LCST and UCST Transition of Poly(DMAEMA‐b‐MEO2MA) Copolymer in KHP Buffer

Abstract

AbstractBlock copolymers of poly(2‐(dimethylamino)ethyl methacrylate) and poly(di(ethylene glycol) methyl ether methacrylate) (poly(DMAEMA‐b‐MEO2MA)) are successfully prepared by sequential reversible addition‐fragmentation chain transfer polymerization and evaluated its thermoresponsive behavior in acidic potassium hydrogen phthalate buffer. Individual block of the corresponding block copolymers exhibits lower critical solution temperature (LCST) transition whereas the synthesized block copolymers are found to exhibit dual thermoresponsive behavior: LCST at low temperatures due to the MEO2MA block and upper critical solution temperature (UCST) at high temperatures due to phthalate crosslinked protonated PDMAEMA block. The agglomeration at LCST is effectively enhanced by the ion–ion interactions within the chains. However, at higher temperature the hydrophobicity by the low hydration due to inter‐ionic interactions is disrupted at UCST, resulting in a transparent solution. The temperature‐dependent phase transition of the copolymer (i.e., from micelles to agglomerates, and reversibly to micelles) is confirmed using dynamic light scattering, UV–visible spectroscopy, and transmission electron microscopy. The unique dual thermoresponsive behavior upon heating and cooling cycles is found to exhibit very small hysteresis. The morphological transformation during LSCT and UCST‐type phase transition is explained via a proposed schematic illustration.