Generation of well relaxed all atom models of stereoregular polymers: a validation of hybrid particle-field molecular dynamics for polypropylene melts of different tacticities

ABSTRACT

The tacticity of vinyl polymer chains strongly affects the physical properties of polymeric materials, as example the chain conformations and stiffness. In the present work we tested how the hybrid Particle-Field Molecular Dynamics (PF-MD) technique is capable to describe conformational differences of polymer chains as function of the tacticity. In particular, we focus on tacticity effect of atactic, isotactic, and syndiotactic polypropylene (PP) homopolymer melts. We found that PF-MD simulations exhibit dependence of Flory’s Characteristic Ratio from the fraction of racemo diads along the PP chains in qualitative agreement with Small Angle Neutron Scattering (SANS) experiments and theoretical previsions. Finally, we calculated and compared the packing length parameter on very high stereoregular syndiotactic PP systems with rheological measurements. A qualitative agreement between the calculated and experimental packing length is found.

KEYWORDS:

• Tacticity
• polypropylene
• hybrid Particle-Field
• atomistic model
• molecular dynamics
• packing length
• Flory’s characteristic ratio

Acknowledgments

The computer resources and related technical support used for this work have been provided by CRESCO/ENEAGRID High Performance Computing Infrastructure and its Staff. CRESCO/ENEAGRID High Performance Computing Infrastructure is funded by ENEA, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development and by Italian and European research programs.

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