Micro- and Macrophase Separations of Hydrophobically Solvated Block Copolymer Aqueous Solutions Induced by Pressure and Temperature

Abstract

The pressure-and temperature-induced micro-and macrophase separations of hydrophobically solvated block copolymer aqueous solutions, consisting of poly[2-(2-ethoxy)ethoxyethyl vinyl ether]-block-poly-(2-methoxyethyl vinyl ether) (pEOEOVE-b-pMOVE), have been investigated with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The following facts were disclosed. (1) For an increase in temperature under atmospheric pressure, a series of scattering peaks appeared in SANS intensity curves at about 40 °C, indicating microphase separation with pEOEOVE domains in a bcc packing in the matrix of pMOVE and water. This was followed by a precipitation of the polymer at about 65 °C. (2) A pressure-temperature (P-T) phase diagram for microphase separation was determined by DLS, which was a convex-upward function of P with a symmetric axis of P 0 ≈ 150 MPa. (3) At ambient temperature, an increase of the correlation length was observed by increasing P. This was confirmed to be due to macrophase separation by pressurizing. (4) On the other hand, the solution underwent a reentrant microphase dissolution-separation transition at 45 °C with increasing P. The SANS peaks disappeared and the intensity decreased at 100 MPa. Then, by further increasing P, the SANS intensity increased accompanying a scattering maximum. In view of the symmetry of the phase diagram, it is conjectured that this reentrant microphase separation at high pressure is different from one at low pressure. These findings lead to a conclusion that the selectivity of hydrophobic solvation is suppressed at high pressures.

Small-angle neutron scattering on polymer gels: phase behavior, inhomogeneities and deformation mechanisms

“…We performed a series of high-pressure SANS studies on polymer-aqueous systems to elucidate the pressure dependence of the hydrophobic interactions in PNIPA neutral gels, 17 PNIPA/AAc charged gels, 18,19 hydrophilic-hydrophobic block copolymer aqueous solutions [20][21][22] and globular proteins. 56 Figure 8 shows a pressure cell for SANS (PCI-400-SANS, Teramex, Kyoto, Japan).…”

“…Figure 9 shows the pressure-temperature phase diagram of poly(2-(2-ethoxy)ethoxyethyl vinyl ether)-block-poly(2-methoxyethyl vinyl ether) (pEOEOVE-pMOVE) in D 2 O and the corresponding SANS patterns. 20,22 The degrees of polymerization of the individual block chains, that is, pEOEOVE and pMOVE, were 200 and 400, respectively. Both pEOEOVE and pMOVE are soluble in water at low temperatures, but they become insoluble at B40 and 65 1C, respectively.…”

“…Third, we review the applications of SANS to harsh environments, that is, phase behavior of polymeric systems under very high hydrostatic pressures. [17][18][19][20][21][22] Here, the roles of hydrophobic interactions in aqueous systems are discussed as a function of pressure. Fourth, the structural characterization of various types of super-tough gels will be shown by focusing on deformation mechanisms.…”

New stage in living cationic polymerization: An array of effective Lewis acid catalysts and fast living polymerization in seconds

“…Under appropriate conditions, the living cationic polymerization of several functional monomers in the presence of an added base allowed the selective preparation of a new series of well-defined stimuli-responsive polymers such as thermo-, [60][61][62][63][64] pH-, 65 pressure-, 66 or photoresponsive 36,67,68 polymers (Scheme A2). A typical example was as follows.…”

Lewis acid‐specific polymerization behaviors in living cationic polymerization of vinyl ether with a malonate group

“…Our group has demonstrated that the base-assisting living cationic polymerization permits selective synthesis of a new series of well-defined stimuli-responsive poly(vinyl ethers) (VEs) 3,10 including pH-, 11 photo-, 12 solvent-, 13 and pressureresponsive 14 polymers as well as novel types of thermosensitive polymers. 10,[15][16][17][18] These studies showed that fine control of stimuli-responsive behavior was not achieved without the appropriate design of primary polymer structures and functional groups.…”