Double thermoresponsive di- and triblock copolumers based on N-vinylcaprolactam and N-vinylpyrrolidone: synthesis, micellisation ang gelation

The development of stimuli-responsive polymers, especially thermo-responsive ones, has been a tremendous field of research in the last years. The solubility of such macromolecules can be reversibly triggered by small changes of temperature without additives. Poly(N-vinylcaprolactam) (PNVCL), which exhibits a lower critical solution temperature (LCST) around 36°C and a low toxicity, is of particular interest especially for biomedical applications. For these reasons, the insertion of well-defined PNVCL segments in more complex architectures is highly desirable but it requires efficient synthetic tools.

In this context, we have developed a cobalt-mediated radical polymerization (CMRP) for synthesizing novel well-defined NVCL-based copolymers. First, the LCST of PNVCL was tuned over a wide range of temperature by incorporation of specific amounts of N-vinylpyrrolidone (NVP) in the backbone. Then, CMRP of NVCL followed by statistical NVCL/NVP copolymerization led to diblocks having two discrete LCSTs. Finally, double.

The thermal response and multistep assembly behavior of these NVCL-containing di-and triblock copolymers were studied by turbidimetry and dynamic light scattering in dilute aqueous solution (~ 1 wt%). Rheological measurements performed on more concentrated copolymer solutions (~ 15 wt%) also emphasized their ability to form thermo-reversible gels. Gelation occurred at lower concentration and stronger gels were obtained with the triblocks because a real tridimensional network formed in this case. thermoresponsive triblocks were obtained by cobalt-mediated radical coupling (CMRC) of the parent diblocks upon treatment with isoprene.