Micrometer-sized aqueous droplets serve as a unique reactor that drives various chemical reactions not seen in bulk solutions. However, their utilization has been limited to the synthesis of low molecular weight products at low reactant concentrations (nM to μM). Moreover, the nature of chemical reactions occurring outside the droplet remains unknown. This study demonstrated that oil-confined aqueous microdroplets continuously generated hydroxyl radicals near the interface and enabled the synthesis of polymers at high reactant concentrations (mM to M), thus successfully converting the interfacial energy into the synthesis of polymeric materials. The polymerized products maintained the properties of controlled radical polymerization, and a triblock copolymer with tapered interfaces was prepared by the sequential addition of different monomers into the aqueous microdroplets. Furthermore, a polymerization reaction in the continuous oil phase was effectively achieved by the transport of the hydroxyl radicals through the oil/water interface. This interfacial phenomenon is also successfully applied to the chain extension of a hydrophilic polymer with an oil-soluble monomer across the microdroplet interface. Our comprehensive study of radical polymerization using compartmentalization in microdroplets is expected to have important implications for the emerging field of microdroplet chemistry and polymerization in cellular biochemistry without any invasive chemical initiators.

We report that an alternating semifluorinated copolymer of chlorotrifluoroethylene (CTFE) and vinyl ether (VE) is an attractive platform for the synthesis of heterograft copolymers consisting of two distinct side chains. The radical terpolymerization of CTFE with PLA-tethered vinyl ether (PLAVE) synthesized by ring-opening polymerization and isobutyl vinyl ether (IBVE) as a spacer produced PLA-grafted fluorinated copolymer via a “grafting-through” manner. Two PLAVEs with different molar masses (2 and 10 kg mol–1) were successfully incorporated, and the grafting density could be controlled by varying the [PLAVE]/[IBVE] initial molar ratio. From the chlorine atoms in the CTFE repeating units, atom transfer radical polymerization (ATRP) of styrene was further employed to grow PS side chains following a “grafting-from” mechanism per each (CTFE-alt-VE) repeating unit dyad. First-order kinetics was observed for the styrene polymerization and supported controlled growth of PS. The resulting heterograft copolymers possessed regularly spaced PS chains and statistically distributed PLA chains on the backbone, generating a nanoscopic disordered morphology via microphase separation driven by incompatibility between PLA and PS. By copolymerization of styrene and divinylbenzene (DVB) in neat ATRP condition, a cross-linked polymer monolith with the disordered bicontinuous morphology could be also prepared via polymerization-induced microphase separation. The cross-linked precursor was converted into a mesoporous polymer with pore size of 3.7–10.4 nm by removal of PLA. The mesopore size was tunable by adjusting the PLA molar mass and styrene/DVB molar ratio.

We investigated the influence of heavy halogen atoms (Br and I) on xanthene dyes for polymerization based on visible-light photoredox initiation. Since the heavy atoms directly affect intersystem crossing (ISC), which can act as a gatekeeper in the photoredox cycle and which was expected to also affect intermolecular photoinduced electron transfer (PET), we attempted to quantify the influence of the halogens. Six different xanthene dyes were chosen based on the number and types of heavy atoms on the xanthene ring. Thus, the photopolymerization degree clearly increased in the following order: fluorescein < 4′,5′-dibromofluorescein ≤ 2′,4′,5′,7′-tetrabromofluorescein < 2′,4′,5′,7′-tetraiodofluorescein. Furthermore, 4′,5′-dibromorhodamine 6G showed a drastic enhancement in the photopolymerization degree, compared with rhodamine 6G. Therefore, we concluded that the presence of halogens on the xanthene ring increases the photoredox initiating performance due to the enhanced ISC efficiency and PET rate.