Effect of γ-substituted poly(ɛ-caprolactone) chain length on its coil-to-globule transition temperature in water: A molecular dynamics simulation study

The influence of chain length on the coil-to-globule transition temperature (T_cg) of poly{γ-2-[2-(2methoxyethoxy)ethoxy]ethoxy-3-caprolactone} (PMEEECL) chains was investigated via full atomistic molecular dynamics (MD) simulation. Chains with different repeating unit numbers (N) of 5, 10, 15, and 20 were simulated over a wide temperature range. It was found that T_cg increased with increasing N of the PMEEECL chain. The simulation results showed that as the chain contour length is of the order of the Kuhn length, the chain bending and chain collapse become more involved. The chains exhibit significant sensitivity to the temperature when the contour length exceeds the Kuhn length. Nonetheless, for the short chains, i.e. pentamer, the oligomer was temperature insensitive in the studied temperature range. Furthermore, aggregation of five PMEEECL chains with N = 20 was clearly observed at the temperatures above T_cg.