Unveiling thermal transitions of polymers in subnanometre pores

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Nature Communications – Unveiling thermal transitions of polymers in subnanometre pores Knowing how to build nanosized assemblies of polymers (long molecular chains) holds the key to improving a broad range of industrial processes, from the production of nanofibers, filters, and new materials to the manufacture of low-energy, nanoscale circuits and devices. Scientists in Japan at Kyoto University and Nagoya University have succeeded in manufacturing custom-designed sub-nanometer scale channels, or pores, which can be manipulated to trap polymers and allow researchers to observe how these chains respond to temperature changes. Previously this level of observation was not possible, and hence much about polymer behaviors in subnanometer spaces — in particular thermal transitions — was unknown. The technique uses specially designed substances known as porous coordination polymers (PCPs), which are notable for the high-degree to which their pore sizes and other characteristics can be controlled. PCPs enables custom designed cages in which to trap specific molecules. This could lead to future breakthroughs in nanoscale manufacturing based on assemblies of small numbers of polymer chains.

The thermal transitions of confined polymers are important for the application of polymers in molecular scale devices and advanced nanotechnology. However, thermal transitions of ultrathin polymer assemblies confined in subnanometre spaces are poorly understood. In this study, we show that incorporation of polyethylene glycol (PEG) into nanochannels of porous coordination polymers (PCPs) enabled observation of thermal transitions of the chain assemblies by differential scanning calorimetry. The pore size and surface functionality of PCPs can be tailored to study the transition behaviour of confined polymers. The transition temperature of PEG in PCPs was determined by manipulating the pore size and the pore–polymer interactions. It is also striking that the transition temperature of the confined PEG decreased as the molecular weight of PEG increased.

19 pages of supplemental information

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