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Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization in cononsolvents of poly(N-isopropylacrylamide) (PNIPAM) was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture. Cononsolvents composed of mixtures of methanol, ethanol and isopropanol with water were first screened for their suitability as the media for dispersion polymerization of NIPAM, v : v) solution was selected due to good RAFT control, efficient formation of nanogels and low toxicity. RAFT dispersion polymerization of NIPAM in the cononsolvent using poly(N,N-dimethylacrylamide) (PDMA) as the macromolecular chain transfer agent (Macro-CTA) showed good control over the molecular weight, polydispersity and pseudo linear polymerization kinetics, as characterized by gel permeation chromatography (GPC)and 1 H NMR. The effect of the molecular weight of Macro-CTA, the degree of polymerization of PNIPAM, the molar ratio of [crosslinker] : [Macro-CTA] and the solid content on the formation and size of nanogels was investigated. The thermal profiles of nanogels were characterized by dynamic light scattering (DLS) both in cononsolvents and water. This cononsolvency strategy for dispersion polymerization was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide (HEAM) and diacetone acrylamide (DAAM). The nanogel containing DAAM was demonstrated for postpolymerization modification using ketone-alkoxyamine chemistry. More importantly, dispersion polymerization in cononsolvents allowed various hydrophobic components, e.g. butyl acrylate (BA), fluorescein O-acrylate (FLA), and 1,6-hexanediol diacrylate (HDDA), to be reliably copolymerized with NIPAM, showing well controlled polymerization, composition, nanogel size and colloidal stability. Finally, an amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the PDMA-b-PBAb-PNIPAM triblock copolymer and triple-layered nanogel, taking advantage of the solubility of PDMA-b-PBA and the insolubility of PNIPAM in the water-ethanol solution at the polymerization temperature. † Electronic supplementary information (ESI) available: GPC traces of PDMA-b-PNIPAM synthesized in different water-methanol, water-ethanol and water-isopropanol solutions, PDMA-b-P(NIPAM-co-HEAM) synthesized in water-ethanol (75 : 25, v : v), and the PDMA-b-PBA-b-PNIPAM triblock copolymer before purification; a summary table, 1 H NMR spectra and thermoresponse profiles for nanogels synthesized by copolymerization of NIPAM with HEAM. See

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Polymerization-induced self-assembly (PISA) is a rapidly evolving method for the efficient preparation of well-defined nano-objects. PISA-generated nano-objects have been explored in this work for the responsive formation of multidomain hydrogels by thermally induced assembly of doubly thermoresponsive triblock terpolymer nanogels. The nanogels consist of a thermoresponsive poly­(diethylene glycol ethyl acrylate) (PDEGA) outer block with a lower thermal transition temperature, a hydrophilic poly­(N,N-dimethyl­acrylamide) (PDMA) midblock, and a N,N′-methylene­bis­(acrylamide) (BIS) cross-linked, thermoresponsive poly­(N-isopropyl­acrylamide) (PNIPAM) core block with a higher thermal transition temperature. The unique location of these two thermoresponsive blocks of differing transition temperatures in the PDEGA–PDMA–P­(NIPAM-co-BIS) nanogels is rationally designed to facilitate room-temperature gelation and is synthetically realized via judicious selection of water–ethanol mixtures under dispersion polymerization conditions. The nanogels were characterized by turbidimetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Gelation behavior of the nanogels was investigated by the inverted vial method as well as dynamic rheology sweeps. In comparison with PNIPAM–PDMA–P­(DEGA-co-BIS) nanogel and a triblock terpolymer of similar composition, the PDEGA–PDMA–P­(NIPAM-co-BIS) nanogels exhibit a good combination of gelation sensitivity and gel strength. The gelation ability, sensitivity, and mechanical properties are affected by the block ratios as well as the cross-linking density in the core of the nanogels.

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