Chain conformation of polymer melts with associating groups

Abstract

Molecular association has profound influences on the viscoelastic properties of polymers with associating side groups. The conventional wisdom is that interchain association dominates in the melt state, and the dynamics of the associative polymer network therefore might be understood by extending the classical molecular approaches such as the Rouse and reptation models for linear chains. Using small-angle neutron scattering and molecular dynamics simulation, here we show that while interchain association is important, intrachain association can not be neglected in determining the static structures of associating polymers in the melt state. Analyses of the radius of gyration, static structure factor, and intrachain mean-square distance of polymers with associating side groups have revealed a substantial deviation from the random walk structure at even moderate association strength and degree of functionality. This finding emphasizes the important role of intrachain loops in associative polymer networks.

Mechanisms of Self-Diffusion of Linear Associative Polymers Studied by Brownian Dynamics Simulation

“…As shown in Figure B and Figure S16, increasing N s at a constant chain length and concentration results in a monotonic increase in the loop fraction, from 19% for the 4-sticker chains to 93% for the 49-sticker chains. The increase in the loop fraction with N s occurs due to both the smaller volume of the strands between stickers and the greater number of sticker combinations that can intramolecularly react, as also shown in recent MD simulations studying the static properties of associative polymer melts . This higher loop fraction counteracts the increase in N s by decreasing the number of stickers per chain that are intermolecularly bound, as shown by the histograms in Figure B.…”

“…The increase in the loop fraction with N s occurs due to both the smaller volume of the strands between stickers and the greater number of sticker combinations that can intramolecularly react, as also shown in recent MD simulations studying the static properties of associative polymer melts. 53 This higher loop fraction counteracts the increase in N s by decreasing the number of stickers per chain that are intermolecularly bound, as shown by the histograms in Figure 6B. The average number of intermolecularly bound stickers per chain, ⟨N s, inter ⟩, increases with sticker density up to N s = 17 before decreasing at higher N s , where the enhancement of looping reactions begins to outweigh the increase in the total number of stickers per chain.…”

Anomalous Diffusion in Associative Networks of High-Sticker-Density Polymers

“…This includes the assumption that the chains contain a large number of stickers per chain and have a high degree of polymerization between the stickers, which may not hold for the polymers in this study. 20 Molecular dynamics simulation by Wang et al 31 has shown that associative polymers with an association strength of 1−10 k B T can have a nonmonotonic dependence of R g with increasing S. As the sticker density is increased, the reduced spacing between the stickers results in the formation of higher fractions of intrachain bonds and this drives the collapse of the chains. The number fraction of elastically active strands estimated based on the affine network assumption was in the range of 0.8−1.0 for the highest concentration investigated for each polymer (Figure S5).…”

Coarse-Grained Molecular Dynamics Modeling of Segmented Block Copolymers: Impact of the Chain Architecture on Crystallization and Morphology

“…46 Besides, a recent study has shown the modification of the chain conformations when adding associating groups to the copolymer, resulting in the formation of intramolecular loops. 47 Apart from that, no molecular dynamics model describing the morphology and phase transitions in crystallizable segmented block copolymers has been reported to our knowledge.…”