Association Behavior of Poly(ethylene oxide)–Poly(propylene oxide) Alternating Multiblock Copolymers in Water toward Thermally Induced Phase Separation

Abstract

Thermal changes in the association behavior of poly(ethylene oxide)-poly(propylene oxide) alternating multiblock (PEO-PPO AMB) copolymers in water are investigated by the use of transmittance and light scattering measurements. Two PEO-PPO AMB copolymers with a different weight fraction of PEO, (EOPO) and (EOPO), are prepared. The weight-average molecular weights of (EOPO) and (EOPO) estimated by static light scattering measurements are 1.3 × 10 and 4.1 × 10 g mol, respectively. The number of PEO-PPO repeating pairs is over 8. It is found that the aqueous solution of (EOPO) undergoes phase separation with a lower critical solution temperature (LCST) of around 58 °C at 0.3 wt %. For the aqueous (EOPO) solution, the LCST is estimated to be ca. 42 °C. The critical solution concentration for (EOPO) is not clear because of a small concentration dependence of T at a higher concentration range. Dynamic light scattering measurements indicate that a micellelike aggregate is formed below the LCST. From the Debye plot, it is elucidated that the second virial coefficient, A, starts going down at around 32 °C for (EOPO) and below 15 °C for (EOPO). The A value of (EOPO) approaches 0 near 50 °C, whereas that of (EOPO) approaches 0 at around 35 °C. At a high temperature, the attractive interaction among the copolymers becomes dominant, thereby inducing the formation of micellelike aggregates.

Effect of Molecular Weight on Cloud Point of Aqueous Solution of Poly (ethylene oxide)–Poly (propylene oxide) Alternating Multiblock Copolymer

“…The intercept of the solid line in the inset gives a value of 39 , which corresponds to the T θ of the system. In previous papers, we reported that the micellization temperature of EO 220 PO 33 6 is around 41-50 20 and the second virial coefficient, A 2 , of EO 220 PO 33 8 approaches zero around 50 23 . The results shown here imply that the Shultz-Flory theory is applicable even to PEO-PPO AMB copolymers.…”

“…The PEO-PPO AMB copolymer was prepared by a dehydrated condensation reaction according to the literature 23 . Briefly, α,ω-diamino PPO JEFFAMINE D-2000; weight-average molecular weight M w 2,000 was kindly supplied by Huntsman Corporation.…”

“…The PEO-PPO AMB copolymer prepared herein is denoted as EO 220 PO 33 n , where EO is the ethylene oxide unit, PO is the propylene oxide unit, and n is the number of PEO-PPO repeating units. The characterization details can be found in previous reports 20,23 .…”

“…In a previous paper, however, we reported that the T c of the aqueous solution of PEO-PPO AMB copolymers is insensitive to the polymer concentration above T cp , which is located at ca. 0.3 wt 23 . Thus, the T c measured for the 1.5 wt aqueous solution of the copolymers is expected to be close to the T cp .…”

Unimer Structure and Micellization of Poly(ethylene oxide)-Stereocontrolled Poly(N-isopropylacrylamide) Alternating Multiblock Copolymers in Aqueous Solution

“…21 As a result, A 2 of PEO− PNiPAm AMB copolymers systematically changes depending upon the stereoregularity of the PNiPAm block. A 2 of 3−5 × 10 −6 L mol g −2 has been reported for (EO 220 PO 33 ) 8 and (EO 68 PO 33 ) 9 (PEO−PPO AMB copolymers) in water at 25 °C, 16 which is larger by 10 times than that for AMBm45. That is, (EO 220 PO 33 ) 8 and (EO 68 PO 33 ) 9 chains are more repulsive in water than AMBm45.…”