Phosphorus rubber: Multinuclear NMR

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  • Published: Jul 15, 2017
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Phosphorus rubber: Multinuclear NMR

Improving natural rubber, again

Poly-(1-phospha-isoprene) is a phosphorus-containing analogue of natural rubber that might find applications in creating macromolecular gold complexes for use in nanotechnology. 31P{1H} nuclear magnetic resonance (NMR) spectroscopy was used to provide a preliminary structure of the compound. Credit: Wiley-VCH

Poly-(1-phospha-isoprene) is a phosphorus-containing analogue of natural rubber that might find applications in creating macromolecular gold complexes for use in nanotechnology. 31P{1H} nuclear magnetic resonance (NMR) spectroscopy was used to provide a preliminary structure of the compound.

Back in 1839, Goodyear discovered a way to toughen up natural rubber by incorporating sulfur crosslinks in a process we know as vulcanization. This modification of natural rubber obtained from rubber trees was a turning point in the industrial revolution leading to the vast rubber industry with its myriad applications perhaps most obviously in tires for almost every vehicle on our roads. The twentieth century saw the development of many synthetic and semi-synthetic and composite rubber products with a wide range of physical and chemical properties and applications. Now, research published in the journal Angewandte Chemie reveals another variation on the theme in the form of an entirely novel, phosphorus-containing rubber. The presence of phosphorus atoms gives it many unique properties but its structure corresponds nevertheless with that of the original natural rubber.

Functionalisation, that's the name of the game

The team, Klaus Dueck, Benjamin Rawe, Michael Scott, and Derek Gates of the Department of Chemistry, at the University of British Columbia, Vancouver, Canada, explain how the similarity between double bonded carbon atoms (C=C) and phosphorus=carbon double bonds (P=C) led them to the idea that they might use general polymerization techniques to make macromolecules containing phosphorus. The researchers successfully made several phosphorus-carbon macromolecules and with their growing skill in this area then turned to the idea of starting with phosphorus-containing analogues of the building blocks, the monomers, of natural rubber, isoprene (2-methylbuta-1,3-diene) and its chemical cousin, 1,3-butadiene.

The team began with phosphorus-containing precursors, as one would expect, and from those precursors synthesized what are the first examples of poly(1-phospha-isoprene) and poly(1-phospha-1,3-butadiene). They were able to obtain precise characterization of the macromolecules using multinuclear NMR spectroscopy and other techniques. As with the polymerization of isoprene and related dienes, the team demonstrated that one of the double bonds present in each monomer building block is retained. Indeed, the polymerization occurs primarily through the C=C double bonds and only a tiny proportion happens at the P=C double bonds. This, the team suggests, means that only a few phosphorus atoms are incorporated into the polymer backbone and the majority make side chains featuring a P=C double bond. Such side chains are then open to any number of functionalisations to alter the final polymer structure to suit a particular application.

Analogously

"Our functional phosphorus-containing materials are rare examples of polymers containing phosphaalkene moieties and offer many prospects for further derivatization and crosslinking," Gates explains. The team has already demonstrated that they can bind gold ions to their polymers, which could open the door to a whole range of new supports for catalytic gold clusters or nanoparticles. "As a macromolecular ligand for gold ions, the new polymers may be of future interest in catalysis and nanochemistry," says Gates. "Furthermore, the successful polymerization of P=C/C=C hybrid monomers opens the door to incorporate phosphorus functionalities into commercial rubbers such as butyl rubber or styrene-butadiene rubber that traditionally use isoprene or butadiene comonomers. Such new copolymers promise unique architectures, properties, and functionality when compared to their carbon-only analogues."

"We intend to use these P-monomers to modify the properties of existing rubber materials that normally incorporate isoprene or butadiene functions," Gates told SpectroscopyNOW. "For the long term, I foresee polymers from a variety of heteroatom-containing diene monomers that incorporate elements such as silicon, boron, nitrogen, sulfur and others."

Related Links

Angew. Chem. Int. Ed. 2017, 56, 1–6: "Polymerization of 1-Phosphaisoprene: Synthesis and Characterization of a Chemically Functional Phosphorus Version of Natural Rubber"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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