Synthesis and Characterization of Biocompatible, Thermoresponsive ABC and ABA Triblock Copolymer Gelators

Abstract

The synthesis of doubly thermoresponsive PPO-PMPC-PNIPAM triblock copolymer gelators by atom transfer radical polymerization using a PPO-based macroinitiator is described. Provided that the PPO block is sufficiently long, dynamic light scattering and differential scanning calorimetry studies confirm the presence of two separate thermal transitions corresponding to micellization and gelation, as expected. However, these ABC-type triblock copolymers proved to be rather inefficient gelators: free-standing gels at 37 degrees C required a triblock copolymer concentration of around 20 wt%. This gelator performance should be compared with copolymer concentrations of 6-7 wt% required for the PNIPAM-PMPC-PNIPAM triblock copolymers reported previously. Clearly, the separation of micellar self-assembly from gel network formation does not lead to enhanced gelator efficiencies, at least for this particular system. Nevertheless, there are some features of interest in the present study. In particular, close inspection of the viscosity vs temperature plot obtained for a PPO43-PMPC160-PNIPAM81 triblock copolymer revealed a local minimum in viscosity. This is consistent with intramicelle collapse of the outer PNIPAM blocks prior to the development of the intermicelle hydrophobic interactions that are a prerequisite for macroscopic gelation.

Micellization and gelatinization in aqueous media of pH- and thermo-responsive amphiphilic ABC (PMMA82-b-PDMAEMA150-b-PNIPAM65) triblock copolymer synthesized by consecutive RAFT polymerization

“…32 However, almost 20 wt% polymer was required to be gel, the gelation efficiency was sufficiently lower than that observed in the PNIPAM-PMPC-PNIPAM triblock copolymers. Besides high critical gelation concentration, these hydrogels oen exhibit broad or slow sol-gel transitions.…”

“…Besides high critical gelation concentration, these hydrogels oen exhibit broad or slow sol-gel transitions. 32,33 Comparing to ABA model, ABC triblock copolymers, which the C block is hydrophobic and the B and A blocks are water-soluble below the sol-gel transition temperature, are more efficient to realize the sol-gel transition. 18,19 Because the three blocks are mutually immiscible, they can form diverse nanostructures in aqueous solution in response to the change of the environment.…”

Fast Multiresponsive Micellar Gels from a Smart ABC Triblock Copolymer

“…These systems, however, proved to be moderately effective gelators, with a required copolymer concentration around 20 wt %. [30] Herein, we report the first bottom-up demonstration of a multiresponsive gel made from original micellar self-assemblies.We describe the preparation and investigation of threecomponent micellar gels endowed with stimuli-responsive properties. For this purpose, an amphiphilic ABC terpolymer,…”

Disulfide-Functionalized Diblock Copolymer Worm Gels

“…After (co)polymer synthesis, the latter bond can be cleaved to yield two chains each possessing terminal primary thiol groups. In related work, Li et al 34 and Madsen et al 35,36 designed free-standing gels consisting of ABA triblock copolymer 'flower micelles' which formed a 3D network comprising flower-like micelles inter-connected via bridging triblock copolymer chains. In this case, the central disulfide bond acts as a 'keystone':…”