Some mechanisms for subtle influences of stereochemical composition on the physical properties of macromolecules

Abstract

Coarse‐grained chains can be designed so that they successfully capture subtle effects arising from the local covalent structure of real chains. Constraining the conformations of the coarse‐grained chains with an appropriate rotational isomeric state model can achieve this objective. This claim has been documented by simulations of the dependence of the mixing behavior of polypropylene melts on the stereochemical composition of the chains; atactic polypropylene and isotactic polypropylene are miscible, but the replacement of either component with syndiotactic polypropylene can lead to immiscibility. This has also been documented by a comparison of simulations and infrared–visible sum frequency generation spectroscopy studies of the surface structures of atactic polystyrene and random copolymers of ethylene and propylene. The success of this method when the stereochemical composition is defined by side chains as small as CH3 suggests that it should also be applicable to other problems in which the influence of the stereochemical composition is less subtle because the stereochemistry is defined by larger side chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1271‐1282, 2005

Coarse‐grained molecular dynamics simulations of stereoregular poly(methyl methacrylate)/poly(vinyl chloride) blends

“…Note that the peaks of the unlike pairs (PMMA/PVC) are higher than those of the like pairs (PMMA/PMMA, PVC/PVC). According to the assumption proposed by Mattice et al this suggests that the blend systems tend to be miscible, which agree with some experimental observations . Besides, as compared to the cases in the iPMMA/iPVC blend, the peaks of the like pairs in the sPMMA/iPVC blend are lower and those of the unlike pairs are higher.…”

“…The values of R g and R e and the trend with respect to chain tacticity are not yet reproduced. Besides, all the ratios ( R e / R g ) deviate from six as expected for Gaussian chains, and the characteristic ratios are somewhat lower than the results from AA simulations. Similar differences were also found in other works .…”

“…In particular, disagreements in the literature regarding miscibility of polymer blends were often attributed to differences in sample preparation methods, thermal history and characterization techniques, where subtle intermolecular interactions played the key roles. One fascinating characteristic is that trivial changes in covalent structure of a monomer can lead to dramatic changes in the phase diagram . The binary blend comprising poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) serves as one typical example, for which almost all experiments consistently pointed out that syndiotactic PMMA (sPMMA) was more miscible with PVC than was isotactic PMMA (iPMMA) .…”

“…One fascinating characteristic is that trivial changes in covalent structure of a monomer can lead to dramatic changes in the phase diagram. 2 The binary blend comprising poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) serves as one typical example, for which almost all experiments consistently pointed out that syndiotactic PMMA (sPMMA) was more miscible with PVC than was isotactic PMMA (iPMMA). 3 However, it is not yet quite clear how intermolecular interactions, which are indirectly detected in the experiments, influence the phase behaviors of polymer blends.…”

Υπολογιστική Μελέτη Πολυπροπυλενίου Για Υλικά Συσκευασίας

“…Το πολυπροπυλένιο (PP) είναι ένα βινυλικό πολυμερές με μεγάλη κλίμακα εφαρμογών, η ισοτακτική του μορφή είναι το κύριο βιομηχανικό προιόν και είναι ένα ημικρυσταλλικό πολυμερές ευρείας κατανάλωσης λόγω των ιδιοτήτων του και της προσαρμογής του στις απαιτήσεις των εφαρμογών του.Στο παρελθόν το PP έχει μελετηθεί μέσω διάφορων τεχνικών προσομοίωσης όπως η μέθοδος της Μοριακής Μηχανικής13,64,27 (MM), της Μοριακής Δυναμικης 12,14-16, 65-67 (MD) και της Monte Carlo (MC) [68][69][70][71][72][73][74][75]. Για τη μοντελοποίησή του έχουν χρησιμοποιηθεί μεσοσκοπικά μοντέλα (coarse-grained models), μοντέλα ενοποιημένων ατόμων (united atom model) και τέλος ατομιστικά μοντέλα διακριτών ατόμων (explicit atom model).…”