Mesoscopic modeling of the polymerization, morphology, and crystallization of stereoblock and stereoregular polypropylenes

Abstract

Thermoplastic elastomers require domains that act as physical crosslinks, and these can be either glassy regions or crystallites. For crystallites in a polymer such as polypropylene (PP), the challenge is to develop polymerizations that form the long stereoregular chain sequences required to produce crystallites large enough to act as stable temporary crosslinks but not so many of them that the material becomes a significantly crystalline thermoplastic rather than an elastomer. For PP, the requirement is for long isotactic sequences within predominantly elastomeric atactic chains, and catalysts required to achieve such an unusual stereoblock structure are now available. This provided encouragement for the simulations described herein that illustrate some relationships between polymerization mechanisms and distributions of isotactic sequences (particularly those long enough to crystallize). A Windle‐type Monte Carlo algorithm was then applied to arrays of the representative PP chains in searches for matches of crystallizable sequences. This approach provided estimates of degrees of crystallinity, melting points, interfacial free energies, standard free energies of fusion, and Young's moduli at small extensions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 840–853, 2002

Molecular modeling investigation of the fundamental structural parameters of polymers of intrinsic microporosity for the design of tailor-made ultra-permeable and highly selective gas separation membranes

“…After the construction is complete, each simulation cell was minimized using the MS Discover module till complete convergence [20]. Once the simulation cells were minimized, they were all subjected to annealing procedures involving five annealing cycles with initial temperature of 300 K and mid-cycle temperature of 800 K [21]. Each annealing cycle had five heating ramps per cycle and ran for 10,000 dynamics steps per ramp.…”

Polyolefins with Long Chain Branches Made with Single‐Site Coordination Catalysts: A Review of Mathematical Modeling Techniques for Polymer Microstructure

“…In the solid state, the crystalline segments may act as physical crosslinks between the amorphous chains, providing the polymer with properties of a thermoplastic elastomer (TPE). [39,40] Some of these branch-block TPEs are attractive materials because they combine the advanced properties of specialty polymers with the low production cost of commodity polyolefins. Similar results can be obtained for the homopolymerization of propylene with a dual catalyst system containing one stereospecific linear-catalyst and one aspecific LCBcatalyst.…”

Molecular Dynamics Investigation into the High Permeability and High Selectivity of Nano-Porous Polyimide Membranes for the “Green” Separation of Natural Gas

“…The simulation study will be used to investigate the self diffusion of the various components of natural gas such as methane, ethane, propane and butane through a polyimide membrane known as PIM [27]. Figure 1 illustrates the molecular structure of the polyimide, PIM, employed in this study.…”

“…Once the simulation cells were minimized, they were all subjected to molecular dynamics runs using NVT ensemble for 300 ps with 1 fs time step at the temperature of 298K. Recent studies showed that running the simulations for 300 ps produces meaningful trajectories with reproducible results and allows for better sampling averages over the whole course of the simulation [26,27]. Full trajectories were saved every 100 steps.…”