Graft copolymerization of N,N-
Dimethylacrylamide to cellulose in
homogeneous media using atom transfer radical
polymerization for hemocompatibility
Graft copolymerization of N,N-
Dimethylacrylamide to cellulose in
homogeneous media using atom transfer radical
polymerization for hemocompatibility
Li-Feng Yan, Wei Tao
Hefei National Laboratory for Physical Science at Microscale, and Department of Chemical Physics, University of Science and Technology of
China, Hefei, 230026, P.R.China. * Correspondence should be addressed to Li-Feng Yan (
of the cellulose backbone during the formation of
ABSTRACT free radical grafting sites, and the presence of a con-
siderable amount of ungrafted cellulose in the prod-
In homogeneous media,N,N-Dimethylacrylamideuct. In addition, these techniques usually results in
(DMA) wasgrafted copolymerization to cellulose the graft copolymer with poor control over the com-
by a metal-catalyzed atom transfer radical poly-position, such as molecular weight and the
merization (ATRP) process. First, cellulose waspolydispersity of the grafted chains [3]. Recently,
dissolved in DMAc/LiCl system, and it reacted controlled/livingradical polymerization methods
with 2-bromoisobutyloyl bromide (BiBBr) to pro-have been developed [4], which is able to minimize
duce macroinitiator (cell-BiB). Then DMA was chain transfer and to control the molecular weight
polymerized to the cellulose backbone in a and polydispersity.Among them atom transfer radi-
homogeneous DMSO solution in presence of cal polymerization (ATRP) and reversible addition
the cell-BiB. Characterization with FT-IR, NMR,fragmentation transfer polymerization (RAFT) are
and GPC measurements showed that there the two convenient methods to prepare well-defined
obtained a graft copolymer with cellulose back-polymers. Using living free radical polymerization
bone and PDMA side chains (cell-PDMA) in well-methods to prepare cellulose graft copolymer is an
defined structure. The proteins adsorption stud-attractive topic and some investigations had been car-
ies showed that the cellulose membranes modi-ried out. Perrier,et al. reported a preparation of poly-
fied by the as-prepared cell-PDMA copolymer styrene graft cellulose by a RAFT process [5].
own good protein adsorption resistancet. Carlmark and Malmstromsynthesized a poly(2-
hydroxyethyl methacrylate) graft cellulose using an
ATRP process [6]. However, in both the studies, the
graft copolymerization occurs only on the surface of
cellulose fiber due to the heterogeneous process.
Huang, et al. reported a homogeneous ATRP process
1. INTRODUCTIONto prepare cellulose graft copolymers with different
Cellulose is the most fluent feedstock in the worldmonomers; the reason why ethyl cellulose was
that could be used to prepare new kinds of materials, selected as the feedstock is its easily dissolving abil-
and cellulose derivatives have potential applicationity in many solvents[8, 9, 25, 26, 27]. By now there
as functional polymers. Graft copolymers are the are still less reports to synthesize cellulose graft
important topic for their novel properties. Today,copolymer through a living radical polymerization
“grafting from method has been widely used to pre-directly from cellulose in its homogeneous solution,
pare cellulose copolymers. Ceric ion initiation,and it is important to prepare well-defined structures
Fenton's reagent and-radiation are the widely used of the graft copolymer.
methods to graft monomers to cellulose [1,2]. How-Poly(N,N-dimethylacrylamide) (PDMA) is well-
ever, there are some drawbacks of these methods,known for its remarkable water solubility and
such as the production of unwanted homopolymer biocompatibility [10]. Recently, well-defined PDMA
together with the graft copolymer, chain degradation has been prepared by both RAFT [11] and ATRP pro-
Keywords:Cellulose; Atom transfer radical
polymerization (ATRP); Homogeneous; Graft
copolymerization; Hemocompatibility
J. Biomedical Science and Engineering, 2008, 1, 37-43Scientific
Published Online May 2008 in SciRes.
