All-Aqueous SI-ARGET ATRP from Cellulose Nanofibrils Using

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All-aqueous SI-ARGET ATRP from cellulose nanofibrils using hydrophilic and hydrophobic monomers Tahani Kaldéus, Maria Rosella Telaretti Leggieri, Carmen Cobo Sanchez, and Eva Malmström Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.9b00153 • Publication Date (Web): 19 Mar 2019 Downloaded from http://pubs.acs.org on March 20, 2019

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Biomacromolecules

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All-aqueous SI-ARGET ATRP from cellulose nanofibrils using

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hydrophilic and hydrophobic monomers

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Tahani Kaldéus‡, Maria Rosella Telaretti Leggieri†, Carmen Cobo Sanchez† and Eva Malmström†*

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KTH Royal Institute of Technology, School of Engineering Sciences in Chemistry,

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Biotechnology and Health, †Fibre and Polymer Technology, ‡Wallenberg Wood Science Center,

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Teknikringen 56, SE-100 44, Stockholm, Sweden

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Keywords: Aqueous SI-ARGET ATRP, cellulose nanofibril modification, matrix-free composite

ACS Paragon Plus Environment

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Biomacromolecules 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract

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An all-water based procedure for “controlled” polymer grafting from cellulose nanofibrils

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is reported. Polymers and copolymers of poly(ethylene glycol) methyl ether methacrylate

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(POEGMA) and poly(methyl methacrylate) (PMMA) were synthesized by surface-initiated

15

activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET

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ATRP) from the cellulose nanofibril (CNF) surface in water. A macroinitiator was electrostatically

17

immobilized to the CNF surface, and its amphiphilic nature enabled polymerizations of both

18

hydrophobic and hydrophilic monomers in water. The electrostatic interactions between the

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macroinitiator and the CNF surface was studied by quartz crystal microbalance with dissipation

20

energy (QCM-D) and showed the formation of a rigid adsorbed layer, which did not desorb upon

21

washing, corroborating the anticipated electrostatic interactions. Polymerizations were conducted

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from dispersed modified CNFs as well as from preformed modified CNF aerogels soaked in water.

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The polymerizations yielded matrix-free composite materials with a CNF content of approximately

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1-2 wt. % and 3-6 wt. % for dispersion-initiated and aerogel-initiated CNFs, respectively.

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Biomacromolecules

Introduction

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In light of the increasing demand for more sustainable, biodegradable and/or bio-based

30

reinforcing components in future nanocomposites, nanocellulosic materials have rendered much

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attention during the past decades due to unique mechanical properties in combination with wide

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availability and versatility.1 However, the hydrophilic nature of native cellulose requires

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modification to increase its compatibility with hydrophobic matrices and prevent agglomeration,

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as well as improving other characteristics such as water and oxygen properties, essential in the field

35

of packaging materials and coatings.2,

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nanocellulosic materials,4 ranging from physical adsorption of small surfactants

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molecules7, 8 to various covalent grafting approaches, such as grafting-from9, 10 or grafting-to.11-13

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Numerous protocols have been described, however, they often require the use of solvent exchange,

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organic solvents and/or tedious drying/redispersion steps and may cause irreversible aggregation.

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Water is the preferred reaction medium, not only from an environmental point of view but also

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since it is superior in dispersing CNFs than any other liquid.

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There are numerous modification possibilities for 5, 6

or large

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In the last decade, atom transfer radical polymerization (ATRP), a reversible-deactivation

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radical polymerization technique, has proven to be a promising route for the modification of

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(nano)cellulosic substrates.14,

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defined polymers, with controlled molecular weights and polydispersities and it can be applied for

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the polymerization of a wide variety of vinyl monomers with a wide range of organic solvents.

