Polymer-Functionalized Carbon Nanofibers

Carbon nanofibers (CNFs) are considered as analogs of carbon nanotubes (CNTs), and have comparatively excellent properties of CNTs such as high electric and thermal conductivity and strong mechanical strength. Therefore, CNFs can replace CNTs in some applications such as polymer additives, gas storage materials, electrode for fuel cell, and catalyst supports. But CNFs are hard to disperse in water or most organic solvents, so they are difficult to blend with macromolecular materials such as rubber, this greatly limits the application of CNFs in nanocomposites. So it is meaningful to functionalization of CNFs, especially for grafting polymer on the surface of CNFs to improve their solubility or wettability in organic solvents.In this paper, functionalization of CNFs with biodegradable poly(ε-caprolactone) (PCL) by surface-initiated ring-opening polymerization (ROP) ofε-caprolactone was successfully executed through importing hydroxy groups on surfaces of CNFs. This"grafting-from"strategy makes the content of grafted polymer controllable and high grafting efficiency.First, surface oxidation treatment of the pristine CNFs afforded carboxylic CNFs (CNF-COOH). Reaction of CNF-COOH with excess thionyl chloride (SOCl₂) and glycol produced hydroxyl-functionalized CNFs (CNF-OH), the hydroxyl density of CNF-OH is 0.60 mmol g^-1 from the TGA measurement.Using CNF-OH as macroinitiator, PCL was covalently grafted from the surfaces of CNFs by ROP. The content of grafted polymer can be controlled from 19.8 wt% to 64.2 wt% by adjusting the feed ratio of monomer to macroinitiator (CNF-OH). After surface functionalization of poly(ε-caprolactone), the D band of CNFs became stronger and a shoulder peak associated with the functionalization (D') appeared at 1615 cm^-1 in the Raman spectra. The intensity of such a shoulder peak increased with increasing the polymer content. The PCL Raman signals were not detected for the...