NHC) organocatalysts. Sterically unencumbered NHCs were found to be highly effective for the living ring-opening polymerization of e-caprolactone under mild conditions. The NHCs were able to produce poly(e-caprolactone)s with controlled molecular weights, low polydispersities, and well-defined end groups derived from the alcohol initiator. Star-shaped poly(e-caprolactone)s with three and four arms were prepared using NHC organocatalysts and characterized by 1H NMR and GPC.

The Depolymerization of Poly(ethylene terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids

Abstract: The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic organic catalysts that provide an alternative to traditional metal alkoxide depolymerization catalysts. Deprotonation of the imidazolium generates an N-heterocyclic carbene, which catalyzed the glycolysis of PET in 1 h at atmospheric pressure in refluxing anhydrous tetrahydrofuran to afford bis(2-hydroxyethyl) terephthalate (BHET). BHET is characterized by NMR and IR spectroscopy and melting point determination. This laboratory is designed for individual student work where each student depolymerizes PET prepared from a common water bottle or other source. This experiment is well suited for an introductory organic chemistry laboratory course or a polymer chemistry...

Stable Cyclic Carbenes and Related Species beyond Diaminocarbenes

Abstract: The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong σ-donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus-based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger σ-donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made.

Organocatalysis: Opportunities and Challenges for Polymer Synthesis

Abstract: Organocatalysis offers a number of opportunities in polymer synthesis and was among the earliest methods of catalyzing the synthesis of polyesters. In the following Perspective we attempt to highlight the opportunities and challenges in the use of organic molecules as catalysts or initiators for polymerization reactions. The ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and to compare them to metal-based approaches. The convergence of convenience, functional group tolerance, fast rates, and selectivities will continue to drive innovations in polymerization catalysis, and it is our perspective that organocatalysis will continue to play an important role in these developments.

Lactic acid as a platform chemical in the biobased economy: the role of chemocatalysis

Abstract: Upcoming bio-refineries will be at the heart of the manufacture of future transportation fuels, chemicals and materials. A narrow number of platform molecules are envisioned to bridge nature's abundant polysaccharide feedstock to the production of added-value chemicals and intermediate building blocks. Such platform molecules are well-chosen to lie at the base of a large product assortment, while their formation should be straightforward from the refined biomass, practical and energy efficient, without unnecessary loss of carbon atoms. Lactic acid has been identified as one such high potential platform. Despite its established fermentation route, sustainability issues – like gypsum waste and cost factors due to multi-step purification and separation requirements – will arise as soon as the necessary orders of magnitude larger volumes are needed. Innovative production routes to lactic acid and its esters are therefore under development, converting sugars and glycerol in the presence of chemocatalysts. Moreover, catalysis is one of the fundamental routes to convert lactic acid into a range of useful chemicals in a platform approach. This contribution attempts a critical overview of all advances in the field of homogeneous and heterogeneous catalysis and recognises a great potential of some of these chemocatalytic approaches to produce and transform lactic acid as well as some other promising α-hydroxy acids.

Catalysis as an Enabling Science for Sustainable Polymers

Abstract: The replacement of current petroleum-based plastics with sustainable alternatives is a crucial but formidable challenge for the modern society. Catalysis presents an enabling tool to facilitate the development of sustainable polymers. This review provides a system-level analysis of sustainable polymers and outlines key criteria with respect to the feedstocks the polymers are derived from, the manner in which the polymers are generated, and the end-of-use options. Specifically, we define sustainable polymers as a class of materials that are derived from renewable feedstocks and exhibit closed-loop life cycles. Among potential candidates, aliphatic polyesters and polycarbonates are promising materials due to their renewable resources and excellent biodegradability. The development of renewable monomers, the versatile synthetic routes to convert these monomers to polyesters and polycarbonate, and the different end-of-use options for these polymers are critically reviewed, with a focus on recent advances in c...