SciRes Copyright ©2008
cesses [12]. Also PDMA has been grafting polymer-pyridine as shown in [25, 26, 27]. In a 250
ization to polystyrene colloid by ATRP method [13].ml three-necked round-bottom flask, 60 ml of the cel-
Hemodialysis is one of the most important meth-lulose solution in DMAc/LiCl and 5 ml of pyridine
ods for blood purification [14], and cellulose mem-were added and mixed, then 6.3541 g of BrBiB was
branes, especial cellulose acetate (CA) membranes,slowly dropped into the solution at 0 C in an
are still the major materials for hemodialysis [15].ice/water bath. The reaction mixture was further
The cellulose membranes could take the porous andstirred at room temperature overnight. Then the mix-
asymmetrical structure and have both good perme-ture was added with de-ionized water and plenty of
ability and mechanical strength. However thrombusprecipitate appeared, and after washed by plenty of
formation on the blood-contact surface could not sup-de-ionized water, the precipitate was dried at 50C in
pressed by the membrane. Thus, its hemocompatibility vacuum overnight. Finally, there obtained white pow-
must be further improved for better hemodialysis [16].der product of macroinitiator(cell-BiB) with weight
Several efforts had been carried out to solve these of 4.81 g. The cell-BiB can be well dissolved in
problems, such as modification of the surface of the dimetyl sulfoxied (DMSO).
membrane with low-molecular-weight compounds,
hydrophilic polymers and biologically active heparin2.4. Grafting copolymerization of DMA by the
[17,18]. cell-BiB
In this paper, synthesis of the graft copolymer com-The cell-BiB(0.1737 g, 0.9 mmol) was dissolved in
posed of PDMA chains and cellulose backbone (cell-30 ml of DMSO in a 100 ml of flask. Then 7.92 g
PDMA) in homogeneous solution have been studied (0.08 mol) of DMA was added, and the solution was
via an ATRP. Moreover, the protein adsorption resis-evacuated and flushed with nitrogen for 30 min.
tivity on the cellulose membrane surface modified Finally, 0.1021 g of bpy (0.7 mmol) and 0.0444 g of
with the cell-PDMA was evaluated to understandCuBr (0.31 mmol) were added, and the polymeriza-
hemocompatibility of the cell-PDMA.tion was carried out at room temperature under the
protect of nitrogen. A few milliliter of samples were
2. EXPERIMENTAL SECTIONwithdrawn from the flask at different reaction time
2.1. Materialsusing degassed syringes to determine monomer con-
The chemical formula of the DMA is shown inversion and molecular weight.
Scheme 1. Commercial product of microcrystalline
(Sigma, DP = 121) was used without further purifica-
tion. 2,2'-Bipyridine (bpy) purchased from Aldrich
was recrystallized from ethanol to remove impurities.
DMA, CuBr with purity of 99.999% and 2-
bromoisobutyloyl bromide (BrBiB) were purchased
fromAldrich and used without further purification.
Other solvents and reagents were extra-pure grade
reagents and used without further purification.
2.2. Dissolution of cellulose in N,N-dimethyl
acetoamide (DMAc)/LiCl
After dried in vacuum at 35C overnight microcrystalline
cellulose (5.167 g) was put into a 250 ml three-necked
round-bottom flask, and adding 100 ml of distilled
water for 30 min to swell it, then water was removed
and fresh water was added again, and the process was
repeated for three times. Then removing the water
and adding 100 ml of methanol to swell again for 30
min for three times. After removing methanol the cot-
ton was dried in vacuum at 50 C for 3 h. Then cooling
down the solution and adding 120 ml of DMAc and
heated at 160 C for 1.5h, and removing 20 ml of
DMAc under reduced press by a rotary evaporator.At
the same time, about 10.22 g of LiCl was dried in
baker at 60 C.After the removing process of DMAc
finish, adding the dried LiCl into the system, and stir-
ring at 80C for 13 h, and the cellulose solution was
obtained at the end [19].
