Data in support of dual-functionalized cellulose nanofibrils prepared through TEMPO-mediated oxidation and surface-initiated ATRP

We previously studied a suitably 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) that can be further functionalized with initiating sites and overcame the obstacle of performing atom transfer radical polymerization (ATRP) in the presence of neutral carboxylic acid sodium salt groups [1]. Herein, characterization of the modified TOCNs and of the products from surface-initiated (SI) ATRP of the (nano)celluloses with styrene (St) was performed using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and contact angle (CA) measurements. From the analysis of 1H NMR, a high purity of sacrificial initiator (i.e., 2-hydroxyethyl 2-bromoisobutyrate (HEBiB)) was confirmed. HEBiB was utilized to trace the SI ATRP with the generated free PSt. Gradually molecular weight evaluations were revealed from GPC analysis (ca. Mn=21,000 and Đ=1.10) using different TOCNs, implying the insignificant contribution to the kinetics from the grafted initiating sites. The TOCN-g-PSts were further characterized by contact angles and displayed an obvious reversibility between hydrophilicity and hydrophobicity in tens of minutes. These results illustrated a simple and facile approach for controlling the graft length and composition of TOCNs through SI ATRP.


a b s t r a c t
We previously studied a suitably 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) that can be further functionalized with initiating sites and overcame the obstacle of performing atom transfer radical polymerization (ATRP) in the presence of neutral carboxylic acid sodium salt groups [1]. Herein, characterization of the modified TOCNs and of the products from surface-initiated (SI) ATRP of the (nano) celluloses with styrene (St) was performed using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and contact angle (CA) measurements. From the analysis of 1 H NMR, a high purity of sacrificial initiator (i.e., 2-hydroxyethyl 2-bromoisobutyrate (HEBiB)) was confirmed. HEBiB was utilized to trace the SI ATRP with the generated free PSt. Gradually molecular weight evaluations were revealed from GPC analysis (ca. M n ¼ 21,000 and Đ¼ 1.10) using different TOCNs, implying the insignificant contribution to the kinetics from the grafted initiating sites. The TOCN-g-PSts were further characterized by contact angles and displayed an obvious reversibility between hydrophilicity and hydrophobicity in tens of minutes. These results illustrated a simple and facile approach for controlling the graft length and composition of TOCNs through SI ATRP.
& Value of the data A sacrificial initiator with high purity to monitor the SI ATRP kinetics was characterized. Contact angle measurements for comprehensive of surface images were shown. A living/controlled fashion using surface-initiated atom transfer radical polymerization was displayed.
The data presented here can be used to characterize the tailor-made surface grafted polymer in length, length distributions, and compositions.

Preparations of TEMPO-oxidized cellulose nanofibrils (TOCNs)
TEMPO (0.10 g, 0.64 mmol) and NaBr (0.80 g, 7.8 mmol) were added to wood pulp (8.0 g) dispersed in deionized water (DI water, 600 mL). 1 M NaOH was added slowly until the mixture achieved pH 10, and then NaClO (80 g, 1.08 mol) was added to begin the oxidation/reduction reactions. After a desired time, the reaction was stopped by diluting with copious DI water. The product was purified by repeating the DI water washing/centrifugation cycle a few times, until the aqueous solution reached neutral pH. The solution was concentrated and a hydrogel was obtained (5 wt% of TOCN solid content; yield: 94.5%).

Surface modification of TOCN with ATRP initiating moiety (TOCN-Br)
To obtain a well-dispersed TOCN/DMF mixture, solvent exchange from TOCN/H 2 O to TOCN/DMF was conducted by sequential washing steps acetone-DMF extractions for three times using a hydrophilic polytetrafluoroethylene membrane filter (H010A090C, Toyo Roshi Kaisha, Ltd.). A mixture of TOCN (0.18 g) and DMF (45 mL) was sonicated in a round-bottom flask for 15 min using an ultrasonic homogenizer (200 W), and then 4,4-dimethylaminopyridine (DMAP) was added. Desired amounts of triethylamine (TEA) and 2-bromoisobutyryl bromide (BiB) were added dropwise into the mixture through an addition funnel. Reaction compositions and temperatures are summarized in Table 1. After the reaction was complete, saturated NH 4 OH (aq) (40 mL) was added to stop the reaction; the product was washed through two cycles of Soxhlet extraction, with CH 2 Cl 2 and MeOH, for 48 h. The product (i.e., TOCN-Br) was dried and stored in a desiccator (yield: 84.1%).

Synthesis of 2-hydroxyethyl 2-bromoisobutyrate (HEBiB) [2,3]
Anhydrous ethylene glycol (270 mL, 4.84 mol) and TEA (13 mL, 95 mmol) were mixed with dry DCM 100 mL in a three-neck 500 mL flask under nitrogen. 2-Bromoisobutyryl bromide (11.7 mL, 95 mmol) was dissolved in 50 mL dry DCM, and then was added gradually to the solution by an addition-funnel while the solution temperature was kept below 5 1C with the aid of an ice-cooled water bath over 1 h. The reaction mixture was stirred for another 48 h at room temperature. The formed salt was filtered off. The crude solution was washed twice with 1 M HCl (aq) , twice with saturated NaHCO 3 solution, and twice with distilled water. The organic phase was dried with sodium sulfate. Then passed through silica column using EA/Hexane ¼1/6 as eluent. Pale yellow oil was obtained for 13.6 g (68%).
Characterization of HEBiB was shown in Fig. 1. In Fig. 1a  and capped with a rubber septum. The mixture was degassed through three freeze-pump-thaw cycles to remove O 2 and backfilled with N 2 . CuBr (HEBiB/CuBr¼1:1) was added to the frozen solution. The flask was closed, evacuated, and degassed through two additional freeze-pump-thaw cycles. At this stage (t¼0), a sample was taken via syringe and then the flask was immersed in a thermostatted oil bath at 90 1C. During the polymerization process, aliquots were regularly removed to allow monitoring (through gas chromatography (GC), using anisole as an internal standard) of the St conversion. The polymerization was stopped by cooling the flask in an ice bath and exposing the contents to air. The resulting mixture was diluted with tetrahydrofuran (THF); the product was precipitated into MeOH, collected, and dried under vacuum. The free PSt homopolymer and residual catalyst were removed through a few cycles of Soxhlet extraction, using THF (24 h) and MeOH (24 h). After drying under vacuum, TOCN-g-PSt was obtained as a white powder. In our previous study of Ln(M 0 /M) vs time plots [1], it showed gradual increases in conversion over time and linear first-order kinetics. In Fig. 2, GPC traces of the SI ATRP of St from two different TOCN-Br samples were recorded in various periods of reaction time. Clear changes in molecular weight (values of M n increased to ca. 20 k) and narrow unimodal GPC peaks (Đr1.1) are clearly evident from the onset of the reactions. The influence of the content of immobilized initiating groups on the reaction kinetics was negligible. The results depicted a typical RDRP fashion, implying successful SI ATRPs could be achieved in the presence of TOCNs presenting neutral carboxylic acid sodium salt groups.

Contact angle measurements
Dried samples were pressed at ca. 50 psi to obtain flat platelets under ambient and dried in vacuum prior to measure CAs using a KRÜSS G10 instrument. As shown in Fig. 3   hydrophilicity and hydrophobicity in a certain period of time was observed. This reversibility has demonstrated its effectiveness on the adsorbing organic compounds and metal ions in aqueous media [1].