Synthesis and Characterization of Temperature-Responsive N-Cyanomethylacrylamide-Containing Diblock Copolymer Assemblies in Water.

We have previously demonstrated that poly(N-cyanomethylacrylamide) (PCMAm) exhibits a typical upper-critical solution temperature (UCST)-type transition, as long as the molar mass of the polymer is limited, which was made possible through the use of reversible addition-fragmentation chain transfer (RAFT) radical polymerization. In this research article, we use for the first time N-cyanomethylacrylamide (CMAm) in a typical aqueous dispersion polymerization conducted in the presence of poly(N,N-dimethylacrylamide) (PDMAm) macroRAFT agents. After assessing that well-defined PDMAm-b-PCMAm diblock copolymers were formed through this aqueous synthesis pathway, we characterized in depth the colloidal stability, morphology and temperature-responsiveness of the dispersions, notably using cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and turbidimetry. The combined analyses revealed that stable nanometric spheres, worms and vesicles could be prepared when the PDMAm block was sufficiently long. Concerning the thermoresponsiveness, only diblocks with a PCMAm block of a low degree of polymerization (DPn,PCMAm < 100) exhibited a UCST-type dissolution upon heating at low concentration. In contrast, for higher DPn,PCMAm, the diblock copolymer nano-objects did not disassemble. At sufficiently high temperatures, they rather exhibited a temperature-induced secondary aggregation of primary particles. In summary, we demonstrated that various morphologies of nano-objects could be obtained via a typical polymerization-induced self-assembly (PISA) process using PCMAm as the hydrophobic block. We believe that the development of this aqueous synthesis pathway of novel PCMAm-based thermoresponsive polymers will pave the way towards various applications, notably as thermoresponsive coatings and in the biomedical field.

RAFT-Polymerized N-Cyanomethylacrylamide-Based (Co)polymers Exhibiting Tunable UCST Behavior in Water.

In this present work, the synthesis of a new family of upper critical solution temperature (UCST)-thermoresponsive polymers based on N-cyanomethylacrylamide (CMAm) is reported. It is demonstrated that the thermally initiated reversible addition fragmentation chain transfer (RAFT) polymerization of CMAm conducted in N,N-dimethylformamide (DMF) is well controlled. The homopolymer presents a sharp and reversible UCST-type phase transition in pure water with a very small hysteresis between cooling and heating cycles. It is demonstrated that the cloud point (TCP ) of poly(N-cyanomethylacrylamide) (PCMAm) is strongly molar mass dependent and shifts toward lower temperatures in saline water. Moreover, the transition temperature can be tuned over a large temperature range by copolymerization of CMAm with acrylamide or acrylic acid. The latter copolymers are both thermoresponsive and pH responsive. Interestingly, by this strategy sharp and reversible UCST-type transitions close to physiological temperature can be reached, which makes the copolymers extremely interesting candidates for biomedical applications.