The samples were diluted with DMSO and filtering
the solution through a silicon gel column to remove
2.3. Synthesis macroinitiator for ATRPthe Cu ions catalyst, and then plenty of hexane was
Cellulose was acylated with BrBiB in the presence of
Scheme 2
SciRes JBiSE Copyright © 2008
L.F. Yanet al./J. Biomedical Science and Engineering 1 (2008) 37-43
Scheme 1.Chemical structure of DMA.
Scheme 2. Synthesis route for the macroinitiator (cell-BiB).
Scheme 3. Graft copolymerization of DMA on cellulose
backbone in homogeneous solution via the ATRP route.
added to produce the precipitate of the products. ThefromtheXPSelementalanalysis.
products were dried at 40 C in vacuum overnight.
2.8. Protein adsorption on the membrane sur-
2.5. Isolation of the grafted PDMA chains by
Amount of proteins adsorbed on the membrane was
hydrolysis measured by almost the same method reported previ-
The copolymers were hydrolyzed by 70% H SO for
24 ously [20]. The round (diameter: 1.5 cm) cellulose
8h at boiling point. At the end, the residual polymermembranes were placed into a 24-well plate. To
was participated into plenty of hexane and was driedequilibrate the membrane surface, phosphate buffer
by freeze drying, then the products were analyzed by solution (PBS, pH 7.4, ionic strength : 0.15 mol/l)
GPC. was added into each well and allowed to remain for
15 h at room temperature. Protein solutions were pre-
2.6. Characterizationpared in the concentration of 4.5 mg/ml of albumin,
The chemical structure was confirmed using an FT-1.6 mg/ml of-globulin, and 0.3 mg/ml of fibrinogen,
IR (FT/IR-615, JASCO, Tokyo, Japan).H- andC-which are 10% of the concentration of the human
NMR spectra were obtained on a NMR spectrometer plasma level. After removing the PBS, 1.0 ml of each
(-300, JEOL, Tokyo, Japan) with D Oas the sol-protein solution was poured onto each membrane and
vent. The molecular weights of these polymers wereallowed to remain at 37 C for 3 h. After rinsing the
determined bygel permeationchromatography (GPC).membrane three times with PBS, the membrane was
The mixture of methanol/water = 7/3 containing 10 taken out of the 24-well plate, and was rinsed again
mmol/L of lithium bromide was used as an eluent forsufficiently with the 50 ml of PBS. The membrane
the GPC measurement at a flow rate of 0.4 ml/min was placed into a glass bottle with a 1 wt% aqueous
(Column:SB-804HQ,Shodex, Tokyo, Japan). The solution of sodium dodecyl sulfate (SDS) and shaken
number-averaged molecular weight (M) and weight-(150 rpm) in a shaking bath for 3 h at room tempera-
nture to detach the adsorbed protein on the surface. A
averaged molecular weight (M) were calculated
wprotein analysis kit (Micro BCA protein assay
using poly(ethylene glycol) standards.reagent kit, #23235, Pierce, Rockford, IL, USA)
X-ray photoelectron spectroscopy (XPS) was con-based on the bicinchoninic acid method was used to
ducted on an AXIS-HSi (Shimadzu/KRATOS, Kyoto,determine the protein concentration in the SDS solu-
Japan) employing Mg Kexcitation radiation (1253.6 tion.
eV). The take-off angle of the photoelectron for each
atom was fixed at 90 deg.3. RESULTSAND DISCUSSION
ForAtomic force microscopy (AFM) measurement, The cell-BiB was prepared by partial esterification of
the sample was dissolved in DMF at a concentrationthe hydroxyl groups of the glucose units of cellulose
of 810 g/m. Then a droplet (20l) of the solutionwith BiBBr in the presence of pyridine. The reaction
was deposited onto freshly cleaved mica, and it waswas carried out homogeneously in DMAc/LiCl solu-
spin-coated at speed of 900 rpm for 8 s and then 4000tion at room temperature for 23 h. The formation of
rpm for 30s. The height image of the copolymer onthe ester bond resulted in the appearance of the char-
mica were measured by an AFM (Nanoscope IIIa, D.I.) -1
acteristic peaks at 1743 cm for the C=O stretching
in tapping mode with silicon TESP cantilevers. Theband in the FTIR spectrum, as shown in .
