ИСТИНА

ABC-copolymers with several types of stimuli-responsive units are excellent candidates for design of smart polymeric materials. Such materials are able to change their structure and properties in response to small changes in environmental parameters1). Here we report the synthesis and solution behavior of multiblock copolymers containing “soft” hydrophobic C-block from n-butyl acrylate units (BA) and hydrophilic blocks from thermosensitive B-units of N-isopropylacrylamide (NIPAM) and pH-sensitive A-units of acrylic acid (AA). The synthesis of copolymers with different molecular mass and architecture (P(NIPAM-st-AA)-b-PBA-b-P(NIPAM-st-AA) or PAA-b-PNIPAM-b-PBA-b-PNIPAM-b-PAA)) was performed for the first time by means of controlled radical polymerization via addition-fragmentation chain-transfer mechanism2). All copolymers form molecular-dispersed solutions in nonselective solvent of dimethylformamide (DMF). Aqueous dispersions of copolymers were obtained via water addition to copolymer solution in DMF with subsequent dialysis of resultant mixture against pure water. Solutions were studied by dynamic light scattering. Depending on molecular mass of PBA block ABC-copolymers may form micelles (Rh ~ 30-40 nm) or exist as single macromolecules (Rh ~ 15 nm). All copolymers exhibit strong tendency for association of hydrophilic A-st-B or A-b-B blocks. As a result intermicellar associates (Rh ~ 100-400 nm) can be found in solution. The association of copolymers with A-st-B blocks was temperature and pH dependent, monotonously increasing with the growth of temperature. The association was in minimum point at neutral pH and increased with shifting pH both to acid or alkaline values. Contrariwise, A-b-B-b-C-b-B-b-A copolymers form stable intermicellar associates, which are temperature and pH resistant. Overall, the conducted research has shown that association behavior of amphiphilic ABC-copolymers in dilute solutions can be easily manipulated through changes in the copolymer architecture, solution pH and temperature. Such copolymer solutions with controllable degree of association may further be transformed into pH and thermo responsible membranes/films with changeable mechanical properties, hydrophilic/hydrophobic balance and permeability towards small ions and water molecules.