Synthesis and properties of heterografted toothbrush-like copolymers with alternating PEG and PCL grafts and tunable RAFT-generated segments

The synthesis and properties of novel (A-g-D)(B-alt-C)mD-type heterografted toothbrush-like copolymers are described. The target copolymers comprised three types of building blocks, involving a terminal comb-like block with a quaternization bridging poly(N,N-dimethylaminoethyl methacrylate) (PDMA, A) substrate and D grafts, a middle comb-like block with a poly(styrene-alt-maleimide) backbone and alternating PEG (B) and PCL (C) grafts, and a terminal D segment involving poly(N-isopropylacrylamide) (PNIPAM), poly(methyl methacrylate) (PMMA), polystyrene (PSt) and poly(methyl acrylate) (PMA). The combination of quaternization and RAFT processes allowed for the controlled synthesis of the target copolymers with a precise microstructure and tunable composition and grafting density. With the changes in macromolecular architecture, chemical composition and grafting density, toothbrush-like copolymers were liable to exhibit different physicochemical properties such as chain relaxation, melting, crystallization and self-assembly behavior. The introduction of chemical heterogeneity into non-responsive toothbrush-like copolymers could endow polymer films with notable thermo-dependent wettability due to accelerated surface penetration and reconstruction. Meanwhile, the drug release properties of PNIPAM-based aggregates were significantly affected by temperature, additives and end groups, revealing their potential as promising controlled delivery vehicles. In addition to developing a general approach towards the construction of sequence-defined toothbrush-like copolymers with multicomponent grafts and variable grafting densities, our study further extended their potential applications in stimuli-sensitive surfaces and biomedical materials via changing the compatibility and supramolecular interactions.