Uniaxial ordering and rotator phase of ribbonlike polymers

The phase transition in bended and twisted ribbonlike polymer systems is described in meanfield approximation by use of the lattice model with directed self-correlated walks. This phase transition can be of either first or second order depending on the ratio of the constants in the effective energy of interaction of a polymer with the environment. For the first-order phase transition it is found, in particular, that the phase transition temperature depends on polymer length, decreasing linearly with reciprocal length for lengths exceeding 100 monomer units. On the other hand, the jump of the specific entropy is independent of the polymer length for the molecules containing more than 30 monomers. The obtained results are in full agreement with the existing experimental data.