Architecture- and Composition-Controlled Self-Assembly of Block Copolymers and Binary Mixtures With Crosslinkable Components: Chain Exchange Between Block Copolymer Nanoparticles.

Panpan Li,Jesse L Davis,S Michael Kilbey,Xu Wang,Jimmy W Mays

doi:10.3389/fchem.2022.833307

Abstract

Chain exchange behaviors in self-assembled block copolymer (BCP) nanoparticles (NPs) at room temperature are investigated through observations of structural differences between parent and binary systems of BCP NPs with and without crosslinked domains. Pairs of linear diblock or triblock, and branched star-like polystyrene-poly(2-vinylpyridine) (PS-PVP) copolymers that self-assemble in a PVP-selective mixed solvent into BCP NPs with definite differences in size and self-assembled morphology are combined by diverse mixing protocols and at different crosslinking densities to reveal the impact of chain exchange between BCP NPs. Clear structural evolution is observed by dynamic light scattering and AFM and TEM imaging, especially in a blend of triblock + star copolymer BCP NPs. The changes are ascribed to the chain motion inherent in the dynamic equilibrium, which drives the system to a new structure, even at room temperature. Chemical crosslinking of PVP corona blocks suppresses chain exchange between the BCP NPs and freezes the nanostructures at a copolymer crosslinking density (CLD) of ∼9%. This investigation of chain exchange behaviors in BCP NPs having architectural and compositional complexity and the ability to moderate chain motion through tailoring the CLD is expected to be valuable for understanding the dynamic nature of BCP self-assemblies and diversifying the self-assembled structures adopted by these systems. These efforts may guide the rational construction of novel polymer NPs for potential use, for example, as drug delivery platforms and nanoreactors.

Highlights

Self-assembly of amphiphilic block copolymers (BCPs) has been viewed as a scalable and robust method for the fabrication and engineering of nanomaterials (Ozin et al, 2009; Bates et al, 2012; Gröschel et al, 2013; Jia et al, 2020; Liu et al, 2020; Kang et al, 2021)
The BCPs were first dissolved in THF, a good solvent for both the PS and PVP blocks, and a selective solvent for PVP blocks, methanol, was added dropwise into the systems to promote the formation of BCP NPs
We have demonstrated a strategy based on binary mixing of self-assembled PS–PVP BCP NPs formed from architecturally and compositionally diverse copolymers, which leads to different nanostructures

Summary

INTRODUCTION

Self-assembly of amphiphilic block copolymers (BCPs) has been viewed as a scalable and robust method for the fabrication and engineering of nanomaterials (Ozin et al, 2009; Bates et al, 2012; Gröschel et al, 2013; Jia et al, 2020; Liu et al, 2020; Kang et al, 2021). Using transmission electron microscopy (TEM) or cryogenic-TEM, the chain exchange-induced evolution of particle sizes in mixed micelles (Zhang et al, 1997; Esselink et al, 1998b), time- or concentration-dependent micelle growth (Esselink et al, 1998a; Kelley et al, 2014), and the dynamics of metal nanoparticle-encapsulated micelles (Li et al, 2019) were observed in model systems of spherical micelles formed from polystyrene-block-poly(acrylic acid) (PS-b-PAA), PS-blockpoly(2-vinylpyridine) (PS-b-PVP) or polybutadiene-blockpoly(ethylene oxide) (PB-b-PEO) diblock or PEO-blockpoly(propylene oxide)-block-PEO (PEO-b-PPO-b-PEO) triblock copolymers Despite these achievements, direct and accurate observation of chain exchange behaviors in BCP NPs is still challenging because of the lack of morphological diversity in self-assembled BCP NP structures—most often, self-assembly of linear BCPs generates spherical structures. For XPS measurements, the polymer solution was drop-cast on a silicon substrate

RESULTS AND DISCUSSION

D1 D1-C70 D2 D2 D2-C70 S2 S2 S2-C70 S2 S2-C70 S2-C20

CONCLUSION

DATA AVAILABILITY STATEMENT