Precise Control over the Rheological Behavior of Associating Stimuli-Responsive Block Copolymer Gels

“Smart” materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double hydrophilic block copolymers that incorporate thermo-responsive sequences. These macromolecular building units are synthesized via a three-step controlled radical copolymerization and then hierarchically assembled to yield coordination micellar hydrogels. The dynamic mechanical properties of this particular class of materials are studied in shear flow and finely tuned via temperature changes. Notably, rheological experiments show that structurally reinforcing the micellar network nodes leads to precise tuning of the viscoelastic response and yield behavior of the material. Hence, they constitute promising candidates for specific applications, such as mechano-sensors

Supramolecular interactions for controlling the structure, self-organization and dynamics of stimuli-responsive polymeric systems

In the last years, the advent of supramolecular chemistry has provided chemists with new possibilities to synthesize complex structures and dynamic materials by self-assembly. By virtue of their properties, metal–ligand interactions are particularly promising for the synthesis of supramolecular polymers and the construction of “smart” materials with self-restructuring abilities. Among them, supramolecular gels constitute a very interesting sub-class because of numerous applications in various fields. In this frame, the goal of this thesis is to gain an unprecedented control over the structure, self-organization and molecular dynamics of polymeric gels by exploiting a novel combination of classical macromolecular architectures and supramolecular interactions of the metal–ligand type. The first goal of this thesis relies on the synthesis of well-defined copolymers, functionalized with a ligand of interest. These building blocks will then be used in the design of supramolecular materials with responsive properties. Precisely, the coordination of metal to ligands will be used to link micellar objects, obtained by the self-assembly of covalent block copolymers. The rheological behaviour of the accordingly obtained materials will be thoroughly characterized in order to establish relationships between their structure, dynamics and mechanical properties. The present thesis aims at studying in details the response of these systems to external stimuli. These stimuli-responsive properties will be inherent to the supramolecular materials and further obtained by using stimuli-responsive polymer sequences as building blocks.(SC - Sciences) -- UCL, 201

Polymer Gels Constructed Through Metal–Ligand Coordination

In the past few years, combining supramolecular and macromolecular chemistries has become of great interest to yield dynamic and responsive assemblies with self-restructuring abilities. Among them, polymer networks, that are held together by one or a combination of supramolecular interactions, offer new possibilities to scientists for the creation of artificial materials with selfhealing properties. In particular, incorporating coordination complexes into polymeric architectures opens up the possibility of imparting the physicochemical properties of both partners to the resulting material. Here, recent achievements in the field of supramolecular gels that are formed via self-assembly of oligo- and polymeric units through reversible metal–ligand interactions are reviewed. The different strategies and routes for the elaboration of those materials are reported as well as the properties that the coordination centers confer to the supramolecular assemblies

Controlling the cross-linking density of supramolecular hydrogels formed by heterotelechelic associating copolymers

Associating polymers constitute a fascinating class of materials because of the richness in their rheological behaviors. They may find application in numerous areas, provided that their mechanical properties can be tailored to fulfill specific requirements. In this context, this study aims to control the magnitude of the viscoelastic response of coordination micellar hydrogels built through the hierarchical assembly of heterotelechelic poly(N- isopropylacrylamide). The influence of different variables on the rheological properties of those materials is investigated and discussed in term of cross-linking density. In this respect, two distinct regimes are distinguished that correspond to the well percolated network, with a high cross-linking density, and the weakly percolated network, with a low cross-linking density. © 2014 American Chemical Society

Control over the assembly and rheology of supramolecular networks via multi-responsive double hydrophilic copolymers

Stimuli-responsive double hydrophilic diblock copolymers have been prepared that consist of poly(N-isopropylacrylamide)-block-poly(2-(dimethylamino)ethyl methacrylate) sequences terminated by a terpyridine ligand. These building blocks are assembled in aqueous media in a stepwise manner, by first forming metallo-supramolecular ABA triblock copolymers and then gels by thermo-induced micellar aggregation. This study sheds light on the subtle interplay that exists between the responsive behaviour of the core and corona forming blocks. Due to the intrinsic sensitivity of the constituting polymer chains and the non-covalent interactions between them, supramolecular gels respond to specific external triggers. These stimuli allow the manipulation of numerous rheological aspects of the assembled materials, including network formation and dynamics. Interestingly, an independent control over the network formation and dynamics is notably achieved via an appropriate choice of the metal ions and of the length of the associating block. By playing with the architecture of the associating copolymers and the nature of the metal ions, this work further demonstrates the possibility to build materials possessing either a mono or dual relaxation mechanism via a unique approach

Thermo-responsive properties of metallo-supramolecular block copolymer micellar hydrogels

Metallo-supramolecular micellar hydrogels exhibiting thermo-mechanical responsiveness are prepared through the hierarchical assembly of a heterotelechelic associating copolymer. The copolymer consists of a linear thermo-sensitive water-soluble sequence terminated by a short hydrophobic sticker at one end, the other being functionalized by a chelating ligand. As the first level of assembly, the associating copolymer is dissolved in aqueous solution to yield micellar nanostructures, bearing coordinative motifs at the end of the coronal chains. The second level of assembly is achieved when transition metal ions are added to the micellar solutions, resulting in almost instantaneous gelation. The thermo-mechanical response of those materials is investigated in detail by rotational rheometry, showing abrupt changes within the temperature boundaries corresponding to the phase transition of the polymer block located in the micellar corona. This journal is © the Partner Organisations 2014

Synthesis and self-assembly of terpyridine end-capped poly(N-isopropylacrylamide)-block-poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers

At the basis of smart self-assembled materials are lying small building blocks that can hierarchically assemble in response to stimuli, e.g., temperature or chemical species. In this context, the synthesis of terpyridine end-capped poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N-isopropylacrylamide) diblock copolymers via controlled radical copolymerization is reported here. The self-assembly of those copolymers is investigated in dilute aqueous solutions while varying temperature or adding transition metal ions, respectively, leading to the formation of micellar nanostructures or metallosupramolecular triblock copolymers. (Figure Presented). © 2014 Wiley-VCH Verlag GmbH & Co. KGaA

Precise Control over the Rheological Behavior of Associating Stimuli-Responsive Block Copolymer Gels

“Smart” materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double hydrophilic block copolymers that incorporate thermo-responsive sequences. These macromolecular building units are synthesized via a three-step controlled radical copolymerization and then hierarchically assembled to yield coordination micellar hydrogels. The dynamic mechanical properties of this particular class of materials are studied in shear flow and finely tuned via temperature changes. Notably, rheological experiments show that structurally reinforcing the micellar network nodes leads to precise tuning of the viscoelastic response and yield behavior of the material. Hence, they constitute promising candidates for specific applications, such as mechano-sensors

Metallo-supramolecular hydrogels based on copolymers bearing terpyridine side-chain ligands

A well-defined amphiphilic poly(triethyleneglycol methylether methacrylate)-block-polystyrene (PTEGMAb-PS) block copolymer with terpyridine groups randomly distributed within the water-soluble block has been sequentially synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Its self-assembly into micellar structures was analyzed in dilute aqueous solution by dynamic light scattering measurements (DLS). Metallo-supramolecular hydrogels were obtained after the addition of Ni(II) ions to either the precursor PTEGMA homopolymer solution or the PTEGMA-b-PS micellar solution. The PTEGMA-b-PS micelles formed gels at a much lower concentration than the corresponding PTEGMA homopolymer, thus evidencing the influence of the hydrophobic PS block on the critical gelation concentration. The mechanical properties of both hydrogels were finally investigated by rotational rheometry