LCST-Type Phase Separation of Poly[poly(ethylene glycol) methyl

Nov 23, 2015 - Upon heating, P2 was sharply phase-separated in 2HPFP at which the cloud point was 46 °C (Figure 1, Table 1). The turbid solution in t...
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LCST-Type Phase Separation of Poly[poly(ethylene glycol) methyl ether methacrylate]s in Hydrofluorocarbon Yuta Koda, Takaya Terashima,* and Mitsuo Sawamoto* Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan S Supporting Information *

ABSTRACT: Poly[poly(ethylene glycol) methyl ether methacrylate]s [poly(PEGMA)s] sharply and reversibly exhibited lower critical solution temperature (LCST)-type phase separation in 2H,3H-perfluoropentane (2HPFP). The cloud points decreased from 52 to 41 °C with increasing the PEG pendant length [−(CH2CH2O)mCH3: m = 4.5, 9, 19]. The cloud point was precisely controlled via the addition of perfluoroalkanes (e.g., perfluorooctane) to the 2HPFP solution: typically, it was inversely proportional to the amount of perfluorooctane in the mixture. The unique thermoresponsive solubility further afforded the temperature-mediated micellization of a block copolymer of PEG19MA and methyl methacrylate (MMA) in 2HPFP to uniquely give a PEG-core micelle with PMMA shell. Therefore, the LCST phase separation properties in the hydrofluorocarbon would open new vistas for thermoresponsive polymeric materials.

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hermoresponsive polymers1−3 are now key materials in creating intriguing functions for sensors, catalysis, and bioapplication. For their applications, lower critical solution temperature (LCST)-type phase separation in water is often utilized with poly(ethylene glycol) (PEG),4 poly(ethylene oxide) (PEO),4 poly[poly(ethylene glycol) methyl ether methacrylate (poly(PEGMA))],5−8 poly(N-isopropylacrylamide),9 and their related derivatives.10 Among them, poly(PEGMA) [PEGMA: CH2C(CH3)CO(OCH2CH2)mOCH3], consisting of a hydrophobic polymethac r y l a t e ba c k b o n e an d m u l t i p l e h y d r o p h i l i c a n d thermoresponsive short PEG methyl ether pendants, allows us to tune LCST in water on demand by varying the pendant PEG length (m), i.e., PEGMA species (m = 3, 4.5, 9)5 and/or copolymerization with other hydrophobic monomers.11 The phase separation of PEGMA polymers in water is driven by dehydration upon heating via the cleavage of hydrogen bonding interaction between polyether oxygen and water. As a result, the LCST-type phase separation of PEG usually takes place in water under mild conditions (0−100 °C, 1 atm). In contrast, LCST-type phase separation of polymers in organic media generally required tough conditions (e.g., high temperature and pressure),12−14 except for unique examples of LCST phase separation under mild conditions (