Abstract: Three Dimensional Monte Carlo simulation of phase transitions is performed at high density of polymers with limited chain length by introducing intramolecular conforma-tional interaction E_cand intermolecular orientation-dependent interaction E_p, the later is considered as the process of compact pairing of non-bond segments according to our "cooperative pairing model". We prove that at E_p/E_c=1, the phase transition corresponds to polymer crystallization (Fig. 1,2). Then by randomly introducing non-crystallizable segments which do not take part in cooperative pairing process, we find that the phase transitions move to lower temperature (Fig. 3) and the depression of melting temperatures follows Flory's prediction for random copolymer, accompanying the loss of lamellar structure which agrees with experiments. These results illustrate that the cooperative pairing model is a special behavior for crystallizable segments.

Key words: Computer simulation, Orderly phase transition, Random copolymer