A coarse-grained model for capturing the helical behavior of isotactic polypropylene

Abstract

Understanding the process-property relations of helical polymers using molecular simulations has been an attractive research field over the years. Specifically, isotactic polypropylene still remains a challenge for current computational experimentation,...

Effect of Temperature on Flow-Induced Crystallization of Isotactic Polypropylene: A Molecular-Dynamics Study

“…The method used for generating the initial structure, following the work of Theodorou and Suter, and the subsequent three step equilibration process described in Section , resulted in an iPP conformation representative of a melt with an average characteristic ratio C ∞ = 6.0 ± 0.4, measured in equilibrium conditions. Experimental C ∞ = 6.2 and simulation C ∞ = 6.4 values are in good agreement. The simulated melt is highly entangled with entanglement molecular weight M e = 3092 g/mol (74 monomers per entanglement), which was estimated by using the CReTA (Contour Reduction Topological Analysis) algorithm .…”

“…After the equilibration, five different configurations were extracted from the trajectory produced at step three at not equidistant times (100.0, 230.0, 456.0, 601.5, and 750.5 ns). All the configurations had a characteristic ratio of C ∞ = 6.4, close to the computational value that was estimated for well relaxed single unperturbed iPP polymer chains using the TraPPE-UA force field . The five configurations were cooled with a cooling rate of 1 K/ns to the desired temperature.…”

“…All the configurations had a characteristic ratio of C ∞ = 6.4, close to the computational value that was estimated for well relaxed single unperturbed iPP polymer chains using the TraPPE-UA force field. 42 The five configurations were cooled with a cooling rate of 1 K/ns to the desired temperature. In total, 40 equilibrated systems were studied at eight different temperatures from 350 to 420 K with step 10 K, five systems at each temperature.…”

Pulling on grafted flexible polymers can cause twisted bundles

“…Finally, in order to identify the conjectured helical twist of the bundles quantitatively, it is helpful to include an observable that tracks the angular component directly, i.e., not only by inference via extension or spaciousness. From the study of α-helices (see, e.g., refs [35][36][37][38][39] it seems convenient to utilize the dihedral angle, which yields the twist of the fourth monomer with respect to the first around the axis defined by monomers 2 and 3. 40 For our multi-polymer system, we first sum up all N − 3 dihedral angles of an individual polymer and then average over all M polymers yielding the helical twist parameter…”

“…From the study of a-helices (see, e.g., ref. [35][36][37][38][39] it seems convenient to utilize the dihedral angle, which yields the twist of the fourth monomer with respect to the first around the axis defined by monomers 2 and 3. 40 For our multi-polymer system, we first sum up all N À 3 dihedral angles of an individual polymer and then average over all M polymers yielding the helical twist parameter…”