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Several activator regeneration ATRP methods have been developed18 among others activator

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regenerated by electron transfer (ARGET) ATRP, which regenerates the activator by utilizing a

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non-radical forming reducing agent such as ascorbic acid allowing the polymerization to be

50

conducted with copper concentration reduced to ppm levels.19 Moreover, ARGET ATRP may be

15

ATRP is a versatile method with a potential to produce well-


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conducted in the presence of limited amounts of air17 and it has also been employed in aqueous

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medium20, making it appropriate for industrial scale. Although, several studies using surface

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initiated ARGET ATRP (SI-ARGET ATRP) have been reported on the modification of

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macroscopic cellulose-based substrates, including filter paper,21-23 cotton fibres,24-26 wood,27

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dissolving and Kraft pulps,22 only one report on the grafting of cellulose nanofibrils (CNFs) via

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ARGET ATRP is found.28

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As aforementioned, aqueous SI-ARGET ATRP has been employed for hydrophilic

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monomers from cellulosic surfaces, but no reported studies have been found in literature of

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polymerizations via ARGET ATRP of hydrophobic monomers in 100 % water from CNF surfaces.

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This work was aimed at developing a “green” and facile protocol for polymer modification

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of nanocellulosic materials using controlled radical polymerization. The protocol targeted the

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grafting of both hydrophilic and hydrophobic monomers, respectively or combined, from CNF via

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SI-ARGET ATRP in water. This was achieved by immobilizing an amphiphilic water-borne

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quaternised macroinitiator (MI) to the CNF surface through electrostatic interactions.

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Subsequently, the monomer(s) and other reagents were directly added to the CNF:MI aqueous

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dispersion and the polymerization was started, hence yielding a one-pot modification approach.

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Moreover, the grafting-from the surface of CNF:MI-aerogels submerged in water was also

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explored. This facile approach allows for the formation of matrix-free composites and open up for

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the construction of unique composite designs as well as the neat tailoring of the composite

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characteristics by varying the monomers.


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Biomacromolecules

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Experimental Section

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Materials

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Never-dried softwood pulp fibers were kindly donated by Aditya Birla, Domsjö Fabriker

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AB, Örnsköldsvik, Sweden and the CNFs were prepared (TEMPO-oxidized followed by

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homogenization in a high-pressure fluidizer) according to a previously described procedure.29

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Conductometric titration (SCAN-CM 65) was used to determine the total charge density of the

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homogenized fibers (800 μeq g-1) and the surface charge of the CNF dispersion was determined by

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polyelectrolyte titration (PET) and assessed to be 600 μeq g-1. The cationic macroinitiator, q-

79

PDMAEMA-stat-PHEMA-I (MI) (Mn = 9400 g mol-1, Đ = 1.3, 20 initiating sites), was synthesized

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according to a previously described procedure.30 The total surface charge of the MI was determined

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by PET and assessed to be 2000 μeq g-1. Methyl methacrylate (MMA, ≥ 99 %), poly(ethylene

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glycol) methyl ether methacrylate (OEGMA500, ≥ 99 %), poly(ethylene glycol) dimethacrylate

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(OEGDMA200, ≥ 99 %), ethyl-α-bromoisobutyrate (EBiB), 2,2’-bipyridine (bipy, ≥ 98 %), copper

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(II) bromide (CuBr2), and L-ascorbic acid (AA, ≥ 99 %), were purchased from Sigma Aldrich and

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used as received. Methanol (MeOH, ≥ 99.8 %) was purchased from VWR Chemicals.

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Tetrahydrofuran (THF, for analysis) was purchased from Merck KGaA. Unless stated otherwise,

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deionized water was used.

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Characterization

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Proton nuclear magnetic resonance spectroscopy (1H-NMR) spectra were obtained from a Bruker

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Avance NMR at 400 MHz using D2O or MeOD as solvent.

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Fourier transform infrared spectroscopy (FT-IR) spectra were obtained using a Perkin–Elmer

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Spectrum 100 FT-IR equipped with a MKII Golden Gate, single reflection ATR System from


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Specac Ltd., (London, UK). The ATR-crystal used was a MKII heated Diamond 45 ATR Top Plate.

