A magazine providing a snapshot of the latest developments across the chemical sciences.
New paradigm for permeable polymers
15 October 2007
Scientists in Japan have designed a new class of gas-permeable polymers that could replace materials currently used to separate gases.
Polymer membranes can be used to separate mixtures of gases, for example to separate nitrogen from air or to remove carbon dioxide from natural gas. Different gases travel through a polymer membrane at different speeds because of the varying solubility and diffusivity of the gas within the polymer. Membrane gas separation is much less energy intensive than other gas separation technologies, such as cryogenic distillation.
Now, research directed by Toshio Masuda at Kyoto University has led to the creation of a polymer that is highly permeable to gases even though it has a fundamentally different structure to previous polymers of this type.
Numerous methyl groups are the key to the polymers' permeability |
Polyacetylenes are an important class of gas separation membranes and the most permeable of these, poly(1-trimethylsilyl-1-propyne) or PTMSP, was developed by Masuda in 1983.The polymer's high permeability stems from its large 'free volume', which is the space within the material that is not occupied by the polymer atoms. The large free volume is attributed to factors such as the polymer's stiff main chain and its bulky spherical substituents. Such features prevent the polymer chains from getting too close.
But Masuda proposed that bulky substituents might not be necessary to make a polymer gas-permeable. 'We made a hypothesis that the incorporation of many methyl groups could enhance the gas diffusivity due to their rotational movement,' he explained. 'We synthesized several aromatic phenylacetylenes with many methyl groups and eventually we found a new category of polyacetylenes with gas permeability as high as PTMSP.' The polymer also benefits from a greater stability at higher temperatures.
Benny Freeman, an expert in the field of gas separation membranes at the University of Texas at Austin, US, said the work was a remarkable advance and 'provided a new breakthrough in materials design strategies for the preparation of extremely permeable membranes'.
Gavin Armstrong
Link to journal article
Synthesis and extremely high gas permeability of polyacetylenes containing polymethylated indan/tetrahydronaphthalene moieties
Yanming Hu, Masashi Shiotsuki, Fumio Sanda and Toshio Masuda, Chem. Commun., 2007, 4269
DOI: 10.1039/b712327b
Also of interest
Soft and stretchy polymers can be hardened by dynamically incorporating new components into the polymer chain.
Temperature responsive cell scaffolding
A porous polymer scaffold for tissue engineering, which has tuneable cell adhesion, has been developed by Swedish and Belgian scientists.
New twist for switchable polymers
Controlling the twist of a polymer backbone has enabled US chemists to tune the polymer's optical and electronic properties.
