RESUMEN
The synthesis of a series of dual thermosensitive nonionic-ionic random copolymers with varying compositions by reversible addition-fragmentation chain transfer polymerization is described. These copolymers contain oligo(2-ethyl-2-oxazoline)acrylate (OEtOxA) and either triphenyl-4-vinylbenzylphosphonium chloride ([VBTP][Cl]) or 3- n-butyl-1-vinylimidazolium bromide ([VBuIm][Br]) ionic liquid (IL) units. The copolymers having low content of ionic poly(ionic liquid) (PIL) (P[VBTP][Cl]/P[VBuIm][Br]) segments show only lower critical solution temperature (LCST)-type phase transition with almost linear increase of their cloud points with increasing percentage of ionic PIL segments. Furthermore, LCST-type cloud points ( TcLs) are found very sensitive and tunable with respect to the nature and concentration of halide ions (X- = Cl-, Br-, and I-) and copolymer compositions. However, copolymers with high content of ionic PIL segments show both LCST-type followed by upper critical solution temperature (UCST)-type phase transitions in the presence of halide ions. Dual LCST- and UCST-type phase behaviors are prominent and repeatable for many heating/cooling cycles. Both types of cloud points are found to be sensitive to copolymer compositions, concentration, and nature and concentration of the halide ions. The phase behaviors of both types of copolymers with a very high ionic content (>90%) are exactly similar to that of P[VBTP][Cl] or P[VBuIm][Br] homopolymers showing only UCST-type phase transition in the presence of halide ions. The inherent biocompatibility of the P(OEtOxA) segment along with the interesting dual thermoresponsiveness makes these copolymers highly suitable candidates for biomedical applications including drug delivery.
RESUMEN
The design and synthesis of a series of zwitterionic ionic liquids (ZILs) to understand the structure-property relationship towards an increase of the thermal stability, a variation of the glass transition temperature, the shape-tuning of nanostructured aggregates and the tuning of the stimuli responsiveness are demonstrated. The substitution reaction of imidazole with various aliphatic and aromatic bromides followed by the reaction of the corresponding substituted imidazoles with bromoalkyl carboxylic acids of varying spacer length produces the ZILs. In aqueous solution, a ZIL molecule either exist in its ionic liquid (substituted imidazolium bromide) form or its zwitterionic (substituted imidazolium alkyl carboxylate) form with an isoelectric point (pI) depending on the pH value of the solution. Upon changing the pH to near or above the pI, the aqueous ZIL solution undergoes transition from a transparent to a turbid phase due to the formation of insoluble hierarchical nanostructured aggregates of various morphologies, such as spheres, tripods, tetrapods, fern-like, flower-like, dendrites etc. depending on the pH of the solution and the nature of the alkyl/vinyl/aryl substituents. Upon heating the solution a phase transition occurs from turbid to transparent, exhibiting a distinct reversible upper critical solution temperature (UCST)-type cloud point (Tcp ). It is observed that the cloud point varies with the nature of the substituent, an increase of the concentration of the ZIL as well as with changes of the pH of the solution.
