Search Results (3)

Macrosurfactants consisting of water-soluble poly(vinylcaprolactam) (PVCap) or poly(vinylpyrrolidone) (PVP) segments with comparatively shorter hydrophobic poly(styrene) (PS) or poly(2,3,4,5,6-pentafluorostyrene) (PPFS) segments were used as kinetic hydrate inhibitors (KHIs). These were synthesized with 2-cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)dithiocarbamate switchable reversible addition–fragmentation chain transfer (RAFT) agent at 60 °C or 90 °C for 1-P(S/PFS) or 1-PVCap, respectively, followed by chain extension at 90 °C or 70 °C with PVCap or PVP, respectively. The addition of PVCap to the pure methane-water system resulted in a 53% reduction of methane consumption (comparable to PVP with 51% inhibition) during the initial growth phase. A PS-PVCap block copolymer comprised of 10 mol% PS and 90 mol% PVCap improved inhibition to 56% compared to the pure methane-water system with no KHIs. Substituting PS with a more hydrophobic PPFS segment further improved inhibition to 73%. By increasing the ratio of the hydrophobic PS- to PVCap- groups in the polymer, an increase of its inhibition potential was measured. For PPFS-PVCap, an increase of PPFS ratio from 5% to 10% decreased the methane formation rate by 6%. However, PPFS-PVCap block copolymers with more than 20 mol% PPFS were unable to dissolve in water due to increase in hydrophobicity and the attendant low critical micelle concentration (CMC). Full article

Crosslinked-polymer brushes give rise to new opportunities for functionalizing, protecting, and structuring both organic and inorganic materials. In this study, pH- and temperature-switchable crosslinked-polymer brushes were easily prepared by combining the in situ method with reversible addition–fragmentation chain transfer (RAFT) polymerization. Initially, the RAFT agent was immobilized on an amine-terminated silicon wafer surface and utilized in the surface-initiated RAFT polymerization of 2-N-morpholinoethyl methacrylate (MEMA) as a monomer, and β-cyclodextrin methacrylate (CDMA) was used as a crosslinker on the silicon substrate. Measurements of film thickness, water contact angle, surface morphology, and structural characteristics of the resulting surfaces confirmed the poly(2-N-morpholinoethyl methacrylate) (PMEMA) brush-gels. Reversible capture and release measurements of methylene blue as a model molecule were also performed by UV–vis analysis. The switchable properties of the PMEMA brush-gels were maintained over five cycles. The results indicate that these PMEMA brush-gels with reversible capture and release properties might have widespread potential applications, including improved diagnostic tools as well as bioseparation. Full article

The combination of reversible addition–fragmentation chain transfer (RAFT) and emulsion polymerization has recently attracted much attention as a synthetic tool for high-molecular-weight block copolymers and their micellar nano-objects. Up to recently, though, the use of thermoresponsive polymers as both macroRAFT agents and latex stabilizers was impossible in aqueous media due to their hydrophobicity at the usually high polymerization temperatures. In this work, we present a straightforward surfactant-free RAFT emulsion polymerization to obtain thermoresponsive styrenic block copolymers with molecular weights of around 100 kDa and their well-defined latexes. The stability of the aqueous latexes is achieved by adding 20 vol % of the cosolvent 1,4-dioxane (DOX), increasing the phase transition temperature (PTT) of the used thermoresponsive poly(N-acryloylpyrrolidine) (PAPy) macroRAFT agents above the polymerization temperature. Furthermore, this cosolvent approach is combined with the use of poly(N,N-dimethylacrylamide)-block-poly(N-acryloylpiperidine-co-N-acryloylpyrrolidine) (PDMA-b-P(APi-co-APy)) as the macroRAFT agent owning a short stabilizing PDMA end block and a widely adjustable PTT of the P(APi-co-APy) block in between 4 and 47 °C. The temperature-induced collapse of the latter under emulsion polymerization conditions leads to the formation of RAFT nanoreactors, which allows for a very fast chain growth of the polystyrene (PS) block. In dynamic light scattering (DLS), as well as cryo-transmission electron microscopy (cryoTEM), moreover, all created latexes indeed reveal a high (temperature) stability and a reversible collapse of the thermoresponsive coronal block upon heating. Hence, this paper pioneers a versatile way towards amphiphilic thermoresponsive high-molecular-weight block copolymers and their nano-objects with tailored corona switchability. Full article