Direct Synthesis of Vinylidene Fluoride-Based Amphiphilic Diblock Copolymers by RAFT/MADIX Polymerization

We herein report the synthesis of original vinylidene fluoride (VDF)-based amphiphilic block copolymers by RAFT/MADIX polymerization. The controlled polymerization of VDF could be successfully mediated by a xanthate chain transfer agent as evidenced by size exclusion chromatography (SEC), ¹⁹F NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis. Copolymers of VDF and perfluoro­(methyl vinyl ether) (PMVE) of varying controlled chain lengths were also obtained. Finally, the direct synthesis of main-chain fluorinated amphiphilic block copolymers was performed from hydrophilic poly­(<i>N</i>,<i>N</i>-dimethylacrylamide) macro-RAFT agents. It is expected that this finding will open interesting perspectives for the development of new class of polymeric surfactants for the stabilization of emulsions based on water and supercritical carbon dioxide media

Understanding the Role of ω‑End Groups and Molecular Weight in the Interaction of PNIPAM with Gold Surfaces

Modification of nanoparticle surfaces by adsorption or grafting of polymers allows fine control of hybrid materials properties for diverse applications. To obtain such a control, it is of paramount importance to understand the impact of the polymer structure on the nature and strength of its interaction with the nanoparticle. We investigated here a simple model of hybrid materials made of poly­(<i>N</i>-isopropylacrylamide) of different molar masses and end groups interacting with gold surfaces. A series of poly­(<i>N</i>-isopropylacrylamide) with number-average molar masses ranging from 3700 to 10000 g·mol^–1 were synthesized by reversible addition–fragmentation chain transfer/macromolecular design by interchange of xanthates (RAFT/MADIX). The terminal xanthate group was then reduced into either a thiol or a hydrogen group. Quartz crystal microbalance adsorption/desorption experiments demonstrated that the polymer termini have a strong impact on the mechanism of polymer adsorption on flat gold surfaces. These differences in polymer structure have, in return, a strong influence on the colloidal stability and growth mechanism of nanoparticles when directly synthesized in polymer solution. For those properties, the effect of xanthate group compared very favorably to the conventional thiol moiety. Interestingly, the properties of nanohybrids were poorly affected by the molar mass of the polymer

Enhancement of Poly(vinyl ester) Solubility in Supercritical CO₂ by Partial Fluorination: The Key Role of Polymer–Polymer Interactions

An enhancement of poly­(vinyl ester) solubility in supercritical carbon dioxide (sc-CO₂) can be achieved by decreasing the strength of the polymer–polymer interactions. To demonstrate this, a library of statistical copolymers of vinyl acetate and vinyl trifluoroacetate was synthesized by RAFT/MADIX polymerization with varying compositions at a given number-average molecular weight. These copolymers exhibited unprecedentedly low cloud-point pressures in sc-CO₂ at 40 °C compared with previously reported poly­(vinyl esters). Surface tension measurements combined with a computational approach evidenced the prominent role played by polymer–polymer interactions

Thermoresponsive Properties of PNIPAM-Based Hydrogels: Effect of Molecular Architecture and Embedded Gold Nanoparticles

Thermoresponsive hydrogels were successfully prepared from poly­(<i>N</i>-isopropylacrylamide)-based polymers with different architectures (linear, branched, or hyperbranched). The macromolecular architectures strongly influence the internal structure of the hydrogels, therefore modulating their thermoresponsive and rheological properties. These hydrogels were used for the in situ synthesis of gold nanoparticles. Significant changes in hydrogel microstructures and in average pore size due to the presence of gold nanoparticles were observed. Additionally, their presence significantly increases both the mechanical strength and the toughness of the hydrogel networks

Enhanced Solubility of Polyvinyl Esters in scCO₂ by Means of Vinyl Trifluorobutyrate Monomer

The novel monomer, vinyl trifluorobutyrate (VTFBu), when polymerized in a controlled fashion by RAFT/MADIX polymerization with a xanthate transfer agent, yields poly­(vinyl ester)­s with improved solubility in supercritical carbon dioxide. The thermodynamic parameters controlling the solubility of VTFBu/vinyl acetate statistical copolymers are discussed based on ab initio calculations, glass transition temperatures of the copolymers, and surface tension measurements. The enhanced solubility of this new class of CO₂-philic polymer combined with its good chemical stability render it attractive for the preparation of next-generation macromolecular surfactants for the formation of water–scCO₂ emulsions

Enhanced Stabilization of Water/scCO₂ Interface by Block-Like Spontaneous Gradient Copolymers

There is an increasing interest in the specific physicochemical properties of gradient copolymers at interfaces. In this work, the phase behavior and interfacial properties of amphiphilic gradient copolymers at the water/CO₂ interface are explored and compared to that of diblock copolymer counterparts. It is observed that spontaneous amphiphilic block-like gradient copolymers made of N,N-dimethylacrylamide, vinyl pivalate, and vinyl acetate exhibit slightly lower cloud point pressures in supercritical carbon dioxide (scCO₂) than the corresponding diblock copolymers. Much more pronounced differences are established at the water/scCO₂ interface, with larger critical aggregation concentration (CAC), much faster adsorption kinetics and equilibration, and lower surface tension for gradient copolymers. RAFT/MADIX polymerization allows the control of molar mass, composition, and microstructure of the copolymers of the study. These findings shed light on how microstructural control in amphiphilic copolymers can give access to a new range of macromolecular emulsifiers for CO₂ media with improved properties

Assembly of Poly(vinylphosphonic acid)-Based Double Hydrophilic Block Copolymers by Gadolinium Ions for the Formation of Highly Stable MRI Contrast Agents

Mixing double-hydrophilic block copolymers containing a poly(vinylphosphonic acid) block with gadolinium ions in water leads to the spontaneous formation of polymeric nanoparticles. With an average diameter near 20 nm, the nanoparticles are stable after dilution or change of pH and ionic strength. High magnetic relaxivities were measured in vitro, and in vivo magnetic resonance imaging on rats demonstrates the high potential of such polymeric assemblies