Macromolecules, Vol.44, No.8, 3140-3148, 2011
Three Dimensional Picture of the Local Structure of 1,4-Polybutadiene from a Complete Atomistic Model and Neutron Scattering Data
An efficient method of combining neutron diffraction data over an extended Q range with detailed atomistic models is presented. A quantitative and qualitative mapping of the organization of the chain conformation in both glass and liquid phase has been performed. The proposed structural refinement method is based on the exploitation of the intrachain features of the diffraction pattern by the use of internal coordinates for bond lengths, valence angles and torsion rotations. Models are built stochastically by assignment of these internal coordinates from probability distributions with limited variable parameters. Variation of these parameters is used in the construction of models that minimize the differences between the observed and calculated structure factors. A series of neutron scattering data of 1,4-polybutadiene at the region 20-320 K is presented. Analysis of the experimental data yield bond lengths for C-C and C=C of 1.54 and 1.35 angstrom respectively. Valence angles of the backbone were found to be at 112 degrees and 122.8 degrees for the C-C-C and C-C=C respectively. Three torsion angles corresponding to the double bond aid the adjacent alpha and beta bonds were found to occupy cis and trans, s +/-, trans and g +/- and trans states, respectively. We compare our results with theoretical predictions, computer simulations, RIS models, and previously reported experimental results.