Preparation of a Mini-Library of Thermo-Responsive Star (NVCL/NVP-VAc) Polymers with Tailored Properties Using a Hexafunctional Xanthate RAFT Agent

Abstract

Abstract:A mini-library of star-shaped thermoresponsive polymers having six arms was prepared using a hexafunctional xanthate by reversible addition-fragmentation chain transfer (RAFT) polymerization. Star polymers with homopolymeric arms of poly(N-vinylcaprolactam) (PNVCL), copolymeric arms of poly(N-vinylcaprolactam-co-N-vinylpyrrolidone) (PNVCL-co-PNVP) and also arms of block copolymers of PNVCL-b-PVAc, (PNVCL-co-PNVP)-b-PVAc, and combinations of them changing the order of the block was achieved exploiting the R-RAFT synthetic methodology (or R-group approach), wherein the thiocarbonyl group is transferred to the polymeric chain end. Taking advantage of the RAFT benefits, the molecular weight of the star polymers was controlled (M n = 11,880-153,400 g/mol) to yield star polymers of different sizes and lower critical solution temperature (LCST) values. Removing the xanthate group of the star polymers allowed for the introduction of specific functional groups at the ends of the star arms and resulted in an increase of the LCST values. Star PNVCL-b-PVAc diblock copolymers with PVAc contents of 5-26 mol % were prepared; the hydrophobic segment (PVAc) is located at the end of the star arms. Interestingly, when the PVAc content was 5-7 mol %, the hydrodynamic diameter (D h ) value of the aggregates formed in water was almost the same sa the D h of the corresponding PNVCL star homopolymers. It is proposed that these star block copolymers self-assemble into single flowerlike micelles, showing great stability in aqueous solution. Star block copolymers with the PVAc hydrophobic block in the core of the star, such as PVAc-b-(PNVCL-co-PNVP), form micellar aggregates in aqueous solution with D h values in the range from~115 to 245 nm while maintaining a thermoresponsive behavior. Micellar aggregates of selected star polymers were used to encapsulate methotrexate (MTX) showing their potential in the temperature controlled release of this antineoplasic drug. The importance of the order in which each block constituent is introduced in the arms of the star polymers for their solution/aggregation behavior is demonstrated.

Constrained thermoresponsive polymers – new insights into fundamentals and applications

“…In a salted brush, the concentration outside and inside the brush is approximately the same and the swelling properties are determined by excluded volume interactions between the segments. In an osmotic brush, the concentration of trapped counterions inside the brush is greater than the concen- PDEGA-PHEA synthesis/analysis [159] P(DEGMA-OEGMA-GMA) as nanolayers for controlled cell sheet detachment, synthesis [160] PDMAEMA-PDEGA synthesis/analysis [161] other polymers MPEP-PCL-PPE synthesis/analysis [162] PVAc-PNVCL-PNVP synthesis/analysis [163] tration outside. The resulting osmotic pressure depends on the interconnected polymer segments, the chain elasticity and the trapped counterions.…”

Biodegradable Polymeric Architectures via Reversible Deactivation Radical Polymerizations

“…These star block copolymers could self-assemble into single flowerlike micelles, showing great stability in aqueous solution. Micellar aggregates of selected star polymers were used to encapsulate methotrexate showing their potential in the temperature controlled release of this antineoplasic drug (Figure 4) [67].…”

Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking

“…Poly(N-vinylcaprolactam) (PNVCL) is a thermosensitive, nonionic polymer that exhibits an LCST in water at around 32 • C. In the case of PNVCL, the transition temperature depends on the molecular weight, polymer concentration and presence of hydrophobic or polar groups at the chain-ends [16,17]. Due mainly to its biocompatibility, this thermosensitive polymer has attracted interest in the biomedical field [18].…”