The molecular structure of the phase-stable at room temperature-for the polymer with formula [-p-C6H4-COO-p-C6H3(R)p-C6H3(R)-OOC-p-C6H4-O-(CH2)(10)O-](x), with R =-CH2-=CH=CH2, is reported. The cell is hexagonal (a = b = 13.43 Angstrom, c = 33.3 Angstrom, gamma = 120 degrees), space group P6(3), six chains per unit cell (d(calcd) = 1.23 g cm(-3)). The six chains are packed together to give a, bundle with the center of mass set at the origin of the unit cell. The allyl groups are placed inside the bundle, thus explaining the unexpected reactivity of the double bonds to give crosslinking when fiber samples are annealed in the solid state.