Tuning Hydrophobicity To Program Block Copolymer Assemblies from the Inside Out

Abstract

Hydrophobicity inherently affects a solutes behavior in water, yet how polymer chain hydrophobicity impacts aggregate morphology during solution self-assembly and reorganization is largely overlooked. As polymer and nanoparticle syntheses are easily achieved, the resultant nanoparticle architectures are usually attributed to chain topology and overall degree of polymerization, bypassing how the chains may interact with water during/after self-assembly to elicit morphology changes. Herein, we demonstrate how block copolymer hydrophobicity allows control over aggregate morphology in water and leads to remarkable control over the length of polymeric nanoparticle worms. Polymerization-induced self-assembly facilitated nanoparticle synthesis through simultaneous polymerization, self-assembly, and chain reorganization during a block copolymer chain extension from a hydrophilic poly­( N , N -dimethyl­acrylamide) macro-chain-transfer agent with diacetone acrylamide and N , N -dimethyl­acrylamide. Slight variations in the monomer feed ratio dictated the block copolymer chain composition and were proposed to alter aggregate thermodynamics. Micelles, worms, and vesicles were synthesized, and the highest level of control over worm elongation attained during a polymerization is reported, simply due to the polymer chain hydrophobicity.

New Insights into RAFT Dispersion Polymerization‐Induced Self‐Assembly: From Monomer Library, Morphological Control, and Stability to Driving Forces

“…While copolymerization of DAAM with DMA generates thermally responsive core‐forming copolymers, a] more recently it was reported that PDMA 30 ‐PDAAM x (60 ≤ x ≤ 90) lamellae exhibited a temperature‐induced postpolymerization morphological transition (Figure b) . The latter case is somewhat surprising given the insoluble nature of PDAAM.…”

“…The effect of comonomer on PISA morphologies has been studied by several research groups. Zhang group introduced polar 4‐vinylpyridine (4VP) as a comonomer to adjust the solvophobic/solvophilic ratio of BCPs, thereby changing the morphologies in RAFT dispersion polymerization of nonpolar styrene (St) in methanol/water mixture . b] Similarly, Sumerlin group increased the degree of solvation of the core‐forming block by adding a more polar N , N ‐dimethylacrylamide (DMA) as a comonomer in RAFT aqueous dispersion polymerization of diacetone acrylamide (DAAM).…”

“…b] Similarly, Sumerlin group increased the degree of solvation of the core‐forming block by adding a more polar N , N ‐dimethylacrylamide (DMA) as a comonomer in RAFT aqueous dispersion polymerization of diacetone acrylamide (DAAM). Significantly, BCP worms can be easily accessed and the worm length can be controlled to a certain degree ( Figure ) . a] Pan and coworkers demonstrated that copolymerization of St with polar methyl methacrylate (MMA) decreased the solvated T g , thus enhancing the mobility of the core‐forming block and promoting morphological transition in RAFT dispersion polymerization of St in methanol .…”

“…In a further study, Sumerlin group increased the hydrophilicity of the core‐forming block by copolymerization of DAAM with hydrophilic DMA to generate a thermoresponsive core‐forming block. They locked the morphologies by postpolymerization cross‐linking of the shell‐forming block . a] Worms could be prepared over a relatively broad composition and it seemed that the worm length could be controlled by the DP of the core‐forming block.…”

Beyond Simple AB Diblock Copolymers: Application of Bifunctional and Trifunctional RAFT Agents to PISA in Water

“…PISA is considered as an efficient and reliable strategy not only to produce amphiphilic diblock copolymers but also to prepare nanoobjects with controllable morphologies including spheres, worms, or vesicles in high yields and at high solid contents (typically 10–40 wt%) . It is nowadays well established that numerous parameters, mainly the monomer concentration, the chemical nature and the respective length of the blocks have an impact on the nanoobject morphology . Another important parameter that has been less considered in PISA so far is the macromolecular architecture .…”