scanning rate ranged from 0.5 Hz to 1.0 Hz, andThe substitution of the hydroxyl groups on the cel-
512512 pixels images were record.lulose backbone with BiBBr was also confirmed by
2.7. Coating of the cell-PDMA on cellulose
The regenerated cellulose membrane, Cuprophan,
was obtained from Enka, A. G. (Wappertal-Barmen,
Germany). The thickness of the membranes was
20m. First the cellulose membranes were cut into
pieces with diameter of 1.5cm, and they were
immersed into deionized water for 30 min, and then
were dried at 35 C in vacuum for 15h. Then the cellu-
lose membranes were immersed into the 0.5 wt%
aqueous solution of the cell-PDMA for 3 min, and the
membranes were took out and dried under atmo-
spheric conditions for 2h, and then was dried at 35C
in vacuum for 15 h. The structure of the grafted DMA
on the cellulose membranes were confirmed using
XPS and FT-IR. The ratio of nitrogen atom (N) in the
DMA unit versus carbon atom (C) was determined
Figure 1
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L.F. Yanet al./J. Biomedical Science and Engineering 1 (2008) 37-43
Figure 1. FT-IR spectra of cotton (1), cell-BiB (2), DMA (3)
and cell-PDMA (4).
Wavelength(cm )
113 PDMA was compared with that of the cell-BiB and
both the H-NMR and C-NMR.As shown in-1
, there appears a new single peak at 1.8 ppm (peak DMAmonomer,theabsorptionsat1642cm
a) for methyl protons in the ester group of BiB,andappeared after grafting, which was assigned to the
the peaks at = 2.8-5.6 ppm (peak b) for the methy-freeC=OofPDMA,andthepeaksatabout3100-
lene protons and hydroxyl protons in the glucose3500 cmwas assigned to the OH group of cellulose
units of cellulose[21]. The total substitution degree[23].
(DS) of BiB is obtained by the ratio of the integral of shows a H-NMR spectrum for the cell-
the methyl groups to the integral of protons of glu-o
PDMA in methanol-d at 25C, the spectra is about
13 4
cose, and the DS is 0.2. shows the C-the same as that of PDMA. The resonance bands
NMR of the cell-BiB, and clearly both the methyl car-observed at 2.9-3.1 ppm are attributed to the
bon from BiB (peak a) and the carbon in glucosedimethyl group, and those observed at 1.3~1.8 ppm is
(peak b) appear, and the peak c at 176 ppm attributedattributed to the methyl amd methylene protons of
to the C=O carbon of BiB [22].PDMA [24]. Part of the resonance bands of cellulose
The as-prepared cell-BiB can be dissolved well inprotons are overlapped with that of PDMA while
DMSO. The graft copolymerization of DMA to cellu-there appear peaks at 2.9-4.0 ppm for the characteris-
lose was carried out in DMSO at 100 C,tics of cellulose.shows a C-NMR spec-
[DMA]:[cell-BiB]:[CuBr]:[bpy] = 88:1:2.9:1.3, andtrum for cell-PDMA in DO at 25C. The characteris-
[DMA] = 2.7 M. shows the kinetic plot of
0tic of the resonance peak for PDMA was observed at
the reaction, and the variation of ln([M]/[M]) is lin-
035 ppm, which is attributed to the dimethyl moiety
ear with time, indicating a constant concentration of[25]. The weak peaks appear at 75-85 ppm are attrib-
propagating radicals which is the characteristic of theuted to the carbon for cellulose back bone, and the
controlled/“living radical polymerization.peak appear at 182 ppm is attributed to the carbon for
The chemical structure of the cell-PDMA was iden-the carbonyl groups.