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For each spectrum, 8 scans were recorded.

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Polyelectrolyte titration (PET) was used to determine the charge density of the MI by titration with

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potassium polyvinyl sulphate (KVPS) as titrant with the aid of a Stabino Particle Charge Mapping

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unit (Particle Metrix GmbH, Germany).

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Thermo-gravimetrical analysis (TGA) was obtained using a Mettler Toledo instrument, calibrated

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with Indium, under air and nitrogen flow, from ambient temperature to 800 °C at a heating rate of

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10 °C min-1.

101

Differential Scanning Calorimetry (DSC) analyses were performed using a Mettler Toledo

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TGA/DSC1 apparatus in order to access the Tg of the samples. A heat/cool/heat procedure was

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applied over a temperature range from -60 °C to 150 °C at 10 °C min-1.

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Electrostatic immobilization of MI to CNF (CNF:MI)

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MI was immobilized to CNFs with a 1:1 charge ratio between CNF and MI. In general, MI

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dissolved in 0.5-1 mL Milli-Q water was added dropwise to the CNF dispersion (1 g L-1) under

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continuous stirring. For the preparation of CNF:MI-aerogels, CNF:MI dispersions in aluminum

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pans were instantly frozen, using liquid nitrogen, and then lyophilized for 48 hours.

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Surface-initiated ARGET ATRP (aq.) of polymers from CNF:MI dispersion (D-CNF:MI-

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g-polymer)

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EBiB and MI-initiated polymerizations were conducted and used as model systems in order

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to optimize the general polymerization protocol for CNF:MI-initiated polymerizations (see

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Supporting Information for full details). The following describes the general procedure for the

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grafting of monomers from CNF:MI aqueous dispersion. Details about monomers are found in


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Biomacromolecules

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Table

1.

Polymerizations

were

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[M]:[I]:[CuBr2]:[bipy]:[AA] = 500-1000:1:0.2:1.6:1.6 and with a monomer concentration of 20 wt.

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% in water. MI (20/10 mg, 40/20 µmol) dissolved in water (1 mL) was added dropwise to the CNF

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dispersion in a round bottom flask. The flask was placed in an ice bath and monomer was added

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under magnetic stirring. The flask was sealed with a rubber septum and the mixture was degassed

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by vacuum (5 min) and argon (5 min). AA, bipy and CuBr2 were added under argon flow and the

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cooled mixture was degassed by two vacuum/argon cycles. The reaction was allowed to proceed

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at 30 °C for 120 minutes and quenched by placing the reaction flask in an ice water bath. The

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grafted CNF dispersion was purified by centrifugation at 20 000 rpm and 20 °C. The purified

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product was lyophilized and the mass fraction of CNFs was determined by weighing. The dried

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product was stored at 4 °C.

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Table 1. Polymerization details. Sample name CNF:MI-g-POEGMA CNF:MI-g-PMMA CNF:MI-g-POEGMA-co-PMMA

carried

out

CNF:MI (charge ratio) 1:1 1:1 1:1

with

the

following

Monomer(s) (mol %) 100 100 50:50

molar

ratios

DPtarget 500 1000 500:500

127 128

Surface-initiated ARGET ATRP (aq.) of polymers from CNF:MI aerogels (A-CNF:MI-g-

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polymer)

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The following describes the general procedure for the grafting of monomers from CNF:MI

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aerogels. Details about the monomers are found in Table 2. Polymerizations were carried out with

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the following molar ratios [M]:[I]:[CuBr2]:[bipy]:[AA] = 500-1000:1:0.2:1.6:1.6 and with a

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monomer concentration of 20 wt. %. The monomer was added with the water to a round bottom

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flask under magnetic stirring and the flask was placed in an ice bath and after 15 minutes the


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CNF:MI aerogel was added to the flask to soak. The flask was sealed with a rubber septum and the

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mixture was degassed by vacuum (5 min) and argon (5 min). AA, bipy and CuBr2 were added

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under argon flow and the cooled mixture was degassed by two vacuum/argon cycles. The reaction

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was allowed to proceed at 30 °C for 120 minutes and quenched by placing the reaction flask in an

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ice bath. The grafted aerogel was purified by washing and subsequent filtering. The purified aerogel

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was dried in a vacuum oven (50 °C) and the mass fraction of CNFs was determined by weighing.

