Stimulus‐Responsive Nanoparticles and Associated (Reversible) Polymorphism via Polymerization Induced Self‐assembly (PISA)

Abstract

"smart" materials rely on very distinct material responses on a macroscopic and/or microscopic level. This can be achieved by crafting stimulus-responsive polymers into nanostructured materials, including smart nanoparticles, which are receiving increasing attention specifically in the biomedical field. [2,3] Amphiphilic block copolymers are well-known to undergo self-directed assembly in selective solvents providing access to a range of soft matter nanoparticles [4][5][6][7] with applications in coatings, [8] electronics, [9] drug delivery, [10] and cancer therapy, [11,12] among others. Traditionally, the preparation of such nanoparticles has been accomplished by initial synthesis and molecular dissolution of well-defined parent copolymers which are subsequently "processed", often via time-consuming step-wise dialysis, to give the targeted nano-object. Another drawback of this well-established approach is the generally low concentration of the final copolymer nanoparticles (≤1.0 wt% is common) which limits industrial application and study of such nanoparticles in areas where high Polymerization-induced self-assembly (PISA) is an extremely versatile method for the in situ preparation of soft-matter nanoparticles of defined size and morphologies at high concentrations, suitable for large-scale production. Recently, certain PISA-prepared nanoparticles have been shown to exhibit reversible polymorphism ("shape-shifting"), typically between micellar, worm-like, and vesicular phases (order-order transitions), in response to external stimuli including temperature, pH, electrolytes, and chemical modification. This review summarises the literature to date and describes molecular requirements for the design of stimulus-responsive nano-objects. Reversible pH-responsive behavior is rationalised in terms of increased solvation of reversibly ionized groups. Temperature-triggered order-order transitions, conversely, do not rely on inherently thermo-responsive polymers, but are explained based on interfacial LCST or UCST behavior that affects the volume fractions of the core and stabilizer blocks. Irreversible morphology transitions, on the other hand, can result from chemical post-modification of reactive PISA-made particles. Emerging applications and future research directions of this "smart" nanoparticle behavior are reviewed.

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

“…However, variable‐temperature 1 H NMR spectra revealed no obvious change in hydration degree of the core‐forming PDAAM block, suggesting that PDAAM is indeed water‐insoluble even after being attached to a hydrophilic PDMA block. The temperature‐induced morphological transition for this non‐thermoresponsive PDMA‐PDAAM BCP was explained by interfacial plasticization phenomenon . Further studies on cross‐linked lamellae revealed that the kinetics of morphological transition as well as the rheology properties of the dispersions could be adjusted by changing the cross‐linking density.…”

“…Although PHPMA is insoluble in water, it becomes thermally responsive when being attached to a hydrophilic block . PGMA–PHPMA nano‐objects were reported to exhibit a thermally reversible worm‐to‐sphere transition upon cooling from ambient temperature (20–25 °C) to 4 °C .…”

Synthesis of Film‐Forming Photoactive Latex Particles by Emulsion Polymerization–Induced Self‐Assembly to Produce Singlet Oxygen

“…The recent development of polymerization‐induced self‐assembly (PISA) offers new perspectives in the design of latex particles by surfactant‐free emulsion or dispersion processes, up to a high solids content. The simultaneous self‐assembly and particle growth enables the synthesis of well‐defined core–shell spherical or anisotropic particles formed by self‐assembled block copolymer chains . Moreover, the absence of molecular surfactant circumvents some detrimental effects of molecular surfactant like transparency loss.…”

Polymerization‐Induced Self‐Assembly for Artificial Biology: Opportunities and Challenges

“…As documented in the literature, the thermal activation method could be extended to most of the studied macro‐RATF agents/monomer combinations when the raw materials and formed vesicles are thermally stable . However, in some cases, the high reaction temperature (or later quenching reaction by cooling down) may significantly result in morphology changes for the formed vesicles . From the perspective of downstream construction or application of PISA to artificial bioinspired protocells, thermally powered PISA presents substantial challenges.…”