Synthesis of Poly[N-(2-((3-Morpholino-3-Oxopropyl)Thio)Ethyl)Methacrylamide]: A New Thermoresponsive Polymer with Tunable LCST- and UCST-Type Phase Transition in Aqueous and Alcoholic Solutions
A novel monomer, N -(2-((3-morpholine-3-isopropyl)thio)ethyl)methacrylamide (MTMA), is synthesized and polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization to give a thermoresponsive polymer poly[ N -(2-((3-morpholino-3-oxopropyl)thio)ethyl)methacrylamide] (PMTMA). PMTMA exhibits reversible thermoresponsive phase transitions of the lower critical solution temperature (LCST) type in water and the upper critical solution temperature (UCST) type in ethanol and methanol. The degree of polymerization and concentration of PMTMA, and solvent type have a significant influence on the transition temperature. PMTMA shows complicated thermoresponse in water–alcohol mixtures. In water–ethanol mixtures, the phase diagram of PMTMA can be divided into three regions according to ethanol volume percentages, φ : 0 ≤ φ < 15% for an LCST region; 15% ≤ φ < 91.5% for a complete dissolution region; 91.5% ≤ φ ≤ 100% for a UCST region. At high water content, the LCST increases with increasing ethanol content; and at high ethanol content, the UCST decreases with increasing water content. In water–methanol mixtures, PMTMA shows more complex thermoresponse. In the range of 0–50 °C, the phase diagram can be divided into five regions, depending on the methanol volume percentages φ : 0 ≤ φ < 15% for LCST region; 15% ≤ φ < 25% for immiscible region; 25% ≤ φ < 85% for UCST region; 85% ≤ φ < 95% for fully dissolved region; 95% ≤ φ ≤ 100% for another UCST region.
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