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Table 2. Polymerization details. Sample name

142 143

D- or A-CNF:MI-g-POEGMA D- or A-CNF:MI-g-POEGMA-co-POEGDMA D- or A-CNF:MI-g-PMMA D- or A-CNF:MI-g-POEGMA-co-PMMA 1 wt. %. 2 Based on OEGMA.

CNF:MI (charge ratio) 1:1 1:1 1:1 1:1

Monomer(s) (mol %) 100 200:11 100 50:50

DPtarget 1000 5002 1000 500:500

144 145

Results and Discussion

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In this work, a facile and versatile one-pot polymer modification protocol of nanocelluloses

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in water has been developed, using an amphiphilic water-borne quaternised macroinitiator (MI)

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immobilized to the CNF surface (Figure 1). The selected MI has previously been anchored to

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graphene oxide nanoparticles used for controlled precipitation polymerization of hydrophobic

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monomers.30 Herein, we explored the possibilities of using MI in pure water, targeting the grafting

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of both hydrophilic and hydrophobic monomers, respectively or combined, via SI-ARGET ATRP.


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Biomacromolecules

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Figure 1. Grafting-from CNF through MI using SI-ARGET ATRP.

154 155

The design of MI and adsorption to CNFs

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The amphiphilic structure of MI was designed in order to accommodate several purposes;

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an initiator with ability to initiate controlled polymerization in water, a high affinity to cellulose as

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well as a high compatibility to both hydrophilic and hydrophobic monomers. The fulfillment of the

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targeted design was achieved by an amphiphilic macroinitiator consisting of hydrophilic units of

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quaternised PDMAEMA, enabling electrostatic adsorption to the negatively charged CNFs, and

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hydrophobic HEMA-units end-functionalized with the initiator moiety, α-bromoisobuturyl

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bromide (α-BiB), through esterification of the OH-groups of HEMA. The overall design of MI

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enables the initiation of both hydrophilic and hydrophobic monomers in aqueous medium.

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The adsorption of MI to CNFs was studied by QCM-D. As seen in Figure 2, the negative

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change in frequency shows that MI adsorbed to the CNF surface. Furthermore, MI did not desorb

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after the ensuing washing with Milli-Q water where after a large decrease of the energy dissipation

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was observed, indicating that the adsorbed MI layer is becoming more rigid upon washing.31 This


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is attributed to the large amount of water being expelled from the CNF surface, similar to what has

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been observed by Rojas and co-workers.32

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171 172 173

Figure 2. QCM-D adsorption of MI on CNFs. The following adsorption sequence was employed; adsorption of PEI, CNF and MI, subsequently, and washing with Milli-Q between each adsorption.

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Based on the charge ratio (1:1) between CNF and MI, the initiator density (MI), i.e. the number of

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MI molecules per area unit of CNF can be calculated. For our system, an initiator density of 0.5

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nm-2 was obtained. However, there are 20 initiating units on one MI molecule, hence, the theoretical

177

initiation that can occur from one single MI molecule is substantially larger compared to

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conventional initiators generally employed for grafting-to procedures.33 Due to the large number

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of initiating sites, it is hypothesized that the formed polymer chains assume the shape of dense

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polymer brushes.


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Biomacromolecules

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To assess the stability of the interaction between CNF and MI interaction, the grafted products

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were extensively washed with good polymer solvents (THF, acetone etc.) and dried several times.

