Non-ionic amphiphilic block copolymers by RAFT-polymerization and their self-organization

Abstract

Water-soluble, amphiphilic diblock copolymers were synthesized by reversible addition fragmentation chain transfer polymerization. They consist of poly(butyl acrylate) as hydrophobic block with a low glass transition temperature and three different nonionic water-soluble blocks, namely, the classical hydrophilic block poly(dimethylacrylamide), the strongly hydrophilic poly(acryloyloxyethyl methylsulfoxide), and the thermally sensitive poly(N-acryloylpyrrolidine). Aqueous micellar solutions of the block copolymers were prepared and characterized by static and dynamic light scattering analysis (DLS and SLS). No critical micelle concentration could be detected. The micellization was thermodynamically favored, although kinetically slow, exhibiting a marked dependence on the preparation conditions. The polymers formed micelles with a hydrodynamic diameter from 20 to 100 nm, which were stable upon dilution. The micellar size was correlated with the composition of the block copolymers and their overall molar mass. The micelles formed with the two most hydrophilic blocks were particularly stable upon temperature cycles, whereas the thermally sensitive poly(N-acryloylpyrrolidine) block showed a temperature-induced precipitation. According to combined SLS and DLS analysis, the micelles exhibited an elongated shape such as rods or worms. It should be noted that the block copolymers with the most hydrophilic poly(sulfoxide) block formed inverse micelles in certain organic solvents.

Synthesis and characterization of sensitive hydrogels based on semi‐interpenetrated networks of poly[2‐ethyl‐(2‐pyrrolidone) methacrylate] and hyaluronic acid

“…PEPM, due to its hydrophilic groups, as the cyclic amide in the pyrrolidone, can create hydrogen bonds with the water molecules and presents a critical transition temperature associated to a lower critical solution temperature (LCST) of 34°C, meaning that when the temperature is below this value the polymer becomes highly soluble 40. Although in comparison with other methacrylate‐based polymer, poly( N ‐acryloyl pyrrolidone), with LCST of 56°C, presents a lower transition temperature due to the presence of hydrophobic groups 41. So, it would be expected that with the crosslinking of the EPM in the presence of a highly hydrophilic biopolymer, HA, the transition temperature of the polymeric system would be increased.…”

Synthesis of Symmetrical Triblock Copolymers of Styrene and N‐isopropylacrylamide Using Bifunctional Bis(trithiocarbonate)s as RAFT Agents

“…[21] The choice of an appropriate hydrophobic ''B'' block seems a priori nearly unlimited from the pool of water-insoluble polymers. Whereas still for micellar systems, hydrophobic blocks with low glass transition temperatures are favored in order to avoid ''frozen'' hydrophobic domains, [22][23][24][25][26] such ''frozen'' systems [27,28] seem attractive for hydrogel applications, as a high glass transition temperature of the physical cross-links should enhance the mechanical stability of the gels formed.…”

Synthesis of Double‐Hydrophilic BAB Triblock Copolymers via RAFT Polymerisation and their Thermoresponsive Self‐Assembly in Water

“…However, this combination is especially useful if a ''surfactant on demand'' is needed, as this approach avoids the painstaking procedures that are often necessary to disperse amphiphilic block copolymers in water. [22][23][24] Examples of double-hydrophilic polymers with thermoresponsive blocks also comprise ''schizophrenic'' [11,[25][26][27] and multi-responsive systems. [28,29] In contrast to classical surfactants, amphiphilic block copolymers allow for a much larger degree of compositional and architectural control and can be precisely designed to fulfil particular applications.…”