Abstract
Poly[(vinylbenzyl) trimethylammonium chloride] (PVBTMAC) has been used as a stabilizer in the polymerization-induced self-assembly polymerizations of diacetone acrylamide (DAAM). A whole spectrum of particle morphologies was obtained simply by adjusting the ionic strength of the reaction mixtures; no dilution of the cationic charges with noncharged comonomers or with noncharged polymers was needed. In addition to the ionic strength, the effects of solid content and the length of the PDAAM block on the morphologies of the particles were studied in detail. The experiments are a continuation to previous studies on solution properties of PVBTMAC. It has been shown earlier that the solubility of the polycation may be tuned with counterions. Hydrophobic triflate ions induce an upper critical solution temperature behavior. In the present case, the chains bound to hydrophobic cores of the particles show either a one-step phase separation in aqueous triflate solutions or under certain conditions, a two-step transition. The step-wise transition is typical for responsive polymers with limited mobility.
Highlights
Amphiphilic block copolymers are able to build up various nano-objects such as spherical micelles, worm-like micelles, and lamellae or vesicles.[1−3] The morphology of the nanoobjects depends on the ratio of the hydrophobic and hydrophilic block lengths, temperature, solvent composition, and chemical nature of the blocks.[4,5]
Ionic or nonionic copolymers may self-assemble during the polymerization process, preferably when controlled radical polymerization techniques are used in aqueous emulsions or in dispersions.[13−19] A polymerization-induced self-assembly (PISA) technique has become a straightforward tool for synthesizing amphiphilic nano-objects with different morphologies.[20−25] In PISA, polymers self-assemble during the polymerization in which solvophilic chains are extended with another monomer that forms an insoluble block
We have shown that the solubility of polycations in water can be changed with various salts.[46−49] Depending on the cationic moiety and the counterion, the polycations phase-separate above the lower critical solution temperature (LCST) and/or below the upper critical solution temperature (UCST)
Summary
Amphiphilic block copolymers are able to build up various nano-objects such as spherical micelles, worm-like micelles, and lamellae or vesicles.[1−3] The morphology of the nanoobjects depends on the ratio of the hydrophobic and hydrophilic block lengths, temperature, solvent composition, and chemical nature of the blocks.[4,5] In charged block copolymers, the charge density of the polyelectrolyte blocks and their length influence the morphologies.[6−9] Morphological changes may be induced by changing the pH or salt concentration.[10−12]. Syntheses of diblock copolymer nanoparticles were first conducted in water by changing various parameters such as DPs of PDAAM, total solids, and salt concentrations. The theoretical molar masses of the macro-CTAs were obtained from the monomer conversions determined by 1H NMR spectroscopy. The final mean DPs and molar masses of the macro-CTAs were measured with NMR and UV end group analysis (see Supporting Information, Section S2). PVBTMAC−PDAAM block copolymer nanoparticles were synthesized by the chain extension of cationic macro-CTAs with water-miscible monomer DAAM via RAFT polymerization (Scheme 1B). The first series of nanoparticles was synthesized in salt-free water, varying the target DP of PDAAM and solid content (Table S2). The copolymer nanoparticles were synthesized with targeting to constant DP of PDAAM while changing the NaCl concentration and the solid content (Table S3).
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