Planar polymers of 60 undergo irreversible transformations at high pressure, related with formation of new polymer bonds perpendicular to the two-dimensional polymer planes. It is established that tetragonal (2D-T) polymer transforms into a new three-dimensional polymer phase at pressure ~20 GPa (Fig. 1).The high pressure phase in the 2D-T polymer is characterized by narrow lines in Raman spectrum and high degree of ordering. The new polymer phase of 60 is metastable at normal pressure - upon heating to 580 it transforms into a mixture of monomer and dimer of 60. It is shown that the rhomboedric polymer (2D-R) transforms into a highly disordered phase at pressure ~14 GPa. The new phase is characterized by chaotic formation of polymer bonds between molecules, belonging to neighboring planar polymer planes. This phase is also metastable at normal pressure and upon heating to 580 it transforms into a mixture of monomer and dimer of 60.

Fig. 1 Raman spectrum of a 2D-T polymer at pressure up to 27.5 GRa. Right graph - increase of pressure, left graph - decrease of pressure. At pressure about 20 GPa irreversible transition into a new high pressure phase occurs.

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