Thermo-Induced Self-Assembly of Responsive Poly(DMAEMA-b-DEGMA) Block Copolymers into Multi- and Unilamellar Vesicles

A series of thermoresponsive diblock copolymers of poly[2-(dimethylamino)ethyl methacrylate-block-di(ethyleneglycol) methyl ether methacrylate], poly(DMAEMA-b-DEGMA), were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerizations. The series consist of diblock and quasi diblock copolymers. Sequential monomer addition was used for the quasi diblock copolymer synthesis and the macro-chain transfer approach was utilized for the block copolymer synthesis. The focus of this contribution the controlled variation of the ratios of DMAEMA to DEGMA in the copolymer composition, resulting in a systematic polymer library. One of the investigated block copolymer systems showed double lower critical solution temperature (LCST) behavior in water and was further investigated. The phase transitions of this block copolymer were studied in aqueous solutions by turbidimetry, dynamic light scattering (DLS), variable temperature proton nuclear magnetic resonance (H-1 NMR) spectroscopy, zeta potential, and cryo transmission electron microscopy (cryo-TEM). The block copolymer undergoes a two-step thermo-induced self-assembly, which results in the formation of multilamellar vesicles after the first LCST temperature and to unilamellar vesicles above the second LCST transition. An interplay of ionic interactions as well as the change of the corresponding volume fraction during the LCST transitions were identified as the driving force for the double responsive behavior.