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No significant weight loss was observed, suggesting that no polymer grafted MI had desorbed.

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SI-ARGET ATRP from CNF in aqueous medium

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This work provides a versatile modification protocol for the controlled polymerization of

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polar and non-polar monomers in aqueous medium employing ARGET ATRP. Polymerizations of

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homo- and copolymers of OEGMA500 and MMA were achieved from the CNF surface, utilizing

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the amphiphilic MI immobilized to the CNFs. Polymerizations were conducted in water from either

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dispersed CNFs, where MI was added and adsorbed to the CNF surface, or from CNF:MI aerogels

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soaked in the aqueous medium. Polymerizations proceeded for 120 minutes at 30 °C.

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Characteristics of the polymers are found in Table 3.

192 193 194

Table 3. Characteristics of homo- and copolymers of OEGMA500, OEGDMA and MMA polymerized from CNF:MI via SI-ARTET ATRP. The prefix D or A indicates dispersion (D) or aerogel (A), respectively. Conv.1 Mgraft2 Mpolymer2 CNF -1 (%) (w/w %) (g mol ) (g mol-1) D-CNF:MI-g-POEGMA 61 155 000 3 050 000 0.7 D-CNF:MI-g-PMMA 51 50 000 1 020 000 2.0 D-CNF:MI-g-POEGMA-co-PMMA 44 0.8 A-CNF:MI-g-POEGMA 23 60 000 1 150 000 2.7 A-CNF:MI-g-PMMA 48 50 000 960 000 3.2 A-CNF:MI-g-POEGMA-co-PMMA 15 3.4 A-CNF:MI-g-POEGMA-co-POEGDMA 10 6.1 1Calculated based on gravimetry, using the weight of the dried D/A-CNF:MI-polymers, and the weights of monomers and CNF:MI added. 2Based on conversion and assuming 20 initiating sites per MI. Sample

195 196 197 198 199

Polymerizations initiated from EBiB (I) and MI, respectively, were used to optimize the

200

CNF:MI initiated polymerizations (see SI), since attempts conducted to monitor the progress of the

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SI-ARGET ATRP, by analyzing aliquots by 1H-NMR with the addition of an internal standard


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(DMF), was not successful. Most likely, attributed to the strong affinity between monomers and

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the CNFs, resulting in a phase separation with high concentrations of monomer and succeeding

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polymer in the CNF rich phase. The results from the I- and MI-initiated polymerizations showed

205

that MMA undergoes a faster polymerization in the presence of MI compared to I. This is

206

accredited to the amphiphilic nature of the MI, increasing the accessibility to MMA. Further, the

207

amphiphilic nature of MI decreases the initiation rate of OEGMA, yielding a more controlled

208

polymerization (Figure S1, Tables S2 and S3). Moreover, it is noted that the resulting co-polymers

209

yielded compositions reasonably close to targeted values (Tables S2 and S3).

210

FT-IR spectra of CNF:MI grafted polymers exclusively showed the characteristic peaks of

211

the polymers without disclosing any characteristic peaks of CNF:MI (Fig. S11 and S12) which is

212

explained by the fact that the amount of polymer is tremendously large as compared to CNFs, Table

213

3.

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Thermogravimetrical analysis (Figure 3, Figures S5-S8 and Table S4) revealed interesting

215

results. A significant increase of the thermal stability was noted for POEGMA and PMMA initiated

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from MI or D-CNF:MI compared to I-initiated POEGMA and PMMA, respectively (50/35 °C for

217

POEGMA and 20/40 °C for PMMA, respectively). The TGA analyses were conducted under

218

nitrogen (pyrolysis) hence, the decomposition is not limited by the diffusion of gases or the

219

architecture of the polymer but rather the bond strengths. The increased thermal stability is

220

somewhat puzzling and at the present point in time, we so not have a plausible explanation for this

221

observation. Interestingly, all the aerogels displayed lower thermal stability compared to their

222

dispersion counterparts, attributed to structural differences between dispersed CNFs and preformed

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aerogels. A higher surface area, due to a more open or porous structure of the aerogels, from which

224

gases can diffuse faster, would imply a decrease in thermal stability. At the same time, the PMMA-


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Biomacromolecules

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based composites, with a glass transition temperature (Tg) above 100 °C, would trap the gases from

226

the organic volatiles originating from the burnt CNFs. Hence, restricting diffusion and hence,

227

increasing the thermal stability.