tified by FT-IR spectroscopy, NMR and GPC. AsThe grafted PDMA chains were converted to indi-
shown in , when the FT-IR spectrum of cell-vidual molecules through hydrolysis of the backbone
Figure 2c
Figure 2b
Figure 2d
Figure 3
Figure 1
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40L.F. Yanet al./J. Biomedical Science and Engineering 1 (2008) 37-43
Figure 2.113
H-NMR and C-NMR spectra of cell-BiB (a, b) and cell-PDMA (c, d).
ppm 020406080100120
Cellulose OCBr
OCellulose OBr
Cellulose OH2CNn
H )
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L.F. Yanet al./J. Biomedical Science and Engineering 1 (2008) 37-43
Figure 3. Time-conversion and the first-order kinetic plot for
the polymerization of DMA initiated by the cell-BiB in the
homogeneous solution of DMSO at 100C. [M] and [M] are
concentrations of monomer at polymerization time = 0 and at
corresponding time, respectively.
Figure 4.Dependence of M and M/M on monomer conversion in
the graft polymerization of DMA in DMSO, the PDMA was hydrolyzed
from the side chain of the copolymer before the GPC measurements.
Figure 5. TypicalAFM image of the cell-PDMA (a) and the
perimeter distribution of the particles (b).
Figure 6. XPS spectra of P, N, C, and O observed on
2p 1s 1s1s
the original cellulose membrane (down row) and that coated
with the cell-PDMA (upper row).
Figure 7. Amount of proteins adsorbed on original cellulose
membrane (a) and cellulose membrane coated with cell-
PDMA (b).
to determine their molecular weight. shows
the plot of M and the M/M versus the monomer con-
version during the polymerization. The molecular
weight of the graft copolymer is increased linearly
with the monomer conversion, and the polydispersity
is decreased with the monomer conversion. The
results also confirmed that the graft copolymerization
is a controlled/living radical polymerization.
Figure 4
a: cellulose membrane
b: polymer-coated cellulose membrane
Albumin -Globulin Fibrinogen
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42L.F. Yanet al./J. Biomedical Science and Engineering 1 (2008) 37-43
Figure 5
Figure 5b
Figure 6
Figure 7
shows the AFM image of the cell-PDMAcontrolled/”living radical polymerization. The char-
copolymer deposited on surface of the new cleaved acterizations indicate that the graft copolymerization
mica. Many nanoparticles appear with a homoge-is efficient and the obtained copolymer owns well-
neous size, and gives the perimeter distri-defined structures.After coated the cell-PDMA onto
bution of the particles. Clearely, there are two kindsthesurface of commercial cellulose membrane, there
of particles exist, one with the diameter about 200 nm, obtained membrane with good hemocompatibility,
and the other about 38 nm in diameter. Huang alsowhich was confirmed by the protein adsorption
reported similar result when they measrued the size experiments. This provides a new chance to modify
of celluose-PS graft copolymer by AFM, and they con-the surface of polysaccharide materials to improve
cluded that the smaller particles are the graft copoly-their hemocompatibility. The cell-PDMA has a strong
mer and the bigger one are the micelles of the graft potential application on surface treatment to enhance
copolymer when comparing the AFM data to dynamic separation ability and selectivity on every cellulose
laser light scattering results. Here, we believe that membrane including CA and nitrocellulose, which
the smaller particles result from the cell-PDMAare applied in biotechnology research and bioengi-
copolymer while the bigger one is the aggregates or neering field.
micelle of the graft copolymer.
The as-prepared cell-PDMA was a water-soluble
polymer having both affinities to the cellulose baseACKNOWLEDGEMENT
membrane, and its potential blood compatibilityThis work is supported by the National Basic Research Program of
China (No. 2007CB210201) and the National Key Technology R&D
could improve the surface blood compatibility of theProgram (No. 2006BAF02A09).
cellulose membrane by a convenient technique, such
as coating by its aqueous solution. Coating of cellu-
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