Structural properties of poly(propylene oxide) from diffraction experiments and reverse Monte Carlo simulation

Abstract

Structural characteristics of an amorphous polymer melt, poly(propylene oxide) (PPO), have been studied by combining neutron and x-ray diffraction experiments and computer modeling using the reverse Monte Carlo (RMC) technique. The neutron diffraction experiments were performed on hydrogenous as well as deuterated samples. The experimentally determined nearest-neighbor distances were found to be in good agreement with literature data. The RMC modeling was applied for interpretation of the diffraction data to obtain more detailed structural information on bond angles, intermediate and long range correlations. For the intermediate range structure, the experimental structure factors demonstrate a first diffraction peak at about 1.45 Å−1, which from the RMC produced model can be related to the interchain distance of an almost random packing of the polymer chains. To investigate the chain conformation, partial atomic pair correlation functions have been calculated for atoms belonging to monomers close in sequence. The results show that the most probable conformation is a “stretched” trans conformation, where two consecutive methyl groups are pointing in almost opposite directions. Calculated bond and dihedral angle distributions support this finding and demonstrate the ability of the RMC method to produce polymer structures in good agreement with experimental results.

Free volume in poly(propylene glycol) and its relationships to spin probe reorientation

“…One possibility is the onset of percolating free volume space accessible to the o-Ps probe in atomistic microstructures as obtained from either neutron diffraction (ND) data as treated using reverse Monte Carlo (RMC) method or molecular dynamic (MD) simulations followed by cavity analysis (CAVA) on small molecular systems such as found in glycerol [27] and propylene glycol [28]. Our CAVA on the PPG 4000 microstructure as obtained from the former approach [29] confirmed the presence of the totally percolated static free volume for o-Ps probe at room temperature (300 K), at least. However, the validity of this hypothesis for our polymer system remains to be verified by performing either temperature dependent ND combined with RMC or MD, both associated with CAVA approach over a wider temperature range including T L b2 .…”

Molecular-dynamics simulation of structural and conformational properties of poly(propylene oxide)

“…20 The initial polymer structure was generated by a random walk procedure and subsequently adjusted to experimental data using the reverse Monte Carlo technique. 5,19 MD trajectories of approximately one nanosecond were generated. 19 Explicit hydrogen atoms were then added and the force field was changed to the one defined in Ref.…”

“…Recently such studies have been performed on PPO and the experimental data were analyzed using reverse Monte Carlo ͑RMC͒ modeling. [5][6][7] Two systems were investigated with molecular weight 4000 g/mol and about 1900 g/mol, respectively, corresponding to about 70 and 30 monomers/molecule.…”

The Segmental and Rotational Dynamics of PPO, Above the Glass‐Transition, Investigated by Neutron Scattering and Molecular Dynamics Simulations

“…The system was generated using a random walk technique and subsequently adjusted to experimental data using the RMC technique (16). This was followed by a united atom simulation (22), in which MD trajectories were generated for a nanosecond with, essentially, the GROMOS force field (23).…”

“…Previously, reverse Monte Carlo (RMC) modeling was used to investigate the structure of PPO (16). Then, using the RMC model as a starting structure, the force field proposed in Reference (17) was successfully used in Reference (18) to describe the structure of PPO.…”