228 229 230

Figure 3. Thermograms (left) and 1st derivatives (right) for POEGMA polymers initiated from I, MI and D-CNF:MI, respectively.

231

Indeed, these two effects, based on the structural differences of the material and Tg, are observed

232

in the SEM micrographs (Figure 4, Figures S10 and S11). The laminar macrostructure observed in

233

the original CNF aerogel changes significantly to a bulky and sheet-like cavity structure upon

234

polymer grafting (Figure S10), specifically for the material with lower Tg, A-CNF:MI-g-POEGMA

235

and A-CNF:MI-g-POEGMA-co-PMMA. The microstructure is also affected (Figure 4),

236

transforming from a micro-sized, porous CNF aerogel to a more open structure upon the adsorption

237

of MI (CNF:MI), to a fully covered CNF:MI aerogel by the grafted polymers. A-CNF:MI-g-

238

PMMA is observed as a solid and rigid, almost continuous phase all over and throughout the

239

aerogel, only slightly fractured and with the formation of islands due to the shrinking of PMMA

240

during polymerization.34,

241

POEGMA and A-CNF:MI-g-POEGMA-co-PMMA, which appear much softer and less

242

continuous, with the folds of a brain-like landscape. Ultimately, these observations of the micro

243

and macro structural differences, due to the differences in Tg, are in accordance to the measured

35

Significantly distinct are the microstructures of A-CNF:MI-g-


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thermal stabilities of the different materials, in which a more rigid polymer (high Tg), would trap

245

the gases and impede their diffusion upon heating while a soft polymer would not hamper the gas

246

diffusion in the same way.

247 248

Figure 4. SEM-images of unmodified and grafted CNF:MI aerogels.

249

As expected, DSC (Figure S9 and Table S5) showed no significant changes in glass

250

transition temperatures, Tg, for any of the PMMA-based polymers, with values ranging between

251

123 and 127 °C. The POEGMA-based materials showed cold crystallization (Tcc) behavior,

252

independently of the initiator used. For A-CNF:MI-g-POEGMA the Tcc decreased approximately

253

from -15 to -35 °C and the melting temperature (Tm) increased around 6-7 to 0.7 °C, compared to

254

I- and MI-initiated POEGMA samples. These data indicate that the crystals are more easily formed

255

in a confined space, presumably attributed to the restriction in movement of the grafted POEGMA

256

in the aerogel, compared to other samples. Interestingly, the energy required to create/melt the

257

crystals increased by one order of magnitude for A-CNF:MI-g-POEGMA, suggesting that the

258

tethered polymer in a constrained volume, as in the case of the aerogel, decreases its degree of

259

freedom.36 Cold crystallization is also observed for A-CNF:MI-g-POEGMA-co-PMMA, with Tcc


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Biomacromolecules

260

and Tm values of around – 23 °C and 1.2 °C, respectively, again confirming that the restricted chain

261

mobility in the aerogel samples is indeed interfering with the crystallization behavior of the

262

polymers.

