Abstract
Size control has been successfully achieved in inorganic materials, but it remains a challenge in polymer nanomaterials due to their polydispersity. Here, we report a facile approach to tailor the diameters of polyurethane (PU) nanoparticles (490 nm, 820 nm and 2.1 µm) via perylene bisimide (PBI) assisted self-assembly. The formed morphologies such as spindle, spherical and core–shell structures depend on the ratio of PBI and polymer concentrations. It is shown that the formation of PU nanoparticles is directed by π–π stacking of PBI and the morphology transition is not only affected by the amount of PBI incorporated, but also influenced by solvent, which controls the initial evaporation balance. Furthermore, the prepared PUs exhibit retained optical stability and enhanced thermal stability. The PUs, designed to have conjugated PBI segments in backbones, were synthesized via ring-opening and condensation reactions. Compared with the neat PU, gel permeation chromatography shows narrower molecular weight distribution. Fluorescence spectra and ultraviolet–visible spectra indicate retained maximum emission wavelength of PBI at 574 nm and 5.2% quantum yields. Thermo-gravimetric analysis and differential scanning calorimetry reveal 79°C higher decomposition temperature and 22°C higher glass transition temperature. This study provides a new way to fabricate well-defined nanostructures of functionalized PUs.
Highlights
Polyurethanes (PUs) have been widely used in medical, automotive, packaging, automobile, coating and consumer care products because of their unique characteristics such as biodegradability and mechanical properties [1,2]
To adjust the ratio of Perylene bisimide (PBI) incorporated into the main chain, ε-CL was grafted onto PBI-OH first and used as a chain extender
To synthesize linear PUs, the oligomers were further reacted with Hexamethylene diisocyanate (HDI) by strictly controlling ratio and reaction temperature
Summary
Polyurethanes (PUs) have been widely used in medical, automotive, packaging, automobile, coating and consumer care products because of their unique characteristics such as biodegradability and mechanical properties [1,2]. [10] reported that amphiphilic block PUs prepared by poly(caprolactone)b-poly(ethylene oxide) and tetramethylrhodamine-5-carbonyl azide could self-assemble into spherical nanoparticles (10–100 nm) in aqueous media. The obtained PUs could form stable micelles through the interaction between hydrophilic poly(ethylene glycol) (PEG) segments, carboxylic groups and hydrophobic poly(lactic acid) chains in water. Cheng et al [12] reported phosphate ester incorporated PUs (PUP) These amphiphilic PUPs could self-assemble into spherical, worm-like micelles, vesicles and large vesicles in aqueous solution controlled by the hydrophilic phosphates that interrupted the electrostatic force balance between chains. The planar structure with delocalized π bonds could promote intermolecular interactions with neighbouring molecules through π–π stacking [19] In line with these properties, various PBI assemblies and their photophysics were investigated [19,20]. Assembled behaviour of PUs was investigated via X-ray diffraction (XRD) and the optical properties were characterized using UV–visible (UV–vis) spectroscopy and fluorescence spectroscopy
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