We developed a methodology, inspired by the folding of proteins, for the precision synthesis of hairy polymer nanoparticles. High-molar mass and narrowly dispersed graft copolymers were synthesized by graft-through ring opening metathesis polymerization, to incorporate a designated number of side chains and dimerizable cinnamic acid groups. Intrachain photodimerization collapsed the backbone and arrested it into a compact globular conformation, resulting in hairy nanoparticles topologically equivalent to a core cross-linked star polymer. The single-chain collapse process translates the molecular information written on the 1D graft copolymer into the 3D globular polymer nanoparticle, like protein folding. Unprecedented control over structural parameters was achieved, including the length, number, and composition of the side chains as well as cross-linking density. Different side chains formed distinct subdomains in the sterically congested nanoparticle state and further self-assembled into micellar aggregates in a selective solvent. Both experimental observations and computational simulations indicated that preorganization of the side chains in the block sequence produces subdomains which primarily follow the backbone length scale, while random sequences showed side chain-dependent scaling. Polymer nanoparticles with discrete multiple subdomains were produced by folding of the ternary block graft copolymers. Drastic differences in the self-assembly behavior of ABC- and ACB-sequenced nanoparticles indicate that the spatial organization of subdomains can be achieved by sequence control.
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.
