  The thermal stability of C60 dimers and 2D pressure-polymerized C60 is
studied using high-resolution capacitance dilatometry. The transformation of
both the dimer and the polymer phases back to 'normal' C60 is excellently
described by a simple thermally activated process, with activation energies of
1.75 1 0.1 eV (dimer) and 1.9 1 0.2 eV (polymer). These results are compared to
previous data of 1D-polymerized C60 and photo-polymerized C60. The thermal
expansivity of the 2D-polymer phase is as much as a factor of ten smaller than
that of pure C60 and approaches values for diamond.
