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Keywords:

  • bridging methods;
  • coarse-grained models;
  • conformation;
  • helix;
  • lattice models;
  • poly(silylenemethylene);
  • Monte Carlo;
  • simulations

Abstract

A coarse-grained model has been developed for asymmetrically substituted poly(silylenemethylene)s in which the side chain is a flexible spacer terminated by a biphenyl unit. Each monomer unit is represented by four coarse-grained beads that interact via a Lennard–Jones potential and are subject to the first- and second-order interactions deduced from the atomistically detailed model. Metropolis Monte Carlo simulations were performed for isolated syndiotactic, isotactic, and atactic chains. Snapshots from the equilibrated coarse-grained chain on the discrete space of a high coordination lattice were reverse-mapped to atomistically detailed structures in continuous space. At 373 K, the chains were disordered independent of the stereochemical composition. The occupancy of bond pairs depended on the stereochemical composition, with the trans-gauche (tg) sequence being favored by the isotactic chain. When the simulation was performed with the backbone constrained to specific periodic structures, the g helix was the lowest energy structure for either the atactic or isotactic chains. For the syndiotactic chain, the g and gt helices were favored. The appearance of the g helix as the favored periodic structure of the isolated chain was consistent with the chain conformation reported previously for the smectic phase of this polymer in the bulk state. The g helix was disrupted when the backbone was allowed to access nonhelical conformations, even though these conformations may have been slightly higher in energy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 886–896, 2005