263

In this work, both CNF dispersions and aerogels were used to show the versatility of the

264

modification protocol. However, one could argue the need to form CNF:MI aerogels prior to

265

grafting. Hence, to elucidate the strengthening effect of CNFs, as preformed aerogels versus post-

266

formed aerogels, aerogels were made from polymers initiated by D-CNF:MI, and compared to A-

267

CNF:MI-polymers. Additionally, to further emphasize the structural integrity obtained by CNFs,

268

shapes of I- and MI-polymers were made and compared to CNF:MI-aerogels. As seen in Figure 5,

269

it is apparent that forming aerogel-like structures from I- and MI-polymers is not feasible. Although

270

D-CNF:MI-polymers were reasonably shapeable and had a structural integrity, the structures were

271

doubtfully classified as aerogels due to the lack of a porous structure, which is initially present and

272

to some extent maintained for A-CNF:MI-polymers. Moreover, post-formed aerogels of D-

273

CNF:MI-polymers are limited to polymers that are readily solubilized in water in order to undergo

274

lyophilization, while the variety of monomers that can be polymerized from A-CNF:MI is greater.

275

(Although not reported in this work, polymerizations of more hydrophobic monomers such as butyl

276

methacrylate (BMA), with a water solubility of 0.8 g L-1, compared to 15 g L-1 for MMA, were

277

also explored from A-CNF:MI.). It is also apparent that the structural integrity and the homogeneity

278

of the samples are more defined for A-CNF:MI-polymers, although optimization may be needed

279

in some cases. An example of this is seen in Figure 6, where the shape and integrity of A-CNF:MI-

280

g-POEGMA has been further improved by the addition of a monomer with crosslinking

281

functionality (OEGDMA) during polymerization. The crosslinks impair the tendency of the

282

POEGMA-aerogel to swell in water during the polymerization, consequently strengthening its


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structural integrity, while still maintaining the properties of POEGMA. It can be concluded that

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the preforming of aerogels sets no limits to the possibilities of shapes that can be formed.

285 286 287

Figure 5. Comparison of aerogels/shapes formed prior or post polymerization initiated by I, MI and CNF:MI, respectively.

288

289 290

Figure 6. Comparison of A-CNF:MI-g-POEGMA and A-CNF:MI-g-POEGMA-co-POEGDMA.

291 292

Conclusions

293

An amphiphilic macroinitiator was synthesized and successfully employed for the

294

controlled surface-initiated polymerization (SI-ARGET ATRP) from CNFs of both hydrophilic

295

and hydrophobic monomers in water. A green, facile, water-based approach was used for both the

296

electrostatic immobilization of the macroinitiator to the CNFs as well as for the polymerizations,

297

which were conducted in water, either from CNF dispersions or CNF:MI aerogels. The amphiphilic

298

structure of the macroinitiator enabled the polymerization of both hydrophilic and hydrophobic

299

monomers. It was observed that polymers containing less than 5 wt. % grafted CNFs increased the


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Biomacromolecules

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thermal stability by shifting the onset temperature by at least 20 °C. Moreover, polymerization

301

from the preformed CNF:MI aerogels resulted in composites with morphological properties

302

different from those of the corresponding homopolymers, with less than 10 wt. % CNFs. This opens

303

up for the use of CNFs as templating and strengthening substrate of future nanocomposite

304

materials. Additionally, this work showed that there are possibilities to combine different

305

monomers with various polarity and function to tailor the properties and shape of the desired CNF

306

composite.

307 308

ASSOCIATED CONTENT

309

Protocols for the EBiB- and MI-initiated polymerizations including monomer conversion data from

310

1H-NMR,

311

well as polymers initiated from EBiB, MI and CNF:MI. SEM images of A-CNF:MI-polymers.

312

AUTHOR INFORMATION

313

Corresponding Author

314

*[email protected]

315

ACKNOWLEDGMENT

316

Dr. Wåhlander is gratefully acknowledged for providing the synthesized macroinitiator. The

317

authors acknowledge the Wallenberg Wood Science Center and Stiftelsen AB Wilhelm Beckers

318

jubileumsfond for financial support.

319 320 321

References

SEC-data. TGA and DSC thermograms and FT-IR spectra of CNF, MI and CNF:MI as

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Graphical Abstract

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All-Aqueous SI-ARGET ATRP from Cellulose Nanofibrils Using

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