The role of hydrophobic hydration in the LCST behaviour of POEGMA₃₀₀ by all-atom molecular dynamics simulations

Abstract

The solubility and lower critical solution temperature (LCST) behaviour of poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMA300) in water were comprehensively investigated by all-atom molecular dynamics (MD) simulations for 5-, 20-, 50- and 75-mer homopolymers. According to various structural and dynamic properties, the water-solubility of POEGMA300 below the LCST is mainly provided by hydrophobic hydration around the side chain carbon atoms, which is achieved by cage-like water formations. The LCST phase transition occurs when these cage-like structures are disrupted by increasing the temperature above the LCST. During this process, significant amounts of water molecules are released and the local water-ordering is reduced. Moreover, the number of hydrogen bonds and hydrogen bond lifetime results indicate that the hydrogen bonding between polymers and water molecules has relatively little effect on the phase transition. Also, the diffusion rates of 50- and 75-mer POEGMA300 decrease with increasing temperature, which may be due to the breakage of cage-like water structures when the polymer exceeds a certain chain length. Our atomistic level findings will enhance the understanding of the LCST phase transition of OEGMA based homopolymers and will be helpful to design homo- and co-polymers of OEGMAs with required properties.

The Hofmeister series: Specific ion effects in aqueous polymer solutions

“…In addition, one must consider the complex nature of polymer hydration. Thermo-responsive polymers generally comprise both polar and apolar regions, each of which possesses unique hydration characteristics that are differently affected by ions (Figure 1b) [84][85][86][87][88]. The polar parts on the polymer backbone typically form hydrogen bonds with water molecules that introduce a favorable enthalpic term to the free energy of mixing.…”

Investigation of the LCST-Thermoresponsive Behavior of Novel Oligo(Ethylene Glycol)-Modified Pentafluorostyrene Homopolymers

“…LCST-thermoresponsive polymers are commonly described as subject to a coil-to-globule transition. This describes the conformational changes that a dissolved polymeric chain in an unfolded random coil conformation undergoes when reaching cloud point temperature, a contraction of the structure into a compact globule, which is accompanied by an aggregation of polymers due to hydrophobic interactions becoming dominant upon the loss of bound water [10,11]. However, LCST-like phase separation is also a feature of other kinds of systems where polymer chains are not dissolved into a random coil conformation, but rather are dispersed into small globular structures even below the cloud point.…”

Dynamic Fluctuations of Thermoresponsive Poly(oligo-ethylene glycol methyl ether methacrylate)-Based Hydrogels Investigated by Dynamic Light Scattering

“…Through the statistical copolymerization of diethylene glycol methacrylate (MeO 2 MA, n = 2) and OEGMA ( n = 4 or 5), copolymers can be prepared that display the LCST ranging anywhere from ∼20 to ∼63 °C (Figure ). − They also exhibited all the advantageous nonimmunogenic, noncytotoxic, and protein (and consequently cell)-repellent properties of PEG. , Indeed, many studies related to POEGMA-based materials have been developed to use the advanced biomedical applications, such as bioconjugates, , surface coatings, , microspheres for carriers, − and injectable gels. ,− …”