Nonaqueous Dispersion Formed by an Emulsion Solvent Evaporation Method Using Block-Random Copolymer Surfactant Synthesized by RAFT Polymerization

As surfactants for preparation of nonaqueous microcapsule dispersions by the emulsion solvent evaporation method, three copolymers composed of stearyl methacrylate (SMA) and glycidyl methacrylate (GMA) with different monomer sequences (i.e., random, block, and block-random) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Despite having the same comonomer composition, the copolymers exhibited different functionality as surfactants for creating emulsions with respective dispersed and continuous phases consisting of methanol and isoparaffin solvent. The optimal monomer sequence for the surfactant was determined based on the droplet sizes and the stabilities of the emulsions created using these copolymers. The block-random copolymer led to an emulsion with better stability than obtained using the random copolymer and a smaller droplet size than achieved with the block copolymer. Modification of the epoxy group of the GMA unit by diethanolamine (DEA) further decreased the droplet size, leading to higher stability of the emulsion. The DEA-modified block-random copolymer gave rise to nonaqueous microcapsule dispersions after evaporation of methanol from the emulsions containing colored dyes in their dispersed phases. These dispersions exhibited high stability, and the particle sizes were small enough for application to the inkjet printing process.

Solubility and self-assembly of amphiphilic gradient and block copolymers in supercritical CO2

This work aims at demonstrating the interest of gradient copolymers in supercritical CO(2) in comparison with block copolymers. Gradient copolymers exhibit a better solubility in supercritical CO(2) than block copolymers, as attested by cloud point data. The self-assembly of gradient and block copolymers in dense CO(2) has been characterized by Small-Angle Neutron Scattering (SANS), and it is shown that it is not fundamentally modified when changing from block copolymers to gradient copolymers. Therefore, gradient copolymers are advantageous thanks to their easier synthesis and their solubility at lower pressure while maintaining a good ability for self-organization in dense CO(2).

Micelle Formation Induced by Disproportionation of Stable Nitroxyl Radicals Supported on a Diblock Copolymer

Micelle formation induced by disproportionation was attained for a diblock copolymer containing 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO). Poly(4-vinylbenzyloxy-TEMPO)-block-polystyrene (PVTEMPO-b-PSt) showed no self-assembly in 1,4-dioxane, a nonselective solvent. Light scattering studies demonstrated that the copolymer self-assembled into micelles in this solvent with the addition of hydrochloric acid (HCl). The hydrodynamic diameter of the copolymer was estimated to be ca. 55 nm based on the cumulant analysis of the complete micellization. A UV analysis confirmed that the micellizarion proceeded through the disproportionation of the TEMPO into the oxoaminium chloride and the hydroxylamine by the reaction with HCl, because the absorption based on the oxoaminium chloride increased with an increase in the amount of HCl. ESR verified that the radical concentration of the TEMPO decreased with an increase in the HCl. Before the addition of HCl, the PVTEMPO-b-PSt copolymer showed broad signals based on the random orientation. As the amount of HCl increased, the broad signals changed to the typical triplet of TEMPO, accompanied by a decrease in the signal intensity. The g values had a negligible change throughout the micellization. Finally, 40% of the TEMPO remained unreacted when the micellization was completed. The micellization prevented the dispropotionation of the TEMPO, because the PVTEMPO blocks formed the micellar cores which were covered with the micellar coronas of the PSt blocks. TEM observations demonstrated that PVTEMPO-b-PSt formed spherical micelles through the dispropotionation-induced micellization.