Cellulose nanocrystal surface modification via grafting-from sonogashira coupling of poly(ethynylene-fluorene)

Cellulose nanocrystals (CNCs) were grafted with poly(2-ethynylene-9,9-dihexyl fluorene) via Sonogashira cross-coupling chemistry to yield environmentally friendly, composite nanoparticles. CNCs were first surface functionalized with 4-bromobenzoyl chloride to provide aryl halide tethering sites for Sonogashira cross-coupling. Poly(ethynylene fluorene) was then grafted-from the bromide functionalized CNC (s-Br-CNC) surface. The intermediate product, s-Br-CNC, was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS), validating the success of the esterification reaction and giving an approximate degree of substitution. The grafted product, g-PEF-CNC, was analyzed and validated using XPS, showing the expected trends in C1s deconvolutions with addition of solely carbon based polymer. Grafted chains were cleaved via acid hydrolysis and were revealed to be n = 2–4 short chain oligomers thru analysis by matrix assisted laser desorption/ionization-time of flight mass spectrometry. A number of the potential end group pairs were observed. As such, the authors have successfully demonstrated and analyzed a novel grafted composite nanomaterial based on renewable nanocellulose substrates and semiconductive conjugated polymers.