Bryan T. Tuten

Single-chain polymer nanoparticles via reversible disulfide bridges

We report the fabrication of single-chain polymer nanoparticles (SCNP) that can reversibly undergo a coil to particle transition via formation and cleavage of intramolecular disulfide cross-links. Characterization of this behaviour via shifts in SEC retention time confirm the changes in solution conformation in response to oxidative or reductive stimuli.

Intra-chain photodimerization of pendant anthracene units as an efficient route to single-chain nanoparticle fabrication.

An efficient route to architecturally defined, sub-20 nm soft nanoparticles fabricated from single polymer chains via intramolecular photodimerization of pendant anthracene units is presented. Photodimerization is confirmed by the disappearance of the characteristic anthracene π-π* absorption peak at ≈ 360 nm measured by UV-vis spectroscopy. Size exclusion chromatography (SEC) with UV, multi-angle light scattering (MALS), and viscometric detection confirms that as photodimers form, the chains fold to form nanoparticles, demonstrated by shifts in the SEC traces to longer retention times as a function of increased irradiation time. These shifts indicate a reduction in hydrodynamic radius, corroborated and quantified by viscometric data. MALS detector traces reveal the presence of a small amount of chain-chain coupling during this process, but confirm that this is primarily a single-chain phenomenon. Electron microscopy provides visual confirmation of nanoparticle formation.

Characterization of single-chain polymer folding using size exclusion chromatography with multiple modes of detection

We highlight here recent work from our laboratory on the subject of fabricating nanostructures from single polymer chains. These so-called single-chain nanoparticles are synthesized by inducing intra-molecular cross-linking on discrete macromolecules in dilute solution. Among the biggest challenges in this rapidly expanding area of research is reliable and accurate means to characterize this process. In this paper, we review our preferred method of characterization: size exclusion chromatography featuring multiple modes of detection. Multi-angle light scattering in conjunction with a concentration detector can provide absolute molecular weight data; viscometric detection can provide information about solution size and conformation. Correlation of these data provides a simple and robust way to quantify the process by which we fold single polymer coils into architecturally defined unimolecular nanostructures.

Characterizing single chain nanoparticles (SCNPs): a critical survey

We provide the results of a critical literature survey on the reported sizes of single chain polymer nanoparticles (SCNPs), an emerging class of functional nanomaterials with sub-30 nm diameters. Comparing different size evaluation techniques (DLS, 2D DOSY NMR, viscometry as well as microscopic techniques) by plotting the SCNPs’ estimated diameters, D, versus their measured (apparent) number average molecular weight, Mn, we demonstrate the vast data scatter that besets their analysis. We show that while relative reductions in measured diameter certainly indicate chain collapse, accurately describing the absolute size of SCNPs in solution remains a challenging task. Critically, conformation-size relationships emerge depending on the method used for size determination. We submit that the vast majority of reported sizes are only indicative of the relative size reduction during chain collapse and that absolute size determination approaches currently in use need to be further refined.

Intra-chain radical chemistry as a route to poly(norbornene imide) single-chain nanoparticles: structural considerations and the role of adventitious oxygen

Attempting to design an efficient and scalable method for producing functionalized single-chain nanoparticles, we investigated intra-chain radical polymerization of pendant methacryloyl decorated poly(norbornene) imides. Upon radical initiation, nanoparticle formation ensues, but this process is relatively inefficient in these materials as currently designed. Further, we discovered that the presence of adventitious oxygen plays a key role in this system.

Imaging Single-Chain Nanoparticle Folding via High-Resolution Mass Spectrometry

Herein, we introduce the first approach to map single-chain nanoparticle (SCNP) folding via high-resolution electrospray ionization mass spectrometry (ESI MS) coupled with size exclusion chromatography. For the first time, the successful collapse of polymeric chains into SCNPs is imaged by characteristic mass changes, providing detailed mechanistic information regarding the folding mechanism. As SCNP system we employed methyl methacrylate (MMA) statistically copolymerized with glycidyl methacrylate (GMA), resulting in p(MMA-stat-GMA), subsequently collapsed by using B(C6F5)3 as catalyst. Both the precursor polymer and the SCNPs can be well ionized via ESI MS, and the strong covalent cross-links are stable during ionization. Our high-resolution mass spectrometric approach can unambiguously differentiate between two mechanistic modes of chain collapse for every chain constituting the SCNP sample.