A series of well-defined diblock, triblock, and star-block copolymers composed of polystyrene and poly(acrylic acid) were synthesized by controlled/living radical polymerization and used as stabilizers in emulsion polymerization under alkaline conditions. The structure of the copolymers, the size of the blocks, and the composition were varied and their efficiency as stabilizers was correlated with their structural characteristics. The block length was varied from 10 to 30 units for the polystyrene block and from 13 to 266 units for the poly(acrylic acid) block. The copolymers appeared to be efficient stabilizers down to a block copolymer-to-monomer ratio of less than 0.5 wt %. From the comparison of the effect of the different structures and compositions, it was shown that the diblock copolymers were particularly efficient and that the optimal composition was about 10 styrene units and a maximum of 50 acrylic acid units. The triblock and star-block copolymers with external hydrophilic blocks did not behave much differently than diblock copolymers. In contrast, for the triblock copolymers with an internal hydrophilic segment, the efficiency strongly depended on the respective length of both blocks. The evolution of the number of latex particles, N p, with the concentration of surfactant was also studied and N p was shown to be proportional to [surfactant]α over a wide range of surfactant concentrations. The value of α was a function of the block copolymer composition irrespective of the individual block lengths: it was 1 for block copolymers with a poly(acrylic acid) content lower than 75 mol % and decreased to 0.4 when the hydrophilic content was increased. This trend was correlated with the exchange dynamics of the stabilizer. The results obtained with various initiator concentrations, temperatures, and ionic strengths corroborated the previous observation that the important point to explain the evolution of α with the copolymer composition was the competition between nucleation of the micelles and exchange of the block copolymers between the micelles and the continuously created polymer /water interfaces in the system. The time scale of this exchange (which is very fast for small-molecule surfactants) was on the same order of magnitude as the nucleation step for emulsion polymerizations carried out in the presence of block copolymers.

Copper(I)-mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n-butyl methacrylate) [P(n-BMA)] and poly [(2dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n-BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2-bromo-2-methylpropionic acid 4-methoxyphenyl ester, 1,4-(2Ј-bromo-2Јmethyl-propionate)benzene, and 1,3,5-(2Ј-bromo-2Ј-methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow-polydispersity polymers for which the number-average molecular weight increased fairly linearly with time with good first-order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2-dimethylamino)ethyl methacrylate to obtain well-defined [P(n-BMA) x -b-PDMAEMA y ] z diblock (15,900; polydispersity index ϭ 1.60), triblock (23,200; polydispersity index ϭ 1.24), and star block copolymers (50,700; polydispersity index ϭ 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac ϭ 3.22-7.13 ϫ 10 Ϫ3 g L Ϫ1 ) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size.

Click and drug: A combination of orthogonal click reactions is employed for the preparation of functional iron oxide nanoparticles (IONPs) that show unprecedented hyperthermia‐induced drug release through a magnetically stimulated retro‐Diels–Alder (rDA) process. Magnetic stimulation induces sufficient local energy in close proximity to the cycloadduct to initiate the rDA process.