Structural Properties of Micelles Formed by Telechelic Pentablock Quaterpolymers with pH-Responsive Midblocks and Thermoresponsive End Blocks in Aqueous Solution

We investigated the structural properties of dynamic micelles arising from the self-assembly of the multiresponsive pentablock quaterpolymer P(nBuMA(8)-co-TEGMA(8))-b-PDMAEMA(50)-b-PEG(46)-b-PDMAEMA(50)-b-P(nBuMA(8)-co-TEGMA(8)) (nBuMA, TEGMA, DMAEMA, and EG are n-butyl methacrylate, tri(ethylene glycol) methyl ether methacrylate, 2-(dimethylamino)ethyl methacrylate, and ethylene glycol, respectively) in aqueous solution using a combination of scattering methods. In this multisegmented polymer, a pH-responsive BAB triblock copolymer from the weak cationic polyelectrolyte PDMAEMA and the hydrophilic PEG is end-capped by two blocks comprising random sequences of thermoresponsive TEGMA units and hydrophobic nBuMA units. Dynamic light scattering revealed the existence of single micelles and small clusters in dilute aqueous solution. The hydrodynamic radius of the micelles depends strongly on pH and temperature. The inner structure of the micelles was investigated by small-angle X-ray scattering, small-angle neutron scattering, and static light scattering, and micelles with a hydrophobic core containing a rather high fraction of water and a strongly swollen corona were found. The ratio of loops and dangling ends depends on temperature and pH.