Monte Carlo simulation of the order-disorder transition of a symmetric cyclic diblock copolymer system

The microphase separation of symmetric cyclic diblock copolymer with decrea sing temperature is simulated using the Monte Carlo method. In order to inv estigate the effect of the ring-shape chain architecture on order-disorder transition (ODT), the microphase separation of the cyclic diblock copolymer is compared with that of a symmetric linear diblock copolymer with the sam e chain length. For both systems, the ODT is observed as a first-order tran sition, and the ordered structure formed through the ODT is lamellar. The r atio of the domain spacing in the cyclic diblock copolymer to that in the l inear one is 0.7 at the ODT, and the scattering intensity of the former is weaker than that of the latter. The ring-shape chain architecture suppresse s the random thermal force, so that the cyclic diblock copolymer still show s a mean-field behavior at the temperature at which the linear diblock copo lymer does not obey the mean-field prediction. The value of (chi(eff)N)(ODT ) of the linear diblock copolymer is calculated to be in the range of 25.36 <(chi(eff)N)< 26.04, which is in good agreement with the theoretical predi ction, (chi(eff)N)(ODT)=25.61, indicating that this simulation properly des cribes the ODT of the diblock copolymer. The value of (chi(eff)N)(ODT) of t he cyclic diblock copolymer is predicted to be in the range of 40.83 <(chi( eff)N)< 43.02. (C) 1999 American Institute of Physics. [S0021-9606(99)51228 -2].