Intra‐Chain Photodimerization of Pendant Anthracene Units as an Efficient Route to Single‐Chain Nanoparticle Fabrication

Abstract

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

“…This indicates a decrease in hydrodynamic volume based on the inherent principles of size exclusion chromatography [51][52][53]. This is clearly demonstrated in all of the polymer series discussed here [10,31,49].…”

“…In our experience, MALS is capable of detecting larger nanoaggregates in very minute concentrations while traditional SEC detectors such as UV and RI do not show the characteristic aggregate peak [10,49]. For series 1, multi-chain aggregates were detectable via MALS while virtually unseen in RI traces (Fig.…”

“…4 cycloaddition when irradiated with 350 nmcentered UV light, resulting in photodimers that can be reversed via irradiation with wavelengths \300 nm or thermally at temperatures [180°C [50], providing an attractive route to synthesizing thermally responsive and photosensitive nanomaterials. In addition, using light as stimulus for SCNP fabrication offers additional functional group tolerance that other cross-linking strategies lack [49].…”

“…The second route we are using to fabricate SCNPs involves the homocoupling of a built in functional unit [49]. For series 2, foldable methacrylic chains bearing pendant anthracene units were synthesized by RAFT polymerization (Scheme 2).…”

Synthesis of Activated Ester Functional Polyesters through Light‐Induced [4+4] Cycloaddition Polymerization

“…For instance, a variety of organo-and hydrogels, organic materials for rewritable photopatterning, 3D optical memory devices, and shape memory polymers have been exploited by taking the advantage of anthracene photodimerization. [5][6][7][8][9][10][11][12][13][14][15] Besides the abovementioned photoswitching ability, the anthracene has another unique feature which abilities have been prepared by employing the activated ester substitution reactions. [33][34][35][36][37][38][39][40] It is well known that preparing a polymer under mild condition is always desirable.…”