Poly(N-isopropylacrylamide) Brushes Grafted from Cellulose Nanocrystals via Surface-Initiated Single-Electron Transfer Living Radical Polymerization

Abstract

Cellulose nanocrystals (CNCs) or nanowhiskers produced from sulfuric acid hydrolysis of ramie fibers were used as substrates for surface chemical functionalization with thermoresponsive macromolecules. The CNCs were grafted with poly(N-isopropylacrylamide) brushes via surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) under various conditions at room temperature. The grafting process was confirmed via Fourier transform IR spectroscopy and X-ray photoelectron spectroscopy and the different molecular masses of the grafts were quantified and found to depend on the initiator and monomer concentrations used. No observable damage occurred to the CNCs after grafting, as determined by X-ray diffraction. Size exclusion chromatography analyses of polymer chains cleaved from the cellulose nanocrystals indicated that a higher degree of polymerization was achieved by increasing initiator or monomer loading, most likely caused by local heterogeneities yielding higher rates of polymerization. It is expected that suspension stability, interfacial interactions, friction, and other properties of grafted CNCs can be controlled by changes in temperature and provide a unique platform for further development of stimuli-responsive nanomaterials.

Cationic Poly(2-aminoethylmethacrylate) and Poly(N-(2-aminoethylmethacrylamide) Modified Cellulose Nanocrystals: Synthesis, Characterization, and Cytotoxicity

“…The initiator modified CNCs were prepared according to a previously reported procedure with slight modifications. 39 Freeze-dried CNCs were reacted with 2-bromoisobutyryl bromide at two different ratios with respect to anhydroglucose units (AGU) in CNCs ([Br]/[AGU]), 5:3 for CNC-BriB-1 and 5:12 for CNC-BriB-2. Freeze-dried CNCs (1.00 g, 6.17 mmol of AGU, equivalent to 18.5 mmol of OH groups) was dispersed in dry THF and stirred continuously in a 250 mL flask under N 2 gas at room temperature.…”

Synthetic Strategies for the Fabrication of Cationic Surface-Modified Cellulose Nanocrystals

“…However, it is crucial to make sure no damage to the original morphology of the nanocrystals occurs during the surface functionalization process and as such, mild chemical methods are required to maintain the integrity of the nanocrystals. A number of surface covalent functionalizations of CNCs has been reported and some common examples include oxidation (tetramethylpiperidinyloxyl radical (TEMPO) oxidation for conversion of the primary hydroxyl groups to carboxylic acids [32] and periodate oxidation of vicinal diols to afford dialdehyde functionalities [33]), esterification [34,35], amidation [36,37], carbamation [38,39], amine functionalized CNCs (conversion of hydroxyl group to a terminated primary amine group) [40,41], radical polymerization [42][43][44][45], etherification, and other chemical modifications [2,29]. Readers are directed to a more detailed and critical review by Eyley and Thielemans on surface modifications of CNCs [29].…”

“…The main LRP techniques include atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT), and nitroxide-mediated polymerization (NMP), which have been exploited for the modification of polysaccharides towards the formation of high-performance hybrids [66,67]. These LRP techniques have also been employed on the surface of colloidal CNCs for the grafting of several functional polymer brushes with tunable or stimuli-responsive properties [42][43][44][45][68][69][70][71]. Surface-initiated atom transfer radical polymerization (SI-ATRP) and single-electron transfer living radical polymerization (SI-SET-LRP) are the most widely used methods for grafting from of polymers on the surface of CNCs.…”

Functionalized Polymers from Lignocellulosic Biomass: State of the Art

“…To increase the grafting density, the "grafting from" approach can be employed. In this method, polymer chains are formed by in situ polymerization of monomers onto immobilized initiators [145]. Molecular growth can be achieved by conventional radical, ionic, and ring-opening polymerizations.…”

“…"Grafting from" via ring-opening polymerization has been developed for polylactide (PLA)- [146], polycaprolactone (PCL)- [147,148] and PCL/PLA blends-based nanocomposites [149]. Surface-initiated radical polymerization has been successfully applied to graft CNW with poly(N-isopropylacrylamide) brushes [145].…”