High-pressure synthesis of a polyethylene/zeolite nano-composite material. 
Meso/micro-porous solids, such as zeolites, are complex materials used in an impressive range of applications.  Here we photo-polymerized ethylene using non-catalytic high-pressure techniques at 0.5-1.5 GPa under ultraviolet (351-364 nm) irradiation on a sub-nanometre scale in the channels of a pure SiO2 zeolite, silicalite, to obtain a unique nano-composite material with drastically modified mechanical properties.  The structure obtained contains single polyethylene chains, which adapt very well to the confining channels as shown by optical spectroscopy and X-ray diffraction.  The formation of this nano-composite results in significant increases in bulk modulus and density, and the thermal expansion coefficient changes sign from negative to positive with respect to silicalite.  Mechanical properties may thus be tuned by varying the amount of polymerized ethylene.  Our findings could allow the high-pressure, catalyst-free synthesis of a unique generation of technological, functional materials based on simple hydrocarbons polymerized in confining meso/micro-porous solids.