Conformations and mobility of polyethylene and trans -polyacethylene chains confined in α-cyclodextrins channels

Abstract

Conformational properties and mobility of two polymeric chains containing 30 repeating units of either polyethylene (PE) or trans-polyacethylene (PA) confined into the channel formed by eight α-cyclodextrins (αCDs) are studied by Molecular Dynamics simulations performed at 500 K and compared with the behavior exhibited by the same chains when they stand alone in vacuum. The rotaxane structure (i.e. polymeric chains threaded into the αCDs channel) is stabilized with respect to the separated chain and αCDs mostly because of van der Waals interactions. As it might be expected, large differences are observed in the molecular characteristics of the isolated chains as compared to their confined counterparts. The differences are in the sense of decreasing the conformational mobility in favor of extended conformations in the case of confined chains. Comparison of the results obtained for confined PE and PA chains indicates a noticeably larger mobility of the PA chain. Molecular dimensions obtained for the isolated PE chain agree with the results published in the literature.

Cyclodextrin Rotaxanes and Polyrotaxanes

“…Since polyethylene is one of the most hydrophobic and most insoluble polymers known, only ethylene oligomers form α-CD inclusion compounds. The stoichiometry quotient of q exp = 3 reveals that the CD rings are densely packed in channel structures. , The solid-state structures of both polyethylene and trans -polyacetylene included in α-CD were calculated by molecular mechanics using the TRIPOS force fields …”

“…149,162 The solidstate structures of both polyethylene and trans-polyacetylene included in R-CD were calculated by molecular mechanics using the TRIPOS force fields. 202 Inclusion of substituted polyethylenes is easier to perform because of their higher solubility and their weaker intermolecular interactions. Since the cross-sectional areas of these derivatives are larger, the wider CDs have to be used for complexation.…”

Chain Dynamics of Poly(oxyethylene) in Nanotubes of α‐Cyclodextrin by Solid‐State 2H NMR

“…Contained within the channels of nanotubes, polymer chains are isolated from other chains and exhibit vastly different dynamics as compared to their dynamics in the bulk. Chain motions within nanoscopic cyclodextrin channels have been examined for polyethylene,26 poly(dimethylsiloxane),27 poly(caprolactone),28 and a triblock poly( ε ‐caprolactone)‐poly(oxyethylene)‐poly( ε ‐caprolactone) 29. Polymers can also be isolated within nanoscopic channels by co‐crystallization with certain small molecules such as urea and perhydrotriphenylene to form solid inclusion complexes.…”

Modification of statistical threading in two-component pseudorotaxane melts using the amphiphilic approach and variations in the confinement geometry

“…Such studies can contribute substantially to the field by allowing us to increase the yield of threading. Most of the computational work [15][16][17][18][19][20][21][22][23] has focused on single chain and ring systems. There has also been a growing interest in studying the dynamic properties of rotaxanes systems, e.g., the diffusion of threaded and unthreaded macrocycles, 42 and the shuttling of the macrocycle along the linear chain backbone.…”

“…However, relatively few studies on the synthesis and characterization of rotaxanes in which both components are made of the same species, and thus do not have any specific binding sites, have been conducted. [1][2][3][4][5][6][7][8][9]22,31,32 Our goal in this paper is to study rotaxane formation by statistical methods when the chain and the ring are constructed from the same repeat unit. Such systems have been referred to in the literature as homorotaxanes and homopolyrotaxanes depending on whether the linear chain is short or long enough to thread multiple rings.…”