Atomistic insights on the LCST behavior of PMEO₂MA in water by molecular dynamics simulations

Abstract

Fully atomistic molecular dynamics simulations of poly(2-[2-methoxyethoxy]ethyl methacrylate) (PMEO 2 MA) in water at temperatures below and above its lower critical solution temperature (LCST) were performed to improve the understanding of its LCST behavior. Atomic trajectories were used to calculate various structural and dynamic properties. Simulation results show that PMEO 2 MA undergo a distinct coil-to-globule transition above LCST. Detailed analyses of the number of first hydration shell water molecules around various atomic regions are revealed that the water solubility of PMEO 2 MA below LCST is mainly provided by the hydrophobic hydration around the side chain carbon atoms. This is achieved by the cage-like water network formations which are disrupted when the temperature is increased above LCST, accompanied by significant amount of water molecule release and local water-ordering reduction, which leads to the LCST phase transition. Furthermore, other analyses such as the number of hydrogen bonds and hydrogen bond lifetimes suggest that intermolecular hydrogen bondings between polymer and water molecules have little effect on the phase transition. Our results will contribute to a better understanding on the LCST phase transition of oligo(ethylene glycol) methyl ether methacrylate (OEGMA)based homopolymers at atomistic level that will be useful when designing homo-and co-polymers of OEGMAs with desired properties.

A Computational Study on the LCST Phase Transition of a POEGMA Type Thermoresponsive Block Copolymer: Effect of Water Ordering and Individual Behavior of Blocks

“…Meanwhile, the backbone conformation of the 5-mer POEGMA 300 block does not change significantly. These results are consistent with the findings of our previous studies; 44,45 that is, 5-mer polymer length is not sufficient for a single POEGMA chain to provide LCST transition under our simulation conditions.…”

“…The average R g values calculated over the last 50 ns of each temperature are given in the Supporting Information, Table S1. These results are quite close to our previous POEGMA homopolymer studies. , For example, for the 20-mer PMEO 2 MA homopolymer, we found the average R g as 12.96 and 11.06 Å at 290 K ( T < LCST) and 330 K ( T > LCST), respectively. In this study, we found the average R g of the PMEO 2 MA block in 20/5 and 20/20 copolymers as 13.80 and 12.87 Å at 290 K and 12.12 and 11.15 Å at 330 K, respectively.…”

“…These trends seen in the average numbers of first shell water molecules per monomer of the PMEO 2 MA block that are explained above are also true for the POEGMA 300 block of the 50/20 copolymer and also for the 20/5 and 20/20 copolymer systems (Tables S2 and S3, Supporting Information). All of these findings are consistent with the results of our previous PMEO 2 MA and POEGMA 300 homopolymer studies. , Accordingly, side chain carbon atoms do not only provide the water solubility of PMEO 2 MA- co -POEGMA 300 in primary but also play a critical role in the LCST phase transition with temperature, as similar to PMEO 2 MA and POEGMA 300 homopolymers.…”

“…In our PMEO 2 MA and POEGMA 300 homopolymer studies, we showed that the high number of first shell water molecules seen around the side chain carbon atoms is provided by the cage-like water structures formed due to hydrophobic hydration. , In order to determine whether this hydrophobic hydration in the homopolymers is also present in the copolymer, we investigated the formation of hydrogen bonds between the first hydration shell water molecules around the copolymers according to the following geometric criteria: (1) donor–acceptor distance ≤ 3.5 Å; (2) donor–hydrogen–acceptor angle ≥ 135°. The snapshots of the hydrogen bonding network around the copolymers at 290, 307, and 330 K are given in Figures S5–S7, Supporting Information.…”

100th Anniversary of Macromolecular Science Viewpoint: Modeling and Simulation of Macromolecules with Hydrogen Bonds: Challenges, Successes, and Opportunities

“…Atomistic studies explain the role of H-bonds in driving chain conformation changes (e.g., polyaminoamide dendrimer conformations in ref ) and phase transitions in polymer solutions. For example, in the latter case of phase transitions in polymer solutions, atomistic MD simulation studies have shown the extent of H-bond interactions between the polymer (e.g., poly­( N -isopropylacrylamide)) and water, within the polymer chain and between polymer chains, and below and above phase transitions. , In polymer nanocomposites, the impact of H-bonds between the surface of a particle and the polymer chains in the matrix (e.g., graphene oxide and poly­(vinyl alcohol), modified silica and poly­(dimethylsiloxane)) on the overall binding energies between the various components have been calculated using atomistic simulations. These have been used to explain the observed improvements in the mechanical properties (e.g., frictional stress, storage modulus) of the polymer nanocomposites.…”