Detailed atomistic molecular dynamics simulation of cis-1,4-poly(butadiene)

G Tsolou and VG Mavrantzas and DN Theodorou, MACROMOLECULES, 38, 1478-1492 (2005).

DOI: 10.1021/ma0491210

Well-relaxed atomistic configurations of model cis-1,4-poly(butadiene) (PB) systems, ranging in molecular length from C-32 to C-400, have been subjected to detailed molecular dynamics simulations in the NPT ensemble for times up to 600 ns. Results are presented for the static and (mainly) dynamic properties of these systems, such as the segmental and terminal relaxation properties, the self-diffusion coefficient, D, and the single-chain dynamic structure factor, S(q,t), at pressure P = 1 atm and temperatures, T, between 298 and 430 K. Our simulation data demonstrate that, around C-200, D is seen to exhibit a change in its power-law dependence on molecular weight, M, deviating from a Rouse (where D approximate to M-b with b congruent to 1) toward a reptation- like (where D approximate to M-b with b congruent to 2.1) behavior. Following the methodology introduced by Harmandaris et al. Macromolecules 2003, 36, 1376 for linear polyethylene (PE) melts, we have further been able to successfully project atomistic cis-1,4-PB chain configurations to primitive paths, thereby mapping simulation trajectories onto the reptation model. This has allowed us to consistently calculate the friction coefficient, zeta, per carbon atom of cis-1,4-PB melts both below and above the molecular weight for the formation of entanglements. The dependence of D on T is also presented.

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